We read with interest the study by Elhami et al. [1] demonstrating that the incidence of multiple sclerosis (MS) in Tehran has substantially increased over the past 20 years, from 0.68/100,000 in 1989 to 5.68/100,000 in 2006, an 8.3-fold rise. MS is a complex neurological disorder resulting from genetic and environmental risk factors and their interactions. As discussed by Elhami et al., previous studies have indicated a genetic predisposition to MS in the Iranian population but genetic changes are unlikely to account for the substantial rise in MS prevalence over the last few decades [2-4]. An environmental risk factor garnering substantial support for involvement in MS aetiology is vitamin D deficiency [5]. We believe that the influence of decreased sunlight exposure and vitamin D levels on increasing MS risk needs to be strongly considered in the context of Iran's history.
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