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Taking aspirin, ibuprofen or similar pain relievers for at least 10 years significantly reduces the risk of colorectal cancer but also greatly increases the risk of serious bleeding in the stomach or intestines, a new study shows.
The pain relievers offer no significant protection to patients who take them for less than a decade, says Andrew Chan, a gastroenterologist at Massachusetts General Hospital and lead author of the article, published in today's Journal of the American Medical Association.
The more pain relievers people take, the lower their risk of colo-rectal cancer, the study shows.
Based on the study's results, Chan says, taking more than 14 aspirin a week might prevent one or two cases of colorectal cancer in a community of 10,000 people over a year. However, that amount might also cause eight cases of bleeding severe enough to require hospitalization or a blood transfusion.
That suggests most people should not take pain relievers to try to prevent colon cancer, Chan says.
He and his colleagues analyzed 20 years of data from 83,000 women in the Nurses' Health Study. Chan says earlier studies suggest that his results probably apply to men as well, although researchers should confirm them.
Women who took two regular, 325-milligram aspirin lowered their risk of colon cancer but only after taking the tablets for more than a decade, Chan says. For example, women who took more than 14 aspirin a week for at least 10 years had a 53% lower risk of colorectal cancer. Women who took ibuprofen or other non-steroidal anti-inflammatory drugs enjoyed similar benefits.
Chan says his findings confirm the results of the Women's Health Study, published in the same journal last month. In that 10-year study of nearly 40,000 women, scientists also found that taking low doses of aspirin, or 100 milligrams every other day, did not lower the risk of colon cancer.
Other doctors say the new study's design could lead researchers to underestimate aspirin's effects. Ernest Hawk, a prevention expert at the National Cancer Institute, notes that previous studies have found that smaller doses of aspirin reduced the risk of colon polyps in only one to three years. About 85% of colon cancers develop from polyps. Those earlier studies, in which doctors randomly assigned patients to take either aspirins or placebos, allow doctors to spot smaller changes in less time. Hawk notes that patients must weigh aspirin's risks against its benefits for the heart. Studies show that patients at risk for heart disease can protect themselves by taking much lower daily doses, such as an 80-milligram pill.
Institute researchers are studying ways to make aspirin safer, such as by combining it with drugs that protect the stomach or with other drugs that seem to combat cancer growth, Hawk says. Doctors are studying calcium and folic acid to prevent colon cancer.
Eric Jacobs, a senior epidemiologist at the American Cancer Society, suggests two proven ways to reduce the risk of cancer: exercise and regular colon screenings beginning at age 50.
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