Taking a low-dose aspirin every other day may reduce the risk of colorectal cancer, according to a study of 40,000 women age 45 and older.

The protection does seem to take some time to surface, said researcher Nancy Cook, a professor of medicine at Brigham and Women's Hospital and Harvard Medical School. "After 10 years, we started to see an effect," she noted.

"After 18 years of follow-up, we saw a 20 percent reduction in colon cancer over the whole time period," she said. When they looked at the 10-to-18 year mark, the reduction was 42 percent, she said.

However, risks linked with aspirin, such as gastrointestinal bleeding, must be considered, Cook said.

The study, funded by the U.S. National Cancer Institute and U.S. National Heart, Lung, and Blood Institute, is published in the Annals of Internal Medicine.

This year, 102,480 patients will be diagnosed with colon cancer and 40,340 will be diagnosed with rectal cancer. About 50,830 people will die from colon or rectal cancer, according to the National Cancer Institute.

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