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A new study from Germany involving over 1700 people with MS shows evidence that sunlight exposure, as indicated by blood levels of vitamin D  and latitude (distance from the equator) of residence, were associated with the severity of MS. They also found evidence related to how sunlight may influence beneficial immune cell activity. Sun exposure in excess is not recommended due to the risk of skin cancer – see below for some recommendations.

• Sunlight and vitamin D have previously been linked to the risk of developing MS. Evidence suggests that higher lifetime exposure to sunlight (through which the skin makes vitamin D) and higher blood levels of vitamin D are associated with a lower risk of developing MS. MS is more common at latitudes that are farther from the equator and less common in areas closer to the equator – a factor that also suggests the influence of sunlight exposure on MS. This study examined the association between sunlight exposure, latitude, and vitamin D levels and MS disease activity and severity.
• The investigators examined data from two large ongoing studies of people with MS: 908 people with early MS who had not yet received disease-modifying therapy, and 808 people with MS who were mostly treated, most often with interferon beta-1a. They looked at information collected from clinical examinations, MRI imaging, and disability measures. They also looked at vitamin D levels and gene activity (in particular, the MC1R gene which is associated with sunlight sensitivity) in blood samples, and also included information on several people who had been treated with ultraviolet light therapy.
• The team conducted a series of analyses with the results suggesting the following:
  • Lower latitudes (indicating greater sun exposure) were associated with increased blood levels of vitamin D, except in a subgroup of people treated with interferon, where there was no association.
    • Lower latitudes and higher levels of vitamin D were associated with a reduced risk of relapses and less accumulation of disability (as measured by the standard EDSS disability scale).
    • In people with the MC1R gene who reported being sensitive to sunlight, lower latitudes were associated with more MS disease activity (as seen on MRI scans), whereas in people without this gene, lower latitudes were associated with less disease activity. 
• Higher latitudes (less sun exposure) and lower levels of vitamin D were associated with more severe MS, except in a subgroup of people treated with interferon.
• Examining immune cells from people treated with light therapy showed the activation of genes associated with the production of both vitamin D and interferon beta (which is not just an MS therapy, but is also produced by the body’s own immune cells to fight infection). 

This study provides evidence for the role of sun exposure and the course of MS, and also suggests that sunlight may influence immune activity beyond its effect on vitamin D. Clinical trials of vitamin D supplements are currently underway, which will help to tease out its effects.
 
What you can do now: Sun exposure (about 15 minutes/day) allows our body to make its own Vitamin D by absorption through the skin. How can you make this happen during the winter? If it’s warm enough, go outside in the morning or other times when sunburn risk is lower. Read recommendations for other sources of vitamin D.
 
“Sunlight exposure exerts immunomodulatory effects to reduce multiple sclerosis severity,” by Patrick Ostkamp,  Nicholas Schwab, PhD (University of Münster, Münster) and colleagues, was published on December 29, 2020 in Proceedings of the National Academy of Sciences (2021;118(1):e2018457118).