Higher doses of aspirin were associated with an even lower risk, but that could be problematic as large doses of aspirin can cause bleeding and other side effects. These higher doses, as many as 14 tablets per week, were much higher than those recommended to stave off heart disease.
Too early for definite recommendations
"At this point, we cannot recommend that people take higher doses until we do more studies to determine the overall risks and benefits," says Dr Andrew Chan, lead author of a study appearing in the February issue of the Annals of Internal Medicine and a gastroenterologist at Massachusetts General Hospital in Boston.
For reducing heart attacks and stroke, it seems to be relatively safe to take a baby aspirin, usually one a day. But it appears that you need to take more to prevent colon polyps, and that really has to be balanced against the risk of gastrointestinal bleeding from aspirin, adds Dr Steven Itzkowitz, a professor of medicine at the Mount Sinai School of Medicine in New York City.
Some previous evidence has suggested aspirin can reduce the risk of colorectal polyps, but it has not been known at what dose. Based on current studies, it appears that standard doses really only have a modest benefit, and studies until now have not been able to determine what dose was most beneficial, Chan says. This gets a little closer to that answer.
The research study
Chan's study used information from the Nurses' Health Study, which started in 1976 and which is following more than 120 000 female registered nurses. For the purposes of this investigation, the authors focused on data from 27 000 nurses, aged 34 to 77, who reported having had colon examinations between 1980 and 1998.
Overall, women who reported taking aspirin regularly had a 25 percent lower risk of adenoma, the polyps that can turn into cancer, than women who took no aspirin. Women who took one tablet weekly had a 20 percent lower risk, while those who took 14 tablets weekly (two a day) had about a 50 percent lower risk than those who took no aspirin.
Similar results were seen among participants who had been taking aspirin for fewer than five years and longer than five years. Our study really suggests that duration was of secondary importance, Chan says.
While it is unlikely that extremely short-term use of aspirin will have a beneficial effect, a person may not need to start taking aspirin regularly at a very young age to reap the advantages. Starting it later in life may be just as useful.
More research needed
Future studies will need to evaluate what the side effects of taking that much aspirin might be, and also if there are certain groups of people who might benefit more than others. It's difficult to imagine long-term that the general population would be able to take higher doses, but it may be that certain individuals may benefit more, Chan says.
"What we tend to think is if you are on aspirin for some other reason, such as cardiovascular prevention or arthritis, then you're likely to be protected. If you're minding your own business and not taking it for anything else, it's still a little bit uncertain whether you ought to be starting now just to prevent colon cancer and colon polyps," Itzkowitz says. "My own bias is that we have such effective other ways of prevention, meaning colonoscopy. If it was me, I'd rather have a colonoscopy every five or 10 years than take two aspirins a day."
"It's a real landmark kind of study," he adds. What remains to be seen is how this will translate into common usage. - (HealthDayNews)