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The study participants were recruited till their age was 60 years, whereas the exposure to sun till 16 years only was asked in the case-control study(1,2). The common sense says that the sun would continue to shine on their bodies even after the stipulated age of 16 years and would have continued to stay as a risk factor and its exposure should have been measured. In my opinion a prospective study should have been designed with strict exclusion criteria and matching, so that confounding of other risk factors should have been taken care of. The amount of sunlight exposure should have been measured prospectively and appearance of symptoms, signs and positive investigations of multiple sclerosis should have been gauzed and not overlooked. Then and only then any conclusions should have been drawn.
1. Van der Mei IAF, Ponsonby A-L, Dwyer T, Blizzard L, Simmons R, Taylor BV, et al. Past exposure to sun, skin phenotype, and risk of multiple sclerosis: case-control study. BMJ 2003;327:316.