An aspirin a day may keep cancer at bay...

People who take a low-dose aspirin daily may not only be helping their hearts, but also reducing their odds of dying from cancer, according to American Cancer Society researchers.

The lower risk of dying from cancer associated with aspirin, however, may not be as great as previously thought, say the authors of the large new study.

And aspirin's possible side effects -- notably the higher risk of bleeding episodes -- need to be taken into account when considering its use, they added.

"Expert committees that develop clinical guidelines will consider the totality of evidence about aspirin's risks and benefits when guidelines for aspirin use are next updated," said lead researcher Eric Jacobs, the society's strategic director of pharmaco-epidemiology.

Jacobs said, until there are new guidelines, he doesn't recommend taking aspirin for cancer prevention.

"Although recent evidence about aspirin use and cancer is encouraging, it is still premature to recommend people start taking aspirin specifically to prevent cancer," he said.

Even low-dose aspirin can substantially increase the risk of serious gastrointestinal bleeding, Jacobs pointed out.

"Decisions about aspirin use should be made by balancing the risks against the benefits in the context of each individual's medical history. Any decision about daily aspirin use should be made only in consultation with a health care professional," he added.

The study was published in the online issue of the Journal of the National Cancer Institute.

To look at the potential effect of daily aspirin use on cancer deaths, Jacobs' team used data from the Cancer Prevention Study II Nutrition Cohort, part of a larger long-term study on the effects of lifestyle factors on mortality.

This study included more than 100,000 men and women without a history of cancer, some of whom were taking aspirin daily. Of the study participants, 5,138 eventually died from cancer.

Aspirin use was associated with an up to 16 percent lower risk of dying from cancer, which, however, was less than seen in another recent study, the researchers noted. In that analysis of randomized trials (where people were randomly assigned to either take aspirin or not take aspirin), aspirin use reduced cancer deaths by 37 percent during five years of follow-up and 15 percent during 10 years of follow-up, the authors noted in the report.

Nevertheless, "even a relatively modest benefit with respect to overall cancer mortality could still meaningfully influence the balances of risk and benefits of prophylactic [preventative] aspirin use," Jacobs' team concluded.

A limitation of the study is that it was an observational study, not a randomized trial. This could mean that the reduction in cancer deaths tied to aspirin use may be over- or under-estimated, the researchers noted.

Dr. John Baron, a professor of medicine at the University of North Carolina at Chapel Hill School of Medicine, who authored an accompanying journal editorial, said, "It's a remarkable idea that something that's in medicine cabinets around the world, and has been around for more than a century, can prevent cancer."

However, Baron is not recommending that people start taking aspirin to cut their odds for malignancy.

Why it works against cancer isn't known, Baron said, and he noted that the effect of aspirin is seen over time. For example, aspirin might start preventing colon cancer after a person had taken it for about 10 years.

During that time, however, that person might have gastrointestinal or brain bleeding caused by aspirin. So those risks and benefits need to be balanced, he noted.

The question is no longer whether aspirin prevents cancer, according to Baron, but rather whether the risks associated with aspirin are overshadowed by its benefits, he suggested. "But even the most pessimistic study shows a meaningful reduction," he added.

But while the new study found an association between aspirin use and reduced cancer risk, because it is not a randomized, controlled trial -- the "gold standard" for research -- it did not prove a cause-and-effect relationship.