Southerners May Be Less Likely to Have Crohn's

Oct. 31, 2011 (Washington, D.C.) -- Women who live in the southern part of the U.S. are less likely to have ulcerative colitis and Crohn's disease than those who live in the North, a new study suggests.

Researchers suspect that's because people in the South spend more time in the sun's ultraviolet rays, one of our body's main sources of vitamin D. Studies have linked vitamin D deficiency to an increased risk of inflammatory bowel disease.

A second, preliminary study of 20 people suggests that high doses of vitamin D may help to relieve symptoms of Crohn's disease. But it's too soon to recommend supplements at this time, researchers say.

Both studies were presented here at the annual meeting of the American College of Gastroenterology.

Inflammatory Bowel Disease

Ulcerative colitis and Crohn's disease are the most common forms of inflammatory bowel disease. Ulcerative colitis causes ulcers and inflammation of the colon and rectum. Crohn's disease may affect any part of the digestive tract.

Both cause symptoms such as abdominal pain, bloody diarrhea, and bleeding from the rectum. Inflammatory bowel disease affects as many as 1.4 million people in the U.S.

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.

Women who lived in the South at birth and age 15 were somewhat less likely to have the gut disorders than those who lived in the North at those ages, but those findings were not as robust, according to Khalili.

Impact of Moving From North to South

Fewer than 10% of nurses moved from one area of the country to another during the 20 years they were followed. Moving from the North to the South was associated with a 35% lower risk of ulcerative colitis and a 50% lower risk of Crohn's disease. There weren't enough women who moved from the South to the North to assess its impact on inflammatory bowel disease.

The study does not show cause and effect. Future research will be aimed at separating out the protective effects of vitamin D from those of ultraviolet light, Khalili says.