Many women have been told by their doctors to take aspirin to reduce their risk of cancer and vitamin E to lower their risk of heart disease. But two studies involving nearly 40,000 women suggest that the supplements have very little or no effect in protecting healthy women from these illnesses.

The aspirin study, however, left some questions unanswered because it involved a dose some medical experts believe is too small to show an effect.

Reporting in Tuesday’s issue of the Journal of the American Medical Association, scientists from Harvard and Boston’s Brigham and Women’s Hospital said low-dose aspirin had no overall effect on preventing cancer, except for a trend toward lower incidence of lung cancer.

The 10-year study also found that 600 international units, or IUs, of vitamin E every other day had no overall protective benefit against heart attacks, except for a trend toward fewer cardiovascular deaths.

Those trends were not considered to be statistically significant, though researchers said the findings should be followed up with further studies.

Patients are commonly advised to take aspirin and vitamin E because earlier observational studies of large populations indicated they worked. But such studies are often flawed by many confounding factors and can only suggest a benefit.

To determine if a benefit is real, researchers conduct randomized controlled studies where one half of a group gets aspirin or vitamin E and the other half receives a placebo.

Although the new report indicated low-dose aspirin doesn’t protect against cancer, the same study showed last year that low-dose aspirin reduced the risk of a first stroke.

The U.S. Food and Drug Administration has approved the use of aspirin to reduce the risk of a recurrent stroke in men and women with prior cardiovascular disease.

In addition, an earlier randomized study from Dartmouth University showed that aspirin doses six times larger than those used in the Women’s Health Study prevented colon polyps and colon cancer. The Women’s Health Study used 100 milligrams of aspirin, less than the dose in a baby aspirin. A standard aspirin has 325 milligrams.

“It may be that we missed aspirin’s effect on cancer that would have come up with larger doses,” said Charles Hennekens, an epidemiologist at Florida Atlantic University and the University of Miami School of Medicine. Hennekens set up the aspirin and vitamin E studies when he was at Harvard.

“The overwhelming message is: Don’t forget your therapeutic lifestyle changes,” Hennekens said. “We have a population that would rather take pills than change their lifestyle. Even if aspirin reduced the risk of colon cancer, that would be small compared with the benefits you’d get from a better diet, regular exercise and not smoking.”

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