A dose of sunshine

Vitamin D found to protect against MS;
should we pile on the supplements?

By Owen Dyer

Currently, one of the few factors known to reduce risk of multiple sclerosis (MS) is growing up in a sunny climate. Since sunshine is the body's main source of vitamin D, some observers suggested that the vitamin could be protective against MS, but there was a dearth of hard evidence to support this. Two new large studies are making some headway in filling that gap in our knowledge.

According to a study published in the January 13 issue of Neurology, women who take vitamin D supplements through multivitamins are 40% less likely to develop MS than women who take no supplements. If true, these findings would be the first to point to possible effective preventive measures against the disease.

"Because the number of cases of MS increases the farther you get from the equator, one hypothesis has been that sunlight exposure and high levels of vitamin D may reduce the risk of MS," said study author Kassandra Munger, MSc, of the Harvard School of Public Health in Boston, MA. "This is the first prospective study to look at this question. These results need to be confirmed with additional research, but it's exciting to think that something as simple as taking a multivitamin could reduce your risk of developing MS."

There is evidence to suggest that vitamin D is protective against a range of chronic diseases linked to inflammatory processes, including many systemic cancers. In North America rates of colorectal and stomach cancer are lowest in areas with the most sunlight. A study published in the Journal of the American Medical Association last month found that dietary vitamin D reduced the risk of colorectal cancer.

In Europe, some northern countries fortify bread and milk with vitamin D, and milk in Canada is also commonly fortified. But there has never been any proof that vitamin D taken as a food supplement has the same effect as vitamin D synthesized from sunlight. This study, which found a health benefit from vitamin D in supplement form, appears to vindicate those who argue in favour of adding vitamin D to staple food items.

The researchers examined data from two large studies involving women, the 20-year Nurses' Health Study and the 10-year Nurses' Health Study II. The women's diets and use of multivitamin supplements were assessed as the studies began and then again every four years. Women with preexisting MS were not included. There were 187,563 women enrolled, of whom 173 women developed MS during the course of the study.

The risk of developing MS was lower, both for those with high intake of vitamin D from supplements only and for those with high intake from both supplements and food. However, for those whose intake of vitamin D was from food only, the risk of developing MS did not lessen. Those with the highest intake of vitamin D from supplements (400 IU or more per day) were 40% less likely to develop MS than those who used no supplements.

Ms Munger acknowledged that since most of these supplements were in multivitamin form, it was impossible to be sure the effect came from vitamin D rather than some other vitamin. "However, none of these vitamins was itself significantly associated with risk of MS after adjusting for total vitamin D intake or vitamin D from supplements," she said.

Other studies have shown that people with MS tend to have insufficient levels of vitamin D, that periods of low vitamin D occur before times of high disease activity and periods of high vitamin D precede times of low disease activity. Ms Munger suggested that future prospective studies should measure vitamin D levels in the blood prior to the onset of MS.