NUTRITION IN HEALTH
NUTRITION IN HEALTH HUEC 2010
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CHAPTER 10 WATER SOLUBLE VITAMINS 1Z240VVX7PP82230397 25863648 FIX SPACING BEFORE PRINTING EXAM 3 0 There are 9 essential watersoluble vitamins eight B vitamins and vitamin C Vitamin Major Functions Deficiency Toxicity Recommended Excellent food sources Structure Intakes Thiamin o Coenzyme 39I39I39P Beriberi Males 12 mg Pork 0 Energy metabolism Females 1391 mg Whole Grains Synthesis of DNA RNA and Legumes NADPHH Fortified and enriched Nerve Function foods Tuna Soy milk Riboflavin o coenzyme FAD and FMN Ariboflavinosis Males 13 mg Liver 32 0 Energy metabolism redox Females 1391 mg Mushrooms Metabolism of folate Dairy products vitamin A niacin vitamin 36 Fortified and enriched and vitamin k foods Neurotransmitter Tomatoes metabolism spinach Niacin Ba o coenzyme NAD and NADP Pellagra Skin Males 16 mg Liver energy metabolism redox infiamation Females 14 mg Fish 0 protein synthesis and ushing Meat including chicken 0 glucose homeostasis Ui 35 mg Fortified and enriched cholesterol metabolism foods 0 DNA repair Tomatoes mushrooms Pantothenic o coenzyme CoA Burningfeet A of 5 mg liver aCid 35 0 energy metabolism syndrome mushrooms heme synthesis sunflower seeds cholesterol fatty acid fortified foods steroid and phospholipid yogurt synthesis turkey Vitamin 36 o coenzyme PLP Microcytic Neurological 13 17 mgday fish o amino acid metabolism hypochromic problems for adults chickpeas transamination anemia diffiCUit l liver nerotransmitter and walking and Ui 100 mg fortified foods hemoglobin synthesis numbness in potatoes glycogenesis the hands bananas regulation of steroid and f t hormone function Biotin o coenzyme Depression A of 30 peanuts o energy metabolism loss of muscle micrograms almonds carboxylation control and mushrooms regulation of gene skin irritations egg yold expression tomatoes avacados Folate o coenzyme THF Macrocytic 400 micrograms Organ meats singlecarbon transfers anemia DFE for adUits Legumes amino acid metabolism ra DNA and RNA synthesis 500 micrograms39 Leafy vegetables Pregnant women Enriched foods UL 1000 micrograms Vitamin B12 0 Coenzyme MaCI39OCYtiC 1 micrograms 0 Mollusks CObalamin 0 Homocystein metabolism anemia o Liver Energy metabolism 0 Salmon and Meat Fortified foods 0 Cottage cheese Vitamin C o Antioxidant Scurvey Gastrointesti Men 90 mg Peppers quotrechargingquot enzymes nal Women 75 mg Papayas Collagen synthesis PFOblemS Citrus fruits Tyrosine neurotrnasmitter 5m ker5 Broccoli and hormone synthesis additional 35 mg 0 Strawberries Protection from free radicals Brussels sprouts UL 2 g 2000 mg ChOIine 0 Phospholipid synthesis Liver damage Fishy body Als 0 Eggs and legumes Neurotransmitter synthesis odor men 550 mg 0 Liver and pork women 425 mg UL 35 g 3500 mg o 0 Common Characteristics of watersoluble vitamins o Vitamins in foods I Bound to proteinsthat must be cleaved priorto absorption I Easily destroyed during cooking 0 Digestion I Digested mostly in small intestine 0 Absorption I Absorbed mostly in small intestine but also in stomach I Absorbed via simple diffusion when intake is high and active transport when intake is low I Bioavailability is influenced by many factors 0 Circulation I Transported via blood to liver 0 Functions I Many coenzyme and other roles especially in energy metabolism 0 Toxicity Effects I Minimalalthough some exist 9 0 Naming the vitamins o Orginally vitamins were sorted into two groups based on their solubility in lipids and water I Vitamin A fat soluble and vitamin B water soluble o What researchers thought was a single B vitamin turned out to be several vitamins amp each was given a number 0 B vitamins often referred to as Bcomplex vitamins because they tend to be physically associated with each other 39239 Memorizing the B vitamin names and numbers o 0 Fortification and Enrichment of Foods 0 Fortified food a food to which nutrients have been added I B vitamin thiamin is often added to milled rice and other processed cereal products such as flour o The outer coating and the inner portion of grains contain most ofthe thiamin and these parts are removed during processing milling ofthe grain into quotwhite ricequot 0 Enrichment the fortification of a select group of foods rice flour bread or rolls farina pasta corn meal and corn grits with FDAspecified levels of thiamin niacin riboflavin folate and iron I Often makes the nutritional content of the food similarto what it was before processing I Federal enrichment standards which nutrients to add and how much to add were first established in 1938 and have been since revised several times 9 Protecting watersoluble vitamins in foods o o Watersoluble vitamins can be easily destroyed during cooking and storage 0 Not overcooking vegetables can help prevent the destruction of vitamins 0 Thiamin Vitamin 311 an essential watersoluble vitamin involved in energy metabolism synthesis of DNA RNA and NADPHH and nerve funciton 0 Was given the name thiamin because it contains a thiol sulfur group and an amine nitrogen group o In the body two phosphate groups are combined with thiamin to form the coenzymethiamin pyrophosphate TPP o Thiamin is also present as thiamin triphosphate 39I39I39P which hasthree phosphate groups Dietary Sources and Regulation of Thiamin o 0 Good sources include pork peas fish such as tuna legunes such as black beans whole grain foods enriched cereal products and soy milk 0 Whole grain foods tend to be good sources of watersoluble vitamins Bioavailability and Regulation of thiamin in the Body a o Bioavailability percent absorption of thiamin increases when intake is low I because the cells ofthe small intestine actively transport thiamin from the intestinal lumen intothe absorptive epithelial cell I When thiamin intake is high its absorption proceeds more slowly and by simple diffusion which does not require energy 0 Several dietaryfactors quotantithiamin factorsquot can destroy thiamin or interfere with its absorption I Found in raw fish coffe tea berries brussels sprouts and cabbage I They work in several ways one is by inactivatingthiamin via oxidation Consumingfoods high in vitamin C can help counteract this because vitamin C prevents thiamin from being oxidized it acts as an antioxidant I Alcohol 39 can 39 4 the 39 39 quot ofthiamin I Once absorbed thiamin is circulated away form the small intestine via the blood tothe liver I Excessthiamin is not stored being metabolized and excreted in the urine 39239 Functions of Thiamin o Thiamin is not an energyyielding nutrient directly but its coenzyme form TPP is needed for ATP production I TPP removes a molecule of carbon dioxide C02 from a substrate I Specifically TPP is needed for converting pyruvate to acetyl coenzyme A acetylCoA I TPP is also needed for one of the chemical reations in the citric acid cycle and is involved in reactions allowing some amino acids to enter the citric acid cycle 0 TPP is also needed forthe synthesis of deoxyribonucleic acid DNA and ribonucleic acid RNA I DNA is the genetic material that together with RNA directs protein synthesis 0 TPP is also required for the synthesis of nicotinamide adenine dinucleotide phospate NADPHH I Needed for triglyceride synthesis 0 39I39I39P also plays noncoenzyme roles in the body I It is needed for nerve function 39239 Beriberi a disease that results from thiamin deficiency o Uncommon in the US but is prevalent in regions of the world that rely heavily on unfortified milled rice as a major source of energy 0 quotberiberiquot thought to be derived from the Indonesian word meaning quotI can39t I can39tquot said in response to weakness and impaired functions brought on by thiamin deficiency o Fourforms of Beriberi I Dry beriber39 found mostly in adults and is characterized by severe muscle wasting leg cramps tenderness and decreased feeling in the feet and toes I Wet beriberi involves severe edema swelling in the arms and legs as well as enlargement ofthe heart and respiratory problems often resulting in heart failure Infantile beriberi occurs in babies breastfed by thiamindeficient mothers can cause cardiac arrest and therefore is very serious I Cerebral beriberi WernickeKorsakoff syndrome typically associated with alcoholism alcohol decreases the body39s ability to absorb thiamin characterized by pralysis fo the eye muscles involuntary eye movement poor muscle coordination confusion and shortterm memory loss Thiamin intake by alcoholics can be low and alcoholisminduced liver damage decreases the liver39s ability to convert thiamin to TPP A genetic component predisposes some people to cerebral beriberi 39239 Recommended intakes of thiamin o The Recommended Dietary Allowances RDAsforthiamin I Adult males 12 milligrams mg I Adult females 11 milligrams mg 0 There is no ULforthiamin because toxicity ofthiamin is almost unheard of o 0 Riboflavin Vitamin 3 involved in energy metabolism the synthesis of a variety of vitamins nerve function and protection of lipids 0 consists of a multiring structure attached to the sismple sugar ribose o typically found in the body as one oftis coenzymes I f I flavin adenine dinucleotide FAD avin mononucleotide FMN 39239 Dietary sources and regulation of Riboflavin 0 found in liver meat dairy products enriched cereal produts and other fortified foods 0 relatively stable during cooking but it is easily destroyed by exposure to light I Forthis reason milk is packaged in cardboard or cloudy plastic containers and it is recommended that food be stored in opaque containers or covered with paper orfoil o Roboflavin in food can be in its free form bound to protein or as a coenzyme FMN or FAD 0 Only free riboflavin can be absorbed I Stomach acid and intestinal enzymes convert all forms of riboflavin to its free unbound form prior to absorption in the small intestine 0 Absorption occurs via simple diffusion when intake is high and active transport when intake is low like thiamin I Bioavailability increases at low intakes I Riboflavin in animal foods is somewhat more bioavailable that from plant sources and alcohol can inhibit its absorbtion 0 Upon absorption riboflavin is ciculated in the blood to the liver 0 Riboflavin is not readily stored in the body and excess is excreted in the urine 39239 Functions of riboflavin o Riboflavin is important in energy metabolismthe biosynthesis or activation of several compounds including some vitamins and protection of cell membranes from oxidative damage 0 Riboflavin is a coenzyme for several chemical reactions involved in energy metabolism I Many of which are reductionoxidation redox reactions 0 FAD participates in the citric acid cycle being reduced to FADHZ o FADHZ is reoxidized in the electrom transport chain resulting in the formation of ATP water and carbon dioxide 0 FADHZ is also needed for the breakdown or oxidation of fatty acids into acetylCoA molecules I Process is called betaoxidation I Allows the body to use fatty acids to synthesize ATP 0 FAD is also needed to convert vitamin A and folate a B vitamin to their active forms convert trytophan an amino acid to niacin a B vitamin and form vitamins 36 and K o FAD is also needed forthe metabolism of some important neurotransmitters such as dopamine and is involved in several important reactions that protect biological membranes from oxidative damage o a o a o a a o o o 0 As FMN riboflavin is needed for activating vitamin 36 Riboflavin Deficiency o Ariboflavinosis a disease caused by riboflavin deficiency I Typically associated with broader nutrient deficiencies I Signs and symptoms include Weakness Cheilosis sores on the outside and corners ofthe lips inflammation of the mouth enarged and inflamed tounge Anemia Confusion 0 Rare in the US but can occur in alcoholics consuming poor diets and in people with diseases that interfere with riboflavin utilization such as thyroid disease Recommended intakes of riboflavin 0 Recommended Dietary Intakes RDAs for I Males 13 mgday I Females 11 mgday 0 There is no UL because even at very high doses there are no known toxic effects of riboflavin consumption 0 Riboflavin supplementation can cause the urine to become bright yellow but has no detrimental health consequences