Reduced exposure to sunlight, previously reported as a risk factor for developing multiple sclerosis (MS), also seems to increase the risk for relapse and worsening disability, data from two clinical studies suggest.
The beneficial effects of sunlight exposure were linked to increased levels of vitamin D, but also modulation of immune pathways, including the type I interferon response.
The study “Sunlight exposure exerts immunomodulatory effects to reduce multiple sclerosis severity” was published in the journal PNAS.
Low exposure to ultraviolet-B (UV-B) radiation from sunlight, which results in a defective synthesis of vitamin D, have been suggested to increase the risk for developing MS. However, it remains a matter of debate whether sunlight and vitamin D levels also influence disease severity and progression.
In this study, researchers in Germany assessed the impact of two independent measures of sunlight exposure — vitamin D levels and latitude — on MS disease severity. (Decreasing latitude is linked with an increase of sunlight that reaches the Earth’s surface.)
Also, they assessed whether the effects of sunlight exposure were modulated by medication or variations in the gene coding for the melanocortin 1 receptor (MC1R) gene, which plays an important role in the color of the skin and, consequently, sensitivity to sunlight. MC1R signaling also has immunosuppressive functions and a protective effect in mouse models of MS.
The team reviewed data from patients previously enrolled in two studies, the German National MS cohort and the French BIONAT cohort (NCT00942214) studies.
Overall, the group from the MS study included 908 patients with clinically isolated syndrome (CIS) or relapsing remitting MS (RRMS), who had not received prior treatment. The BIONAT group included 808 MS patients, the majority of whom had received treatment. The most common treatment, given to more than half of patients, was interferon-beta.
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