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Tuesday, January 13, 2004 - Page updated at 12:00 A.M.
Vitamin D may reduce multiple sclerosis risk
By John Fauber
MILWAUKEE A study testing a long-held theory about the cause of multiple sclerosis has found that women who took a vitamin D supplement cut their risk of developing the incurable neurological disorder by 40 percent, compared with those who did not take a supplement.
The study, which involved 187,563 women, is the first large examination of an observation that has been around for decades that MS might be caused, in part, by a lack of sunlight sufficient to allow the body to make its own vitamin D.
In roughly the northern half of the United States, the incidence of MS is 110 to 140 cases per 100,000, compared with 60 to 80 cases per 100,000 in the Southern U.S. And in areas near the equator, the rate of MS is very low.
"What we found is (vitamin D) is protective against MS," said Kassandra Munger, the study's lead author and a researcher in the department of nutrition at the Harvard School of Public Health. "How long that protection lasts, I'm not sure."
The study, which appears in the January issue of the journal Neurology, is part of the ongoing Nurses' Health Study. The women in this study were followed for 10 to 20 years.
Those who took a daily multiple-vitamin supplement with at least 400 international units of vitamin D had 40 percent less incidence of MS than those who did not take a supplement with vitamin D. Depending on a person's age, 200 to 600 international units a day is recommended.
Vitamin D also is made in skin cells, which interact with sunlight. But with aging, a person's ability to make vitamin D is reduced.
Supplemental vitamin D also can be toxic. In excessive amounts, it can cause kidney failure, bone weakness and damage to heart and blood vessels. Doctors cautioned people against taking more than the recommended daily amount.
Multiple sclerosis is a chronic disease that is diagnosed mainly in young adults, according to the National Institute of Neurological Disorders and Stroke, part of the National Institutes of Health, which funded the study. In the United States, as many as 350,000 people have the disease.
MS is caused by an inflammation of nerve fibers in the central nervous system, which, in turn, results in the destruction of myelin, a substance that insulates nerve fibers in the brain and spinal cord.
Most people with MS have a normal life expectancy.
The fact that vitamin D supplements may play a role in preventing the disease is intriguing, but there likely are other important factors, such as infectious agents and genetics, said Roland Martin, a neurologist and MS specialist at the NIH.
"I think the study is very sound," Martin said. "They looked at very, very large numbers" of people.
One caveat in the Harvard study is that because most of the women were getting their vitamin D from a multivitamin, it was difficult to isolate the role of vitamin D from other vitamins. However, the researchers said no other vitamins were significantly associated with a reduced risk of MS.
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