BOSTON, MASSACHUSETTS. Multiple sclerosis (MS) is the most common demyelinating disease. It involves damage to myelin sheaths (the "insulation" covering certain nerve fibers) in the central or peripheral nervous system. The lesions caused by MS can be observed by a MRI scan of the brain. Some observers have noted that the extent of the lesions varies from time to time with more extensive lesions being present in the winter months than in the summer months.
Researchers at the Harvard School of Public Health now report that MS may be associated with a vitamin D deficiency and that vitamin D supplementation may help prevent it. The researchers followed a large group of 92,253 female nurses from 1980 to 2000 and another large group of 95,310 female nurses from 1991 to 2001. During this time, 173 cases of MS were diagnosed giving an incidence rate of 7.4 cases per 100,000 person-years.
The nurses had completed food frequency questionnaires every 4 years and had also reported on their use of supplements. Analysis of the data showed that women with a high intake of vitamin D had a 33% lower incidence of MS than did women with low intakes. Further analysis revealed that vitamin D from food sources, mainly milk and fish, contributed very little to overall vitamin D intake and was not, on its own, associated with a decreased risk of MS. Vitamin D from supplements, however, was highly correlated with MS risk. Participants with a vitamin D intake from supplements of 400 IU/day or more had a 40% lower risk of MS than did women who did not supplement. Most of the vitamin D came from multivitamins, so it is possible that other components in the multivitamins could have had a protective effect. However, the researchers believe that vitamin D is the protective agent. They point out that the prevalence of MS increases with distance from the equator in both hemispheres indicating that sunlight, a potent initiator of endogenous vitamin D production, may exert an important protective effect. Several studies have found that MS patients tend to be vitamin D deficient. Vitamin D deficiency is particularly prevalent at latitudes above 42 degrees where blood levels in the winter may drop to half of that observed during the summer months.
The researchers conclude that vitamin D helps protect against MS and urge clinical trials to determine
whether vitamin D supplementation may also help slow the progression of the disease.
Editor's comment: The evidence that a vitamin D deficiency is an important factor underlying many diseases is growing rapidly. Supplementing with 1000 IU/day during the winter months is inexpensive and may well be one of the most effective disease preventing measures available, especially for people living above (or below) 42 degrees latitude.