Niacin Vitamin Bgl involved in energy metabolism electron transport chain synthesis of fatty acids and proteins metabolism of vitamin C and folate glucose homeostasis and cholesterol metabolism 0 Takes two forms nicotinic acid and nicotinamide o The body uses both forms to make the coenzymes nicotinamide adenine dinucleotide NAD and nicotinamide adenine dinucleotide phosphate NADP Dietary sources of Niacin 0 We get niacin by consuming dietary niacin and by converting the essential amino acid trypotophan to niacin I About 1 mg of niacin can be made from 60 mg of tryptophan o Niacin eguivalent NE a unit of measure that describes the niacin content andor tryptophan in food 0 Niacin ortryptophan is found in liver chicken fishtomatoes beef mushrooms whole grain foods enriched cereal products and other fortified foods 0 Niacin is quite stable and not easily destroyed by cooking or exposure to light Bioavailability of Niacin o Niacin in animal products is more bioavailable than that in grain products I The niacin in grains such as corn and wheat is pound to proteins and these niacinprotein complexes are difficult to absorb Treating grain products with alkaline basic substances such as lime water derived from limestone not the same as limejuice or baking soda can cleave the protein from the niacin increasing its bioavailability 0 Because alkaline conditions can destroy other vitamins in foods it is not recommended that we routinely increase the pH of foods to enhance niacin absorption Regulation of Niacin in the Body 0 Small amounts of niacin can be absorbed in the stomach but most absorption occurs in the small intestine 0 Absorption of niacin is by simple diffusion when intake is high and by active transport when intake is low 0 Niacin is then circulated to the liver where most of it si attached to transport proteins or converted to NAD or NADP the coenzyme forms 0 when needed the liver convertsthe amino acid trytophan to niacin as well I this reaction requiresthe assistance of riboflavin and vitamin 36 Functions of Niacin o Niacin plays many roles as the coenzymes NAD and NADP I NAD is reduced to NADH H during the oxidation breakdown of fatty acids as well as in several reactions of glycolysis and the citric acid cycle NADH H then participates in the electron transport chain to produce ATP I NADP can be reduced to NADPH H NADPH H is needed for synthesizing fatty acids cholesterol steroid hormones and DNA NADPH H is also required for metabolizing vitamin C and folate o Niacin has additional functions unrelated to its role as a coenzyme I It is important for maintaining replicating and repairing DNA I It may play a role in protein synthesis glucose homeostasis and cholesterol metabolism 0 Consuming large amounts of niacin 2 to 4 gday has been shown to lower lowdensity lipoprotein LDL cholesterol and increase highdensity HDL cholesterol in some people I Not well known so consuming large amounts of supplemental niacin for this purpose is not recommended 0 Niacin Deficiency Pellegr a disease caused by niacin andortrytophan deficiency I Italian for quotrough skinquot I Symptoms the four D39s Dermatitis a condition characterized by rough red skin that eventuallythickens and turns dark Dementia neurological problem Other neurological problems include depression anxiety irratability and inability to concentrate Diarrhea gastrointestina distrubance Other gastrointestinal disturbances caused are loss of appetite and a characteristically red and swollen tongue 0 Death I Although once common pellagra is now typically seen only in conjunction with poverty general malnutrition or chronic alcoholism I Genetics and some medications can also cause niacin deficiency by inhibitingthe syntehsis of niacin from tryptophan 39239 Niacin Toxicity 0 Large doses of nicotinic acid 1 gday can cause skin inflammation and itchiness flushing heartburn nausea increased plasma quot1 x n o v m m 3 o E m o m 3 m an m 0 Thus consuming large doses of supplemental nicotinic acid is not recommended 39239 Recommended intakes of Niacin o The RDAs for I Men 16 mgday of niacin or niacin equivalents NE I Women 14 mgday of niacin or niacin equivalents NE 0 The UL is 35 mgday 39239 Pantothenic Acid Vitamin B l nitrogencontaining vitamin involved in energy metabolism hemoglobin synthesis and phospholipid synthesis 0 Named for the Greek work pantos which means quoteverywherequot I Because it is found in almost every plant and animal tissue 0 Pantothenic acid functions as a component of coenzyme A CoA in a variety of metabolic reactions 0 Dietary Sources of Pantothenic Acid 0 Found in mushrooms organ meats such as liver sunflower seeds dairy products turkey fish and coffee 0 High temperatures can destroy pantothenic acid in food 0 Regulation and Functions of Pantothenic Acid in the body 0 Bioavailability of pantothenic acid increases via active transport when pantothenic acid intake is low 0 Once absorbed pantothenic acid is circulated to the liver in the blood 0 Pantothenic acid itself is not stored in the body but concentrations of its coenzyme form CoA are especially high in liver kidney heart adrenal glands and brain 0 The primary function of pantothenic acid as CoA is in the metabolism of glucose amino acids and fatty acids for energy ATP production via glycolysis and the citric acid cycle I Pantothenic acid is needed for one ofthe pivotal steps in energy metabolism ATP production converting pyruvate to acetylCoA o Pantothenic acid is also required for synthesizing many other critival compounds in the body including heme a portion of hemoglobin cholesterol bile salts phospholipids fatty acids and steroid hormones o o o o o O o o o A o a Pantothenic Acid deficiency and Toxicity o Deficiency is rare because it is found in almost all foods 0 A condition called quotburning feet syndromequot is thought to be due to severe pantothenic acid deficiency I Causes tingling in the feet and legs as well as fatigue weakness and nausea Pantothenic acid toxicity has not been reported but very high intakes of this vitamin have been associated with nausea and O diarrhea Recommended Intakes of Pantothenic Acid 0 There is not enough information to establish RDAs for pantothenic acid so an AI of 5 mgday has been set for adults 0 There are no ULs because no evidence exists of toxicity Vitamin BE involved in the metabolism of proteins and amino acids the synthesis of neurotransmitters and hemoglobin glycogenolysis and regulation of steroid hormone function 0 There are three forms pyridoxine pyridoxal and pyridoxamine I All made of a modified nitrogencontaining ring structure I All have similar biological activities in the body involving over 100 chemical reactions Dietary Sources of Vitamin 36 o Chickpeas garbanzo beans fish liver potatoes chicken fortified breakfast cereals and bakery products 0 Not one ofthe vitamins added to quotenrichedquot products o It is somewhat unstable and heating and freezing can destroy it Regulation and Functions of Vitamin 36 in the body o It is readily absorbed in the small intestine and circulated in the blood tothe liver 0 The liverthen adds a phosphate group forming pyridoxal phosphate PLP the coenzyme form of vitamin 36 I PLP is efficiently stored in muscle and to a lesser extent in the liver PLP acts as a coenzyme in over 100 chemical reactions related to metabolism of proteins and amino acids via transamination O I These reactions are required for synthesizing nonessential amino acidsfrom essential amino acids I Only 9 essential amino acids must be obtained from foods whereas 20 amino acids are need for life Without 36 all 20 amino acids would be essential 0 Vitamin 36 is also needed for producing nonprotein substances such as the neurotransmitters serotonin and dopamine as well as heme 0 Vitamin 36 is needed to convert tryptophan to niacin to break down glycogen to its glucose subunits and to regulate some of the steroid hormones 0 Vitamin 36 is also needed to prepare some amino acids to enter the citric acid cycle Vitamin 36 deficiency o microc ic hypochromic anemi a condition in which red blood cells are small microcytic and light in color hypochromic due to inadequate hemoglobin synthesis can be due to vitamin 36 deficiency I decreases oxygen availability in tissues and impairs the ability to produce ATP via aerobic metabolism Vitamin 36 deficiency also causes cheilosis glossitis stomatitis and fatigue O I Symptoms similartothose of riboflavin deficiency 0 Vitamin 36 deficiency is rare when food is abundant 0 During the 1950sthe damaging effect of high temperatures on vitamin 36 was not well understood and vitamin 36 added to infant formula was destroyed during processing I Thus many formulafed infants developed vitamin 36 deficiency I This quotepidemicquot caused serious complications such as seizures and convulsions Vitamin 36 Toxicity 0 Because it is stored vitamin 36 toxicity occurs more frequently than most watersoluble vitamins Toxicity does not result from consuming naturally occurring vitamin 86 but ratherfrom supplement use O o Toxicity causes severe neurological problems including difficulty walking and numbness in the feet and hands 0 High dosages of vitamin 36 1000 mgday may relieve the symptoms of premenstrual syndrom PMS and carpal tunnel syndrome 0 Also relatively large doses may decrease the risk of heart disease But most studies do not support a helpful effect of supplements on these conditions and toxicity is likely at these doses so large doses are not generally recommended Recommended Intakes of Vitamin 36 o RDAs in adults varyfrom 13 to 17 mgday 0 UL has been established at 100 mgday for adults I Supplements containing 500 mg are widely available making it easy to exceed the UL o 0 Biotin Vitamin B1 involved in energy metabolism and regulation of gene expression 0 Sulfurcontaining molecule with two connected ring structures and a side chain 0 Humans obtain biotin from both the diet and via biotinproducing bacteria quotbiotaquot in the large intestine o Biotin is required for gluconeogenesis and the citric acid cycle being important for ATP production 39239 Dietary sources and bioavailability of Biotin o Peanuts tree nuts mushrooms eggs and tomatoes 0 Biotin is frequently bound to proteinsthat are cleaved during digestion 0 Its bioavailability can be greatly reduced when it is consumed with foods containingthe protein avidin a protein present in egg whites that binds biotin making it unavailable for absorption I Avidin binds tightly to biotin in the intestinal tract making it difficult to absorb I Heat destroys avidin so eating raw eggs can decrease biotin bioavailability whereas cooked eggs do not have this effect o Comsuming alcohol can also decrease biotin absorption 0 Extreme heat can destroy biotin in foods 39239 Regulation and Functions of Biotin in the body 0 Enzymes in the small intestine cleave most of the porteinbiotin complexes found in foods releasingfree unbound biotin which isthen absorbed 0 Also produced by bacteria in the large intesine where it can be absorbed I Bacteria do not make enough biotin to meet our needs so biotin is an essential nutrient o Biotin ciculates to the liver in the blood and small amounts are stored in muscle liver and brain 0 Biotin acts as a coenzyme for several enzymes all of which catalyze carboxylation reactions a metabolic reation in which a bicarbonate subunit HCOg is added to a molecule I These enzymes are involved in energy metabolism pathways I Example a biotinrequiring enzyme converts pyruvate to oxaloacetate a key step in gluconegenesis I Biotin is also a coenzyme for the reactionsthat allow the body to use some amino acids in the citric acid cycle forthe synthesis of fatty acids and forthe breakdown of the amino acid leucine o In addition to biotin39s role as a coenzyme it has noncoenzyme functions related to gene expression especiallythat influencing cell growth and development 39239 Biotin Deficiency o Uncommon but it occurs in small portions of the population such as people who routinely consume large quantities of raw egg whites containing avidin I In theory it would take daily consumption of at least 12 raw egg whites for a prolonged period of time to cause biotin deficiency