Epidemiologic Study of Multiple Sclerosis in Israel

THE FREQUENCY of multiple sclerosis increases with latitude both in the northern1-15and southern hemisphere.16,17Ethnic differences apparently do not account for this peculiar distribution, as the disease occurs with essentially the same frequency among different ethnic groups born in the same region.12-14On the basis of these observations, it has been suggested that an environmental factor correlated with latitude may play an etiologic role in multiple sclerosis.1,2,11,14,18-22Numerous factors known to vary with latitude have been suggested as possible etiologic agents including sunlight,11,12,16,19,20temperature,1,19,20humidity,19,23and diet.24-28If an environmental factor is, indeed, of importance in etiology, it would be expected that populations with a high frequency of the disease would have greater exposure to the factor(s) than populations with low frequency. Moreover, within each population, patients with multiple sclerosis might have had a higher frequency of exposure to the