Ask the Doctors

Dear Doctor: Every now and then, I'll see a news story about the benefits of daily aspirin. A recent story linked it to a lower risk of cancer. What gives? Just how healthy is aspirin?

Dear Reader: We've long known that aspirin can reduce the chances of heart attack and strokes in people at high risk for the conditions. In fact, studies on those benefits provided the first inklings of a decreased risk of cancer, especially colon cancer.

Although those studies themselves couldn't verify the benefit of aspirin, what we know about the drug supports such a connection. Aspirin inhibits cyclooxygenase-2, or COX-2, an enzyme important to the formation of inflammatory compounds. Hypothetically, the loss of these inflammatory compounds, called prostaglandins, may lead to decreased cellular replication and decreased recruitment of new blood vessels. That is, with a reduced ability to multiply and grow, cancer cells could have less of a chance to take hold.

One of the earliest assessments of aspirin's impact on cancer came from the Women's Health Study, which randomized 39,876 women to taking a placebo or 100 milligrams of aspirin every other day. The women were followed on average for 10 years, and the majority had additional follow up for 7 1/2 additional years. Researchers found little difference in the rates of breast, lung and many other cancers, but after 10 years, they found a 20 percent reduction in the rate of colon cancer among those taking aspirin. The decrease of colon cancer was even greater among women who continued taking aspirin in the 7 1/2-year follow-up period. Note that there was a 14 percent increase in incidents of gastrointestinal bleeding among those taking aspirin versus placebo, but no change in death rates from bleeding between the two groups.

A 2016 study assessed aspirin use among patients in two large ongoing studies: the Nurses' Health Study and the Health Professionals Follow-Up Study. The combined studies looked at 88,084 women and 47,881 men who had been followed since the 1980s. Those who used aspirin two or more times per week, in either regular or "baby aspirin" doses, had a 19 percent reduction in colon cancer and a 15 percent reduction in stomach and esophageal cancers. However, this benefit was not noted for any other cancer.

Further, the decrease in colon cancer rates became significant only after five years of taking aspirin. The authors note that the population in these two studies was predominantly Caucasian and so may not be applicable to other races.

The same researchers recently presented a follow-up to this study to the American Association for Cancer Research. In this re-evaluation, the authors found a 31 percent decrease in the risk of colorectal cancers -- as well as reductions in breast, prostate and lung cancers. The reasons for such significant improvements are unclear.

Overall, the data point to a 20 percent reduction in colorectal cancer risk with the regular use of aspirin -- specifically 81 milligrams every other day -- but the numbers for other cancers are not convincing.

Be aware, however, of the risk of gastrointestinal bleeding. If you've had an ulcer or stomach problems with aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDS) in the past, daily aspirin use is not for you.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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