o Biotin deficiency can also be caused by conditions impairing intestinal absorption such as inflammatory bowel disease and in some genetic disorders 0 Symptoms of biotin deficiency are poorly understood but include depression hallucinations skin irritations infections hair loos poor muscle control seizures and developmental delays in infants 39239 Recommended Intakes of Biotin 0 There is insufficient information forthe development of RDAs for biotin so an AI level for adults of 30 micrograms per day has been set 0 No ULs are established forthis vitamin o 0 Folate Folic Acid 0 Folate also called folacin involved in singlecarbon transfer reactions needed for amino acid metabolism and DNA synthesis I Consists of three parts A nitrogencontaining double ring structure o A nitrogencontaining single ring structure 0 A glutamic acid also called glutamate I Typically has additional glutamic acids attached to it o The interconversion of these quotpolyglutamatequot forms of folate is important for the functions of folate o Folic acid foates most oxidized and stable form I Rarely found in foods but is commonly used in vitamin supplements and food fortification 39239 Dietary sources of folate o folate is an italian term that meansfoliage reflecting its abundance in leafy plants 0 goods souces include organ meats legumes such as lentils and pinto beans okra spinach and many green leafy vegetables 0 since 1998 all enriched cereal products in the US are fortified with folate making them very good sources 0 orangejuice can now be found fotified with folate 0 heat light and oxygen can destroy folate cooked foods often have less folate than raw foods 39239 Bioavailability and regulation of folate in the body 0 Bioavailability of folate varies depending on the form of folate present 0 Genetic factors and drugs can also influence folate absorption 0 Absorptionof folic acid from supplements and fortified foods is higher than folate naturally found in foods 0 Dietaryfolate equivalents DFE a unit of measure used to describe the amount of bioavailable folate in a food or supplement I Requirements are expressed using DFE because folate absorption is so variable and DFE takesthis into account 0 Dietary folate typically contains multiple glutamate units that must be cleaved prior to absorption I A variety of foods such as cabbage contain compounds that inhibit this process thus decreasing bioavailability 0 Once take up bythe intestinal cell folate is converted to tetrahydrofolate THF the active form of folate by the addition of 4 hydrogen atoms 0 Then a methyl group CH3 is added resulting in the production of 5methyltetrahydrogolate 5methyl THF an inactive form of folate which is released into the blood and ciculated to the liver 0 A limited amount of folate is stored in the liver 39239 Function of Folate SingleCarbon Transfers o Folate in its active form of TH F acts as a coenzyme for many reactions I All of these reactions involve the transfer of singlecarbon gropus such as CH3 I These reactions shift carbons from one molecule to another to form the many organic substances required for life 0 Folate is involved in the metabolism and interconversion of amino acids I In these reactions carbons are moved one at a time from oen compound to anotherto produce what the body needs 0 An example of folate39s singlecarbon transfer role is the conversion of homocysteine to methionine p401 I In this reaction 5methyl THF transfers a methyl group CH3 to homocysteine making THF and methionine I This reaction provides the body with the amino acids methionine as well as THF the active form of folate I This reaction does not happen by itself it occurs in synchrony with another reaction involving a vitamin Biz requiring enzyme 0 This is an example of a coupled reaction meaning the two reactions occur simultaneously and one cannot happen without the other 0 First The methyl group CH3 is transferred from 5methyl THF to vitamin Bu 0 Then vitramin B12 transfers the methyl group to homocysteine resulting in the synthesis of methionine 0 So the production of methionine from homocysteine requires both folate and vitamin Bu I A deficiency in either of these B vitamins results in a buildup of homocysteine in the body I High levels of homocysteine are associated with increased risk of heart disease I High concentrations of homocysteine are also realted to memory loss and difficulty with abstract thought and some researchers hypothesize that impaired folate metabolism may be associated with Alzheimer39s disease 0 THF is also involved in singlecarbon transfer reactions required to make purines and pyrimidine compoundsthat make up DNA and RNA I DNA must be synthesized each time a new cell is made so folate is essential for growth maintenance and repair of all tissues in the body I Especiallytrue during periods of rapid growth and development like fetal growth and in cells with very short life spans such as those liningthe gastrointestinal tract 0 Folate is also required for the normal growth and development of nerve tissue in the fetus I Increased folate intake duringthe reproductive period has been shown to decrease the risk of neural tube defects a malformation in which the neural tissue does not form properly during fetal development 9 0 Folate Deficiency o Mild folate deficiency results in fatigue weakness irregular heart function and headaches 0 Severe folate deficiency causes macrog ic anemi a condition in which red blood cells are large caused by inability of the cell to mature and divide appropriately can be due to folate deficiency andor vitamin B12 I Because of folate39s importance in DNA synthesis and cell maturation severe folate deficiency causes many cells including red blood cells to remain in an immature state Immature red blood cells are large macrocytic and contain organelles not typically foundnin mature red blood cells 0 Mature red blood cells do not have nuclei whereas immature red blood cells do I Deficiencies of other nutrients such as vitamin B12 can also cause this form of anemia I Sometimes hard to determine whether macrocytic anemia is due to folate or to vitamin B12 deficiency o Folate deficiency was once common the US but this is no longerthe case I Partly due to enriched cereal products that are not fortified with folate Folate deficiency occurs most in alcoholics people with intestinal diseases and people taking certain medications O Folate deficiency is quite common in the elderly who take many medications that inhibit folate absorbtion and use 0 Genetic variations among people also influence how folate is absorbed and metabolized 39239 Recommended Intakes of Folate 0 Recommendations have received a lot of attention since its was discovered in the late 1980s that it decreased neural tube defects o It is recommended that adults consume 400 micrograms of folate DFE daily I This increases to 600 micrograms in pregnant women Women capable of andor planning to become pregnant are encouraged to consume 400 micrograms of folate folic acid from supplements fortified foods or both in addition to consuming food folate from a varied diet 0 UL has been set at 1000 microgramsday from fotified foods or supplements I Because high intakes of folate may make it difficult to detect vitamin B12 deficiency I There is no evidence that high intake of naturally occurring folate poses any risk 39239 Vitamin Bg cobalamin involved in energy metabolism and the conversion of homocysteine to methionine o The last of the B vitamins to be discovered 0 Gets it name from the fact that it contains the trace element cobalt Co and several nitrogen N atoms 39239 Dietary Sources of Vitamin B12 Cannot be made by plants or higher animals such as mammals and birds but only by microorganisms such as bacteria and O fungi I Many of our sources do not actually produce it themselves but obtain vitamin B12 from microorganisms either in their environment or in their gastrointestinal tracts 0 Good sources include shellfish such as clams and crabs meat including poultry organ meats fish and dairy products 0 Also many readytoeat breakfast cereals are fortified with vitamin B12 39239 Regulation of Vitamin B12 in the body Most vitamin B12 in foods is bound to proteins that must be cleaved before absorption O 0 These proteins are hydrolyzed in the stomach via acids and the enzyme pepsin 0 Free vitamin B12 is then bound to two proteins that are also made in the stomach I R protein a protein produced in the stomach that binds to vitamin B12 protects vitamin B12 from destruction 0 in the intestine r protein is released whereas intrinsic factor remains bound to vitamin B12 I intrinsic factor a protein produced by exocrine cells in the gastric pits of the stomach needed for vitamin B12 absorption 0 it remains bound to vitamin B12 in the small intestine and this complex istransported into the absorptive cell 0 an inability to produce intrinsic factor can result in severe vitamin B12 deficiency 0 Once absorbed vitamin B12 is released from intrinsic factor and bound to another protein called transcobalamin the protein that transports vitamin B12 in the blood to the liver 0 Most B vitamins are not stored in the body but vitamin B12 is heavily stored in the liver several years worth 39239 Functions of Vitamin B12 0 Participates as a coenzyme in only two reactions I One reaction catalyzesthe production of succinyl CoA an intermediate in the citric acid cycle Allows the body to use some amino acids and fatty acids for energy ATP production I The other reaction catalyzesthe conversion of homocysteine to the amino acid methionine The inactive form of folate 5methyl THF is converted to its active for THF 0 Without adequate vitamin Biz homocysteine levels build up in the blood and folate becomes quottrappedquot as its inactive 5methyl THF form 0 this causes folate deficiency symptoms o In this way vitamin Bu deficiency can cause secondaryfolate defciency 39239 Vitamin Bu deficiency and pernicious anemia o Deficiency can result from inadequate dietary intake or absorption of vitamin Biz 0 Primary deficiency is sometimes seen in vegans or infants being breastfed by vitamin Biz deficient mothers 0 Secondary deficiency can occur when gastric cells stop producing intrinsic factor called pernicious anemia I usually caused by an autoimmune disease in which the body39s immune system destroysthe stomach cellsthat produce intrinsic factor I Can also be casused by other conditions such as aging genetic defects gastrointestinal infections surgeries and some medications I People with this disease cannot be treated with oral vitamin B12 supplements but must be given vitamin B12 by injection 0 Deficiency is especially common in the elderly population effecting as many as 15 I Due to inadequate vitamin Biz intake decreased synthesis of intrinsic factor pernicious anemia decreased acid secretion in the stomach and malabsorption I Signs and symptoms typically include macrocytic anemiafatigue difficulty sleeping numbness memory loss and severe neurological disturbances Resembles other conditions associated with aging so vitamin B12 deficiency may be overlooked o Folate Vitamin Biz and Anemia I Anemia associated with vitamin Bu deficiency is caused by the resultant secondaryfolate deficiency I Vitamin Bu deficiency causes a deficiency in THF even when adequate folate is consumed Because folate gets quottrappedquot as 5methyl THF when vitamin Bu is not available I Foalte deficiency can quotmaskquot vitamin Biz deficiency Because large doses of folate seem to alleviate some of its symptoms such as anemia I Other complications of vitamin Biz deficiency are not allievated with high doses of folate I The other symptoms involve severe neurologic damage and can be fatal so misdiagnosing vitamin Biz deficiencyfor folate deficiency is dangerous 39239 Recommended Intakes for Vitamin Bu RDA is 24 microgramsday for adults 0 Recommended that those over 50 years of age be especially careful to choose vitamin Biz fortified foods or consume supplements if necessary Vegans who do not eat any animal products should take a supplement or eat foodsthat have been fortified with vitamin B12 Although it is actively stored in the liver no ULs are established 