A new long-term study from Norway has found that teenagers who increase their physical activity starting at age 14 are significantly less likely to experience symptoms of depression in the years that follow.

Published in the Journal of the American Academy of Child & Adolescent Psychiatry, the study offers a clear picture of how physical activity affects teen mental health—not just at one moment in time, but across childhood and adolescence.

“Young people who are less physically active over time have an increased risk of developing symptoms of depression,” says author, Silje Steinsbekk.

The research is part of the Trondheim Early Secure Study, a long-running project that tracks children’s mental and physical development. In this phase of the study, researchers used accelerometers to measure physical activity levels objectively, instead of relying on self-reports. Mental health was assessed through clinical interviews.

The data, of 873 participants, spans seven age points between 6 and 18 years, assessed at ages 6, 8, 10, 12, 14, 16, and 18. Researchers paid close attention to how patterns of physical activity related to later symptoms of depression.

The clearest finding: teens who became more physically active from age 14 onward showed fewer signs of depression by age 18.

However, this protective effect didn’t hold for younger adolescents. From ages 10 to 14, the relationship actually seemed to go in the opposite direction where more symptoms of depression were more likely to become less physically active, suggesting that in early adolescence, depression may lead to decreased activity, underscoring the importance of interventions that help kids stay engaged and active even when they’re younger.

The study also explored whether other factors like sports participation, body image, or confidence in physical ability affected the relationship between activity and depression. While these factors mattered somewhat, the protective power of physical activity appears to stand on its own.

Also, the study found  no differences between girls and boys.

Good parenting means making sure your kids stay active through their teen years in a world where teens are increasingly persuaded to be more sedentary by the way of technology. One good way of providing children more activity is for parents to also stay active themselves, ensuring parent-child time includes physical activity as well as setting a good example in the home of proper lifestyle choices.

S Steinsbekk et al. Symptoms of Depression, Physical Activity, and Sedentary Time: Within-Person Relations From Age 6 to 18 in a Birth Cohort. Journal of the American Academy of Child & Adolescent Psychiatry (2025). DOI: 10.1016/j.jaac.2025.03.018