copyright © 2013, 2010 by saunders, an imprint of elsevier inc. chapter 81 vitamins

Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.

Chapter 81

Vitamins

2Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.

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


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


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


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


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


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


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


Water-Soluble Vitamins

Vitamin C Members of the vitamin B complex


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


Vitamin B Complex

Niacin (nicotinic acid) Riboflavin (vitamin B2) Thiamin (vitamin B1) Pyridoxine (vitamin B6) Cyanocobalamin (vitamin B12) Folic acid


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


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


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)


Thiamin (Vitamin B1)

Actions Coenzyme for carbohydrate metabolism Requirements increased slightly during pregnancy

and breast-feeding Deficiency

Beriberi Wernicke-Korsakoff syndrome



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



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


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


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


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


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

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intake of vitamins

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e vitamin d

bleeding slide

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vitamin c action

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