Access to Ample Sun Yields Lower Rates of IBD

Living in sunnier parts of the country appears to be associated with a reduced risk of developing inflammatory bowel disease (IBD), particularly after the age of 30, indicates a long-term prospective US-based study.

The researchers used data from the Nurses' Health Study I, launched in 1976, and the Nurses’ Health Study II, launched in 1989.  At the time they entered the studies, the women—who enrolled between the ages of 25 and 55—had no history of IBD. 

The researchers had access to information on the state of residence at the time of birth, age 15, and age 30 for 175,912 participants. As of 2003, 257 cases of Crohn’s disease and 313 of ulcerative colitis had been diagnosed among these participants.

The researchers found that the incidence of both conditions climbed considerably higher with increasing latitude (i.e. less sunny parts of the country), particularly after the age of 30. Women living in southern parts of the country at the age of 30 were 52% less likely than those living in the north to develop Crohn’s disease and 38% less likely to develop ulcerative colitis.

“A leading explanation for this north-south gradient in the risk of ulcerative colitis and Crohn’s disease may be differences in exposure to sunlight or UVB radiation, which is generally greater in southern latitudes,” said the authors, according to a press release.

This study was published online earlier this week in Gut.