No magic bullet. Taking aspirin regularly does not protect against cancer as thought.

Aspirin Not a Cancer Blocker

John is a Science contributing correspondent.

An aspirin a day keeps the doctor away. Or does it? A 10-year study throws in doubt the widespread idea that taking aspirin at low doses helps prevent cancer.

Aspirin takes the edge off aches and pains by inhibiting cyclooxygenase (COX) enzymes that cause inflammation, which recent studies suggest can trigger cancer. And COX enzymes can also make mischief by helping tumors build blood vessels. So it was exciting when laboratory experiments with animals showed that aspirin helps prevent many cancers. Some studies in humans have also suggested that taking aspirin regularly can reduce the chances of developing the disease. The problem is that such studies have relied on questionnaires about diet and lifestyle and have not included controls. In spite of the lack of hard evidence, many healthy people take aspirin regularly in the hope of dodging cancer among other diseases.

To see if the strategy works, a team led by Nancy Cook and I-Min Lee, public health physicians at Harvard Medical School, enlisted 40,000 healthy women over the age of 45 willing to take aspirin pills over a 10-year period as part of a U.S. randomized trial. Every other day, the women popped identical-looking pills that contained either 100 mg of aspirin, a placebo, or vitamin E.

A tally of all of the cancers and other diseases that appeared among the women shows no benefit of taking either aspirin or vitamin E (which is thought to help prevent cardiovascular diseases), the team reports 6 July in the Journal of the American Medical Association. A possible exception may be lung cancer, which was 22% less likely in aspirin-takers, although the statistical significance is so slim the effect could easily be due to chance, the researchers say. The team argues that the low-dose aspirin used in the study may explain why the positive effects of aspirin seen in laboratory experiments do not translate to long-term health benefits. At higher doses, aspirin may keep cancers at bay, although a similar randomized trial would be needed to prove it. One drawback is that taking more than 100 mg of the painkiller regularly can cause gastrointestinal problems, so the authors say it is unlikely that doctors will ever recommend high doses of aspirin for people who are not already known to be at risk for developing cancer.

"[The study] shows that the cornerstone of health remains a healthy diet and lifestyle," says Rita Redberg, a cardiologist at the University of California at San Francisco. "Americans in particular are very interested in finding a magic pill that will prevent illness, but it doesn't exist."

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