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  • 1. CHAPTER 6 VitaminsEleanor D. Schlenker Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.
  • 2. Vitamins Criteria used to define a compound as a vitamin:  It must be an organic dietary substance that is not an energy-producing carbohydrate, fat, or protein  It is needed in very small quantities to perform a particular metabolic function or prevent an associated deficiency disease  It cannot be manufactured by the body and therefore must be supplied in food Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 2
  • 3. Vitamins: Basic Concepts As our understanding of vitamins has expanded, the following important concepts have emerged:  Individual vitamins are multifunctional  One vitamin cannot substitute for another vitamin  Vitamins work together in carrying out body functions  Vitamins function best when all are present in the appropriate proportions Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 3
  • 4. Classification of Vitamins Vitamins have been grouped according to their solubility in either fat or water  Fat-soluble vitamins • A, D, E, and K • Closely associated with body lipids and are easily stored  Water-soluble vitamins • Vitamin C and the B-complex family • Easily absorbed and transported • Cannot be stored except in the general sense of tissue saturation Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 4
  • 5. Fat-Soluble VitaminsVitamin A Generic name for a group of compounds having similar biologic activity: retinol, retinal, and retinoic acid Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 5
  • 6. Fat-Soluble Vitamins – Cont’d There are two dietary forms of vitamin A: 1. Preformed vitamin A (retinol) • Natural form of vitamin A found only in animal foods and usually associated with fat 2. Provitamin A (beta-carotene) • Plants cannot synthesize vitamin A but instead produce a family of compounds called carotenoids • Beta-carotene, converted to vitamin A in the body, provides about 21% of the total vitamin A intake in the United States • Poor conversion of carotenoids to vitamin A may contribute to vitamin A deficiency in developing countries where persons depend on plant sources Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 6
  • 7. Absorption of Vitamin A Various materials are needed for the absorption of vitamin A or beta-carotene:  Bile salts  Pancreatic lipase  Dietary fat Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 7
  • 8. Conversion of Beta-Carotene Beta-carotene can be absorbed and used by the body in its original form or be converted to vitamin A Carotenoids are important both as vitamin A precursors and as phytochemicals Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 8
  • 9. Transport and Storage of Vitamin A The route of absorption of both vitamin A and the carotenoids parallels that of fat The liver contains up to 85% of the body’s total supply of Vitamin A A prophylactic dose of vitamin A every 6 months prevents deficiency in developing countries Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 9
  • 10. Functions of Vitamin A Visual adaptation to light and darkness Generalized actions that affect the integrity of:  Body coverings and linings (epithelial tissues)  Growth  Immune response  Reproductive function Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 10
  • 11. Vitamin A Deficiency Vision  Normal rhodopsin cannot be made and the rods and cones of the retina become increasingly sensitive to changes in light, causing night blindness  Reversed with retinol injection Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 11
  • 12. Vitamin A Deficiency – Cont’d Cell differentiation  Keratinization: dry and flat cells • Eye—xerophthalmia and blindness • Respiratory tract—dryness and loss of cilia • Gastrointestinal tract—dryness, poor digestion, and absorption • Skin—dry and scaly, follicular hyperkeratosis • Tooth formation—ameloblasts do not develop Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 12
  • 13. Vitamin A Deficiency – Cont’d Growth  Essential for growth of bones and soft tissues  Controls protein synthesis and mitosis  Excessive intakes also cause poor bone health Reproduction  Normal sexual maturation and function  Gene expression and fetal development Immunity  Lack of epithelial and mucosal barrier  Direct effect on cell-mediated and antibody-mediated immunity Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 13
  • 14. Vitamin A RequirementInfluencing Factors A number of variables can modify the vitamin A needs of a given individual:  Liver stores  Intake of preformed versus provitamin A  Illness and infection  Gastrointestinal or hepatic defects Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 14
  • 15. Vitamin A Requirement – Cont’dCauses of Vitamin A Deficiency Inadequate dietary intake  Poor food selection and fast food Poor absorption or metabolism  Lack of bile or dietary fat  Inadequate conversion of beta-carotene  Liver or intestinal disease High intake of alcohol Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 15
