Can Vitamin D Prevent MS?

High circulating levels of vitamin D may reduce the risk for multiple sclerosis (MS) in Caucasians, according to a study published in the December 20 issue of JAMA. The study, conducted by Kassandra L. Munger, MSc, of the Harvard School of Public Health, Boston, and colleagues, sought to draw a correlation between high blood levels of 25-hydroxyvitamin D and a lower risk of MS.

Participants included nearly seven million US military personnel, all of whom have serum samples stored in the Department of Defense Serum Repository. In order to ascertain MS cases within the military, the researchers relied on the Army and Navy physical disability databases, then confirmed those diagnoses by medical review. The cases included 237 definite MS cases and 78 probable cases. Two controls were matched to each case by sex, race/ethnicity, dates of sample collection, and the branch of the military service.

Among Caucasians, there was a 41% decrease in MS risk for every 50-nmol/L increase in 25-hydroxyvitamin D. Analysis by quintiles revealed that MS risk was highest among individuals in the bottom quintile of 25-hydroxyvi­tamin D levels and lowest among those in the top quintile. Those in the top quintile had a 62% lower risk of MS compared to those in the bottom quintile. The researchers also tested participants who were younger than 20, noting, “adolescence appears to be a crucial exposure period for MS.” Results revealed that the inverse relation was strong in adolescents measured for MS risk.

No significant associations between vitamin D and MS risk were found among blacks and Hispanics. However, the researchers reasoned that a smaller sample size than that of Caucasians may have been a factor.

HIGH VITAMIN D LEVELS MAY REDUCE MS RISK

The question that remains is whether increasing levels of 25-hydroxyvitamin D will reduce the incidence of MS. The researchers theorized that while 25 nmol/L of 25-hydroxyvitamin D is considered the norm, half of Caucasians and two thirds of blacks in the US already have levels in the range of 25 to 70 nmol/L. How­ever, they said the highest serum concentrations were found to be between 90 and 100 nmol/L.

They noted that this level is most often found in adolescents, who typically have higher levels of 25-hydroxyvitamin D, but few have levels high enough to be associated with reductions in the risk of MS. They believe that vitamin D supplements could be effective in bridging the gap. However, they cautioned that a recommendation for a dramatic increase in vitamin D intake among adolescents and young adults would require stronger evidence than that from observational studies.

NR