Exercise as an Antidepressant for Teens

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The antidepressant power of cardiorespiratory aerobic exercise doesn't kick in until after age 14, according to a new peer-reviewed study (Steinsbekk et al., 2025) published in the Journal of the American Academy of Child & Adolescent Psychiatry. These findings are based on the ongoing Trondheim Early Secure Study (TESS), which began in 2007.

Understanding when and how cardio starts to fortify someone's ability to fight off depression could help teens and parents make better-informed choices during a psychologically vulnerable window of childhood development.

For data used in their recent analysis, researchers in Norway followed 873 kids (aged 6 to 18), checking in every two years at ages 6, 8, 10, 12, 14, 16, and 18. Interestingly, the correlation between increased physical activity and fewer depressive symptoms within the same person didn't show up until the final two check-ins, at ages 16 and 18.

Aerobic Exercise and Depression: Age 14 Is a Turning Point

"Although we found that physical activity seems to protect against depression symptoms in adolescence, this did not apply to young adolescents aged 10–14," first author Silje Steinsbekk said in a May 2025 news release.

"This finding was true for teens who were 14 to 16 years old and 16 to 18 years old. Both the sum of daily physical activity, and the proportion of activity that is more intense and particularly important for our health, turned out to protect against symptoms of depression," she added.

The researchers also found that teens diagnosed with a major depressive disorder (MDD) were less likely to be physically active or do vigorous workouts. The double whammy of decreased overall physical activity and not engaging in moderate-to-vigorous physical activity (MVPA) was linked to more symptoms of depression between the ages of 14 and 18.

Of course, correlation doesn't imply causation. It's impossible to know for sure if people with fewer depressive symptoms exercise more because they're not depressed, or if people stay less depressed because their daily bouts of physical activity help keep depression at bay.

That said, because the longitudinal TESS study isn't cross-sectional and follows each individual's lifelong patterns of physical activity and symptoms of depression, the researchers were able to show within-person associations between increased MVPA and fewer depressive symptoms over many years.

My Lived Experience Corroborates These Findings

As a young adolescent (aged 10 to 14), I experienced lots of depressive symptoms and wasn't very physically active. Although I was forced to participate in gym classes and endure the dreaded annual "12-minute run" fitness test every fall in seventh and eighth grade, I never associated exercise with feeling good. In junior high, moderate-to-vigorous physical activity felt more like punishment than mood-lifting medicine.

When I experienced a major depressive episode (MDE) at age 16, exercise still wasn't on my radar as a potential way to feel less depressed. Lacking firsthand experience of exercise easing depression, inactivity didn’t seem like a factor in my dysphoria—even though it likely made things worse.

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Luckily, at 17, I got into running. Armed with a Sony Walkman and inspiring self-selected music on mixtape cassettes, I ran every day from June to September. Almost immediately, it was clear that these vigorous jogs were boosting my happiness. As someone on the edge of 18, I was stunned by how quickly running alleviated my symptoms of depression. During the summer of 1983, I went from feeling hopelessly depressed to someone filled with optimism and eudaimonia.

After reading this new (2025) study, it makes sense that I didn't experience exercise's antidepressant effects until age 16 or older. My only regret is that I might have been able to avoid that MDE during mid-adolescence if I'd known that doing more aerobic activity starting at 14 could help buffer against the "black dog" of depression taking hold in high school.

Take-Home Message

In the paper's conclusion, Steinsbekk and colleagues sum up their findings:

"Individuals who increase their physical activity levels from middle to late adolescence are less likely to develop symptoms of depression compared to what they otherwise would. Thus, in this age period, physical activity may protect against depressive symptoms."

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Hopefully, this research on the link between physical activity and symptoms of depression between ages 6 and 18 can be a source of motivation for teens to consider using cardio as a drug-free tool for offsetting their risk of depression—especially starting around age 14.