0 O O 39239 Vitamin C Ascorbic Acid has antioxident functions 0 Important for immune cardiovascular neurological and endocrine systems 0 Can be made from glucose in all plants and most animals but not in humans 0 Primates including humans fruit bats and guinea pigs are some ofthe few animals for which vitamin C is an essential nutrients O Technically referred to as absorbic acid 39239 Dietary Sources of Vitamin C 0 Found in many fruits and vegetables such as citrus fruits peppers papayas broccoli strawberries and peas 0 Bioavailability of vitamin C is generally high although it is easily destroyed by heat oxygen and high pH I Freshly peeled andor prepared fruits and vegetables tend to provide more vitamin C than cooked processed andor stored ones 39239 Regulation of Vitamin C in the body 0 Absorption of vitamin C occurs mainly in the small intestine via active transport using glucose transport proteins I This is because vitamin C is structurally similarto glucose 0 At very high intakes vitamin C is also absorbed by simple diffusion in both the stomach and small intestine 0 Vitamin C then circulates to the liver in the blood 0 As in the intestine the uptake of vitamin C into the body39s cells relies in part on glucose transporters 0 Excess vitamin C is not stored I It is rapidly metabolized and excreted in the urine 39239 Functions of Vitamin C o It is not a coenzyme like the B vitamins are o It acts as an antioxidant a compound the readily gives up electrons and hydrogen ions to other substances I Atoms contain negatively charged electrons I An abundance of elctrons in a atom or molecule can result in an overall negative charge I Such an atom or molecule is therefore said to be quotreducedquot I When electrons are removed the atommolecule has a more positive charge and is said to be quotoxidizedquot I Vitamin C can easily accept and donate electrons so it is involved in a variety of redox reactions 0 The quotrechargingquot of enzymes I Enzymes are not used up or destroyed while catalyzing reactions but sometimes a portion of the enzyme needsto be restored or regenerated between reactions 0 This is especiallytrue when the enzyme contains an element such as copper or iron that gets oxidized duringthe reaction I An enzyme that needs restoration is like a flaslight that requires batteries The flashlight can work for years as long as the battery is replaced or recharged periodically The enzyme is the flashlight Copper and iron atoms are batteries 0 Vitamin C is a battery recharger I During many chemical reactions copper or iron atoms are oxidized made more positively charged and then must be reduced or quotrechargedquot for the enzyme to catalyze another reaction I Example of how vitamin C quotrechargesquot an enzyme is the role of vitamin c in collagen production Collage main protein found in connective tissue skin bones teeth cartilage and tendons For collagen to function properly 3 strands of protein must twist together in just eh right way 0 this requires a coppercontaining enzyme to be oxidized Vitamin C is needed to reduce this coppercontaining enzyme bw reactions so it can continue to form collagen because of this vitamin c is needed forthe health of all connective tissue I Vitamin C is also involved in the synthesis of carnitine by quotrechargingquot two ironcontaining enzymes needed for its synthesis Carnitine allows the body to use fatty acids for energy production I Tyrosine a nonessential amino acid is made in the body from phenylalanine an essential amino acid via iron containing enzyme I The neurotransmitters norepinephrine and serotonin are synthesized via enzymesthat are quotrechargedquot by vitamin C I Enzymes involved in the synthesis of several hormones such as cholecystokinin CCK and gastrin also require the reducing actions of Vitamin C o Enhancing Iron Copper and Chrominum Bioavailability I Several minerals such as iron copper and chrominum are better absorbed in their reduced states Consuming vitamin C with these essential minerals can increase their bioavailability by reducingthem in the gastrointestinal tract 0 Vitamin C and Protection from Free Radical Damage I Free radical a reactive molecule with one or more unpaired electrons in their outer shells makingthem unstable and reactive Destructive to cell membranes DNA and proteins 0 Examples ofthese charged compounds are produced during 0 During normal cellular metabolism many charged compounds are produced 0 Exposure of the body to toxic substances smog cigarette smoke ozone some drugs and intense sunlight I Most substancestryto have an even number of electrons and will take electronsfrom other molecules to do so o In other words free radicals readily oxidize other molecules I Oxidation by free radicals harms the body in several ways o It can break and damage DNA potentially causing mutations in genes and possibly cancer 0 Free radicals can also oxidize fatty acids found in cell membranes causingthem to become weak and break down 0 Free radicals can also damage proteins I The body is equipped to both destroy free radicals and repairthe damage they cause 0 Vitamin C is one such quotantioxidant systemquot I By donating a hydrogen atom and its electron it reduces the dangerous hydroxyl free radical OH to water H20 0 Vitamin C the Common Cold and Other Diseases I Studies suggest that increased consumption of fruits and vegetables containing vitamin C is associated with decreased risk forthe common cold cancer heart disease and cataracts I Large doses of vitamin C can benefit the immune system I The immune system is directly involved in many ofthese diseases so it is possible that vitamin C indirectly affects disease via regulation of immune system 39239 Vitamin C Deficiency and Toxicity o M a condition caused by vitamin C deficiency I Symptoms include bleeding gums bruising poor wound healing and skin irritaions Due to inadequate collagen production I James Lind a British doctor determined that consuming citrus fruits would prevent and cure this disease I Rare because of increased availability of fruits and vegetables but is still seen in developing countries alcoholics and appears to be somewhat common in people with diabetes 0 Most people can consume very large doses 2 to 4 gday of supplemental vitamin C without experiencing harmful effects but in some it can cause nausea diarrhea cramping and kidney stones 39239 Recommended Intakes of Vitamin C o RDAs I Men 90 mgday I Women 75 mgday 0 Because ofthe increased risk for free radical damage from cigarette smoke smokers are advised to increase their vitamin C intake by an additional 35 mgday I Whether is recommendation also applies to people exposed to secondhand smoke is not clear 0 ULfor vitamin C intake from supplements 2 gday 2000 mgday o 0 Choline A quotNewquot Essential Vitamin o Choline used by the body to synthesize acetylcholine a neurotransmitter and a variety of phospholipids needed for cell membrane structure I Considered a conditionally essential nutrient o The body can typically make choline in sufficient amounts so scientiststhought that people did not need to consume it from the diet I More recent work shoes that otherwise healthy men develop liver damage when fed a cholinefree diet I Studies also show that humans fed intravenous solutionsthat do not contain choline develop fatty livers and liver damage 0 Dietary Sources of Choline o Abundant in many plants and animal foods particularly eggs liver legumes and pork 0 We also consume relatively large amounts of choline from products such as mayonnaise and salad dressings I Because the cholinecontaining compound called lecithin also called phosphatidylcholine is often added to these foods as an emulsifier 0 Regulation and Functions of Choline in the Body 0 Free unbound choline found in food is absorbed in the small intestine and circulates to the liver via the blood 0 To be absorbed I the choline component of lecithin is first cleaved from the glycerol backbone by pancreatic enzymes I then it is taken up by intestinal cells and reconstituted into lecithin molecules which are released into the lymph o A large portion of the lecithin that is ultimately delivered tothe liver becomes a component of lipoproteins I such as lowdensity lipoportein or LDL o In most healthy adults choline is readily made in the body from the essential amino acid methionine with the assistance of vitamin B12 and folate o Choline is needed for synthesizing a variety of phospholipids such as lecithin as well as acetylcholine a neurotransmitter o Choline is also an important component of cell membranes and lipoproteins o Choline is also needed for muscle control 0 Other compounds requiring choline fortheir synthesis play structural roles in the body and act as singlecarbon donors in metabolic reactions 39239 Choline Deficiency Toxicity and Recommendations 0 Very little is known about the symptoms of choline deficiency in humans 0 There is limited evidence that choline deficiency can cause liver damage in adult men I Choline deficiency is thought to cause a buildup of lipids in the liver because of the liver39s inability to produce very low density lipoproteins VLDLs which are needed to export triglycerides 0 Very high choline intake from foods can cause a fishy body odor excess perspiration salivation low blood glucose and liver damage I These symptoms may not be desirable but they are generally not fatal 0 There is not enough information to establish RDAs for choline so Als are I Men 550 mgday I Women 425 mgday 0 UL 35 gday 3500 mgday 39239 Carnitine 0 Not an essential nutrient for adults but it is conditionally essential for infants I all mammals can synthesize carnitine but this ability may be inadequate in newborns especiallythose born prematurely o as with choline reasearchers disagree on how to classify carnitine o the best sources of carnitine in the diet are animal sources such as meat and milk I human milk provides relatively high amounts of carnitine as do many infant formulas I the high amount of naturally occurring carnitine in human milk supports the hypothesis that this compound is conditionally essential during infancy 39239 Regulation and Functions of Carnitine in the Body 0 efficiently absorbed in the small intestine and is produced in the body from the amino acids methionine and lysine I requires the assistance of iron niacin vitamin 36 and vitamin C o needed for fatty acids to cross membranes such as the mitochondrial membrane I therefore carnitine is essential for the body39s use of fatty acids for energy ATP production 0 Carnitine supplements are sold as aidsto help build muscle and to increase athletic performance I There is limited scientific evidence to support this claim 39239 Carnitine Deficiency Toxicity and Recommendations 0 Deficiency is rare but it can occur in some gentic conditions I resulting in muscle weakness hypoglycemis and heart irregularities o Deficiency is rare even in vegans who consume very little dietary carnitine I This supports the concept that carnitine is not an essential nutrient for adults 0 No toxic effects of high doses of carnitine are known 0 Not considered essential so no DRs are established vitamins are not nutrients are in energy coenzyme o 0 Summary and Use of supplements 39239 Vitamin Supplements Making Wise Choices 0 Dietary supplement products intended to supplement the diet that contains vitamins minerals amino acids herbs or other plantderived substances botanicals andor a multitude of otherfoodderived compounds I Thus only some dietary supplements contain vitamins I Unlike drugs dietary supplements are not approved by the FDA for safety and effectiveness 0 Instead it is the responsibility of dietary supplements manufacturers and distributors to ensure that their products are safe and that their label claim are accurate and truthful Once a product enters the marketplace FDA hasthe authority to take action against any dietary supplement that presents a risk of illness or injury 0 Sorting Fact from Fiction I Provingthat a nutrient influences health requires proper use of scientific method I An excellent source of uptodate information is the Office of Dietary Supplements ODS part ofthe national institutes of Health 0 