African-Americans with multiple sclerosis have lower vitamin D levels

African-Americans who have multiple sclerosis (MS) have lower vitamin D levels than African-Americans who don't have the disease, according to a study published in the May 24, 2011, print issue of Neurology®, the medical journal of the American Academy of Neurology. However, most of the difference in vitamin D levels was due to differences in climate and geography.

"MS is not as common in African-Americans as it is in whites, although the disease tends to be more severe in African-Americans," said study author Ari J. Green, MD, of the University of California San Francisco and a member of the American Academy of Neurology. "We have known that vitamin D levels are associated with MS and that African-Americans are at increased risk for having low vitamin D levels, but little research has been done to look at vitamin D levels in African-Americans with MS."

Melanin, which determines the level of pigment in the skin, acts as a filter of UV light, which limits the amount of vitamin D that can be produced by the body in response to sunlight.

The study involved 339 people with MS and 342 people who did not have the disease. Researchers looked at vitamin D levels in the blood, the severity of the disease, the amount of UV exposure for participants based on where they lived and the proportion of European genetic ancestry participants had.

A total of 77 percent of the people with MS were vitamin D deficient, compared to 71 percent of those without the disease. The people with MS were exposed to a lower monthly UV index (average of 3.8) than those without the disease (average of 4.8). They also lived an average of about one degree of latitude farther north than those without the disease. The link between low vitamin D levels and MS was weaker, but still present after adjusting for the differences in UV exposure and geography.

People with a higher proportion of European ancestry in their genes were less likely to have low vitamin D levels than people with a lower proportion of European ancestry, but European ancestry was not associated with MS.

There was no association between vitamin D levels and how severe the disease was.

People should talk to their physicians about blood testing for vitamin D levels, whether they should take supplements and how much UV exposure they should get, Green said. "These findings may provide a mechanism to help explain how genes and the environment interact to produce MS," he said.