To protect teens’ mental health, keep them moving

With children sent home from school, unable to attend sports practices or even gather together for vigorous play, parents worry that the lack of exercise will harm their children’s mental health. Do they need to add the role of “coach” or “fitness instructor” to their already expanding list of parenting duties during the coronavirus pandemic?

The answer is a reassuring no, according to the results of a new study: Parents don’t need to lead their teens through vigorous daily workouts; all they need to do is encourage their teens to be somewhat less idle. Simply getting younger adolescents to decrease sedentary behaviors in favor of even very light physical activity appears to lessen their risk of depression as they age into older teens, suggests research recently published in the Lancet.

The majority of major mental illnesses, including depression, begin during the teenage years and can alter the course of an entire life. Any public health measure to prevent such illnesses, particularly those that are relatively low-cost and easy-to-implement, are extremely valuable, particularly during these higher-stress times of staying put.

In this prospective study (a study that follows participants over a long period of time), researchers at University College London followed a large group of teens from age 12 to 18, recorded their physical activity at ages 12, 14, and 16 through use of fitness trackers and then assessed for symptoms of depression at age 18. The use of accelerometers was a key component of the study, as they are a more reliable source of data than self-reporting, as well as more likely to accurately capture time spent engaging in everyday kinds of movement that is difficult to recall when a teen is asked to estimate total time spent in physical activity.

The researchers found that the adolescents’ sedentary behaviors, defined as sitting or reclining while awake, dramatically increased during this time period, from an average of 7.18 hours at age 12 to 8.72 hours by the time the group was 16.

What drove the increase in sedentary behaviors was a decrease in light physical activities, such as walking at a casual pace to get from one place to another. Light physical activity declined during the study period, from an average of 5.43 hours at age 12 to 4.08 hours by age 16. The increase in teens’ sedentary behavior was not due to a general decrease in all physical activity as the teens aged; in fact, the researchers found that daily moderate to vigorous physical activities, such as brisk walking or cycling, remained stable during this time span.

The kids who consistently engaged in moderate to vigorous physical activity showed fewer depressive symptoms at age 18, which has been found in previous studies. The surprising result of this study was that less time spent engaging in sedentary behaviors in favor of light activity also predicted fewer depressive symptoms at age 18. Specifically, each hour increase in light activity predicted a lower depression score at age 18: 9.6% decrease in depression score at 12 years; 7.8% at 14 years, and 11.1% at 16 years.

The trend of more time spent in sedentary pursuits has been found in previous studies of teens, and is likely due to many factors inherent to the developmental period of modern adolescence. These include less recess and more time sitting at desks in middle and high school, more time devoted to homework after school, increasing use of smartphones and social media as a leisure activity, and more sedentary activities when spending time with friends, such as eating out or talking rather than playing games.

The Centers for Disease Control and Prevention recommends that kids ages 6 to 17 engage in 60 minutes of moderate-to-vigorous physical activity each day for maximum health and wellness. But how can we protect teens who won’t or can’t engage in exercise of that intensity? There are many teens who have disabilities or physical limitations that may restrict their ability to engage in regular exercise of moderate to high intensity, as well as many teens for whom regular vigorous exercise is just not their preferred activity. How can they be afforded the same protection against depression that vigorous physical activity affords?

This study, particularly if the findings are replicated in future studies, is so important: It suggests that merely increasing the time spent in light physical activity is protective, as well.

The authors of the study suggested several public-health measures to do just that, mostly at schools: “Light activity requires less effort than moderate or vigorous activity, does not require planned or dedicated time periods, and can be easily and simply incorporated into a daily routine, such as standing or active classes. As a result, light activity might yield a more sustained uptake and be easier to implement at a population level than moderate to vigorous activity.”

They did not make recommendations regarding how to decrease sedentary behaviors at home, but as a child psychologist I wholeheartedly recommend that parents place reasonable limits on recreational screen time and encourage time spent developing other hobbies that involve getting up and moving around, such as gardening, cooking, or training/caring for the family pet.

I also recommend that parents instill the value (and the pleasure) of walking rather than driving wherever possible – this is also an excellent way to increase the amount of positive time spent together as a family.

On that note, decreasing sedentary behavior has also been shown to improve adult mental health in previous studies. Hence, in opting to walk more together as a family, you might not only be protecting your child from developing depression, but protecting yourself, as well.

Katherine Dahlsgaard is clinical director of the Anxiety Behaviors Clinic at the Department of Child and Adolescent Psychiatry and Behavioral Sciences at Children’s Hospital of Philadelphia.