Aspirin seems to offer some pretty reliable health benefits — it has been shown to reduce the risk of heart problems, stroke, and certain cancers. But it also carries some significant risks — like gastrointestinal bleeding — that can be dangerous, so the scientific community has been unclear about to whom daily aspirin should be prescribed, even at low doses.

Now a new study suggests that for women younger than 65, the risks may too great to recommend the medication every day.

There was a slight decrease in the risk for heart disease, stroke, and colon cancer among the women taking aspirin, but two-thirds experienced gastrointestinal bleeding.

The study had one group of women who were participating in the Women’s Health Study take 100 mg of aspirin daily, while another group took placebo pills. The research team followed the women for at least 10 years, and tracked the rates of diseases that developed in each group.

Among the nearly 28,000 women studied, 600 cases of heart disease, 170 cases of colon cancer, and over 1800 cases of other types of cancer were recorded during the 10-year period. There were also 300 cases of gastrointestinal bleeding severe enough to require hospitalization.

Over the next seven years (after the women had stopped taking aspirin or placebo), more than 100 additional cases of colon cancer and almost 1400 other cancers were recorded.

The researchers did find a slight decrease in the risk for heart disease, stroke, and colon cancer for women taking aspirin; and some women had a slightly decreased risk of developing other types of cancer. But for the women taking aspirin, two-thirds experienced gastrointestinal bleeding.

Though aspirin’s benefits did seem to increase with age, the risk of internal bleeding also increased. The team calculated that 29 women over the age of 65 would need to take daily aspirin to prevent just one of them from developing heart disease or stroke.

The daily aspirin recommendation may need to be retired, the authors say, at least for women under 65, since the benefits seem to be overwhelmed by the risks. Aspirin every other day may, at least in some cases, need to replace the daily routine that’s so often recommended as a disease-prevention tool.

Always talk with your doctor before stopping or starting an aspirin (or any other medication) regimen. Though it may be beneficial for some people, as we’re learning more and more, aspirin probably shouldn't be recommended for all people.

The study was carried out at Harvard University and the University Medical Centre Utrecht in The Netherlands, and is published in the journal Heart.