  • 16. Vitamin A Requirement – Cont’dRecommended Dietary Allowance (RDA) For vitamin A the RDA is the amount required to maintain optimum liver stores  The RDA for men ages 19 and over is set at 900 µg  The RDA for women of this age is 700 µg  The RDA increases to 770 µg in pregnancy and 1300 µg in lactation Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 16
  • 17. Vitamin A Toxicity Hypervitaminosis A  High-potency supplements  UL is 3000 µg/day  Especially dangerous in pregnancy Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 17
  • 18. Food Sources of Vitamin A Animal sources:  Liver, milk, cheese, butter, egg yolk, and fish Nonanimal products:  Margarine, ready-to-eat cereals, and cereal bars are being fortified with vitamin A  Deep yellow, orange, red, and dark green vegetables and fruits, contain carotenoid precursors of vitamin A  Carotenoids are more available from cooked vegetables Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 18
  • 19. Fat-Soluble VitaminsVitamin D A prohormone and in its active form functions as a hormone Chemically, vitamin D is a sterol and its precursor found in human skin is the lipid molecule 7-dehydrocholesterol Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 19
  • 20. Fat-Soluble Vitamins – Cont’dVitamin D – Cont’d Two forms: 1. Ergocalciferol (vitamin D2) • Formed by irradiating ergosterol found in ergot (a fungus growing on rye and other cereal grains) and yeast 2. Cholecalciferol (vitamin D3) • Formed by the action of ultraviolet light from the sun on the 7-dehydrocholesterol in the skin • Found naturally in fish liver oils Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 20
  • 21. Vitamin DAbsorption Absorbed in the small intestine along with fat Malabsorption diseases, such as celiac disease, cystic fibrosis, and Crohn’s disease or pancreatic insufficiency, hinder vitamin D absorption Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 21
  • 22. Vitamin D – Cont’dActive Hormone Synthesis 1,25-dihydroxycholecalciferol [1,25(OH)2D3] has the chemical name of calcitriol  Calcitriol is produced by the combined action of the skin, liver, and kidneys, an overall process referred to as the vitamin D endocrine system  Vitamin D3 is used and metabolized in the same way whether obtained from skin synthesis or from food Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 22
  • 23. Functions of Vitamin D Hormone Associated with calcium and phosphorus metabolism and their absorption and deposition in bone tissue Acts on many tissues and functions throughout the body  Cell growth  Muscle strength  Immune function  Insulin levels  Hypertension and cardiovascular disease Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 23
  • 24. Vitamin D DeficiencyBone Disease Without sufficient vitamin D, the body cannot absorb the calcium needed to build normal bones Children develop rickets Adults develop osteomalacia Osteoporosis has different causes Breastfed infants need vitamin D supplements Role in renal osteodystrophy Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 24
  • 25. Vitamin D RequirementsDietary Reference Intake Needs are affected by sun exposure and skin synthesis Vitamin D has an Adequate Intake (AI), not an RDA Persons between 6 months and 50 years of age need 5 µg (200 IU) Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 25
  • 26. Vitamin D Requirements – Cont’dDietary Reference Intake – Cont’d For persons 51 to 70 years, the AI increases to 10 µg (400 IU) For those ages 71 and older, it increases to 15 µg (600 IU)  The elevated AI for those over age 70 points to their critical need to maintain bone mass and their limited ability to synthesize vitamin D in their skin Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 26
  • 27. Food Sources of Vitamin D Fatty fish such as mackerel A small amount occurs in egg yolk Vitamin D-fortified milk, margarine, juices, and ready-to-eat cereals Vitamin D2 is found only in yeast Vitamin D3 is found mostly in fish liver oils and is the form added to fortified foods Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 27
  • 28. Fat-Soluble VitaminsVitamin E Vitamin E is the generic name given to a group of compounds with similar physiologic activity  Includes eight fat-soluble, 6-hydroxychroman compounds having some degree of the biologic activity of alpha-tocopherol Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 28
  • 29. Fat-Soluble Vitamins – Cont’dAbsorption Absorbed in the micelles with the aid of bile Stored in the liver and adipose tissue, where it is held in bulk liquid droplets Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 29
  • 30. Functions of Vitamin E Acts as an antioxidant in destroying molecules called free radicals Free radicals are elements or molecules with unpaired electrons that attack double bonds in membranes and other body tissues Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 30
  • 31. Functions of Vitamin E – Cont’d Changes caused by the “oxidation” of these double bonds affects the function of these membranes and tissues Partners with selenium Unproven role in preventing chronic disease and aging changes in tissues May ameliorate toxicity associated with chemotherapy Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 31
