Higher levels of vitamin D are associated with fewer relapses of the immune-mediated disorder multiple sclerosis (MS). But paradoxically, patients show the fewest relapses in autumn and winter when vitamin D levels are lower.
In a study, published in Cell (10 September 2015)
, researchers looked at a cohort of 139 patients with relapsing-remitting MS. Levels of melatonin —which affect T-cell differentiation — are higher in the autumn and winter, and correlated with lower levels of disease activity. In contrast, levels of vitamin D or environmental factors showed no seasonal correlation.
The results point to potential targets for therapeutic intervention, though further studies are needed to understand the role of melatonin in autoimmune disease, conclude the authors of the study.
 Farez MF, Mascanfroni ID, MÃ©ndez-Huergo SP et al. Melatonin contributes to the seasonality of multiple sclerosis relapses. Cell 2015;162(6):1338–1352.