A study from California has examined the influence of childhood sun exposure on the risk of multiple sclerosis (MS) in monozygotic twins. Seventy-nine twin pairs were identified where there was a quantifiable difference in sun exposure between the pair and where only one twin had MS. A numerical index of sun exposure related activities was calculated for each individual. It was found that sun exposure during childhood conveyed a strong protective effect against MS in this group of twin pairs, with the MS-free twin having a significantly higher sun exposure index. The authors conclude that sun avoidance seems to precede the diagnosis of MS and that this protective effect is independent of genetic susceptibility. (Childhood Sun Exposure Influences Risk of Multiple Sclerosis in Monozygotic Twins. Neurology, 2007, Vol. 69, pp. 381-88).