  • 32. Vitamin E Deficiency Disastrous effects on red blood cells  This vitamin E deficiency disease is called hemolytic anemia  Sometimes observed in newborns Disrupts the making of myelin, the protective lipid covering of the nerve cell axons Degeneration of the pigment in the rods and cones of the retina Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 32
  • 33. Vitamin E RequirementDietary Reference Intakes Approximately 80% of the vitamin E from dietary sources, including fortified foods, is alpha-tocopherol  Approximately 20% comes from other forms RDA for ages 14 and older:  15 mg for males and females Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 33
  • 34. Food Sources of Vitamin E Richest dietary sources of vitamin E are vegetable oils Sunflower, safflower, canola, corn, and olive oils Nuts and peanut butter Certain vegetables and fruits, especially tomatoes Fortified ready-to-eat cereals Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 34
  • 35. Fat-Soluble VitaminsVitamin K Forms  Phylloquinone • Found in plants, named for its chemical structure • Major dietary form and is widely distributed in both animal and vegetable foods  Menaquinone • Synthesized by intestinal bacteria  Menadione • Water-soluble analogue of vitamin K, can be absorbed directly into the portal blood Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 35
  • 36. Absorption of Vitamin K Phylloquinone and menaquinone require pancreatic lipase and bile salts for absorption Packaged in the intestinal chylomicrons Travel via the lymphatic system and then the portal blood to the liver In the liver, vitamin K is stored in small amounts Rapidly excreted after administration of therapeutic doses Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 36
  • 37. Functional Roles of Vitamin KBlood Clotting Initiates the synthesis of four blood-clotting factors in the liver Controls the liver synthesis of other proteins that regulate the speed and duration of coagulationBone Metabolism Stimulates the synthesis of osteocalcin and other proteins that are important in bone Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 37
  • 38. Vitamin K Deficiency and Clinical Application Neonatology  Prophylactic dose soon after birth Malabsorption problems  Defects in fat absorption impair vitamin K absorption Drug therapy  Anticlotting drugs require consistent intake of vitamin K Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 38
  • 39. Vitamin K RequirementDietary Reference Intake AI for men ages 19 and over is 120 µg/day AI for women ages 19 and over is 90 µg/day This amount of vitamin K is adequate to preserve blood clotting Unsure how much is needed for optimum bone health Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 39
  • 40. Food Sources of Vitamin K Phylloquinone is found in many vegetables, highest in dark green vegetables and liver Menaquinones occur in milk, meat, and certain cheeses Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 40
  • 41. Water-Soluble VitaminsVitamin C Associated with the search for the cause of the ancient hemorrhagic disease scurvyAbsorption, Transport and Storage Easily absorbed from the small intestine but requires the presence of acid Distributed throughout body tissues Excess is excreted in the urine Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 41
  • 42. Functions of Vitamin C Antioxidant  Helps to take up the free oxygen arising from cell metabolism, making it unavailable to fuel the destructive actions of free radicals Formation of intercellular cement  Helps build and maintain many body tissues, including bone matrix, cartilage, dentin, collagen, and connective tissue Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 42
  • 43. Functions of Vitamin C – Cont’d Support of general body metabolism  Important in many metabolically active tissues  Helps in the formation of hemoglobin and the development of red blood cells by: 1. Promoting iron absorption 2. Assisting in the removal of iron from the protein-iron complex called ferritin  Assists carnitine synthesis  Assists peptide hormone synthesis  Breakdown of drugs and other foreign molecules Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 43
  • 44. Functions of Vitamin C – Cont’dClinical Applications Wound healing Fever and infection Growth Stress and body response Chronic disease prevention Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 44
  • 45. Vitamin C RequirementDietary Reference Intake Current Dietary Reference Intake takes into account the need for antioxidant protection of body tissues For men the RDA is 90 mg For women the RDA is 75 mg Cigarette smokers require an additional 35 mg each day Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 45
  • 46. Food Sources of Vitamin C Best known food sources of vitamin C are citrus fruits and tomatoes Broccoli, salad greens, strawberries, watermelon, cabbage, and sweet potatoes are other good sources Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 46
