FRIDAY, May 11, 2007 (HealthDay News) -- A daily dose of 300 milligrams of aspirin taken for 10 years can cut colon cancer risk by as much as 74 percent, a new British study suggests.
But the risks associated with taking that large a dose of the pill might not be worth it for most people, the researchers warn. For that reason, aspirin may only prove helpful for those at high risk for the disease. The report is published in the May 12 issue of The Lancet.
"Individuals at increased risk of colorectal cancer should consult their doctor about whether the benefits of daily aspirin are likely to outweigh the risks in their particular case," advised lead researcher Dr. Peter Rothwell, a professor of neurology in the University Department of Clinical Neurology at Radcliffe Infirmary, Oxford.
"However, the benefits in individuals at low risk of colorectal cancer will be small," he added.
More than 50 million adults in the United States take aspirin regularly for long-term prevention against heart attack and stroke. Typically, doses are either 81 milligrams a day or 325 milligrams a day. The appropriate long-term daily dose remains a matter of debate.
In the study, Rothwell and colleagues tracked patients from two large randomized trials of aspirin from the late 1970s and early 1980s -- the British Doctors' Aspirin Trial and the UK-TIA Aspirin Trial.
Long-term follow-up was important, because it takes precancerous growths called adenomas at least 10 years to develop into cancer, Rothwell's group explained.
The researchers found that taking aspirin reduced the incidence of colorectal cancer by 37 percent over the next 5 years, and 74 percent over 10 to 15 years.
However, long-term aspirin use at the 300-milligram daily dose used in the study does pose potential dangers, including gastrointestinal bleeding.
"Individuals at high risk of developing colorectal cancer -- those with a strong family history or previous polyps -- should consider taking daily aspirin," Rothwell said. "However, the risks of long-term treatment with aspirin might still outweigh the benefits in individuals at low risks of colorectal cancer. So we would not advocate widespread use in the general population," he added.
Another expert agreed.
"There is a lot of evidence that aspirin reduces the risk of colorectal cancer," said Dr. Andrew Chan, an assistant professor of medicine at Harvard School of Medicine and author of an accompanying journal editorial. "But this is the first randomized trial that confirms the findings of other studies," he added.
However, Chan said it is too early to recommend that people take aspirin to prevent colon cancer. "We need to take the side effects of aspirin into account before recommending aspirin for the prevention of colon cancer," he said.
He also noted that there are other proven methods for preventing colon cancer -- especially regular screening for the disease. "Other preventative measures to reducing the risk of colon cancer are keeping active, maintaining a normal body weight and reducing how much red meat you eat," he said.
"There may be individual patients for whom the benefits of taking aspirin to prevent colon cancer may outweigh the risks," Chan said. "But as a blanket recommendation, I don't think we are ready for that yet."
In addition, more research is needed to understand how aspirin prevents cancer, Chan said. "Ultimately, the hope is that this research will lead to better understanding of colon cancer, which could lead to therapies that could have the benefits of aspirin, but fewer of the side effects," he said.
For more information on aspirin and colon cancer, visit the American Cancer Society.