I saw this article a few months ago about
vitamin D and UC and CD. Very interesting that they followed 120,000 people for 20 years. Also that they studied what happens when people move to sunny areas (from cloudy/dark).
http://www.webmd.com/ibd-crohns-disease/crohns-disease/news/20111031/southerners-may-be-less-likely-to-have-crohns
Studies in Europe have shown that living at southern latitudes may be protective against inflammatory bowel disease. Boston researchers decided to find out if that holds true in the U.S. too.
They followed nearly 120,000 female nurses who didn't have inflammatory bowel disease at the start of the study. Over a 20-year period, 284 developed Crohn's disease and 332 developed ulcerative colitis.
Women who lived in southern latitudes at age 30 were about 50% less likely to have Crohn's disease than those who lived in northern latitudes, reports Hamed Khalili, MD, of Massachusetts General Hospital in Hospital in Boston.
People who lived in the South were about one-third less likely to have ulcerative colitis than those who lived in the North, he tells WebMD.