Considering the high prevalence of vitamin D deficiency in Iranian subjects either with or without diabetes [17,19] and assuming the same prevalence of "non-responders" among the whole population, a huge number of people may not benefit from intake of the usually recommended amount of vitamin D. This individual variability may be, at least in part, explained by vitamin D receptor (VDR) polymorphisms. The gene discussed is VDR; the disease is diabetes mellitus.