‘May help’…’may prevent:’ Conditional statements water down TIME’s look at exercise and depression study

Does the story seem to grasp the quality of the evidence?

Not Satisfactory

The story explains the results of a study that “followed more than 22,000 healthy Norwegian adults without symptoms of anxiety or depression for an average of 11 years.”  It also explains that, “The study could not prove a cause-and-effect relationship between exercise and the risk of depression.”

The large size and the statement that the findings aren’t causal are both indicators of the quality of the evidence.

But then the story adds, “but the authors say it strongly suggests one,” referring to a causal relationship. Studies like this one cannot prove causality and since they were based on the self-reporting of participants, their conclusions should maintain some skepticism.  Add to that the fact that the story is loaded with conditional statements:  “Regular exercise may prevent,” “If their hypothesis is right,” “depression cases could be prevented,” “People seemed to have mental health benefits,” “benefits of exercise are likely responsible,” “exercise may also have a role in preventing people developing depression”  All of these conditional statements suggest that the evidence may or may not hold up over time.

Other factors: The study is of Norwegians. How generalizable is it? And, the self-reported exercise information was collected only at the start of the study, the amount of exercise that participants completed regularly was not assessed at any other time. The study itself is careful to say this, but the story makes it sound as if ongoing exercise was documented.

Does the story use independent sources and identify conflicts of interest?

Not Satisfactory

The story doesn’t include any content from independent sources.

Does the story establish the true novelty of the approach?

Not Satisfactory

Exercise for mental health is not a new concept. What makes this study novel is that it’s looking at exercise’s potential to prevent depression, and if that impact would be useful enough for a public health level initiative. As the study explains:

“While many agencies are keen to promote the potential mental health benefits of exercise, at present the literature is unable to provide the most basic information needed for effective, targeted, evidence-based public health campaigns concerning depression and anxiety.”

The story didn’t explain this.