Vitamin D is essential to build and maintain healthy bones throughout life. Calcium, the main element of bone, can be absorbed into the body only when vitamin D is present. Vitamin D and calcium are involved in many body functions, including keeping your immune and nervous systems healthy.

Getting enough vitamin D can help prevent a number of serious health conditions, including those listed below:

• Osteoporosis: a preventable condition of soft, fragile, easily fractured bones. Vitamin D protects against the preventable bone diseases of rickets, osteomalacia, osteoporosis, and osteopenia. Seniors in northern climates and people who do not receive direct sunlight daily need to take a vitamin D supplement to keep their bones strong. Calcium supplements will not help prevent or treat osteoporosis if your vitamin D level is low.
• Cancer: Vitamin D is involved in cell growth and has been shown to decrease the growth of leukemia, colon cancer, skin cancer, and breast cancer cells. Researchers have found that people with adequate levels of vitamin D have a lowered risk of prostate and colorectal cancers.
• Multiple sclerosis: Vitamin D may help protect against this condition.
• Heart disease: Vitamin D may help prevent hardening of the arteries (arteriosclerosis) and lower blood pressure.

Vitamin D is also helpful in the following ways:

• Helps control blood sugar
• May help an overactive parathyroid
• Reduces cartilage damage in people with osteoarthritis and may decrease the severity of rheumatoid arthritis
• Has been successful in treating psoriasis

You may benefit from taking a vitamin D supplement if the following applies to you:

• You are on anticonvulsant drug therapy or glucocorticoid therapy.
• You eat a strict vegan diet.
• You are overweight or obese. 

Foods that contain vitamin D include the following:

• Cod liver oil
• Salmon
• Tuna
• Fortified milk
• Oysters
• Mushrooms
• Fortified cereals
• Egg yolk

Sunlight is a natural source of vitamin D. If you are fair-skinned, 20 to 30 minutes a day in bright sunlight will meet your vitamin D needs. If you are dark-skinned, you need three hours to get the same benefit. Clouds, smog, clothing, sunscreen, and window glass all decrease the amount of vitamin D you get from sunlight.

Vitamin D is included in many multivitamins. It can be found in over-the-counter preparations in strengths from 50 IU to 1,000 IU as softgel capsules, tablets, and liquid. Higher-dose prescription preparations are available. If you have trouble digesting fat, vitamin D injections are also available by prescription.

Consideration of vitamin D supplementation should be discussed with your healthcare provider. As with all supplements, check with the healthcare provider before giving vitamin D to a child.

Adequate daily intakes for dietary vitamin D are listed below.

Pediatric

• Infants birth to 12 months: 5 mcg (200 IU)
• Children 1 to 8 years: 5 mcg (200 IU)
• Children 9 to 13 years: 5 mcg (200 IU)
• Adolescents 14 to 18 years: 5 mcg (200 IU)

Adult

• 19 to 50 years: 5 mcg (200 IU)
• 51 to 70 years: 10 mcg (400 IU)
• 70 years and older: 15 mcg (600 IU)
• Pregnant and breastfeeding females: 5 mcg (200 IU)

Taking too much vitamin D (more than 1,000 IU daily) can make you very ill. Symptoms include excessive thirst, metal taste, bone pain, tiredness, sore eyes, itching skin, vomiting, diarrhea, a need to urinate, and muscle problems. Getting too much sunlight will not give you too much vitamin D.

Check with your doctor before taking vitamin D if you have high blood calcium or phosphorus levels or if you have a cardiac or kidney disease.

Isoniazid (INH), cholestyramine, antacids, calcium channel blockers, anticonvulsants, and thiazide diuretics all interfere with vitamin D.

INH, a medication used to treat tuberculosis, may raise blood levels of this vitamin.

Cholestyramine, a cholesterol-lowering medication, interferes with the absorption of vitamin D (as well as other fat soluble vitamins).

Calcium-channel blockers (such as verapamil) that are used to treat high blood pressure and heart conditions may decrease the production of vitamin D by the body. Phenobarbital, phenytoin, and other anticonvulsant medications increase the body's use of vitamin D. Please refer to the consumer depletions monographs on phenobarbital and phenytoin for additional information.

Thiazide diuretics increase the activity of vitamin D and could lead to higher calcium levels.

Hormone replacement therapy with estrogen appears to increase vitamin D levels in the blood; this may be a beneficial effect on calcium and bone metabolism. However, this benefit may be lost with the addition of progesterone.

The hormonal form of vitamin D may enhance the effects of doxorubicin, a medication used to treat a variety of cancers.

Taking some antacids for long periods of time may alter the levels, metabolism, and availability of vitamin D.

American Academy of Sciences. Dietary Reference Intakes: Calcium Phosphorus, Magnesium, Vitamin D, and Fluoride. 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 Metab. 1992;75(2):519-523.

Brenner RV, Shabahang M, Schumaker LM, et al. The antiproliferation effect of vitamin D analogs on MCF-7 human breast cancer cells. Cancer Lett. 1995;92:77–82.

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. 1998. Effects of two 1-year calcium and vitamin D3 treatments on bone remodeling markers and femoral bone density in elderly women. Curr Thera Res. 59(12):850–862.

Drug Facts and Comparisons 1999. St. Louis, Mo: A. Wolters Kluwer Company; 1998.

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 Med. 1984;77(4):747-750.

Hathcock JN. Metabolic mechanisms of drug-nutrient interactions. Fed Proc. 1985;44(1):124-129.

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 Endocrino. 1997;137:495–502.

Henning HV. Aluminum toxicity [in German]. Klin Wochenschr. 1989;67(24):1221-1228.

Hines Burnham T, 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. Leukemia. 1993;7(10):1525–1530.

Kitch BT, Vamvakas EC, Dick IM, et al. Hypovitaminosis D in medical implants. N Engl J Med. 1998;338:777–783.

Knodel LC, Talbert RL. Adverse effects of hypolipidaemic drugs. Med Toxicol. 1987;2(1):10-32.

Langman M, Boyle P, et al. Chemoprevention of colorectal cancer. Gut. 1998;43:578–585.

Mahan K, Arlin M. Krause's Food, Nutrition and Diet Therapy. 8th ed. Philadelphia, Pa: WB Saunders Company; 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.

Matsui MS, Rozovski SJ. Drug-nutrient interaction. Clin Ther. 1982;4(6):423-440.

Nutrients and Nutritional Agents. In: Kastrup EK, Hines Burnham T, Short RM, et al, eds. Drug Facts and Comparisons. St. Louis, Mo: Facts and Comparisons; 2000:4-5.

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; 1998.

Schumann K. Interactions between drugs and vitamins at advanced age. Int J Vitam Nutr Res. 1999;69(3):173-178.

Self TH, Chrisman CR, Baciewicz AM, Bronze MS. Isoniazid drug and food interactions. Am J Med Sci. 1999;317(5):304-311.

Thomas MK., Lloyd-Jones DM, Thadhani RI, et al. Hypovitaminosis D in medical inpatients. N Engl J Med. 1998;338:777–783.