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Trao đổi trực tuyến tại: Reading material • Principles of Biochemistry with a Human Focus by Garrett and Grisham, First Edition, 2002, pages 453-468 • Handbook of NonPrescriptions Drugs, 11th edition, Chapter entitled “Nutritional Products” by Loyd V Allen, Jr Vitamins • a group of organic compounds needed in small quantities in the diet for normal activity of tissues • between 14 – 20 substances have been identified as vitamins • many vitamins act as cofactors, coenzymes or prosthetic groups for enzymes • most vitamins are derived from diet • no calories are derived from vitamins Vitamins • first vitamin discovered was thiamine or B1 • the term vitamin is derived from the fact that the substances are needed for life (vita) and because thiamine happened to be an amine the term was coined as such • however, not all vitamins are amines or nitrogen containing compounds Vitamins • vitamin requirements are usually expressed as RDA’s (recommended dietary allowances) • guidelines are provided by organizations: • the Food and Nutrition Board of the National Academy of Sciences- National Research Council • the Food and Drug Administration (FDA) RDAs • applications of RDAs include: • evaluating the adequacy of the national food supply • establishing standards for menu planning • establishing nutritional policy for public institutions/organizations and hospitals • evaluating diets in food consumption studies • establishing labeling regulations • setting guidelines for food product formulation • developing materials for nutritional education RDAs • RDAs have limitations: • they are too complex for direct consumer use • they not state ideal or optimal levels of intake • the allowances for some categories are based on limited data • the data on some nutrients in foods is limited • they not evaluate nutritional status • they not apply to seriously ill or malnourished patients Vitamin deficiencies • primary food deficiency • crop failure • food storage loss • food preparation loss • diminished food intake • • • • poverty anorexia food fadism chronic diseases Vitamin deficiencies • diminished absorption • absorption defect • parasites • malignancies • increased requirements • • • • rapid growth increased physical activity pregnancy hyperthyroidism • increased loss • drug therapy • diuresis • lactation Vitamin loss Loss is seen mainly in storage or food preparation • Vitamin A: sensitive to oxygen and light • Vitamin D: usually little loss • Vitamin E: sensitive to oxidation especially when heated or with alkali • Vitamin K: sensitive to acids, alkali, light and oxidizing agents • Vitamin C: very sensitive to oxidation, especially when heated in contact with metals • Vitamin B complex: water solubility results in loss in cooking water • Riboflavin is sensitive to light Calcipotriol (Dovonex) a vitamin D derivative approved for the treatment of psoriasis Mechanism of action is unknown Receptor affinity is similar to that of calcitriol, but is less than 1% as active in regulating calcium metabolism HO OH H3 C CH2 OH Calcipotriene • An analog of vitamin D3 with a modified side-chain containing a 24-OH group and a cyclopropyl group • binds strongly to the D3 receptor on keratinocytes in skin and it suppresses their proliferation (used in psoriasis) • has only about 0.5% of the activity of D3 on calcium and phosphorus metabolism Dihydrotachysterol (DHT) A reduction product of vitamin D-2 Used in the management of hypoparathyroidism has only 1/450th the antirachidic activity of vitamin D-2 H3 C CH3 HO Vitamin K • the koagulation vitamin • exists in forms: – plant origin: phylloquinone or vit K1 – bacterial origin: menaquinones or vit K2 • also certain synthetic quinones have vitamin K activity – menadione (vitamin K3) – menadiol sodium phosphate (vitamin K4) O CH3 CH3 O CH3 CH3 PHYTONADIONE (VITAMIN K 1; PHYLLOQUINONE) O CH CH O CH n = -12 CH MENAQUINONE (VITAMIN K SERIES) O CH3 O MENADIONE (VITAMIN K3) CO O 2C CH CH CH CO CH CO O2 O OH CH CH O R R O OH WARFARIN & OTHER ANTICOAGULANTS NADH NAD ANTIVITAMIN K ACTION OF ORAL ANTICOAGULANTS Vitamin E • alpha (E1), beta (E2) and gamma(E3) tocopherol • sources: plant oils (corn, peanut, wheat germ), green leafy vegetables, meat, eggs • value resides in the antioxidant properties of vitamin E (may prevent the formation of peroxides) ALPHA TOCOPHEROL CH3 CH3 O H3C CH3 CH3 CH3 CH3 HO CH3 ALPHA TOCOPHEROL Found in a variey of different sources (primarily vegetable fats) Vitamin E • Estimated requirements: mg/day + 0.6 mg/day of unstaurated fat • Biological function – antioxidant for fatty acids – Acts like vitamin C; prevents lipid peroxidation and/or damage to cells by lipid hydroperoxides Uses for vitamin E • hemolytic anemia in premature infants, unresponsive to B12, Fe and folic acid • macrocytic megaloblastic anemia seen in children with severe protein-calorie malnutrition Other coenzymes O Serves as entry into the electrontransport chain CH CH 3O CH CH CH C CH 3O CH O H 10 Coenzyme Q (Ubiquinone) H N H 2N N N N H H CH CH CH OH OH OH Tetrahydrobiopterin Involved in the conversion of phenylalanine to tyrosine 09/12/02 ... B12 and pantothenic acid) • Ascorbic acid (vitamin C) Bogus vitamins • • • • • • • Vitamin B4 Vitamin B10 Vitamin B11 Vitamin B15 Vitamin B13 Vitamin B17 Vitamin B19 adenine identical with folic... Riboflavin is sensitive to light Vitamins • Vitamins are typically divided into groups: – The fat soluble vitamins • A, D, E, and K – The water soluble vitamins • The B vitamins (B1, B2, B3, B6, B7,... prosthetic groups for enzymes • most vitamins are derived from diet • no calories are derived from vitamins Vitamins • first vitamin discovered was thiamine or B1 • the term vitamin is derived from the
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