Established in 1994 to strengthen knowledge and understanding of dietary supplements by evaluating scientific information and educating the public I The ODS recommends the following tips for buying and using any dietary supplement Safetyfirst some supplement ingredients can be toxic especially in high doses 0 Think twice about chasing the latest headline good health advice is generally based on research over time not a single study touted bythe media Be wary of results claiming a quotquick fixquot 0 Learn to spotfalse claims Remember if something sounds too good to be true it probably is o More may not be better Some products can be harmful when consumed in high amounts for a longtime The term quotnaturalquot does not always smean safe quotnaturalquot simply means something is not synthetic or humanmade Do not assume that this term ensures wholesomeness or safety 0 When shouldyou considertaking a supplement I If someone has difficulty consuming a good variety and balance of foods in adequate amounts taking a deietary supplement may help ensure that the person gets appropriate amounts ofthe essential nutrients This is likely in sever situations 0 When food availability andor variety is limited by time limitations or cooking constraints such as college life 0 In situations when a person does not consume certain foods 0 During periods of rapid growth and development 0 When economic situations are difficult I When a lowcalorie diet is being consumed for weight loss 0 In certain health conditions that increase nutrient requirements CHAPTER 11 FAT SOLUBLE VITAMINS Vitamin Major Functions Deficiency Toxicity Excellent Food Sources Vitamin A 0 Growth 0 Vitamin A deficiency Hypervitaminos A 0 Liver Reproduction disorder VADD Hypercarotenemia Pumpkin 0 Vision 0 Night blindness Blurred Vision 0 Sweet Potato 0 Cell differentiation 0 Xerophthalmia Birth defects o Carrot Immune function 0 vaerkeratosis Liver damage 0 Bone health Osteoporosis Vitamin D 0 Calcium homeostasis Rickets Hypercalcemia Fish 0 Bone health Osteomalacia Shiitake mushrooms 0 Cell differentiation Osteoporosis Fortified milk Fortified cereals Vitamin E Antioxidant Neuromuscular Hemorrhage Tomatoes 0 Cell membranes problems 0 Nuts seeds 0 Eye health Hemolytic anemia o Spinach Heart health Fortified cereals Vitamin K Coenzyme Vitamin K deficiency No known effects Kale carboxylation bleeding VKDB o Spinach Blood clotting Broccoli 0 Brussels sprouts Bone health Tooth health 9 0 Basics of the fatsoluble vitamins 0 Typically absorbed in the small intestine I Requires the presence of other lipids as well as the action of bile o circulated away from the small intestine in the lymph via chylomicrons o eventually circulated in the blood either as components of lipoproteins such as very low density lipoproteinsVLDLs or bound to transport proteins 0 Like watersoluble vitamins each fatsoluble vitamin has several forms some of which are more biologically active than others 0 Most fatsoluble vitamins are stored in the body so consuming large amounts of them especially in supplement form can result in toxicities sometimes with serious consequences 0 Most fatsoluble vitamins are involved in other processes such as regulation of gene expression cell maturation and stabilization of free radicals I Except for vitamin K which acts as a coenzyme 39239 General Characteristics ofthe FatSoluble Vitamins Sources Typically found in fatty portions of food Occurs in intestine Requires incorporation into micelles and the actions of bile Via o 0 Naming of the FatSoluble Vitamins 0 Researchers initially thought there were only two vitamins and they were referred to as vitamine A fatsoluble and vitamine B watersoluble 0 As with vitamin B there turned out to be several kinds of vitamin A each being assigned a different letter as its individual importance was discovered 0 Each fatsoluble vitamin has several forms so numbers are sometimes used to distinguish them from each other 0 Most have been given names that reflect their chemical composition or function 9 0 Vitamin A and the Carotenoids o Retenoid preformed vitamin A a term used to describe all forms of vitamin A I Includes retinol reinoic acid and retinal I Retinol is the most potent form of vitamin A and can be synthesized in the body from retinal I Retinal can also be converted to retinoic acid but retinoic acid cannot be converted to any other retinoid o Carotenoids brightly colored compounds found in some foods I Structures similar to that of vitamin A retinoids I Can be subdivided into two categories Carotenoids that can be converted to vitamin A provitamin A carotenoids o Betacarotene one of the most common provitamin A carotenoids n foods the body can split it to form two molecules of retinal Carotenoids that cannot be converted to vitamin A onprovitamin A carotenoids 0 Include lycopene astaxanthin zeaxanthin and lutein 0 Not classified as vitamins rather they are called phytochemicals and foods containing them are considered functional foods 39239 Dietary Sources of Vitamin A and the Provitamin A Carotenoids o Retinol activity eguivalent RAE a unit of measure used to describe the combined amount of preformed vitamin A and provitamin A carotenoids in foods Allows food containing preformed vitamin A to be easily compared to food containing provitamin A carotenoids such as betacarotene in this way the RAE is similartothe niacin equivalent NE a measure of a food39s quotpotentialquot CO nte nt niacin I Approximately 12 micrograms of betacarotene or 1 microgram of retinol equals 1 RAE o Preformed vitamin A is found in animal foods such as liver and other organ meats fatty fish and dairy products I A single serving of beef liver provides more than seven timesthe daily requirement for vitamin A I Wholefat dairy products such as whole milk cheese and butter are goods sources of vitamin A whereas reducedfat products are not unless they are fortified 0 Animal foods provide preformed vitamin A but plants tend to provide most of the provitamin A carotenoids I Yellow orange and red fruits and vegetables such as cantaloype carrots and peppers are especially good sources of the carotenoids I Leafy greens are also good sources Carotenoids can also be found in brightly colored animal foods such as egg yolks and shrimp Carotenoids tend to be yellowishred in color and their presence in foods makesthem brightly colored too Carotenoids are sometimes added to foods as coloring agents Vitamin A and many of the provitamin A carotenoids are quickly destroyed by extreme cold or hot temperatures as well as exposure to light or oxygen 0 They are easily lost during processing cooking freezing and storage I Betacarotene is an exception processing and heating seem to increase its bioavailability 39239 Regulation ofVitamin A and the Carotenoids in the Body 0 Vitamin A and the carotenoids are absorbed in the small intestine I This requiresthe presence of dietary lipid involvingthe formation of micelles with the assistance of bile A lowfat diet can decrease vitamin A and carotenoid absorption and thus their bioavailability because the body is unnable to form micelles 0 Upon their entrance into the enterocyte lipids are incorporated into chylomicrons o Fatsoluble vitaminsjoin with other dietary lipids and they move from the gastrointestinal tract into the circulation I A lack of dietary lipid can inhibit chylomicron formation in turn inhibitingthe bioavailability of vitamin A 0 Vitamin A and the carotenoids contained in the chylomicrons then enterthe lymph where they ultimately enterthe blood at the thoracic duct 0 Once in the blood vitamin A and the carotenoids are delivered to many issues and organs including adipose tissue muscle and the eyes 0 What is not taken up is transported to the liver as part of the chylomicron remnant 0 Once taken up bythe liver carotenoids are packaged in to VLDLs forfurthertransport but vitamin A is not O Instead vitamin A is attrached to transport proteins for delivery to the cells I Retinolbinding protein and transtheretin proteinsthat carry retinol in the blood 0 Vitamin A not taken up bytissues is stored in the liver 39239 Functions of Vitamin A 0 Vision I Light entering the eye encounters the inner back lining called the retina which consists of a layer of nerve tissue as well as millions of cells called cones and Lds The cones help us see color and the rods are needed to see black and white for night vision Both cones and rods require vitamin A as retinal to work effectively although scientists understand its role in the rod cells better Rhodopsi a compound found in the rods that consists ofthe protein opsin and the vitamin cisretinal When light strikes rhodopsin the cisretinal is converted to transretinal and separates from the opsin This causes a neural signal to be sent to the brain via the optic nerve where it can then form an image that we recognize Vitamin A is also important for maintaining the health of the outermost layer of tissue covering the front of the eye the cornea Vitamin A deficiency is associated with vision problems one of which is difficulty seeing in the dark 0 Because transretinal must be reconverted to cisretinal and then recombined with opsin to reform rhodopsin each time light reaches the back of the eye However transretinal does not recycle to cisretinal with 100 effeciency it is instead metabolized to retinoic acid which cannot be used to form rhodopsin Extra retinal must therefore be available for vision to remain optimal I Lack of vitamin A can also delay vision restoration after exposure to bright light 0 Bright light dissociates rhodopsin amp people who don39t have sufficient vitamin Ato reform rhodopsin have a harder time readjusing their vision and see the bright spot for a longer amount of time leaving them temporarily blinded bythe light 0 Cell Differentiation Growth and Reproduction I Cell differentiation the process in which an immature cell becomes a specific types of mature cell Forthis to occur vitamin A is taken up intothe immature cell where it moves intothe nucleus and binds to specific genes on the strands of DNA 0 The binding of vitamin Ato a gene initiates protein synthesis via cell signaling 0 The proteins that are produced when vitamin A binds to genes helpthe young cell differentiate and mature into a functional epithelial cell Because older epithelial cells are constantly being sloughed off we need a steady supply of vitamin A so that new cells can take their place The mechanisms by which vitamin A influences growth includes regulation of cell differentiation among many other things During embryonic growth vitamin A directs the differentiation and maturation of various cell types that give rise to specific tissues and organs 0 This is why vitamin A is needed for successful reproduction 39239 Vitamin A deficiency o Uncommon in industrialized countries such asthe US 0 Secondary deficiency can occur in people with diseases affectingthe pancreas liver or gastrointestinal tract I Example cystic fibrosis causes inadequate fat digestion and absorption 0 Deficiency is common in alcoholics who have poor diets and suffer from liver damage I Excessive alcohol consumption also depletes the body39s stores of vitamin A 0 Vitamin A deficiengy disorder VADD multifaceted disease resulting from vitamin A deficiency I More pervasive in nonindustrialized societies In its milderform it causes night blindness More severe cases damage the cornea and other portions of the eye leading to dry eyes and scarring Xerophthalmi a condition characterized by serious damage to the cornea due to vitamin A deficiency that can lead to blindness Often accompanies bythe presence of Bitot39s spot white spots on the eye caused by buildup of dead cells and secretions on the surface of the eye I Hyperkeratosis a symptom of vitamin A deficiency in which immature skin cells overproduce the protein keratin causing rough and scaly skin Immature skin cells produce more keratin than do differentiated mature cells Vitamin A is important in supporting a healthy immune system so people especially children with VADD have an increased risk of infection 0 Protein energy malnutrition PEM also an endemic to nonindustrialized parts of the world