Less IBD in southern latitudes. Why?

Women living in the southern latitudes of the United States have significantly lower rates of inflammatory bowel disease (IBD) than those living in the country's northern regions, according to a study in Gut. Similar trends have been reported in Europe in the past;

The authors hypothesize that the main explanation for the reductions in southern latitudes is related to greater levels of sun exposure and to the higher levels of plasma vitamin D that are associated with ultraviolet (UV) radiation. The role of vitamin D in the pathogenesis of IBD is further supported by the observation that animal models of colitis have more severe inflammation in vitamin D receptor knock out animals or animals deficient in 1,25(OH)2 vitamin D. In addition, UV radiation is associated with regulation of T cells, as well as the production of interleukin (IL) 4 and IL-10, and the inhibition of IL-12, which suppresses the inflammatory response, the researchers noted.