Many people believe an aspirin a day keeps the doctor away, and indeed, the US Preventive Services Task Force recommends a daily low-dose aspirin for people over 50 to reduce the risk of heart attacks, strokes and some types of cancer. The results of a study published in the The New England Journal of Medicine calls that advice into question.

“Clinical guidelines note the benefits of aspirin for preventing heart attacks and strokes in persons with vascular conditions such as coronary artery disease,” said Richard J. Hodes, director of the National Institute on Aging, which helped fund the study. “The concern has been uncertainty about whether aspirin is beneficial for otherwise healthy older people without those conditions.”

Bleeding is a known risk of regular aspirin use, and this study found that aspirin was linked to a significant increase in bleeding, mostly in the gastrointestinal tract or brain.

The international study included over 19,000 Australians and Americans age 65 and up who did not have dementia, a physical disability or a condition that required the use of aspirin. Participants were followed for almost five years. Scientists at Monash University in Melbourne, Australia and the Berman Center for Outcomes and Clinical Research at Hennepin Healthcare in Minneapolis, Minnesota led the study.

Some people in the study took a 100 mg low-dose aspirin every day while others took a placebo. Neither the participants nor the researchers were aware of who was taking aspirin and who was taking the placebo.

When the results were compiled, researchers were left with findings that dispute generally accepted beliefs about daily aspirin use.

There was no difference in avoiding dementia or permanent disability between those taking aspirin and those taking the placebo. Among those who took aspirin, 90.3 percent were alive at the end of the study without dementia or permanent physical disability compared to 90.5 percent of those who took the placebo.

Nearly six percent of the participants taking aspirin died during the study compared to 5.2 percent who took the placebo. The researchers urged caution when interpreting this finding since this effect has not been seen in other studies.

The rates of heart disease and stroke were about the same between both groups. Heart disease and stroke were the cause of 19 percent of deaths.

About half of the people who died over the course of the study had some kind of cancer, which is not uncommon in an older population. There was a small increase in new cases of cancer in the group taking aspirin. Again, the researchers were careful to say this could have been due to chance.

Leslie Ford, of the National Cancer Institute, which also helped fund the study, cautioned, “The increase in cancer deaths in study participants in the aspirin group was surprising, given prior studies suggesting aspirin use improved cancer outcomes. Analysis of all the cancer-related data from the trial is under way and until we have additional data, these findings should be interpreted with caution.”

Bleeding is a known risk of regular aspirin use, and this study found that aspirin was linked to a significant increase in bleeding, mostly in the gastrointestinal tract or brain. Five percent of deaths among those in the study were due to major bleeding.

Because longer-term effects may not be the same as those seen during the less-than-five-year study, Evan Hadley of the National Institute of Aging emphasized that there is much more to be learned about the effect of aspirin. Participants will continue to be monitored.

If you have been taking low-dose aspirin daily, you will probably want to have a conversation with your doctor about whether you should continue. Do this before discontinuing your aspirin regimen.