Vitamin D

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.

Uses

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.
• Diabetes: Vitamin D may help regulate blood sugar to prevent diabetes or to help control it.
• 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.

Dietary Sources

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.

Other Forms

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.

How to Take It

To prevent disease, adults who do not get regular exposure to bright sunlight should take between 200 IU and 400 IU daily. Discuss your supplement regimen regularly with your health care provider. As with all medications, check with your health care provider before giving vitamin D to a child.

Precautions

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.

Possible Interactions

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 interfere with the production of vitamin D by the body. Phenobarbital, phenytoin, and other anticonvulsant medications increase the body’s use of vitamin D.

Supporting Research

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.

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.

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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.

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.

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