Regular Exercise Can Reduce Depressive Symptoms in Teens

Physical activity can help alleviate depressive symptoms in teens, according to a systematic review and meta-analysis of clinical trials.

Engaging in physical activity significantly helped to reduce depressive symptoms, with a modest corrected effect size compared with controls (g= -0.29, 95% CI -0.47 to -0.10, P=0.004), found Parco M. Siu, PhD, of the University of Hong Kong, and colleagues.

Across all the studies, the benefits of physical activity in reducing depressive symptoms resulted in a number needed to treat of six, the group reported in JAMA Pediatrics.

But it appeared that physical activity needed to be kept up in order to reap these benefits. In the four studies that looked at follow-up outcomes an average of 21 weeks postintervention, the significant differences in depressive symptoms disappeared (g= -0.39, 95% CI -1.01 to 0.24, P=0.14). However, Siu’s group said this was “possibly due to the limited number of studies with follow-up outcomes.”

In a secondary analysis, the researchers found certain factors that may predict exactly who would reap the biggest mental health benefits from physical activity. For example, teens ages 13 and older (versus children under 13), those with a pre-existing mental illness (versus considered “healthy” or with a physical illness), and those with a depression diagnosis saw the biggest effect sizes between physical activity and mental health.

Characteristics of physical activity itself also appeared to matter. Engaging in physical activity three times per week was linked with the greatest reduction in depressive symptoms, and the effect was greater when the physical activity was unsupervised than when it was fully or partially supervised in the studies. Also, studies in which the physical activity intervention lasted less than 12 weeks in duration had a larger effect size.

Level of intensity (low-to-moderate vs vigorous) and length of activity session (less than 45 min vs 45 min or more) didn’t appear to play a role in the outcome effect size.

Siu’s group referenced a recent cross-sectional study that found a U-shaped association between physical activity and mental health, suggesting that 10 to 15 sessions of physical activity per month were linked to the greatest mental health benefits.

“The individual level moderators identified make sense statistically, as teens and youth with depression may have higher baseline depressive symptoms (more room for improvement on the dependent variable) and lower levels of physical activity (more room for improvement on the independent variable),” pointed out an accompanying editorial by Eduardo E. Bustamante, PhD, of the University of Illinois Chicago, and colleagues.

“The finding that outcomes were less substantial when interventions were too frequent (or not frequent enough) and went on for too long (or not long enough) may reflect that part of the association of physical activity with reduced depression is the sense of accomplishment associated with successful completion — a feature requiring achievable but challenging goals,” they added.

A wide range of physical activity programs were assessed across the studies included in the meta-analysis, ranging from dancing, swimming, sports, running, treadmills, ellipticals, exergames, and more. The common thread, though, was an emphasis on aerobic exercise.

Across the 21 studies included, the average age of participants was 14 and 47% of them were boys. The majority of the studies included (17 of 21) were randomized controlled trials, and the rest were nonrandomized controlled trials.

“The evidence that physical activity is effective medicine for mental health is robust; now we need to find ways to get people to take it,” Bustamante’s group concluded.