Chapter 81

1. Chapter 81 Vitamins

2. Vitamins • Organic compounds • Required in minute amounts for growth and maintenance of health • Do not serve as a source of energy • Essential for energy transformation and regulation of metabolic processes • Several vitamins are inactive in native form; must be converted to active compounds in the body

3. Intake of Vitamins • Recommended dietary allowances (RDAs) for vitamins are set by the Food and Nutrition Board of the National Academy of Sciences • RDAs represent the average daily dietary intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals in a particular life-stage or gender group

4. Intake of Vitamins • The tolerable upper intake limit (UL) for a vitamin is the highest average daily intake that can be consumed by nearly everyone without significant risk for adverse effects • The UL is an index of safety—not a recommendation to exceed the RDA • Estimated average requirement (EAR) is the level of intake that will meet nutrition requirements for 50% of the healthy individuals in any life-stage or gender group

5. Vitamins • Classification of vitamins • Fat-soluble • Vitamins A, D, E, K • Water-soluble • Vitamin C • Vitamin B complex—thiamin, riboflavin, niacin, pyridoxine, pantothenic acid, biotin, folic acid, cyanocobalamin

6. Vitamin A (Retinol) • Multiple functions in the eyes • Toxicity • Birth defects, liver injury, bone-related disorders • Deficiency causes • Night blindness • Xerophthalmia • Keratomalacia • Blindness • Therapeutic uses

7. Vitamins D and E • Vitamin D • Regulates calcium and phosphorus • Deficiency causes rickets or osteomalacia • Vitamin E • Antioxidant properties • Dietary sources—fresh greens, seeds, oils • Toxicity may increase risk for bleeding

8. Vitamin K • Action required for synthesis of prothrombin and other clotting factors • Deficiency produces bleeding • Adverse effects • Hypersensitivity reaction • Hyperbilirubinemia in parenteral administration to newborns • Therapeutic use • Warfarin overdose

9. Water-Soluble Vitamins • Vitamin C • Members of the vitamin B complex

10. Vitamin C • Action required for production of collagen and other compounds that bind cells together • Part of the biochemical reaction for the synthesis of adrenal steroids • Sources • Citrus fruits/juices, tomatoes, potatoes, strawberries, melons, spinach, broccoli • Has antioxidant properties • Facilitates iron absorption • Deficiency can lead to scurvy

11. Vitamin B Complex • Niacin (nicotinic acid) • Riboflavin (vitamin B2) • Thiamin (vitamin B1) • Pyridoxine (vitamin B6) • Cyanocobalamin (vitamin B12) • Folic acid

12. Niacin (Nicotinic Acid) • Deficiency • Pellagra: dermatitis characterized by scaling and cracking of the skin in areas exposed to the sun • GI disturbances • CNS • Irritability, insomnia, memory loss, anxiety, and dementia

13. Niacin (Nicotinic Acid) • Adverse effects • Small doses devoid of adverse effects • Large doses • Vasodilation with flushing, dizziness, nausea • Therapeutic uses • In capacity as a vitamin, used only as treatment for niacin deficiency • If given in large doses, can decrease cholesterol

14. Riboflavin (Vitamin B2) • Actions • Involved in numerous enzymatic reactions • First, must be changed to flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN) • Adverse effects • None for humans, no UL • Therapeutic uses • Riboflavin deficiency • Migraine headaches (see Chapter 30)

15. Thiamin (Vitamin B1) • Actions • Coenzyme for carbohydrate metabolism • Requirements increased slightly during pregnancy and breast-feeding • Deficiency • Beriberi • Wernicke-Korsakoff syndrome

16. Thiamin (Vitamin B1) • Wet beriberi • Fluid accumulation in the legs • Cardiovascular complications (palpitations, ECG abnormalities, high-output heart failure) • May progress to circulatory collapse and death • With treatment: recovery dramatic with replacement therapy • Dry beriberi • Neurologic and motor deficits, no edema or cardiovascular symptoms • Recovery slow

17. Thiamin (Vitamin B1) • Wernicke-Korsakoff syndrome (caused by alcoholism) • Alcoholism: most common cause of thiamin deficiency in United States • Serious CNS disorder (neurologic and psychologic) • Nystagmus, diplopia, ataxia, inability to remember the recent past

18. Pyridoxine (Vitamin B6) • Coenzyme in the metabolism of amino acids and proteins • Must first be converted to its active form: pyridoxal phosphate • Sources • Fortified breakfast cereals, meat, fish, poultry, white potatoes, other starchy vegetables, and noncitrus fruits

19. Pyridoxine (Vitamin B6) • Deficiency • May result from poor diet, isoniazid use, inborn errors of metabolism • Symptoms • Seborrheic dermatitis, microcytic anemia, peripheral neuritis, convulsions, depression, confusion • Dietary deficiency of B6is rare in United States, except in alcoholics

20. Vitamin B Complex • Cyanocobalamin (vitamin B12) and folic acid • Both essential factors in the synthesis of DNA • Deficiency of either manifests as megaloblastic anemia (see Chapter 55) • Cyanocobalamin deficiency produces neurologic damage as well

21. Folic Acid • Food folate vs. synthetic folate • Synthetic form is more stable • FDA ordered synthetic folate to be added to all enriched grain products • Deficiency of folic acid during pregnancy can impair CNS development • Can result in neural tube defects, anencephaly, spina bifida • Important for any patient who may become pregnant to take additional folic acid