can make vitamin A deficiency even worse I This is partly because the body cannot produce the proteins required to transport vitamin A in the circulation such as retinolbinding protein 39239 Vitamin A and Carotenoid Toxicity o Hypervitaminosis A condition where elevated circulating vitamin A levels result in signs and symptoms of toxicity I Can cause blurred vision liver abnormalities and reduced bone strangth 0 Very high doses of either naturally occurring or synthetic vitamin A can lead to birth defects such as neurological damage and physical deformities o highdose carotenoid supplementation can increase risk of lung cancer in some people 0 hypercarotenemi condition in which carotenoids accumulate in the skin causing it to become yelloworange I caused by these brightly colored compounds being deposited int eh skin and subcutaneous fat I not considered dangerous 39239 Recommended Intakes for Vitamin A and the Carotenoids o RDAs for Vitamin A I Men 900 RAEday I Women 700 RAEday 0 UL for Vitamin A 3000 RAEday for adults 0 No DRIs are set forthe carotenoids because there is insufficient evidence to support their essentiality beyond the role as vitamin A precursors 39239 Vitamin D 0 Found in food but significant amounts of vitamin D can also be produced by the body therefore it is considered a conditionally essential nutrient 0 Two forms of vitamin D in foods I Ergocalciferol vitamin Dll found in plant foods and vitaminD fortified foods I Cholecalciferol vitamin Dgl found in animal foods and made by the human body 39239 Dietary Sources of vitamin D 0 Egg yolks butter whole milk fatty fish fish oils and mushrooms 0 Most liquid and dried milk products and brekfast cereals are fortified with vitamin D I Most dietary vitamin D comes from these foods 0 Quite stable and is not destroyed during food preparation processign and storage 39239 Regulation Metabolism and Synthesis of Vitamin D o In the small intestine vitamin D is packaged into micelles with the help of bile o It isthen absorbed into the enterocyte where it is incorporated into chylomicrons and circulated away from the intestine first in the lymph and then the blood 0 Vitamin D not taken up by cells is delivered to the liver in chylomicron remnants 0 Vitamin D can also be synthesized by the body vitamin D in the form of cholecalciferol vitamin D3 can be produced from the metabolite of cholesterol in the skin when it is exposed to ultraviolet light 0 Synthesis of Vitamin D I Synthesis in the skin involves two steps 0 A cholesterol metabolite called 7dehydrocholesterol is converted by ultraviolet light to previtamin D3 precalcifero Previtamin D3 is converted to vitamin D3 cholecalciferol which then diffuses into the blood and circulates to the liver I 10 to 15 minutes of sunlight 3 times a week is enough forthe body to produce adequate amounts of cholecalciferol I Many environmental genetic and lifestyle factors can influence vitamin D synthesis 0 People with darker skin may need up to 3 times more sun exposure to produce enough vitamin D 0 Dark skin contains more melanin a pigment that blocks synthesis of precalciferol Sunscreen can also block the ultraviolet rays needed for vitamin D formation 0 Some agerelated changes decrease vitamin D production in the elderly I Some but not all tanning machines emit the right kind of light to cause vitamin D production in the skin but it is not recommended to use tanning beds because of the increased risk of skin cancer 0 Activation of Vitamin D I Cholecalciferol must be metabolized further before the body can use it I Two step process that occurs in the liver and kidneys First cholecalciferol is converted in the liver to 25hydroxyvitamin D 0 Then 25hydroxyvitamin D is circulated in the blood to the kidneys where it is conveted tol dihydroxyvitamin D calcitriol the active form in the body I This above conversion increases when calcium in the blood is low stimulated by the actions of parathyroid hormone produced in the parathyroid glands Because calcitriol is iportant for calcium absorption the body increases its production when more calcium is needed 39239 Functions of vitamin D 0 Calcium Homeostasis I Vitamin D calcitriol helps maintain helathy levels of calcium in the blood assuring the calcium is always available to the body39stissues I Vitamin D increases calcium absorption in the small intestine dcreases calcium excretion in the urine and facilitates the release of calcium from bones Small intestine Calcitriol is required for calcium absorption in the small intestine and it upregulates several genes that code for proteins required for the transport of dietary calcium into the enterocyes cell signaling Without vitamin D these proteins are not made and calcium absoption is severely limited Kidney calcitriol and PTH cause the kidneys to reduce their excretion of calcium into the urine sothat more calcium remains the in the blood 0 Bone calcitriol and PTH stimulate bone breakdown by osteoclasts and the realse of calcium into the blood I Calcium in bones is important for their structure but calcium in the blood has additional physiological functions muscle contraction blood pressure regulation and the conduction of neural impulses 0 Cell Differentiation and Cancer I Vitamin D plays a critical role in stimulating immature cells to become mature functioning cells cell differentiaion Involves the movement of vitamin D into the nucleus of the cell and the subsequent stimulation of the genes coding for specific proteins 0 Causes immature bone cells to become mature bone marrow cells bone health 0 causes certain intestinal epithelial cells to J39 39 into mature t y 39 39 IunLLiUn I Vitamin D may help prevent certain types of cancers such as those ofthe colon breast skin and prostate 39239 Vitamin D Deficiency Rickets and Osteomalacia o Deficiency can cause inadequate mineralization and increased demineralization of bone 0 Rickets symptom of vitamin D deficiency in young children characterized by deformed bones esp in the legs I Children with rickets have slow growth and characteristically bowed legs or knocked knees caused by the bending of weak long bones that cannot support the stress of weightbearing activities such as walking 0 Vitamin D deficiency in adults is highest in people with dark skin those who live in areas with little sunlight cultures that habitually cover themselves in clothing such as some Muslim women and those who do not consume vitamin Dfortified milk products 0 Osteomalacia softening of the bones in adults that can be due to vitamin D deficiency I Symptoms include diffuse bone pain and muscle weakness I People with osteomalacia are at increased risk of bone fracture o Osteoporosis serious bone disease resulting in weak porous bones I Serious chronic disease that affects 1 in 10 people 0 To prevent osteomalacia and osteoporosis people over 50 years of age are advises to get at least 15 minutes of sun exposure each day when possible and to increase their vitamin D intake 39239 Vitamin D Toxicity o Uncommon but excess supplementation can cause calcium levels in the blood to rise a condition called hypercalcemia I Hypercalcemia can result in the deposit of calcium in soft tissues such asthe heart and lungs and can affect the function of the central nervous system 0 Vitamin D toxicity also promotes bone loss 39239 Recommended Intakes for Vitamin D 0 There are insufficient data to establish RDAs but As have been set I Vitamin D is considered a conditionally essential nutrient so the N values may not apply to segments of the population with adequate sunlight exposure 0 As 5 microgramsday for adults I This si the amount of about 1 liter 4cups of vitaminD fortified milk 0 As increase to 10 microgramsday at the age of 51 and then to 15 microgramsday at age 71 0 UL 50 micrograms of vitamin D in supplemental form 0 Vitamin E o Refers to eight different compounds that all have somewhat similar chemical structures I Alphatocopherol the most active form of vitamin E 0 Dietary Sources of Vitamin E 0 Found in both plant and animal foods but it is especially abundant in vegetable oils nuts and seeds 0 Also found in some dark green vegetables such as broccolli and spinach 0 Can be easily destroyed during food preparation processing and storage I Expose foods with vitamin E to as little heat as possible when cooking and store them in airright containers o 0 Regulation of Vitamin E in the body 0 Absorption fo vitamin E occurs in the small intestine and requires the presence of bile and the synthesis of micelles 0 Vitamin E is circulated in chylomicrons via the lymph and in the blood eventually reaches the liver o In the liver vitamin E is repackaged into VLDLs for further delivery in the body 0 Excess vitamin E is stored mainly in adipose tissue 9 0 Functions of vitamin E o Acts as an antioxidant like the carotenoids preventing oxidation and free radical damage 0 Typically carries out its function within membreans 0 May also protect the cell39s genetic material DNA o Protecting cell membranes I Much ofthe body39s viamin E is associated with various membranes 0 Cell membranes consist of a phospholipid bilayer and many cell organelles such as mitochondria and endoplasmic reticula are encased in phospholipid bilayer membranes I Maintaining these membranes is vital to the stability and function of cells and their organelles and vitamin E plays a major role it protects the fatty acids in the membreane39s phospholipid bilayers from free radicalinduced oxidative damage 0 this occurs because vitamin E can donate electrons to free radicals making them more stable 0 this protection is especially important in cellsthat are exposed to oxygen such as those in the lungs and red blood cells I The ability of vitamin Eto act as an antioxidant is enchanced in the presence of other antioxidant micronutrients such as vitamin C and selenium 0 Relationship with cancer I Because antioxidant nutrients protect DNA from cancercausing free radical damage it is possible that vitamin E might prevent or cure cancer I Although diets high in vitamin E are associated with decreased cancer risk there is little experiemntal evidence that vitamin E by itself decreases the risk of cancer 0 Vitamin E likely interacts with other dietary components to protect the body from cancer 0 Eye Health I Cataract a cloudy growth that develops on the lens of the eye causing impaired vision 0 the development of cataracts inreases as people age leading to impaired vision 0 if left untreated cataracts can lead to blindness because of increased free radical damage people who smoke and those who are exposed to excessive amounts of sunlight are at increased risk for developing cataracts Dietary antioxidants may prevent or delay the growth of cataract and epidemiologic studies have shown the older people who take vitamin E supplements are at lower risk for developingthem 0 Heart Health I Atherosclerosis sometimes called quothardening of the arteriesquot can lead to heart disease or stroke form the accumulation of fatty material called plaque in the arteries 0 Vitamin E slows the rate of plaque formation and increased dietary vitamin E appears to be heart healthy Vitamin E supplementation 400 mgday can cause increased risk of mortality in people with chronic disease therfore supplementation to decrease risk of cardiovascular disease is discouraged 39239 Vitamin D deficiency o Uncommon cases have only been reported in infants fed formulas with inadequate vitamin E peoplewith genetic abnormalities and in diseases causing fat malabsorption o Deficiency is characterized by neuromuscular problems loss of coordination and muscular pain 0 Hemol ic anemia decreased ability ofthe blood to carry oxygen and carbon dioxide due to rupturing of red blood cells I Caused by deficiency because vitamin E is especially important in protecting red blood cells from oxidative damage I Results in weakness and fatigue 0 An example of a wisespread vitamin E deficiency occurred in the 1960s and 1970s when some infant formulas contained high levels of polyunsaturated fatty acids PUFAs and low levels of viamin E Because PUFAs are easily damaged oxidized by free radicals consumption of these formulas caused infants to have