Vitamin D intake and incidence of multiple sclerosis
Munger KL, Zhang SM, O'Reilly E, Hernan MA, Olek MJ, Willett WC and Ascherio A ;
Commented by , 23 Feb 2004
Background
The striking difference in MS incidence between different parts of the world, has been an intriguing question in the epidemiology of the disease. One of the prevailing theories have been, that increased burden of common infections in the tropical areas, cause immunological tolerance early in childhood, which in turn protects against MS.
Exposure to sunlight has also been discussed as a possible protective environmental factor. Recently, seasonal fluctuations in MS disease activity has been shown using MRI, which has been related to exposure to sunlight, and increased vitamin D production. This has led to the hypothesis that vitamin D reduces the risk of developing MS
Aim
To examine if vitamin D intake reduces the risk of MS
Methods
The study population comprised two large cohorts of women (92253 followed from 1980 – 2000, and 95310 followed from 1991 – 2001). Women with symptoms of MS starting before baseline were excluded. During follow-up, 173 cases of MS were confirmed. Semiquantitative food frequency questionnaires were collected. Vitamin D supplements and food items contributing to vitamin D intake were registered at baseline and every 4th year. The validity of vitamin D intake was assessed by comparing it to plasma concentrations of 25-hydroxyvitamin D among 323 healthy women. For each quintile of vitamin D intake, the incidence rate and relative risk were calculated, as well as the separate effect of vitamin D from food or supplements.
Results
Total vitamin D intake at baseline was inversely associated with risk of developing MS. The age adjusted pooled relative risk (RR) comparing highest and lowest quintile of vitamin D consumption was 0.67 (95% CI = 0.40 to 1.12). The RR comparing women with intake of > or = 400 IU/day with those with no supplemental vitamin D intake was 0.59 (95% CI = 0.38 to 0.91). Cumulative average intake of vitamin D during the study showed the same inverse association. There were no association between vitamin D intake from food only, and risk of MS.
Discussion
The study show that women who used supplemental vitamin D had 40% lower risk of MS, compared with women who did not use vitamin D supplements. A drawback of the study is, that the primary vitamin supplement was multivitamins, which means that the authors was not able to distinguish between the effect of vitamin D and other vitamins, such as vitamin E, B1, B2, B6, B12 (or other components such as folic acid or different minerals).
Theoretically, there is evidence supporting vitamin D as a major candidate for a disease modifying agent in MS, since the antiinflammatory effects, such as inhibition of several Th1-associated cytocines, has been described. Furthermore, vitamin D has shown striking effect on the MS animal model EAE, preventing early onset of the disease in vitamin D deficient mice, and slowing the progression of the disease. There is reason to believe that vitamin D and exposure to sunlight might reduce the risk of MS in some individuals, although further research in this field is needed.