What Is the Relationship Between Exercise and Depression?

While doctors will always recommend exercise and fresh air as a means to improve a wide variety of health conditions—and general health, overall—a new international study argues that exercise can have a direct influence on our mood, too.  Or, rather, this study of the genetics of 300,000 people argues that physical activity is not necessarily a cure for depression but instead a means to prevent it. 

We have dozens of existing studies that link exercise and depression (perhaps, more accurately, that they are inversely proportionate).  Until now, though, we have not seen how lack of exercise can cause depression.  For one, the prevailing thought was that depression simply led people to feel less motivated to exercise; and that is a vicious circle. 

However, this new research shows there is actual a causal link between exercise and preventing the onset of depression.  In addition, the team from Massachusetts General Hospital found the opposite is true:  depression does not cause people to exercise less. 

According to Karmel Choi, of the MGH Center for Genomic Medicine, “We know depression is a leading cause of disability around the world but we know much less about how to prevent this difficult condition.”

The lead study author contends, “We wanted to harness the advances of large-scale genomics studies to validate a promising target for depression.”

For the study, the researchers wanted to observe variables that you can change.  Using a Mendelian randomization design, they determined a way to treat genetic variation as a type of natural experiment.  With that, Choi comments that while Mendelian randomization is not a perfect design, even with its limits it is a reliable means to answer some of the most familiar questions in any experiment. 

Indeed, this approach should be a meaningful way to see if exercise causally reduces depression and, more importantly, if it does we can then identify that those who carry certain gene variants should find they are more capable of avoiding depression by increasing their daily physical activity.

Specifically, the researchers found that 15 minutes of vigorous physical activity or an hour of moderate activity could reduce depression risk in these patients by as much as 26 percent.  The difference between vigorous and moderate activity, for example, is essentially the difference between running and walking. 

The results of this study have been published as a report in the journal JAMA Psychiatry.