Effects of Latitude and Sunlight on Multiple Sclerosis Severity Two Peas in a Pod?

There are nearly 3 million people worldwide living with multiple sclerosis (MS). An intriguing aspect of MS epidemiology is the long-standing observation of geographical differences regarding disease prevalence, with the lowest in equatorial regions, and rising prevalence towards the poles, a phenomenon called the "latitude gradient".(1) It is assumed that this gradient is the consequence of varying sunlight exposure along the latitudinal bands and that it might be related to vitamin D. In this issue of Neurology (R), Vitkova and colleagues(2) follow up on this and present current results from an international registry study assessing whether such a latitude gradient also exists for disease severity of established MS and how this relates to sunlight exposure.