  • 47. The B Vitamins All water soluble but with unique metabolic functions Serve as coenzyme partners with cell enzymes that control energy metabolism and build tissues Thiamin, riboflavin, and niacin associated with classic deficiency diseases Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 47
  • 48. The B Vitamins – Cont’d Recently discovered coenzyme factors— vitamin B6 (pyridoxine), pantothenic acid, and biotin Important blood-forming factors—folate and vitamin B12 (cobalamin) Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 48
  • 49. Thiamin A water-soluble and fairly stable vitamin Destroyed in alkaline solutions Name comes from its chemical ringlike structure (thiazole ring) Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 49
  • 50. Thiamin – Cont’d Absorbed efficiently in the acid environment of the upper small intestine before the acidity of the food mass is buffered by the alkaline secretions from the pancreas Carbohydrate increases the need for thiamin, whereas fat and protein spare thiamin Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 50
  • 51. Functions of Thiamin Control agent in energy metabolism Combines with phosphorus to form hiamin pyrophosphate (TPP) TPP serves as a coenzyme in key reactions involving glucose Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 51
  • 52. Deficiency Symptoms of Thiamin Classic deficiency disease is beriberi Gastrointestinal: anorexia, constipation, gastric atony, and poor HCl secretion Nervous: Diminished alertness and reflex responses, general apathy, and fatigue Cardiovascular: Heart muscle weakens, leading to cardiac failure and edema Musculoskeletal: Chronic pain Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 52
  • 53. Thiamin RequirementDietary Reference Intake Minimum requirement is 0.3 mg/1000 kcal RDA is set at 1.2 mg for adult men and 1.1 mg for adult women Extra is needed during pregnancy and lactation Excess thiamin is excreted by the kidneys No UL has been established Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 53
  • 54. Clinical Conditions That Influence Thiamin Needs Alcohol abuse Acute illness or disease Normal growth and development Use of diuretics Gastric bypass surgery Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 54
  • 55. Food Sources of Thiamin Widespread in plant and animal foods Major sources in the American diet:  Whole and enriched breads and ready-to-eat cereals, and legumes Good food sources include lean pork and beef Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 55
  • 56. Riboflavin Yellow-green fluorescent pigment that forms yellowish brown, needlelike crystals Easily destroyed by light and irradiation Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 56
  • 57. Absorption of Riboflavin Absorbed in the upper section of the small intestine Hindered by bulk fiber supplements such as psyllium Small amounts stored in the liver and kidney Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 57
  • 58. Functions of Riboflavin Part of the cell enzymes called flavoproteins Active in both energy production and deamination  Deamination is the removal of a nitrogen- containing amino group from an existing amino acid so a new amino acid can be formed Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 58
  • 59. Deficiency Symptoms of Riboflavin Results in the condition termed ariboflavinosis Tissue inflammation and breakdown and poor healing of even minor injuries Sometimes occurs in newborns  Riboflavin is destroyed by light and so deficiency can occur in infants treated with phototherapy Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 59
  • 60. Riboflavin RequirementDietary Reference Intake RDA based on the amount needed to sustain optimum levels of the flavoprotein enzymes  1.3 mg/day for adolescent and adult men  1.1 mg/day for adolescent and adult women No UL set, but high-dose supplements still carry a risk Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 60
  • 61. Riboflavin Requirement – Cont’dRisk Groups Patients on hemodialysis Pregnant and lactating women and infants and children People who engage in regular physical activity Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 61
  • 62. Food Sources of Riboflavin Major sources of riboflavin are milk and cheese  Riboflavin is destroyed by exposure to light; therefore milk is usually packaged in cardboard or opaque plastic containers  Breast milk stored in clear glass or plastic containers may lose riboflavin Other good sources of riboflavin are meat, whole or enriched grains and ready-to-eat cereals, and vegetables Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 62
  • 63. Niacin In 1937 a researcher at the University of Wisconsin associated niacin with pellagra by using it to cure a related disease (black tongue) in dogs Two forms of niacin have been identified: 1. Nicotinic acid 2. Nicotinamide Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 63
  • 64. Niacin – Cont’d Stable to acid and heat Forms a white powder when crystallized The amino acid tryptophan can be converted to niacin in the body  60 mg tryptophan can produce 1 mg niacin  Measured in niacin equivalents (NE) Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 64
