Vitamin D is fat-soluble and the only vitamin whose active form (calcitrol)
is a hormone. Its most important role is to maintain serum calcium and
phosphorus levels within an acceptable range, which is critical for many body
functions, including the normal development of bones and teeth, normal cell
growth, and regulation of the immune and nervous systems. Low levels of vitamin
D lead to osteomalacia, a mineralization deficit of the bones, associated with
osteoporosis, osteoarthritis, rheumatoid arthritis, multiple sclerosis,
diabetes, heart disease, and an overactive parathyroid.
The elderly, particularly those in northern climates and those who are
housebound, are at significant risk for vitamin D deficiency. A 1998 study in
the New England Journal of Medicine found vitamin D deficiency in 57% of
a random group of 290 hospitalized patients over age 65. Studies support vitamin
D supplementation for the prevention and treatment of osteoporosis in
postmenopausal women. In a 1997 study by Tufts University, supplementation with
calcium (500 mg) and vitamin D (700 IU/day) was provided to 176 men and 213
women over age 65. The results were a significant increase in bone mass and a
50% reduction in fracture rate after three years.
Vitamin D is involved in cell growth and maturation and has shown anticancer
properties. In vitro studies have suggested that vitamin D inhibits growth of
breast and prostate cancer cells. The Physicians' Health Study, published in
1996, found links between dietary vitamin D and a slightly decreased risk of
prostate cancer. A 1996 epidemiological study in Sweden and the 1996 Harvard
Nurses' Health Study found that dietary vitamin D decreased the risk of
Vitamin D is involved in regulating the immune system and is being considered
as a therapy for autoimmune disorders and to suppress rejection of transplanted
organs. Vitamin D analogs have successfully been used to treat the skin disorder
- Cod liver oil
- Fortified milk
- Fortified cereals
- Egg yolk
Few foods are natural sources. The primary source for humans has
traditionally been sunlight. A fair-skinned person can receive adequate vitamin
D through the skin with 20 to 30 cumulative minutes of daily sun exposure. A
dark-skinned person may require three hours for a similar dose. Clouds, smog,
clothing, sunscreen, and window glass all filter the ultraviolet light necessary
for vitamin D3 to be synthesized by provitamin D in the skin. Latitude, time of
day, and season of the year also impact synthesis.
There are three forms of vitamin D.
- D1: calciferol, found in some foods
- D2: ergocalciferol, the form most widely found in food and most
commonly added to food and nutritional supplements
- D3: cholecalciferol, originates in the skin
All these forms of vitamin D are converted into calcitriol, the active form
of the vitamin, in the liver and kidney
- Supplemental vitamin D is available in natural and synthetic
- Fish liver oil is the common natural source and provides vitamin
- Over-the counter preparations of vitamin D2 are available in 50 IU,
100 IU, 400 IU, 500 IU, 600 IU, and 1,000 IU dosage as soft gel capsules,
tablets, and liquid.
- Prescription preparations of vitamins D2 and D3 are available in
tablets from 400 IU to 50,000 IU.
- Synthetic dihydrotachysterol is a reduction product of a close isomer
to vitamin D2, available by prescription.
- Protects against rickets, osteomalacia, osteoporosis, and
- Protects against bone fractures in the elderly
- Recommended in the treatment of osteoporosis in postmenopausal
- Recommended during fall and winter months for the elderly in northern
climates and for those who do not receive daily exposure to direct
- Indicated for those with fat malabsorption disorders, including
celiac disease, tropical sprue, cystic fibrosis, pancreatic disease, and short
- Indicated for those on anticonvulsant drug therapy or glucocorticoid
- Recommended for those on strict vegan diets
- Helps prevent some cancers by inhibiting the growth of human
leukemia, colon cancer, skin cancer, and breast cancer cells
- Involved in the regulation of the immune system; may be indicated to
treat autoimmune disorders and to suppress rejection of transplanted
- Plays a role in the secretion of insulin, thus aiding regulation of
- Suppresses action of parathyroid hormone and may play a role in the
treatment of an overactive parathyroid
- May reduce cartilage damage in osteoarthritis
- May decrease disease activity for rheumatoid arthritis
- May protect against multiple sclerosis
- May prevent diabetes mellitus
- May decrease the risk of arteriosclerosis
- May help prevent inflammatory bowel disease, tuberculosis, stroke,
and high blood pressure
|Dosage Ranges and Duration of
Adequate Daily Intake (AI)* is as follows.
- Infants and children: 5 mcg (200 IU)
- Adults up to age 50: 5 mcg (200 IU)
- Adults ages 51 to 70: 10 mcg (400 IU)
- Adults over age 70: 15 mcg (600 IU)
*AI reflects a level at which normal values and functional indicators of
nutrition are maintained.
- Infants up to 6 months: 7.5 mcg (300 IU)
- Children: 10 mcg (400 IU)
- Adults up to age 25: 10 mcg (400 IU)
- Adults age 25 and older: 5 mcg (200
High daily doses (more than 1,000 IU) of vitamin D can be toxic. The range
between therapeutic and toxic doses is narrow. The major effect of toxicity is
hypercalcemia, with symptoms of excessive thirst, metallic taste, bone pain,
fatigue, sore eyes, itching skin, vomiting, diarrhea, urinary urgency, impaired
muscle function, and cardiovascular and renal failure. Prolonged exposure to
sunlight does not result in vitamin D toxicity.
