A systematic review of several potential non-genetic risk factors for multiple sclerosis.

We reviewed the literature published in the English language to determine the weight of evidence for several potential non-genetic risk factors for multiple sclerosis, including solar ultraviolet radiation (UVR), sex hormones and dietary fat/fatty acids. We ranked the plausibility of each factor and graded the methodological rigour of case-control and cohort studies to determine whether there was a sufficient number of high-quality studies to weigh the evidence. Based on our criteria, the plausibility for solar UVR and sex hormones is good and fair for dietary fat/fatty acids. However, the body of epidemiologic evidence is insufficient for these three sets of risk factors. We did not find a sufficient number of methodologically rigorous studies to weigh the evidence for any of the potential risk factors we examined.