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Correlation vs. causation alert: release overstates evidence with claims on exercise, depression, and heart disease

Exercise reduces heart disease risk in depressed patients

Our Review Summary

Depression and exercise.This American Academy of Cardiology news release follows a well-trodden path in health news of promoting the benefits of regular exercise. We’re not complaining about yet another article telling us exercise is good. But that’s besides the point because, in fact, the news release fails to grasp that the study is observational in nature, rendering the title of the document — “Exercise reduces heart disease risk in depressed patients” — unsubstantiated. The study is much more cautious about drawing any conclusions from this non-randomized research but you won’t find any of those cautions in the release. The takeaway message of the study is not so much that “exercise is good for you.” Rather, the study seeks to establish whether physical exercise modifies the link between depression and cardiovascular risk.

 

Why This Matters

Cardiovascular complications are often observed in people with depressive disorders. The observational study behind this news release seems to suggest that physical exercise could be used to improve cardiovascular risk stratification. The researchers also seemed to be trying to determine the mechanism by which exercise or the lack of it impacts risk factors for cardiovascular disease such as inflammation, oxidative stress and arterial stiffness.

The more we understand about connections between depression, exercise and heart disease the better. To what degree do depression and exercise alone or together impact heart health? The study — but not the release — offers some insight into understanding the relationship but doesn’t claim any definitive conclusions.

A depressed person reading the release might find it counter-intuitive to say they may reduce their risk for developing cardiovascular disease by taking up exercise. Often, a key symptom of mild or major depression is fatigue and the inability to fully engage in activities, even if they know, as most do, that “exercise is good for them.”

Criteria

Does the news release adequately discuss the costs of the intervention?

Not Applicable

It’s hard to put a price tag on regular exercise as there are so many ways to get your physical activity on and many of them are free. So we’ll say this category doesn’t apply.

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

Although the news release does provide some numbers on the association between cardiovascular risk and depression, it does not do enough to quantify the effect of exercise in modulating the relationship between the two.

Stating that people who exercised regularly had less arterial stiffening and inflammation in general than those that didn’t exercise isn’t enough to show causation. Even if the goal was to show causation, numbers weren’t provided.

It should also be pointed out that the patients enrolled weren’t clinically depressed as the title may indicate. They had not previously been diagnosed with depression and were evaluated with a symptom scale for two weeks, with most of them coming up with minimal to mild symptoms.

As any person seeking treatment for depression learns there’s a wide spectrum of diagnoses and treatments falling under the broad heading of depression: general anxiety disorder, dysthymia, major depressive disorder and postpartum depression to name a few. Some, but not all, can be mitigated with exercise alone.

Does the news release adequately explain/quantify the harms of the intervention?

Not Applicable

The release doesn’t delve into harms but we’ll rate this Not Applicable since the release doesn’t give us any specifics on the types of exercise the study volunteers took up. Some exercises are riskier than others.

Does the news release seem to grasp the quality of the evidence?

Not Satisfactory

The news release unfortunately makes a causal claim in the headline despite the study being observational in nature. For the title to work, the study design would have had to recruit a pool of depressed patients, randomly assign some of them to be sedentary and the rest to be physically active, and measure the surrogate outcomes associated with heart disease risk in each group. Of course that didn’t happen.

The release also overstates a finding with this phrase: “the study found regular exercise seems to reduce the adverse cardiovascular consequences of depression.” But the study published in the Journal of the American Academy of Cardiology stated: “Physical exercise appears to prevent the adverse cardiovascular consequences of depression, but these findings need to be confirmed in a randomized trial.”

Does the news release commit disease-mongering?

Satisfactory

The news release is good on this front. It does not commit disease-mongering of cardiovascular diseases.

Does the news release identify funding sources & disclose conflicts of interest?

Not Satisfactory

Neither the funding source nor any conflicts of interest are disclosed.

Does the news release compare the new approach with existing alternatives?

Not Applicable

The study is not a traditional treatment-versus-control study, rather it studies possible interaction effects between physical activity and depression for different cardiovascular disease indicators. A discussion of alternative treatments is not particularly relevant.

Does the news release establish the availability of the treatment/test/product/procedure?

Satisfactory

With the “treatment” being physical exercise, availability is a given. There are countless ways to exercise and there need not be any cost involved.

Does the news release establish the true novelty of the approach?

Not Satisfactory

The novelty of the research lies in its effort to study how the association between depression and cardiovascular disease is moderated by the presence or lack of regular physical activity. If regular exercise were discovered to be a significant moderator, we could use the level of physical activity to further stratify depressive patients into finer categories of cardiovascular risk. This point is missed by the news release.

Does the news release include unjustifiable, sensational language, including in the quotes of researchers?

Satisfactory

The news release contains no sensational language promoting, say, exercise as the holy grail of curing cardio diseases.

Total Score: 3 of 7 Satisfactory

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