Health benefits with moderate sun exposure
Vitamin D is often prescribed for multiple sclerosis based in part on reports that people with low levels of the vitamin (actually a hormone) have a higher risk of developing MS (Munger and colleagues. JAMA 2006;296:2832-2838. Salzer and colleagues. Neurology 2012;79:2140-2145).
While some vitamin D is obtained from food (e.g. fatty fish and vitamin-enriched milk), most vitamin D is synthesized by the body. This process begins with sunlight. The skin produces a chemical (called cholecalciferol) that is processed in the liver before being activated in the kidneys. An interim form, called 25(OH)D, can be measured in the blood to show if a person has low vitamin D levels.
Some studies have indicated that people with MS who have low vitamin D levels have a higher risk of relapses and worsening disability (Smolders and colleagues. Mult Scler 2008;14:1220-1224). So the solution seemed to be simple – increase vitamin D levels with supplements. Unfortunately, that approach appears to be largely ineffective (McLaughlin and colleagues. J Neurol 2018;265:2893-2905). Taking vitamin D supplements doesn’t appear to have much impact on MS.
While the “sunshine vitamin” doesn’t appear to be effective, actual sunshine does appear to provide benefits (Langer-Gould and colleagues. Nutrients 2018;10:268). One study found that higher sun exposure during childhood and adolescence reduced the risk of developing MS by 50% (Tremlett et al. Neurology 2018;90:e1191). So this raised the possibility that the sun’s effects on the body were not only about vitamin D. Vitamin D levels in the blood may be important primarily as a marker of a person’s level of sun exposure.
Indeed, there is a growing appreciation of the benefits of sun exposure on general health. A recent study estimated that avoiding sun exposure was as harmful to health as smoking (Lindqvist and colleagues. J Intern Med 2016;280:375-387).
The health effects of sunshine appear to be many and various. For example, sun-exposed skin releases nitric oxide, which lowers blood pressure by relaxing blood vessels (Liu and colleagues. J Investig Dermatol 2014;134:1839-1846). A Danish study found that boys were more likely to develop Type 1 diabetes (an autoimmune disorder) if their mother had low sun exposure during pregnancy, which suggests an effect of sun exposure on immune function (Jacobsen and colleagues. J Pediatr Endocrinol Metab 2016;29:417-424).
Similarly, animal studies have shown that sun exposure protects against autoimmune inflammatory attacks in the brain (Kok et al. J Autoimmun 2016;73:10-23). Light therapy has been shown to alter the immune profile in people with early MS (Trend and colleagues. Sci Rep 2019;9:7980). A pilot study, called PhoCIS, looked at an 8-week course of light therapy in clinically isolated syndrome (CIS) – people who are at high risk of developing MS. At one year, 70% of the light-therapy group developed MS compared to 100% without light therapy (Hart and colleagues. Mult Scler J Exp Transl Clin 2018;4:2055217318773112). The study was small and the results were not statistically significant, but there was the suggestion that some degree of light exposure may have beneficial effects on the immune response.
These results are preliminary, but they suggest that some degree of sun exposure may be beneficial in MS. Of course sun exposure, as in all things, should be taken in moderation. The amount of effective sun exposure will depend on the season, the latitude and the amount of pigmentation in your skin. The general rules are to wear sunglasses to protect the eyes and avoid sunburn to avoid the cancer risks associated with skin damage.
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