Be skeptical of the news. Low-dose aspirin to prevent breast cancer might work. It might not.More than one in every ten women in the U.S. will develop breast cancer in her lifetime. This means that millions of women, and those who love them, are on the lookout for a reliable way to prevent the disease.

In a perfect world, news organizations would always present the best evidence… Unfortunately this doesn’t always happen.  However, a recent Washington Post report about the use of baby aspirin to prevent breast cancer might have given an inaccurate idea about the research. The Post reported baby aspirin may prevent breast cancer, which is partially true. But the other part of the story is that it may not prevent breast cancer at all.

To understand the missing pieces it is important to first understand the study’s design. The study reported in the Post was an observational study. This means the women in the study were observed – in this case through questionnaires they completed about their habits and health. They weren’t asked to change any habits or behaviors; researchers just noted what was reported on the questionnaires, and how that related to outcomes.

In this case, women who took low-dose aspirin multiple times per week had a lower incidence of a certain type of breast cancer than those who took no aspirin or regular doses of aspirin.

If you are a woman who read the Post’s article you might be tempted to start low-dose aspirin for this purpose. But observational studies, like this one, can only show an association, not causation. This means researchers see the connection between low dose aspirin and lowered breast cancer risk. But they don’t know if it’s the cause of the lowered cancer risk.

It might be that women who take low-dose aspirin – which is often used as a preventive measure for cardiovascular disease – are more health conscious overall. They might be more likely to see the doctor regularly, exercise more often, or make healthier food choices, too. Or it might be that low-dose aspirin really does lower cancer risk. We just can’t be sure from this type of research. The researchers state at the end of their report:

“In summary, our study strongly supports the need for further, perhaps experimental, study of low-dose aspirin as a widely available, inexpensive chemopreventive option for the most common subtype of breast cancer…“

In short, they are saying this is interesting information, let’s do a formal study to determine if there really is a cause-effect relationship there. What they aren’t saying is that all women should start low-dose aspirin to prevent breast cancer.

So when you read a health headline, don’t just accept it. Find out what the research really shows. Most medical research has a discussion toward the end of the paper that lists its limitations. You don’t have to read all the details of the research to get the bottom line from this section. And if you aren’t sure what to make of it, ask your doctor.

The truth is, all medical research is not created equal, regardless of how the headlines report it.