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Overview of Vitamins

Overview of Vitamins. Pages 37–49 in textbook. History. Purified diets of carbohydrate, protein, fat, minerals and water were not capable of normal growth “Accessory growth factors” required Casimir Funk, a Polish biochemist, isolated an anti-berberi substance from rice polishings

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Overview of Vitamins

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  1. Overview of Vitamins Pages 37–49 in textbook

  2. History • Purified diets of carbohydrate, protein, fat, minerals and water were not capable of normal growth • “Accessory growth factors” required • Casimir Funk, a Polish biochemist, isolated an anti-berberi substance from rice polishings • Named it vitamine • Vita means life; amine refers to “nitrogen containing” • Unrelated chemically • Not all vitamins are amines so “e” was dropped

  3. Vitamins • Essential organic compounds required in very small amounts (micronutrients required in amounts of micrograms to milligrams) involved in fundamental functions of the body

  4. Function of Vitamins • Not metabolic fuels (like glucose or fatty acids) or structural nutrients (like amino acids) • Function strictly as individual units • Not connected like molecules of glucose, fatty acids and amino acids • Regulators (catalysts) of reactions, some of which are involved in energy metabolism • Cofactors (or their precursors) • Hormone-like activity

  5. Functions of Vitamins • Specific functions include: • Nurture growth; reproduction; maintain life • Prevent deficiency diseases • Help the enzymes that release energy from carbohydrates, lipids and proteins Do not provide energy!!

  6. Synthesis of Vitamins • All vitamins are metabolically essential but not all required in the diet • Vitamins cannot be synthesized by the body in adequate amounts to meet needs • Most mammals can synthesize vitamin C; not primates, guinea pigs • Some vitamins may be synthesized in body from precursors • Vitamin D synthesized from 7-dehydrocholesterol • Niacin synthesized from tryptophan • Vitamin A synthesized from carotenoids • Others • Bacterial synthesis • B-vitamins in ruminants

  7. Synthesis of Vitamins • Some function as vitamins after undergoing a chemical change • Provitamins (e.g., β-carotene to vitamin A) • Not all animals are equally efficientin converting a precursor to a vitamin

  8. Classification • Based on solubility, and solubility greatly influences how the body absorbs, transports and stores vitamins • Fat-soluble • Vitamins A, D, E and K • Water-soluble • B vitamins and vitamin C

  9. Fat-soluble Vitamins

  10. Fat-soluble Vitamins • Absorbed with dietary fat across small intestine • 40-90% absorption efficiency • Absorption typically regulated by need • need absorption rate • Transported away from small intestine in chylomicra via blood and lymph (depending on size)

  11. Fat-soluble Vitamins • Liver either stores the vitamin or repackages it for delivery to other cells • Excess fat soluble vitamins accumulate in liver and adipose tissue • Toxicities can occur; almost always associated with supplements (not from feeds)

  12. Water-soluble Vitamins

  13. Water-soluble Vitamins • Absorbed across the small intestine • Absorption often highly regulated by either other vitamins or binding proteins in the small intestine • Transported away from small intestine in blood • Typically not stored; instead, kidney filters excess into urine • Thus, more important to provide these vitamins daily • Toxicities rare

  14. Thiamin (B1) Riboflavin (B2) Niacin (B3) Panthothenic acid Biotin Pyridoxine (B6) Folic acid Cyanocobalamin (B12) Pyridoxine (B6) Pathothenic acid Pyridoxine (B6) Thiamin (B1) Folic acid Cyanocobalamin (B12) Niacin (B3)

  15. Energy metabolism Thiamin (B1) Riboflavin (B2) Niacin (B3) Pantothenic acid Transfer of 1-C units Biotin Folic acid Cobalamin (B12) Vitamin K Transfer of carboxyl and amino groups Pyridoxine (PLP, B6) Hormones Vitamin A (retinoids) Vitamin D Reductants or antioxidants Vitamin C (ascorbic acid) Vitamin E (tocopherols) Functions of Vitamins

  16. Fat soluble Closely associated with the absorption and transport of lipids requires bile salts transport by chylomicrons Stored in body lipids Water soluble Absorbed directly into the portal blood Not retained by body for long periods of time exception is B12 Excreted in urine when plasma levels exceed normal Vitamins - Comparison

  17. Vitamins in Feeds • Found in ALL TYPES of feedstuffs • In general, processing can decrease amount of vitamins in feed

  18. Vitamins in Feeds • Stability • Destruction of vitamins • Oxygen, light, heat, acids, (trace) minerals, etc. • Vitamins lose activity over time • Use feed within 3–4 weeks after mixing • Or increase dietary vitamin levels to account for losses Alfalfa storage time Relative vitamin A activity Fresh 100% Baling 42% Six months storage 11% Twelve months storage 9%

  19. Units of Measure • Fat soluble vitamins • International Unit (IU) • Standard unit potency based on bioassay that produces a particular effect • A measure of biological activity • Relative activity: 1 IU of vitamin A activityin rats =0.300 µg retinol 0.344 µg retinal acetate 0.550 µg retinyl palmitate • International Chick Unit (ICU) • Used to express vitamin D requirements of poultry • Other vitamins measured in weight units • mcg, mg, ng, etc.

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