Vitamin D For Disease Prevention

Necessary for strong bones in people of all ages, vitamin D is making news for benefits ranging from cancer and diabetes prevention to strengthened immunity. The “sunshine vitamin” appears more important than ever—but this year a European clinician reported that more than a billion people worldwide may be vitamin D deficient. Do you get enough?

D for Defense

Vitamin D aids the absorption of calcium and helps maintain normal levels of calcium and phosphorus in the blood. In addition to fighting osteoporosis, this vitamin prevents the childhood disease rickets. Recent research suggests that vitamin D also supports strong muscles—resulting in fewer falls among the elderly—and helps guard against many chronic health conditions, including heart disease, Type 2 diabetes, multiple sclerosis, and rheumatoid arthritis. The National Institutes of Health reports that “vitamin D may help maintain a healthy immune system,” and the most biologically active form of the vitamin, D3, seems to reduce the risk for breast, colorectal, and prostate cancer.

Sunshine Vitamin

UV rays from sunlight trigger the body to make vitamin D. As we age, however, our bodies become less effective at using the sun’s rays to produce this vitamin. Melanin, the pigment that gives skin its color, decreases the production of vitamin D during UV exposure, so dark-skinned individuals synthesize less of the vitamin than people with light skin. In latitudes around 40 degrees north (Hartford, Connecticut, and Boulder, Colorado), there is insufficient sunlight for vitamin D synthesis from November to early March.

Tempting as it is to head south (especially during the dark days of winter), dermatologists remind us of the high price of UV exposure. “The amount of sun exposure adequate to produce the necessary levels of vitamin D is not known,” says Hensin Tsao, MD, PhD, at Massachusetts General Hospital. “What we do know is that excessive, unmitigated solar irradiation can lead to harmful secondary effects including skin cancers, immunosuppression, and photodamage.” But five to ten minutes of sun exposure a few times a week plus dietary and supplemental D may provide vitamin D sufficiency.

Other Sources

Unfortunately, this fat-soluble vitamin occurs naturally in just a few foods (fatty fish and fish liver oils, eggs). Fortified foods—milk and ready-to-eat cereals—are other sources of vitamin D. One cup of vitamin D-fortified milk provides half the recommended daily intake for adults ages 19 to 50, a quarter for adults ages 51 to 70, and about 15 percent for those 71 years of age and older.

While the Institute of Medicine defines the adequate intake of vitamin D as 200 to 600 IU, some experts argue that the recommendations should be higher. “We could easily recommend 1,000 IU a day,” says Tufts’ Bess Dawson-Hughes, MD.

Need Supplements?

Dietary supplements may be particularly important for:

• infants who are exclusively breastfed
• children
• older adults
• persons with limited sun exposure or darker skin
• overweight individuals (D remains in body fat, leaving less in the bloodstream)
• anyone with a reduced ability to absorb dietary fat.

Look for supplements that provide D3 (choleciferol), which the body can better utilize, rather than D2 (ergocalciferol).

Adequate Intake for Vitamin D

The chart below shows current government recommendations for adequate intake (AI), which is defined as the amount needed “to maintain a nutritional state of adequacy in nearly all members of a specific age and gender group.”

source: National Institutes of Health

Food Sources of D

source: National Institutes of Health