  • 65. Functions of Niacin Two coenzyme forms 1. Nicotinamide-adenine dinucleotide (NAD) 2. Nicotinamide-adenine dinucleotide phosphate (NADP) Partners with riboflavin in systems that convert amino acids and glycerol to glucose and oxidize the glucose to release energy Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 65
  • 66. Functions of Niacin – Cont’d Pharmacologic dosages of nicotinic acid have been prescribed for cardiovascular patients in an effort to raise blood high-density lipoprotein (HDL) cholesterol levels and reduce blood low-density lipoprotein (LDL) cholesterol and triglyceride levels This treatment carries some degree of risk and requires careful supervision  At high levels, niacin is a vasodilator Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 66
  • 67. Niacin RequirementDietary Reference Intake RDA measured in niacin equivalents (NE) 16 mg NE/day for adolescent and adult men 14 mg NE/day for adolescent and adult women Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 67
  • 68. Niacin Requirement – Cont’d Increase in niacin is needed for the following:  Rapid growth  Pregnancy and lactation  Physical activity  Tissue replacement after surgery or trauma Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 68
  • 69. Food Sources of Niacin Meat and dairy products are major sources of niacin and also high in tryptophan Other foods include peanuts, dried beans and peas, and whole grain or enriched breads and cereals Corn and rice are relatively poor sources because they are low in tryptophan Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 69
  • 70. Pantothenic Acid Synthesized by intestinal bacteria and present in a wide variety of foods  Deficiency is unlikelyAbsorption and Metabolism Absorbed in the intestine and combines with phosphorus to make the active molecule acetyl coenzyme A (CoA) No known toxicity or natural deficiency Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 70
  • 71. Pantothenic Acid – Cont’dFunctions Controls metabolic reactions involving carbohydrates, fat, and proteinRequirements 5 mg/day for all adults will replace the pantothenic acid lost daily in the urineFood Sources Found in both plant and animal foods  Good sources include egg yolk, milk, and broccoli Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 71
  • 72. Biotin Sulfur-containing vitamin Natural deficiency is unknown  May occur in patients receiving long-term total parenteral nutrition without biotin Avidin, a protein found in raw egg white, binds biotin and prevents its absorption  Cooking denatures this protein and destroys its ability to bind biotin No known toxicity for biotin Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 72
  • 73. Biotin – Cont’dFunctions Partners with acetyl coenzyme A (CoA) in reactions that transfer carbon dioxide from one compound to another  Synthesis of fatty acids  Carbon dioxide fixation to form purinesRequirements 30 µg/day for all adults Intestinal bacterial synthesis also adds to the body’s supply Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 73
  • 74. Food Sources of Biotin Found in many foods Bioavailability varies greatly Biotin in corn and soy is well absorbed Biotin in wheat is generally unavailable Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 74
  • 75. Vitamin B6 (Pyridoxine) Chemical structure of vitamin B6 is a pyridine ring Three forms occur in nature:  Pyridoxine, pyridoxal, and pyridoxamine  All three forms are equally active in the body as precursors of the coenzyme pyridoxal phosphate (B6-PO4), or PLP Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 75
  • 76. Absorption of Vitamin B6 (Pyridoxine) Absorbed in the upper segment of the small intestine Stored in muscle but found in tissues throughout the body Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 76
  • 77. Functions of Vitamin B6 Coenzyme in more than 100 amino acid reactions involving the synthesis of important proteins:  Neurotransmitters  Amino group transfer  Sulfur transfer  Niacin  Hemoglobin  Immune function Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 77
  • 78. Functions of Vitamin B6 – Cont’d Coenzyme in fat metabolism  PLP converts the essential fatty acid linoleic acid to arachidonic acid Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 78
  • 79. Vitamin B6 Deficiency Vitamin B6 holds a key to a number of clinical problems:  Anemia  Central nervous system changes  Physiologic demands in pregnancy  Blood homocysteine levels  Medications Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 79
  • 80. Vitamin B6 RequirementDietary Reference Intakes High protein intake increases the need for vitamin B6  Men and women ages 19 to 50 years need 1.3 mg/day  Men over age 50 require 1.7 mg/day, and women of this age require 1.5 mg/day Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 80
  • 81. Vitamin B6 Toxicity Toxicity in women taking supplements 1000 times the RDA to alleviate premenstrual syndrome Interferes with muscle coordination and damages the nervous system UL is 100 mg/day Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 81
