December 3, 2019

Exercise may be linked to a reduced risk of depression, even in people who are genetically predisposed to the condition, according to a study published recently in Depression and Anxiety.  

Cheat sheets: Learn more about why study design matters

Study details

A "growing body of research" indicates that exercise could help prevent depression, Gretchen Reynolds writes for the New York Times' "Well." For instance, some studies have found an association between aerobic fitness and a lower risk for depression, while others have found that exercise can even decrease the severity of depressive episodes in patients who were already diagnosed with the condition.

Still, not many studies have looked into the significance of the type of exercise and the amount of it, according to Reynolds.

As such, Harvard researchers for the new study analyzed health data of thousands of patients in the Boston area that was originally collected for the ongoing Partners Biobank study. The records were for thousands of male and female patients who contributed DNA samples.

The researchers reviewed the records of nearly 8,000 patients who'd completed a questionnaire about their exercise habits. The questionnaire asked patients how much time per week they spent doing a variety of physical activities over the last year, including walking, running, biking, using exercise machines, or attending dance or yoga classes.

The researchers looked at the patients' DNA to identify any genetic variations that might increase their risk for depression. Researchers used the DNA to score individuals' risk of inherited depression as high, moderate, or low.

Physical activity can buffer depression risk, study finds

After a cross-analysis of the data, the researchers found that the patients with a high genetic risk for depression were more likely to develop depression than those with low risk scores. However, the researchers also determined that all participants who did some type of physical activity were less at risk for depression than sedentary participants.

Further, the study revealed that exercise reduced the risk of depression for participants who were genetically predisposed to the condition, including participants who carried multiple genes that were predictors of depression.

In addition, participants who reported exercising were at lower risk for a subsequent depressive episode compared with sedentary participants with a history of the condition, the researchers found.

Further analysis of the type of physical activity the "active" participants performed found that the type of exercise did not impact their depression risk.

The amount of exercise, on the other hand, did matter, the researchers found. People who spent at least three hours per week participating in any physical activity were less likely to become depressed than sedentary people, the researchers found. Overall, the risk of depression decreased by 17% for every additional 30 minutes of daily activity.

Implications

Study leader Karmel Choi, a clinical and research fellow at Massachusetts General Hospital and Harvard's T.H. Chan School of Public Health, said the results indicate that exercise "neutralized" the much of the additional risk for depression for participants who were genetically predisposed to the condition. That said, exercise did not completely eliminate the risk of depression, but the results did imply that it reduced the risks for the majority of participants, Choi added.  

Further, the observational study could not determine causation between physical activity and mental health, only that the two may be linked.  

Even still, Choi noted that the results indicated that "genes are not destiny," when it comes to depression risk (Reynolds, "Well," New York Times, 11/21).

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