THURSDAY, Jan. 12 (HealthDay News) -- People who live in sunnier regions of the United States are less likely to develop inflammatory bowel disease, a new study says.

The findings support previous European research and could lead to new types of treatment and preventive measures, the study authors said.

Inflammatory bowel disease (IBD) includes Crohn's disease and ulcerative colitis, which can be extremely painful and require surgery. The causes of IBD remain largely unknown.

In this study, researchers analyzed long-term data collected from 238,000 participants in the Nurses' Health Study I and the Nurses' Health Study II, which were launched in 1976 and 1989, respectively. None of the participants had inflammatory bowel disease at the start of the studies.

Compared to participants who lived in northern areas of the United States, those living in southern areas were 52 percent less likely to develop Crohn's disease by the age of 30 and 38 percent less likely to develop ulcerative colitis.

The study appears online in the journal Gut.

"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," wrote Dr. Hamed Khalili, of Massachusetts General Hospital in Boston, and colleagues.

"UV radiation is the greatest environmental determinant of plasma vitamin D, and there is substantial experimental data supporting a role for vitamin D in the innate immunity and regulation of inflammatory response," they noted.

More information

The Crohn's and Colitis Foundation of America has more about inflammatory bowel disease.