Vitamin D should not be given to those with high blood calcium levels or high
blood phosphorus levels. Vitamin D should be given with caution to those
suffering from cardiac or kidney diseases.
Antacids that bind phosphate may alter the levels, metabolism, and
availability of vitamin D. There is a case report of osteomalacia in a patient
that consumed large amounts of antacids (Godsall et al. 1984).
Aluminum-containing antacids may also increase the risk of fractures from
osteomalacia resistant to the administration of vitamin D; this is of particular
concern for people at risk for aluminum toxicity including newborns, elderly,
and people with kidney or liver disease (Henning
The hormonal form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3),
interacted synergistically with doxorubicin by increasing the cytotoxic activity
of the drug against breast cancer cells in vitro (Ravid et al. 1999).
In one study, both total and free 1,25-(OH)2D concentrations increased in
women within 5 years of menopause who were being treated with unopposed estrogen
for three cycles (Bikle et al. 1992). With the addition of progestin, the levels
of vitamin D returned toward baseline. Progestin may antagonize some of the
beneficial effects of estrogen on calcium balance and bone metabolism; it is not
clear if vitamin D supplementation will overcome this effect.
Thiazide diuretics enhance the biological activity of vitamin D and increase
the risk of hypercalcemia (Hines Burnham et al 2000).
Verapamil may induce parathyroid hormone (PTH) resistance accompanied by a
decrease in 1,25(OH)D3 levels (Fox 1988). Studies in rats have demonstrated that
the negative correlation between PTH and vitamin D levels is significant.
However, this interaction does not appear to have long-term effects on calcium
homeostasis because of a dose-dependent increase in duodenal absorption of
American Academy of Sciences. Dietary Reference Intakes: Calcium,
Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC:
National Academy Press; 1997.
Bendich A, Deckelbaum R, eds. Preventive Nutrition: The Comprehensive
Guide for Health Professionals. Totowa, NJ: Humana Press; 1997.
Bikle DD, Halloran BP, Harris ST, Portale AA. Progestin antagonism of
estrogen stimulated 1,25-dihydroxyvitamin D levels. J Clin Endocrinol
Brenner RV, Shabahang M, Schumaker LM, et al. The antiproliferation effect of
vitamin D analogs on MCF-7 human breast cancer cells. Cancer Lett.
Dawson-Hughes B, Harris SS, Dallal GE. Plasma calcidiol, season, and serum
parathyroid hormone concentrations in healthy elderly men and women. Am J
Clin Nutr. 1997;65:67-71.
Dawson-Hughes B, Harris SS, Krall EA, etal. Effect of calcium and vitamin D
supplementation on bone density in men and women 65 years of age and older. N
Engl J Med. 1997;337:670-676.
Deroisy R, Collette J, Chevallier T, et al. Effects of two 1-year calcium and
vitamin D3 treatments on bone remodeling markers and femoral bone density in
elderly women. Curr Thera Res. 1998;59(12):850-862.
Drug Facts and Comparisons 1999. St. Louis, Mo: A. Wolters Kluwer Co;
Fox J. Verapamil induces PTH resistance but increases duodenal calcium
absorption in rats. Am J Physiol. 1988;255(5):E702-707.
Godsall JW, Baron R, Insogna KL. Vitamin D metabolism and bone
histomorphometry in a patient with antacid-induced osteomalacia. Am J
Heikkinen AM, Tuppurainen MT, Niskanen L, et al. Long-term vitamin D3
supplementation may have adverse effects on serum lipids during menopause
hormone replacement therapy. J Endocrinology. 1997;137:495-502.
Henning HV. Aluminum toxicity [in German]. Klin Wochenschr.
Hines Burnham, et al, eds. Drug Facts and Comparisons. St. Louis,
MO:Facts and Comparisons; 2000:9.
Kizaki M, Ikeda Y, Simon KJ, et al. Effect of 1,25-dihydroxyvitamin D3 and
its analogs on human immunodeficiency virus infection in monocytes-macrophages.
Komulainen MH, Kroger H, Tuppurainen MT, et al. HRT and Vit D in prevention
of non-vertebral fractures in postmenopausal women; a 5 year randomized trial.
Langman M, Boyle P, et al. Chemoprevention of colorectal cancer. Gut.
Mahan K, Arlin M. Krause's Food, Nutrition and Diet Therapy. 8th ed.
Philadelphia, Pa: WB Saunders Co; 1992.
Martinez ME, Giovannucci EL Colditz GA, et al. Calcium, vitamin D, and the
occurrence of colorectal cancer among women. JNCI. 1996;88:1375-1382.
Ravid A, Rocker D, Machlenkin A, et al. 1,25-Dihydroxyvitamin D3 enhances the
susceptibility of breast cancer cells to doxorubicin-induced oxidative damage.
Cancer Res. 1999;59:862-867.
Reavley N. Vitamins etc. Melbourne, Australia: Bookman Press;
Thomas MK, Lloyd-Jones DM, Thadhani RI, et al. Hypovitaminosis D in medical
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