Chapter 81
description
Transcript of Chapter 81
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Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
Chapter 81
Vitamins
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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
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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
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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
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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
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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
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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
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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
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Water-Soluble Vitamins Vitamin C Members of the vitamin B complex
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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
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Vitamin B Complex Niacin (nicotinic acid) Riboflavin (vitamin B2) Thiamin (vitamin B1) Pyridoxine (vitamin B6) Cyanocobalamin (vitamin B12) Folic acid
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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
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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
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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)
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Thiamin (Vitamin B1)
Actions Coenzyme for carbohydrate metabolism Requirements increased slightly during pregnancy
and breast-feeding Deficiency
Beriberi Wernicke-Korsakoff syndrome
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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
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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
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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
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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 B6 is rare in United States, except in alcoholics
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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
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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