Research: Sunlight and Vitamin D

Epub ahead of print: Bäärnhielm et al. Sunlight is associated with decreased multiple sclerosis risk: no interaction with human leukocyte antigen-DRB1*15. Eur J Neurol. 2012 Jan. doi: 10.1111/j.1468-1331.2011.03650.x.

HLA molecule loaded with peptide (short protein). The immune system uses the HLA to activate immune cells so as to fight off foreign organisms. In autoimmune diseases, such as MS, self-proteins activate the immune system to attack self.
Background: Both insufficient exposure to sunlight and vitamin D deficiency have been associated with an increased risk of MS. An interaction between human leukocyte antigen HLA-DRB1*15 (a gene that is responsible for immune activation) and vitamin D in MS was recently proposed. We investigated the association between previous exposure to ultraviolet radiation (UVR), vitamin D status at inclusion in the study, and MS risk including the interaction of these factors with HLA-DRB1*15.

Methods: A population-based case-control study involving 1013 incident cases of MS and 1194 controls was performed in Sweden during 2005-2010. Subjects were classified according to their UVR exposure habits, vitamin D status, and HLA genotypes. The associations between different sun exposure habits/vitamin D levels and MS were calculated as odds ratios (OR) with 95% confidence intervals (CI) using logistic regression. Potential interaction was evaluated by calculating the attributable proportion due to interaction.

Results:  Subjects with low UVR exposure had a significantly increased risk of MS compared with those who reported the highest exposure (OR 2.2, 95% CI 1.5-3.3). Similarly, subjects who had 25-hydroxy-vitamin D levels less than 50 nM/l had an increased risk for MS (OR 1.4, 95% CI 1.2-1.7). The association between UVR exposure and MS risk persisted after adjustment for vitamin D status. There was no interaction with HLA-DRB1*15 carriage.

Conclusions:  UVR and vitamin D seem to affect MS risk in adults independently of HLA-DRB1*15 status. UVR exposure may also exert a protective effect against developing MS via other pathways than those involving vitamin D.

"These results confirm the association between MS risk and sunlight exposure and vD levels; this is not surprising. No interaction was found between vD/sunlight and HLA genes; this is despite the observation that vD controls how active that gene is within the body. I suspect the study is too small; i.e. lacks sufficient power to see an interaction."

"We can't get away from the data that strongly supports vD as a preventative fator in MS; PLEASE DON'T FORGET TO TAKE YOUR SUPPLEMENTS. 5,000U / DAY!!!"

"The evidence that UVR exposure may also exert a protective effect against developing MS via other pathways than those involving vitamin D is interesting, but speculative. UV may affect the function of immune cells as they pass through the skin. Despite this theoretical advantage of UVB (sunlight) over vD supplements, the case is not strong enough to stop supplementation. From a practical point of view it is difficult to find sunlight in winter, unless you purchase a UVB lamp."

"Please note that most sunbeds provide UVA light and not UVB light; so you can't get the necessary light from popping into your local tanning store."

Additional reading: Human Leukocyte Antigens