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When it comes to coffee, cancer risks, read fine print

Tue., March 27, 2012

Have you read or heard headlines about the “latest” study on caffeine, wine or some other substance and felt confused? You are not alone.

Headlines you may have seen include “Caffeine can increase breast cancer risk,” “Caffeine Consumption Not Associated With Breast Cancer Risk In Most Women, Study Suggests,” “Caffeine, Breast Cancer Link Minimal,” and “Does Coffee Cut Breast Cancer Risk?” Besides being about caffeine and breast cancer, all of them also have this in common: they refer to research published in scholarly journals.

Confusing? You bet. Some of the conflicting headlines even refer to the same study.

What’s a person to do? Cut out caffeine entirely? Have more? Have less?

Start by reading the fine print. In the study that generated the headline “Caffeine can increase breast cancer risk,” all participants were women 45 years or older and the increased risk correlated with drinking more than four cups of coffee daily. This research cannot be generalized to women younger than 45 or who drink fewer than four cups of coffee daily. What other things about the people in a study are like you or different from you?

Go to the original article the story is based on. The name of the journal that published the study and at least one of the authors is usually in the news report. If you cannot get a copy of the original article, look for other stories on the same topic for comparison. Three of the headlines noted above came out on the same day.

In my examples, the research subjects are people, but sometimes you see headlines like this for studies done in animals, petri dishes or test tubes. Again, read the fine print. Animal and laboratory research are important steppingstones, but we cannot assume that human research will show the same results. Also, research that looks at a few people or subjects of only one gender, age or ethnicity cannot be generalized to everyone.

Consider other research on the topic. For instance, many women stopped hormone replacement therapy after one well-publicized study a few years ago. Now, more information on the data from that study and other research allows us to individualize decisions regarding risks and benefits of hormone replacement.

It also helps to know that results can be reported as absolute risk and relative risk.

Imagine a new blood pressure medication is tested against an older medication for one year. Everyone in the study has high blood pressure: 100 people take the new medication, 2 have heart attacks; another 100 people take the older medication, 3 have heart attacks. So for people with high blood pressure taking the new medication, we expect one less heart attack per year for every 100 people using it. This is absolute risk.

Looking at the same information as relative risk, the new medication reduces heart attack risk by 33 percent or one third. If 12 out of 100 of the new medication users have heart attacks and 18 out of 100 people taking the older medication do also, then the new medication still reduces the relative risk of heart attack by one third or 33 percent. Relative risk often sounds more impressive. A brochure with more information on risk and other aspects of medical study results is here.

This may seem awfully complicated. I recommend asking your health care provider to guide you in understanding new research, making sense of the headlines and what it means for you personally.

Dr. Alisa Hideg is a family medicine physician at Group Health’s Riverfront Medical Center in Spokane. Her column appears every other Tuesday in the Today section. Email your comments and column suggestions to drhideg@ghc.org.


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