LONDON — A new analysis suggests that taking a low dose of aspirin may modestly reduce the risk of developing colon cancer or dying of the disease.
But experts say aspirin's side effects of bleeding and stomach problems are too worrisome for most people to take the drug for that reason alone. A U.S. health task force specifically recommends against it for those at average risk.
Previous studies have found a daily dose of at least 500 milligrams of aspirin could prevent colon cancer, but the adverse effects of such a high dose outweighed the benefits. Now, researchers say a low dose, equivalent to a baby or regular aspirin, also appears to work. But side effects are still a concern.
The European researchers pooled the 20-year results of four trials with more than 14,000 people. Those studies were designed to study aspirin's use in preventing strokes, not colon cancer.
The researchers tracked who developed the disease through cancer registries and death certificates in Britain and Sweden, where the studies were done.
They found those who took a low dose daily for about six years reduced their colon cancer risk by 24 percent and their risk of dying from the disease by 35 percent. That was compared to those who took a dummy pill or nothing. There seemed to be no advantage to taking more than a baby-sized dose.
The studies used European baby aspirin of 75 milligrams and regular aspirin, 300 milligrams. US. baby aspirin is 81 milligrams and regular aspirin, 325 milligrams.
Some researchers said the drug would benefit certain people, though no one should start taking aspirin daily without consulting their doctor.
If taken in high doses over a long period, aspirin can irritate the stomach, intestines and bowel, causing lesions and major bleeding.
"Anyone with any risk factors such as a family history (of colon cancer) or a previous polyp should definitely take aspirin," said Peter Rothwell, a professor at the University of Oxford and one of the paper's authors. The finding also "tips the balance" for anyone considering aspirin to prevent heart attacks and strokes, he said.
No funding was provided for the study and it was published online Friday in the journal Lancet. Rothwell and some of his co-authors have been paid for work by the makers of anti-clotting drugs like aspirin.
Other experts warned against aspirin for the general population.
"It's not for everybody," said Robert Benamouzig, of Avicenne Hospital in Bobigny, France, who co-authored a commentary in the Lancet. He said he would advise some of his high-risk patients to take aspirin, but only after explaining its side effects.
Scientists think aspirin works by stopping production of a certain enzyme linked to cancers including those of the breast, stomach, esophagus and colon.
The trials analyzed in the Lancet paper were done before the widespread introduction of screening tests like sigmoidoscopies and colonoscopies. Rothwell said taking aspirin would still help, because the drug seems to stop cancers in the upper bowel, not usually caught by screening tests.
Colorectal cancer is the second most common cancer in developed countries, and there are about 1 million new cases and 600,000 deaths worldwide every year. The average person has about a 5 percent chance of developing the disease in their lifetime.