an increased need for antioxidant nutrients such as vitamin E As a result some babies developed hemolytic anemia especially premature infants who were born with very low stores of vitamin E I This event led to vitamin E fortification of infant formulas 39239 Vitamin E toxicity 0 Rare even with high intakes of vitamin E supplements I May be because the supplemental form of vitamin E is less biologically active than naturally occurring vitamin E o In some people very high doses of vitamin E suplements can casue dangerous bleeding or hemorrhage I Probably involves genetic differences 39239 Recommended Intakes for Vitamin E o RDA 15 mgday 0 UL 1000 mgday 39239 Vitamin K o Refers to three compounds that have similar structures and functions I Phylloguinone vitamin Kll found naturally in plant foods 0 Provides most ofthe vitamin K that we consume from foods but is also found in some supplements I Menaguinone vitamin K produced by bacteria present in the large intestine Because we cannot get enough vitamin K from this bacterial production vitamin K is an essential nutrient I Menadione vitamin Kgl not found naturally in food or made by bacteria but is produced commercially 39239 Dietary Sources of Vitamin K 0 Dark green vegetables such as kale spinach broccoli and brussels sprouts and also fish and legumes 0 Excessive exposure of foods to light and heat can destroy vitamin K 39239 Regulation of Vitamin K in the body 0 Dietary vitamin K is absorbed along with otherfatsoluble vitamins in the small intestine via micelles 0 Vitamin k is then incorporated into chylomicrons and put into lymph eventually entering the blood 0 Vitamin k produced by bacteria in the large intestine is transported into epithelial cells by simple diffusion and then circulated to the liver in the blood 0 The liver packages both dietary and bacterially produced forms of vitamin K into lipproteins for delivery to the rest of the body 39239 Functions of Vitamin K 0 Functions as a coenzyme in a variety of carboxylation reactionsthat add calcium to molecules I These vitamin Kdependent reactions are needed forthe lifeanddeath processes of blood clotting Coagulation when a blood vessel is injured a blood clot forms to stop the bleeding 0 Without this process we might bleed to death even after a minor scrape o For blood to coagulate and form a clot many chemical reactions must take place I In each set of reactions vitamin K carboxylates inactive clotting factors which in turn bind calcium I Bindingto calcium activates the clotting factors and allowsthe next reaction to take place I These ractions untimately convert the protein prothrombin to thrombin another calciumcontaining protein I Thrombin catalyzes the conversion of fibrinogen to fibrin a waterinsoluble protein that forms a weblike clot to stop the bleeding 0 Without adequate vitamin K this cascade of above events shuts down and clots cannot form 0 A drug called Coumadin delays blood clot formation by decreasing the activity of vitamin K 0 Vitamin K also catalyzes the carboxylation of other proteins needed for bone and tooth formation I Only afterthey have been carboxylated can these proteins bind calcium 39239 Vitamin K Deficiency and Toxicity o Deficiency I rare in healthy adults but it does appear in some infants and people with diseasesthat cause lipid malabsorption I Prolonged use of antibiotics can kill bacteria that normally live in the large intestine resulting in vitamin K deficiency I The main sign is excessive bleeding 0 Toxicity no known toxic effects 0 Vitamin K injections during infancy I Healthy infants are born with very low stores of vitamin K 0 At birth the newborn39s large intesinte completely lacks vitamin Kproducing bacteria and human milk contains very low levels of this vitamin 0 Babies esp those that are breastfed have minimal amounts of vitamin K duringthe first few weeks of life 0 Normally doesn39t cause a problem for most babies but some do develop sever vitamin K deficiency amp VKDB I Vitamin K deficiency bleeding VKDB disease that occurs in newborn infantsthat is characterized by uncontrollable internal bleeding hemorrhage from inadequate vitamin K Occurs mostly in breastfed babies who are either sick have difficulty feeding or have some form of liver disease or trouble absorbing lipids 5to 10 babies per 100000 born have VKDB Mortality rate is high about 30 I The American Academy of Pediatics recommend that all babies be given vitamin K injections at birth 0 Since this policy has been initiated the rate of VKDB has decreased by about 75 39239 Recommended Intakes of Vitamin K o RDAs have not been set but As are I Men 120 microgramsday I Women 90 microgramsday o No ULs are established because vitamin K is rarely toxic even in very high amounts 39239 Summary and Overall Recommendations 0 The fatsoluble vitamins are involved in a wide variety of processes encompassing all the physiological systems in the body 0 They do not work independtly of each other similarto the B vitamins which coordinately regulate energy metabolism I Vitamins AD E as well as the carotenoids are involved in regulating gene transcription I Vitamin E and the carotenoids act as antioxidants I Vitamins A D and K contribute to bone health CHAPTER 12 TRACE MINERALS o 0 Trace Minerals 0 Mineral inorganic substance other than water that is required bythe body in small amounts microminerals I All minerals are essential nutrients in that we must get them from the diet because the body cannot make minerals from other compounds as it can with macronutrients I Minerals can be neither created nor destroyed even if you completely combust burn a foodthe minerals will remain as ash o trace minerals an essential mineral that is required in amounts lessthan 100 mgday I the body needs at least eight trace minerals General F39 Food Sources 0 Amount often dependent on mineral content of soil 0 Found in all food groups Wholegrain products tend to contain more than milled ceral products 0 Amount not influences by cooking Digestion 0 Very little needed Absorption Occurs mostly in the small intestine but also in the stomach I 39 39 quot often influenced by form nutritional status and interactions with other dietary components Circulation 0 Via the blood Functions 0 Most are cofactors for enzymes some of which are involved in redox reactions 0 Some are components of nonenzymatic proteins 0 Some have structural roles such as quot 39 Toxicity Rare associated with excess supllement intake or 39 39 exposure 39239 Bioavailability and Regulation of trace minerals o Bioavailability can be influenced by genetics nutritional status and interactions with other components of foods 0 Normal aging processes can also affect mineral bioavailability 0 Trace minerals are absorbed pimarily in the small intestine and circulated to the liver via the blood 0 The amount of most trace minerals in the body is regulated although the site of regulation varies I Iron absorption in the small intestine is adjusted to maintain healthy iron status I Iodine and selenium regulation site is the kidneys and excess amounts are excreted in the urine I Copper and manganese site of regulation isthe liver which incorporates excess minerals into the bile and eliminates it in the feces 0 Both deficiencies and toxicities of the trace minerals are rare except in genetic distorders and environmental exposure I Exceptionsareiron andiodine 39239 Functions of trace minerals in the body 0 Trace minerals particiapate in many chemical reactions by serving as cofactors I Example selenium is part ofthe quaternary structure of an enzyme that protects the body from free radical damage I Matalloenzyme an enzyme that contains a mineral cofactor I The function of a cofactor is somewhat similarto that of a coenzyme binding ofthe mineral cofactorto the enzyme activates it allowing it to bind to its substrate and carry out its functiosn o Othertimes trace minerals are components of larger nonenzymatic molecules such as hemoglobin 0 Some trace minerals also provide structure to mineralized tissues I Example fluoride provides strength to bones and teeth 9 0 Iron Fe needed for oxygen and carbon dioxide transport energy metabolism removal of free radicals and synthesis of DNA 0 Iron deficiency remains the most common nutrient deficiency worldwide 39239 Dietary Sources of Iron 0 Iron in the diet exists in two forms I Heme iron iron that is a component of a heme group 0 Includes hemoglobin in blood myoglobin in muscles and cytochromes in mitochondria Excellent sources include shellfish beef poultry and organ meats such as liver I Nonheme iron iron that is not attached to a heme group 0 Typically accounts for more than 85 of dietary iron 0 Found in green leafy vegetables mushrooms and legumes 39239 Bioavailabilityoflron 0 Complex and influenced by many factors its form a person39s iron status and the presence or absence of other dietary components the major factor being its form I The bioavailability of heme iron is two to three times greaterthan that of nonheme iron Absorption of heme iron is high being most affected by iron status 0 0 Many factors can influence absorption of nonheme iron most importantly its ionic state Nonheme iron is found in two ionic forms in foods I Ferric iron Fegl the oxidized form of iron I Ferrous iron Fez l the reduced form of iron more readily absorbed o Enhancers of nonheme iron bioavailability I One ofthe best known enhancers of iron absorption is vitamin C ascorbic acid It converts ferric iron to ferrous iron in the intestinal lumen vitamin C donates an electron to ferric iron Fey reducing it to its ferous Feb form I stomach acid also helps reduce ferric iron to ferrous iron 0 the chronic use of antacids to neutralize stomach acidity can decrease nonheme iron absorption I meat factor an unidentified compound found in meat poultry and seafood that increases the absorption of nonheme iron 0 Inhibitors of nonheme iron bioavailability I Chelator a substace that binds compounds in the gastrointestinal tract makingthem unavailable for absorption Types of chelators in nonheme iron Ph ates phosphoruscontaining compounds often found in the outer coating of a kernel of grain vegetables and legumes o Often lost during preparation and processing so unprocesses bran oats and fiberrich foods are especially phytate rich whereas milled ceral products are not Polyphenol organic compounds found in some vegetables such as spinach tea coffee and red wine I The negative effect of phytates and polyphenols on iron bioavailability are relatively strong Consuming 1 cup of coffee ortea with a meal can decrease nonheme iron absorption by 4070 0 Although some foods such as spinach contain relatively high amounts of ironthey really are not especially good sources of iron because of the phytates andor polyphenols they contain I Simultaneously consuming vitamin C or meat factor can partly counteract the inhibitory effect of phytates and polyphenols 39239 Iron Absorption Circulation and Storage 0 Iron toxicity is perhaps more dangerous than iron deficiency Humans have complex homeostatis mechanisms to regulate how much iron is sotred in the body making sure there is neither O too little nortoo much 0 Except for bleeding associated with menstruation injury or child birththe body loses very little iron once it is absorbed o The major mechanism by which the amount of iron is regulated in the body is the alteration of its absorption 39239 Iron Absorption o Absoption of iron involves transport across two membranes in the intestinal enterocyte the brush border membrane that faces the intestinal lumen and the basolateral membrane tha tfacesthe submucosa o The transport of heme and nonheme iron across these membranes involves different mechanisms I Heme iron can be transported across both membranes without chemical modification I Nonheme iron must be reduced to its ferrousform priorto transport this is why reducing substances such as vitamin C increases bioavailability of nonheme iron 0 Several membranebound iron transport proteins move iron from the intestinal lumen into the enterocyte 0 Once inside the enterocyteferrous iron is bound to the protein ferr39 39n I The binding of iron to ferritin in the enterocyte is