Chapter 81
Vitamins
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
Vitamins
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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
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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
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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
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Classification of vitamins
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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)
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Multiple functions in the eyes
Toxicity
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Deficiency causes
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Birth defects, liver injury, bone-related disorders
Night blindness
Xerophthalmia
Keratomalacia
Blindness
Therapeutic uses
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Vitamins D and E
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Vitamin D
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Regulates calcium and phosphorus
Deficiency causes rickets or osteomalacia
Vitamin E
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Antioxidant properties
Dietary sources—fresh greens, seeds, oils
Toxicity may increase risk for bleeding
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Vitamin K
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Action required for synthesis of prothrombin
and other clotting factors
Deficiency produces bleeding
Adverse effects
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Hypersensitivity reaction
Hyperbilirubinemia in parenteral administration to
newborns
Therapeutic use
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Warfarin overdose
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Water-Soluble Vitamins
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Vitamin C
Members of the vitamin B complex
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Vitamin C
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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
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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
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Niacin (nicotinic acid)
Riboflavin (vitamin B2)
Thiamin (vitamin B1)
Pyridoxine (vitamin B6)
Cyanocobalamin (vitamin B12)
Folic acid
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Niacin (Nicotinic Acid)
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Deficiency
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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)
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Adverse effects
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Small doses devoid of adverse effects
Large doses
• Vasodilation with flushing, dizziness, nausea
Therapeutic uses
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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)
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Actions
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Adverse effects
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Involved in numerous enzymatic reactions
First, must be changed to flavin adenine
dinucleotide (FAD) or flavin mononucleotide
(FMN)
None for humans, no UL
Therapeutic uses
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Riboflavin deficiency
Migraine headaches (see Chapter 30)
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Thiamin (Vitamin B1)
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Actions
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Coenzyme for carbohydrate metabolism
Requirements increased slightly during pregnancy
and breast-feeding
Deficiency
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Beriberi
Wernicke-Korsakoff syndrome
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Thiamin (Vitamin B1)
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Wet beriberi
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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
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Neurologic and motor deficits, no edema or
cardiovascular symptoms
Recovery slow
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Thiamin (Vitamin B1)
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Wernicke-Korsakoff syndrome (caused by
alcoholism)
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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)
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Coenzyme in the metabolism of amino acids
and proteins
Must first be converted to its active form:
pyridoxal phosphate
Sources
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Fortified breakfast cereals, meat, fish, poultry,
white potatoes, other starchy vegetables, and
noncitrus fruits
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Pyridoxine (Vitamin B6)
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Deficiency
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Symptoms
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May result from poor diet, isoniazid use, inborn
errors of metabolism
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
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Cyanocobalamin (vitamin B12) and folic acid
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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
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Food folate vs. synthetic folate
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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
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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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