A 20-year study of almost 83,000 nurses shows that low doses of aspirin did not lower cancer risk significantly. High doses of aspirin - such as two or more aspirin per day - reduced colon cancer risk by a third but also were linked to dangerous bleeding, according to the study published in Wednesday's Journal of the American Medical Association.
A high-dose aspirin regimen that prevented one or two cases of colorectal cancer also would cause eight additional cases of serious bleeding from irritation of the stomach or intestines, the researchers estimated, The Associated Press reports.
"We can't make a recommendation that you could take an aspirin a day to prevent both heart disease and colorectal cancer,'' says study co-author Dr. Andrew Chan, a researcher at Harvard Medical School.
The best prevention is regular screening, exercise and eating a high-fiber, lowfat diet, Chan and other researchers not involved in the new study say.
"For average-risk people who are getting screening colonoscopies, the added benefit of taking aspirin is very small,'' says Dr. Robert Sandler at the University of North Carolina-Chapel Hill, who was not involved in the new study.
Previous studies suggested that a once-a-day baby aspirin could prevent precancerous polyps that sometimes become colorectal cancer, the second deadliest cancer for Americans after lung cancer.
Those prior studies raised hopes that the same small dose of aspirin shown to fight heart disease could do double-duty against cancer. Aspirin might inhibit an enzyme linked to tumor formation.
Long-term use of high doses of aspirin are not right for most people, cautions Dr. Julie Buring of Harvard's Brigham and Women's Hospital, who has conducted similar research but was not involved in the new study.
