Physical activity’s protective effect on depression is more evident in girls

A long-term study of Canadian adolescents suggests that being physically active may help protect against future symptoms of depression, but not anxiety. The research, which tracked teenagers over several years, also found that this protective effect was most apparent in older adolescence and appeared stronger for girls. Published in Research on Child and Adolescent Psychopathology, the study adds nuance to our understanding of how lifestyle habits relate to mental health during a formative period of development.

Depression and anxiety are among the most common mental health challenges facing teenagers. These conditions can affect everything from school performance to social relationships, and they often persist into adulthood if not addressed. While physical activity is widely recommended as a tool to support mental well-being, the precise nature of this relationship has remained unclear. It has been difficult to determine if exercise reduces depressive symptoms, if feeling depressed leads to less exercise, or if both are happening simultaneously.

Additionally, other modern lifestyle factors complicate the picture. Adolescents today spend a significant amount of time on screens and often get less sleep than recommended. These behaviors compete with physical activity for a limited number of hours in the day.

To gain a clearer view, a research team from the School of Psychoeducation at the Université de Montréal sought to untangle these interconnected variables. They wanted to see how physical activity and mental health symptoms influenced each other over time, while also accounting for the roles of screen time and sleep duration.

The study drew upon data from the Québec Longitudinal Study of Child Development, a large project that has followed a cohort of children born in the late 1990s. The researchers focused on data collected from over 1,500 adolescents when they were 13, 15, and 17 years old. At each of these ages, the participants answered questionnaires about their mental health, lifestyle habits, and other personal factors.

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Participants reported on their symptoms of depression and anxiety over the previous months. They also provided information on their leisure-time physical activity, including how often they exercised, for how long, and at what intensity. Other questions gauged their average weekly screen time from television, video games, and computers, as well as their typical sleep duration.

The researchers used a sophisticated statistical method to analyze these connections over time, allowing them to see how a behavior at one age predicted an outcome at a later age, for both boys and girls separately. The analysis also controlled for other potentially influential factors, such as family income, body mass index, and family functioning.

The results showed a one-way relationship between physical activity and depression. Being more physically active at age 15 was associated with having fewer depressive symptoms at age 17. This finding suggests a protective effect of exercise during later adolescence. While the pattern was observed in both sexes, the connection was statistically significant only for girls.

Conversely, the analysis did not show that having more depressive symptoms led to a decrease in physical activity later on. This finding challenges the idea of a simple two-way street where depression and inactivity reinforce each other over time. Instead, the influence appeared to flow primarily from physical activity to a reduction in depressive symptoms.

When it came to anxiety, the results were different. The researchers found no significant predictive links between physical activity and symptoms of anxiety in either direction. An adolescent’s level of physical activity at one age did not predict their level of anxiety symptoms two years later, and vice versa. This highlights the importance of studying depression and anxiety as distinct conditions, as they may respond differently to lifestyle factors.

The study also investigated whether screen time or sleep could explain the connection between physical activity and depression. The hypothesis was that perhaps exercise helps by displacing screen time or by improving sleep, which in turn reduces depression. However, the analysis did not support this idea. The beneficial association of physical activity on later depressive symptoms seemed to be direct and was not accounted for by changes in screen or sleep habits.

The investigation did reveal other interesting patterns among lifestyle habits. For girls, higher physical activity at age 13 predicted less screen time at age 15. For boys, more screen time at age 15 was linked to shorter sleep duration at age 17. These results point to sex-specific ways in which different behaviors may influence one another during the teenage years.

The researchers note some limitations to their work. The data comes from a group that is primarily White and of a higher socioeconomic status than the general population, so the findings may not apply to all adolescents. All information was based on self-reports, which can be subject to memory errors or social desirability bias. The data was also collected before the COVID-19 pandemic, which has since had a significant impact on adolescent mental health and lifestyle patterns.

Future research could build on these findings by using objective measures, such as accelerometers to track physical activity, and by studying more diverse groups of young people. Such work would help confirm the results and further clarify the complex interplay between daily habits and mental well-being. The study’s findings suggest that promoting physical activity, particularly in older adolescents, may be an effective public health strategy for preventing depressive symptoms.

The study, “Transactional Associations Between Physical Activity and Depressive and Anxious Symptoms in Adolescent Girls and Boys: Considering Screen Time and Sleep Duration,” was authored by Laurianne Fortier, Natalie Castellanos-Ryan, Sophie Chaput-Langlois, and Gabrielle Yale-Soulière.