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Physical activity and dementia: another negative study, another void in news coverage

Kevin Lomangino is the managing editor of HealthNewsReview.org. He tweets as @KLomangino.

If you Google the search terms “physical activity” and “Alzheimer’s disease,” you will be served up a long list of links that almost exclusively tout the notion that exercise could help prevent or slow down the progression of dementia.

They are reassuring and hopeful messages but arguably not representative of the mixed science on this question.

At least two recent studies — one in the BMJ which we blogged about last month, and another that was announced by Johns Hopkins University yesterday with a news release — have reported no association between midlife physical activity levels and long-term cognitive decline or risk of dementia.

These new studies are observational in design (can’t prove cause and effect), have considerable limitations, and are far from the last word on the question. But they have some notable strengths in comparison with other studies that have made headlines.

Despite those strengths, and despite the Hopkins study receiving the full media treatment including a news release carried on the major PR wires, neither study seems to have garnered significant coverage from consumer news outlets — at least none that I could find.

There could be many reasons why news outlets might choose not to cover a study such as this one, including short-staffing due to summer vacations or an assessment that the studies weren’t impactful enough to merit coverage. And in the case of the Hopkins study, it’s possible that it will generate coverage which hasn’t yet materialized.

But this may also reflect some degree of bias against covering negative studies that are deemed less clickable.

We see plenty of coverage of preliminary research in this area when the findings are framed more seductively: e.g. “How exercise keeps us young.”

Whatever the case, it’s a great excuse on a late-August Friday to re-up this gem from our toolkit of resources: Why health journalists need to stop ignoring negative studies.

It’s also a good reason to call attention to a message that might otherwise fall through the media cracks. Specifically, that the protective effect of exercise seen in some dementia studies may result from a type of bias called “reverse causation” — which is where the effects of incipient dementia (confusion, memory loss, etc) could lead to reduced levels of exercise and not the other way around. It’s a “chicken or the egg” problem common to many observational studies and an important reason why such findings usually need to be followed up with randomized trials.

Since it’s not a message you’re likely to see elsewhere, I’ll wrap up by sharing what Alden L. Gross, PhD, and his colleagues concluded in the new Hopkins study: “While physical activity is strongly recommended for many reasons, our data suggest cognitive health may not be one of those reasons. It is probably unrealistic to assume one component of a healthy lifestyle, such as physical activity, can be the magic bullet for prevention of a complex multifactorial condition.”

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Abdullah Moosa

September 1, 2017 at 3:45 pm

Since most of us non-experts get the science we use to make personal decisions from media coverage and not primary sources, media coverage should ideally be representative of the actual state of knowledge on a topic. But how do we deal with the fact that juicy headlines sell better than the truth?

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