The sunshine fix
Vitamins
Everyone knows the virtues of vitamin D. It helps the body build strong bones and has been added to milk since the 1930s to prevent rickets in children. But scientists have long suspected that this nutrient might have other disease-fighting properties as well. Last week, three new studies bolstered that view.
After examining the habits and health of more than 187,000 women, researchers found that taking vitamin D supplements dramatically cut the risk of developing multiple sclerosis, a debilitating disease in which the body's own immune system attacks the nerves. The results, reported this month in the journal Neurology, square with what scientists already know about the disease: One mysterious risk factor for MS is living far from the equator, where sunlight--the major nondietary source of the vitamin--is weaker.
The link between vitamin D and autoimmunity got additional support from a separate study, this one on rheumatoid arthritis. Researchers studied 30,000 women and found that vitamin D helped reduce the chance of developing the disabling joint disease--also an autoimmune disease--by a third.
The results make sense. Previous studies in both humans and animals have suggested that vitamin D calms an overactive immune system, perhaps by suppressing certain T cells. It's not yet clear whether it's possible to get the benefits entirely from vitamin D-rich foods, like salmon, fortified milk, cereal, or eggs. The MS study found a benefit only from taking a multivitamin pill, but that might be because it's difficult to get enough vitamin D through food alone. It's also unclear whether the protective effects came only from vitamin D or from other vitamins or minerals in the multi- vitamin. Still, "vitamin D is the only one with compelling biological evidence," says Kassandra Munger, author of the study and a researcher with the Harvard School of Public Health. The arthritis study found women received slightly more protection by getting the vitamin in a supplement rather than from food. (Neither study took into account the women's sun exposure.)
Don't overdose. These findings, while promising, don't suggest that people should go overboard with supplements. Very high doses of vitamin D--many times the recommended daily allowance--can cause nausea, confusion, and heart arrhythmias. And another study released last week showed that while men with lower-than-average levels of vitamin D in their blood were 50 percent more likely to have prostate cancer than those with normal levels, very high levels of the vitamin also increased risk for the common cancer.
The bottom line? Eat foods rich in vitamin D, and to be on the safe side take a multivitamin dose each day that includes the RDA for D. For adults 50 and under, that's 200 international units (denoted on the pill bottle as "IU") per day. A dose of 400 IU per day is recommended for people ages 51 to 69, and those 70 and over should take 600 IU a day. Those levels are plenty--not only to keep bones strong but also to confer benefits suggested by the latest studies.
This story appears in the January 26, 2004 print edition of U.S. News & World Report.
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