  • 82. Food Sources of Vitamin B6 Many foods contain pyridoxine in small amounts Good sources include whole or fortified grain products, legumes, meat, poultry, bananas, and potatoes Highest contributor of pyridoxine to the diets of U.S. adults is ready-to-eat cereals Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 82
  • 83. Folate Named from Latin word for leaf because it was first extracted from dark leafy vegetables Folic acid is seldom found naturally but is used in supplements  85% absorbed Naturally occurring food folate is pteroylpolyglutamate  50% absorbed Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 83
  • 84. Functions of Folate Folate is the coenzyme with the important task of attaching single carbons to metabolic compounds Key molecules formed in this process include:  Purines  Thymine  Hemoglobin Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 84
  • 85. Folate DeficiencyFactors Associated With Folate Deficiency Lack of gastric acid Chemotherapy Anticonvulsant medications Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 85
  • 86. Folate Deficiency – Cont’dClinical Implications of Folate Deficiency Anemia that responds to folate supplementation  Most likely in pregnant women, growing infants, and young children Inappropriately high blood homocysteine levels:  Uncertain effects on cardiovascular disease, osteoporosis, and age-related cognitive impairment Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 86
  • 87. Folate RequirementsFolate and Birth Defects Plays essential role in the formation and closure of the neural tube in the early weeks of fetal development Demands that mother be in good folate status before becoming pregnant; supplementation after pregnancy is confirmed too late to prevent damage to the fetus Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 87
  • 88. Folate Requirements – Cont’dFolate and Birth Defects – Cont’d Folate deficiency early in pregnancy can result in a neural tube defect in the developing fetus  Mandatory folate fortification of flour or uncooked grain  Incidence of NTDs has declined  Concern that it may mask vitamin B12 deficiency Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 88
  • 89. Folate Requirements – Cont’dDietary Reference Intakes RDA for adolescents and adults of all ages is 400 µg/day Increases to 600 µg/day in pregnancy to support fetal and maternal tissue growth Women of childbearing age should consume at least 400 µg/day of folate Fortification has increased intakes by as much as 200 µg/day Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 89
  • 90. Food Sources of Folate Good sources include dark green leafy vegetables, citrus fruits, tomatoes, cantaloupe, and legumes Fortified grains and ready-to-eat cereals are important sources Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 90
  • 91. Vitamin B12 (Cobalamin) A complex red crystal of high molecular weight with a single cobalt atom at its core Occurs as a protein complex in foods of animal origin only Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 91
  • 92. Absorption of Vitamin B12 (Cobalamin) Gastric acid is required to separate the vitamin from its protein complex Vitamin is bound to a specific glycoprotein called intrinsic factor secreted by the mucosal cells lining the stomach Intestinal absorption occurs in the ileum Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 92
  • 93. Functions of Vitamin B12 Participates in amino acid metabolism and the formation of the heme portion of hemoglobin Involved in the synthesis of important lipids and proteins that form the myelin sheath covering the nerves of the brain and spinal cord Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 93
  • 94. Vitamin B12 DeficiencyDeficiency Symptoms Disrupted formation of red blood cells, resulting in production of megaloblastic cells (megaloblastic anemia) Damage to the nerves of the brain and spinal cord with changes in cognitive function, judgment, and personality Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 94
  • 95. Vitamin B12 Deficiency – Cont’dDeficiency Diseases Pernicious anemia  Results from lack of intrinsic factor  Treated with injections of vitamin B12 Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 95
  • 96. Vitamin B12 Deficiency – Cont’dDeficiency Diseases – Cont’d Vitamin B12 deficiency in older adults  Results from a lack of gastric acid  Treated with injections of vitamin B12 or use of B12 fortified foods (this form of B12 does not require gastric acid for absorption) Excessively high blood folate levels ameliorate anemia, but exacerbate cognitive losses Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 96
  • 97. Vitamin B12 Requirements Needed in minute amounts RDA is 2.4 µg for both younger and older adults Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 97
  • 98. Food Sources of Vitamin B12 Found naturally only in animal foods Rich sources include lean meat, fish, poultry, milk, eggs, and cheese Vitamin B12—fortified grains, cereals, juices, and soy milk or supplements Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 98