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.
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.
In the studies, women in the Nurses' Health Study I and II filled out questionnaires every two years that asked whether they had ulcerative colitis or Crohn's disease. If they said yes, the diagnosis was confirmed by a review of their medical records.
The women were asked where they lived when they were born, and at age 15 and age 30. U.S. regions below 37 degrees latitude were considered southern -- places like Southern California, Florida, and Arizona, according to Khalili. Areas above 42 degrees latitude were considered northern: Massachusetts and Rhode Island, for example.
At age 30, 61,923 of the nurses lived at northern latitudes, 84,286 lived at middle latitudes, and 29,703 lived at southern latitudes.
Sunanda Kane, MD, a gastroenterologist the Mayo Clinic in Rochester, Minn., says there's no reason to think the findings wouldn't apply to men, too. Kane reviewed the findings for WebMD.
Vitamin D Supplements and Crohn's Disease
Brian Bosworth, MD, of Weill Cornell Medical Center in New York City, reported results on the first 20 people in an ongoing study looking at the effects of vitamin D supplementation on Crohn's disease. All had vitamin D deficiency, defined as blood levels less than 30 nanograms per milliliter (ng/ml) of blood.
They took either 1,000 International Units (IU) or 10,000 IU of vitamin D3 daily.
After six months, average vitamin D blood levels were about 74 mg/ml in the high-dose group, compared with 32 ng/ml in lower-dose group. Levels above 30 are considered normal.
Scores on a standard test that measured the severity of symptoms fell from 7 points to 4 points in the high-dose group. There was no change in disease activity in the lower-dose group; their scores hovered around 6 points. Scores above 7 indicate severe symptoms, according to Bosworth.
The high doses didn't cause any side effects.
In people with inflammatory bowel disorder, the body's immune system inappropriately attacks the lining of the gastrointestinal tract, he says. It’s thought that vitamin D calms down some of the more active immune system cells, Bosworth says.
Since the same inappropriate immune attack occurs in people with ulcerative colitis, Bosworth believes they too could be helped by vitamin D supplements.
But no one with inflammatory bowel disease should take supplements based on this small study, Kane tells WebMD.
"People should have their vitamin D levels checked. If there is a deficiency, it should be corrected with supplementation, under the care of a doctor," she says.
But further work is needed to prove whether high doses relieve symptoms and are safe over a longer period of time, Kane says. Taking high doses of vitamin D has been linked to neurological and brain problems.
These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.