MONDAY, Dec. 19 (HealthDay News) -- Women with endometriosis may be up to 80 percent more likely to develop inflammatory bowel disease such as Crohn's disease or ulcerative colitis compared to women without the uterine disorder, according to a new long-term study.

Endometriosis occurs when the uterine lining -- the endometrium -- grows outside of the uterus. Symptoms include abdominal pain, heavy menstrual periods and infertility. Exactly why the conditions may be linked is not fully understood. They may share common causes or perhaps the birth control pills used to treat endometriosis may increase the risk of inflammatory bowel disease. The new findings appear online Dec. 19 in the journal Gut.

The study included nearly 38,000 Danish women who were hospitalized for endometriosis from 1997 to 2007. After 13 years of follow-up, 320 of these women developed inflammatory bowel disease, including 228 cases of ulcerative colitis and 92 cases of Crohn's disease.

Overall, women with endometriosis had a 50 percent higher odds of developing inflammatory bowel disease compared to women in the general population, the study found. The increased risk lasted for up to 20 years after being diagnosed with endometriosis, report researchers led by Dr. Tine Jess, an epidemiologist at Statens Serum Institute in Copenhagen, Denmark.

The risk was even more pronounced among women whose endometriosis was verified surgically, the team noted. Among these women, the risk for inflammatory bowel diseases jumped to 80 percent compared to women without endometriosis in the general population.

Inflammatory bowel disease is the umbrella term for ulcerative colitis, Crohn's disease and related conditions. Ulcerative colitis is an inflammation of the inner lining of the colon. By contrast, Crohn's disease involves all layers of the intestine and can occur in both the small intestine and colon. Symptoms of both include persistent diarrhea, abdominal pain or cramps, blood passing through the rectum, fever and weight loss.

"This is the first study undertaken to investigate the association between endometriosis and inflammatory bowel disease," Jess said. "Persisting abdominal symptoms in patients with endometriosis may be a sign of concomitant inflammatory bowel disease," she said.

One expert said the finding should be taken seriously.

"If you have endometriosis first, this may lead to having an increased risk of ulcerative colitis or Crohn's," said Dr. Maurice Cerulli, the program director of gastroenterology at North Shore-Long Island Jewish Health System in New Hyde Park, N.Y. While more research is needed before any definitive conclusions can be drawn, Cerulli said that doctors should consider both endometriosis and inflammatory bowel disease when a woman has abdominal symptoms and pain. "Both conditions are treated differently," he said.

While the study found an association between endometriosis and inflammatory bowel disease, it did not prove a cause-and-effect relationship.

More information

Visit the Crohn's & Colitis Foundation of America to find out more about inflammatory bowel disease.