Staying Active May Lower Adolescents' Risk of Depression

The more time an adolescent spends sitting, the more likely he or she is to experience depressive symptoms, according to a new University College London-led study. These findings (Kandola et al., 2020) were published on February 11 in The Lancet Psychiatry.

To the best of my knowledge, this is the first accelerometer-based longitudinal study with a large sample size (n = 4,257) to investigate the association between daily physical activity, sedentary behaviors, and the prevalence of depressive symptoms among adolescents age 12-18.

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Accelerometers (i.e., fitness trackers) provide more objective and reliable data than studies that rely on self-reporting of daily physical activity. Depressive symptoms were measured using Clinical Interview Schedule-Revised (CIS-R) depression scores.

The researchers found that adolescents whose daily routine consistently included light physical activity (e.g., walking) were less likely to be depressed. They also identified a dose-response that linked the amount of time sitting vs. the amount of time moving with higher or lower depression scores. Across the board, adolescents who sat less and moved more tended to have fewer depressive symptoms.

In addition to walking, light physical activity can include things like playing a musical instrument in the marching band, dancing in a TikTok video, doing household chores, or making art while standing.

"Light activity could be particularly useful because it doesn't require much effort and it's easy to fit into the daily routines of most young people. Schools could integrate light activity into their pupils' days with standing or active lessons," the study's lead author, Aaron Kandola of UCL said in a news release. "Small changes to our environments could make it easier for all of us to be a little bit less sedentary." (See "Why Prolonged Classroom Sitting Isn't Ideal for Student Health")

On a day-to-day basis, the researchers found that every additional hour of sedentary behavior at age 12, 14, and 16 was associated with an uptick in depression scores of 11.1%, 8%, and 10.5%, respectively, by age 18.

Conversely, every additional 60 minutes of light physical activity per day at age 12, 14, and 16 was associated with depressive symptom scores that were 9.6%, 7.8% and 11.1% lower, respectively, by age 18.

Adolescents who were consistently sedentary at the ages of 12, 14, and 16 had depression scores that were 28.2% higher than their more active peers by age 18.

"Our findings show that young people who are inactive for large proportions of the day throughout adolescence face a greater risk of depression by age 18," Kandola said. "We found that it's not just more intense forms of activity that are good for our mental health, but any degree of physical activity that can reduce the time we spend sitting down is likely to be beneficial."

This is great news. Even if you're a teen who doesn't like to get sweaty and hates vigorous exercise, this research suggests that incorporating some very light and easy physical activity into your daily routine could make you less likely to get depressed. You don't have to subject yourself to a grueling session of HIIT or become an exercise fanatic to reap the mental health benefits of light physical activity. Making a small effort to sit a bit less and move a little more could make a big difference in your risk of depression.

Please note: These findings are correlative. The researchers cannot prove that higher levels of physical activity cause a reduction of adolescents' depressive symptoms; they can only identify a correlation. For example, adolescents suffering from major depressive disorder (MDD)—for reasons that have nothing to do with how much time they spend sitting—may tend to be less active than "happy-go-lucky" peers without any depressive symptoms.

That said, the researchers made a concerted effort to avoid reverse causation by adjusting their data analysis to account for pre-existing depressive symptoms at the outset of the study. They also adjusted for confounding factors such as a parental history of clinical depression and socioeconomic status.

Previous research (Choi et al., 2019) has shown that moderate-to-vigorous physical activity (MVPA) can lower the risk of depression in adults. The latest research (2020) by Kandola et al. suggests that light physical activity, that doesn't require huffing and puffing or breaking a sweat, may also help keep depression at bay for adolescents and adults.

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"Worryingly, the amount of time that young people spend inactive has been steadily rising for years, but there has been a surprising lack of high-quality research into how this could affect mental health. The number of young people with depression also appears to be growing and our study suggests that these two trends may be linked," Kandola concluded. "We should be encouraging people of all ages to move more and to sit less, as it's good for both our physical and mental health."