often temporary and the role of the enterocyte is somewhat like a gate in an aiport The passengers iron must wait in the gate enterocyte until the airplane body is ready to board Ferritin temporarily holds or stores iron in the enterocyte until it receives a signal from the body that the iron shold be released forfurther transport across the basolateral membrane 0 When the body needs more iron both ferrous iron and heme iron are transported acrossthe basolateral membrane into the submucosa for uptake into the blood 0 Effect of iron status on iron absorption I Absorbtion increases during iron deficiency and decreases during periods of iron excess I Iron deficiency the body increases production of the iron transport proteins amp decreases production of ferritin ron transport into the enterocyte is increased and there is less ferritin to bind the iron within the enterocyte Increases movement of iron from the intestinal lumen through the enterocyte and ultimately into the circulation I Adequate or excess iron production of iron transport proteins decreases and production of ferritin increases 0 Causes less iron to be transported into the enterocyte and that which istransported is more likely to be retained in the cell 0 These ironrich enterocytes are eventually sloughed off into the intestinal lumen and eliminated in the feces o The presences of iron in the feces can cause stools toe be black in color I Enterocytes liningthe small intesinte thus serve as important regulators of iron status helping prevent both iron deficiency and toxicity 39239 Iron Circulation uptake into cells and storage 0 Once iron entersthe blood it binds to transferrin a protein produced in the liver 0 Transferrin delivers iron to all body cells to proteins on cell membranes called transferrin receptors I The number oftransferrin receptors on a cell membrane is regulated bythe cell39s needs 0 if enough iron is in the cellthe number of tranferrin receptors decreases inhibiting uptake of more iron 0 cells needing iron produce more receptors so they can bind or quotcapturequot more iron for uptake 0 Excess iron is stored in the liver bone marrow and spleen I There are two iron storage compounds in these tissues ferritin and hemosiderin These large proteins contain about a third of a healthy person39s total iron 0 Small amounts ofthe storage form of ferritin present in liver bone and spleen are continually released into the blood where its concentration is proportional to the amount of iron stored in the body 0 Because ofthis blood ferritin is often measured to assess iron status Ferritin is considered the main storage form of iron but hemosiderin is needed for more longterm storage it protects to body from iron toxicty when intake is chronically high o 0 Functions of Iron 0 Oxygen and Carbon Dioxide Transport Hemoglobin a complex protein composed of four ironcontaining heme groups and four protein subunits needed for oxygen and carbon dioxide transport in the body I As hemoglobin travels through the blood vessesl of the lungs it comes in contact with oxygen which then attaches to iron atoms in hemoglobin As the oxygenated blood then ciculates from the lungs to other tissues in the body hemoglobin delivers oxygen to cells that need it for aerobic energy metabolism I Deoxygenated carbon dioxiderich blood is circulated back to the lungs where the carbon dioxide is eliminated when the person exhales I Without sufficient hemoglobin oxygen availability to tissues decreases which affects energy metabolism 0 Can result in lack of energy and fatigue I Red blood cells contain about two thirds ofthe total body iron and have a normal life span of about 120 days 0 When red blood cells are degraded most of the iron is recycled or stored for later use 0 Oxygen Reservoir Myoglobi a heme protein found in muscle consists of a single heme group and a single protein subunit I Myoglobin acts as a reservoir of oxygen releasing oxygen to muscle celsl when needed for ATP production and muscle contraction 0 Cellular Energy Metabolism I Iron is also needed for ATP production I Cytochrome a heme protein complexthat is part ofthe electron transport chain in mitochondria Serve as electron carriers ultimately allowingthe conversion of adenosine diphosphate ADP to adenosine triphosphate ATP I ron also serves as a cofactor for a variety of nonhemecontaining enzymes involved in the elctron transport chain citric acid cycle and gluconeogenesis o Other roles of iron I Iron is also a cofactor of many other imporant enzymes that help metabolize drugs and remove toxins from the body I Cytochrome P450 a ironcontaining enzyme that helps stabilize free radicals Activity of these enzymes is thought to influence risk for many chronic diseases such as cancer and cardiovascular disease I Iron is also a cofactor for antioxidant enzymes that stabilize free radicals In this way iron is important for protecting DNA cell membranes and proteins from oxidative damage that can be harmful to cells I Iron is also a cofactor for an enzyme needed for DNA synthesis 0 reason why iron is so important for optimal growth and development 39239 Iron Deficiency o The most common nutritional deficiency in the US and the world 0 Typically seen in infants growing children and pregnant women because iron requirements increase during growth and development 0 Women of childbearing age are also at increased risk because iron is lost in the blood each month duringthe menstrual cycle 0 m or geophagia abnormal eating behaviorthat involves consuming nonfood or nonnutritive substances such as dirt or clay I Also thought to be associated with iron deficiency I Most prevelent in pregnant women I Some believe pica causes iron deficiency while others believe iron deficiency causes pica o Mild ron Deficiency I Associated with fatigue and impaired physical work performance I Can also cause behavioral abnormalities and impaired intellectual abilities in children 0 Some ofthese effects are irreversible even after iron supplementation I Also impairs body temperature regulation especially in cold conditions I May negatively influence the immune system I During pregnancy increases the risk of premature delivery low birth weight and maternal mortality 0 Severe ron Deficiency ron Deficiency Anemia I Causes microcytic hypochromic anemia condition characterized by small pale red blood cells Caused by the inability to produce enough heme and thus hemoglobin I Anemia refers to a decreased ability of the blood to carry oxygen 0 Signs and symptoms fatigue difficulties in mental concentration and compromised immune function 39239 Basics of Iron Supplementation o Needed when diet alone cannot maintian iron satus or during specific periods ofthe life cycle such as pregnancy when iron reqirements are especially high 0 Supplemental iron is available in two general forms ferrous iron and ferric iron I Ferrous forms are best absorbed 39239 Iron Toxicity 0 Rare but is sometimes seen with overdoses of medicinal or supplemental iron 0 Accidental consumption of toxic levels of iron is one of the most common causes of childhood poisoning in the US 0 Symptoms vomiting diarrhea constipation and black stools o In severe cases it can cause death because excess iron is deposited in soft tissues such asthe liver heart and muscles impairing theirfunction 0 Iron toxicity can also be caused by genetic abnormalites I Hereditary hemochromatosi a genetic abnormality resulting in increased absorption of iron in the intestine 39239 Recommended Intakes for Iron 0 Iron requirements are highest during periods of rapid growth and development and are influenced bythe amount of lean body mass muscle a person has 0 Because women of childbearing age lose iron each month during menstration requirements forfemales in this age group are relatively high 0 RDAs I Men 8 mgday I Women 18 mgday I Pregnant women 27 mgday o A serving 3 oz of beef contains only about 3 mg of iron I may be difficult for women to meet this RDA so supplements are advised 0 UL 45 mgday I To prevent gastrointestinal distress from iron excess 0 Special recommendations for vegetarians and endurance athletes I Vegetarians may have difficulty consumign the needed amount of iron because meant provides substantial amounts of highly bioavailable iron and nonheme iron found in plant foods has low bioavailability Vegetarian requirements are 80 higherthan nonvegetarians To take advantage of the positive effect of meat factor on iron absorption vegetarians who eat fish should try to consume it together with nonheme iron sources in the same meal I Athletes engaged in endurance sports such as longdistance running may also have increased iron requirements 0 Reasons increased blood loss in feces and urine and chronic rupture of red blood cells within the feet 0 Iron requiremetns may be increased by as much as 70 o 0 Iodine an essential trace mineral that is a component of the thyroid hormones o Needed for only one function in the body it is an essential component ofthe hormones produced bythe thyroid gland I Thyroid hormones regulate growth reporduction and energy metabolism and also influence the immune system and neural development 0 Most iodine in the body is in the anion form of iodide Ii but we still referto this mineral as quotiodinequot 39239 Dietary Sources of Iodine o The iodine content of foods frequently depends on the iodine content of the soil and water used to grow them 0 Ocean fish and mollusks tend to contain high amounts because they concentrate iodine found in seawater to their tissues 0 Seaweed which is used in many asian cuisines also coontains iodine 0 Dairy products are excellent sources because iodine is used in milk processing 0 Most of the iodine we consume comes from iodized salt 39239 Absorption Metabolism and Regulation of Iodine o Iodine is highly bioavailable 0 almost completely absorbed in the small intestine and to a lesser extent the stomach 0 once in the blood iodine is rapidly taken up bythe thyroid gland and incorporated into the thyroid hormones I thyroidstimulating hormone TSH hormone produced in the pituitary gland that stimulates uptake of iodine by the thyroid gland 0 during periods of iodine deficiency TSH release increases inturn increasing uptake of iodine bythe thyroid gland and vice vera o excess iodine is excreted in the urine 0 goitrogen compoundsfound in some vegetablesthat decrease iodine utilization by the thyroid gland I found in cassava a root and in cruciferous vegetables such as cabbage cauliflower and brussels sprouts 39239 Functions of Iodine o Iodine is an essential component of the thyroid hormones I Thyroxine T l a less active form of thyroid hormone contains 4 atoms of iodine Converted to triiodothyronine I Triiodothyronine Tgl the more active form ofthyroid hormone contains 3 atoms of iodine 0 T3 and T4 help regulate energy metabolism growth and development I They are especially critical for proper development of the brain spinal cord and skeleton during fetal growth I A deficiency causes severfatigue and lethargy because of its involvement in regulating energy metabolism 39239 Iodine Deficiency o A significant public health problem worldwide 0 Countries where it is most prevalent are those without iodized salt and those that are not bodered by an ocean or sea 0 Iodine deficiengy disorders IDDs a broad spectrum of conditions caused by inadequate iodine I which type of IDD a person has depends on severity ofthe deficiency and its timing in the life cycle 0 Fetal Iodine Deficiency Cretinism form of IDD that affects babies born to iodinedeficient mothers I Most severe form of iodine deficiency I Causes severe mental retardation poor growth infertility and increased risk of mortality 0 Childhood and Adult Iodine Deficiency m form of IDD that affects children and adults TSH secretion greatly increases I characterized by an enlarged thyroid gland I when a goiter grows very large it can obstruct a person39strachea making it difficult to breathe and swallow 39239 Iodine Toxicity and Recommended Intakes o Iodine toxicity can take several forms underactive thyroid activity hypothyroidism and overactive thyroid activity hyperthyroidism o RDA 150 microgramsday 0 UL 1100 microgramsday