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NEW YORK (Reuters Health) - Compared to people who've never smoked, former smokers have a higher risk of developing two inflammatory bowel diseases, Crohn's disease and ulcerative colitis, according to a new study.
"The increased risk of ulcerative colitis following smoking cessation persisted even two decades after cessation," said Dr. Leslie Higuchi, the lead author of the study and a researcher at Children's Hospital Boston and Harvard Medical School.
Following up on earlier shorter-term studies of the subject, Higuchi and her team collected information from nearly 230,000 female nurses who were surveyed about their behavior and health status from 1976 and 1989.
Over time, Higuchi and her colleagues found, 144 out of about 124,000 never-smokers developed Crohn's disease, while 117 out of 51,000 ex-smokers and 75 out of 53,500 smokers also developed the autoimmune disease.
After taking into account other risk factors, such as age, weight and hormone therapy use, they determined that smokers were 90 percent more likely to develop Crohn's than women who never smoked and ex-smokers were 35 percent more likely.
The more people smoked, the higher their risk.
For instance, women who had smoked a pack a day for 10 to 25 years were 1.7 times as likely to develop Crohn's as someone who never smoked, while women who smoked a pack a day for more than 25 years were 2.3 times as likely.
The researchers found that smoking was also tied to ulcerative colitis, an inflammation of the colon that can cause pain, diarrhea and bleeding.
Higuchi's group found that 190 non-smokers, 167 former smokers and 43 current smokers developed colitis during the study period.
The picture became more complicated when the researchers compared ex-smokers to current smokers, as quitters actually had a 50 percent higher risk of colitis than people who continued the habit.
Current smokers had the same risk as the women who never smoked, something that has been shown in other studies.
The study does not show that smoking is the cause of the increased risks. "The mechanisms aren't clear" as to why smoking is linked to these diseases, and in such different ways, said Higuchi.
"None of this is new at all. Zero," said Dr. Stephen Hanauer, a professor at the University of Chicago Medicine, who was not involved in this study.
What is new, Higuchi said, is that she was able to track the ex-smokers in her study for more than 20 years. Even at that point, there was still an "increased risk of ulcerative colitis 20 years out, compared to current smokers in this study," Higuchi told Reuters Health.
The risk did appear to fade over time, however.
Within two to five years of quitting, women were three times as likely to develop colitis as women who continued to smoke.
But more than 20 years after giving up cigarettes, women were just a little more than one-and-a-half times more likely to get colitis.
Because of the higher risk of colitis found among ex-smokers, some studies have looked into using nicotine or cigarettes as a way to treat patients with colitis.
For rare cases in which former smokers have severe colitis that does not respond to other treatments, Hanauer said resuming low levels of smoking might be useful.
But Hanauer and Higuchi said that the health risks of smoking are too great to advocate that people should use cigarettes as a way to lower their risk of ulcerative colitis.
"The big message still is there is an environmental factor that impacts on autoimmune-type diseases...and researchers are looking at the ingredients (in cigarette smoke) to identify how and why they impact on inflammation," Hanauer told Reuters Health.
SOURCE: bit.ly/MuaQ9W The American Journal of Gastroenterology, online July 10, 2012.