Why “exercise lowers cancer risk” headlines mislead readers

The following post is by Kevin Lomangino, Managing Editor of HealthNewsReview.org, who stresses that he has nothing against exercise and believes that it is a healthy activity that should be encouraged. This post is about inaccurate news media descriptions of an exercise study and how those descriptions could be improved.

The big health story of the day is about a study on exercise and cancer risk. Multiple national outlets are carrying the story, with headlines claiming that exercise lowers risk for 13 different cancers.

NBC: Exercise Lowers Risk for These 13 Cancer Types

LA Times: Exercising drives down risk for 13 cancers, research shows

HealthDay: Exercise may cut risk of 13 cancers, study suggests

TIME: Exercise Can Lower Risk of Some Cancers By 20%

These headlines all loosely follow the framing of a National Institutes of Health news release about the study, “Increased physical activity associated with lower risk of 13 types of cancer.”

And yet there’s a crucial difference in the wording of the appropriately cautious news release and the more definitive-sounding news coverage. The NIH news release states merely that exercise was “associated with” lower cancer risk, whereas the news story headlines all claim that exercise “lowers/drives down/may cut” cancer risk.

It may seem like a small distinction, but it’s a critical signal as to what this observational study can and cannot tell us about the relationship between exercise and cancer risk.

STAT’s Sharon Begley, whom we profiled in a podcast last week, delved into this point in rich detail in her coverage of the study:

An observational study like this — ask volunteers how much they exercised, then see who develops cancer — can’t show that exercise caused a lower risk of cancer. It can only show that the two go together. Proving causality requires assigning some volunteers to exercise, others to be sedentary, and then comparing their cancer incidence. Only that type of study can make sure some third factor is not at work.

She noted that smoking and obesity, for example, are both linked to exercise frequency as well as to cancer risk. Could those factors be skewing the numbers to make exercise look like a bigger player than it really is?

And what about the factors that the researchers didn’t account for and we may not even know about? Notes Begley:

The study did not include genetics, which might influence both exercise and cancer risk, said statistician Rebecca Goldin, a professor of mathematics at George Mason University who was not involved in the research. “Other health factors might influence both, too. Imagine you have something simmering before cancer has reared its ugly head, which might cause you to both not exercise and develop cancer.” That would show up as the association the study found, undermining the idea that exercise helps prevent cancer.

Bottom line: The headlines claiming that exercise “lowers cancer risk” aren’t accurate, because they suggest that exercise directly impacts cancer risk in a causal way. They impart a certainty to the findings that the underlying science simply doesn’t support. (Read more about this issue in our Toolkit explainer: Observational Studies – Does The Language Fit The Evidence? – Association Versus Causation.)

Bear in mind that some stories did appropriately call attention to limitations of the study in the body of their text. For example, HealthDay helpfully noted that “the study only found an association between exercise and reduced cancer risk; it did not prove a cause-and-effect relationship.”

NBC also mentioned that “it’s always possible that people who are able to exercise more are healthier in other ways and less likely to develop cancer for some other reason.” But then it immediately shot down that caveat with this claim: “cancer experts say the evidence is very convincing that exercise directly affects the growth of tumors.”

Are all cancer experts similarly convinced? Even the researchers themselves noted in their paper that they “cannot fully exclude the possibility that diet, smoking, and other factors may affect the results.”

I understand that many reporters have no say over what goes into their headlines and that’s unfortunate. But someone needs to take responsibility for setting the appropriate tone on health news.

Even the most thorough and careful list of caveats in the body of a story is no match for an overstated headline — which may be the only part of a story that most readers see.

In fact, headlines on health stories are so important that we’ve written some tips on how to write them more accurately.

Tip #1 in that piece? “Learn the difference between association and causality.”

You might also like

Comments (5)

Please note, comments are no longer published through this website. All previously made comments are still archived and available for viewing through select posts.

Myra Saunders

May 17, 2016 at 9:12 pm

I appreciate that your site continues to correct misinformation and encourage understanding. However, of all the inaccurate stories that you could have picked, you chose one that encouraged overall health. While, exercise may or may not contribute to a lower cancer risk, it does contribute to better health. Everything you’ve said is true but maybe you should focus on stories that actually damage health instead of encouraging it. Great work but a really poor choice for a focus story.

    Kevin Lomangino

    May 18, 2016 at 6:26 am


    Thanks for your comment. However, I disagree very strongly with the idea that we should selectively point out inaccuracy only in stories “that damage health instead of encouraging it.” That’s a slippery slope, because it requires us to make a judgment as to what the overall health consequences of a story will be — and nobody can know that. You may believe that exercise can only do good, but I am not so certain. What about the elderly woman who, because she heard exercise might lower her cancer risk, decides to take on some activity that results in her breaking a hip? And what if we as a society decide to invest more and more resources in exercise programs because we think they’ll reduce cancer rates — and that idea ends up being totally wrong. Maybe we’ve starved some other program or research effort that might actually have had an impact on cancer.

    I don’t have a crystal ball and I can’t predict what the ultimate impact of misinformation in a health story will be. That’s why I’ll continue to be an equal opportunity critic, and will call attention to misleading stories whether I agree with their overall conclusions or not.

    Kevin Lomangino
    Managing Editor


      May 19, 2016 at 7:00 pm

      Your point is well taken and thank you for sharing it.

      sandi pniauskas

      May 23, 2016 at 9:35 am

      Thank you for this analysis and how difficult the media sometimes make it for the public. My perspective comes from my/ personal journey as well as those of our cancer communities. I see these media reports and then I look at the actual epidemiological evidence.which often conflict. This ‘eating right’ and ‘exercising’ can lead to many psychological harms in patients who are already trying to cope with such things as multiple surgeries/chemotherapies/income issues and the like – the added burden. On a personal note of experience: during chemotherapy I thought the right thing to do was to exercise (media) so I ventured out for a walk – not a long walk just several blocks. I made it to my destination but was too fatigued to get back home. Everyone was at work, too short for a taxi – you get the picture. A little more care on the actual impact on daily lives of patients cannot be understated. For those living with and (possibly) dying of cancer -eat what you want, live your life as you wish and do no harm to yourself. Thanks.

Laurence Alter

May 24, 2016 at 1:47 pm

News reporting has always been indecipherable. Medical or health news is NO – N-O – exception. I am surprised the writer is surprised. Headlines are so unreadable no matter if their content conforms to the text, itself. What about when news used to have the word, “Dateline” and never meant time or date (but place as in: “Dateline: Tokyo” for a foreign news story). You news writers and reporters are to blame for any ignorance of the news or misleading that results. Your penchant for abbreviations just never ends (medical terms, abbreviated for a lay audience, is just sheer willful deception.)