For decades, exercise has been touted as a cornerstone of mental wellbeing. But a new study suggests that the fitness levels we build in our teenage years could cast a long shadow over our psychological health, potentially shielding us from depression decades later.
Researchers in Australia tracked more than 1,000 participants from a nationwide cohort first surveyed in 1985, following them for over three decades. Using diagnostic interviews, they mapped mental health outcomes and correlated them with physical fitness measurements taken during childhood and adolescence.
The study, published in the Journal of Affective Disorders, assessed cardiorespiratory fitness through a 1.6-kilometre run and muscular power via a standing long jump. A smaller subset also underwent cycling and handgrip strength tests. The results were striking: teenagers who ran faster—indicating superior cardiovascular fitness—had a 15% lower relative risk of developing depression later in life.
The average run time was about 8 minutes and 27 seconds. Running roughly 1 minute and 15 seconds faster than that average was associated with the reduced depression risk. The protective benefit was most pronounced five to ten years after the initial tests, when participants were closest to their childhood, and gradually waned over time. Yet the association persisted across the full 34-year follow-up period.
Why fitness might matter for mental health
While the exact mechanisms remain unclear, researchers suggest that better cardiovascular fitness could influence brain function, stress response, and inflammation—all of which are implicated in depression. The findings add to a growing body of evidence that physical health and mental health are deeply intertwined.
“While we cannot say a lack of fitness during childhood causes depression in adults, the findings suggest that childhood fitness may have benefits beyond physical health,” said Kyle Smith, the study’s lead author. “There are many contributing factors to depression, meaning no single factor explains risk on its own. Fitness may be one piece of the puzzle.”
Interestingly, the protective effect was consistently stronger in females than in males across all cardiorespiratory fitness measures. This is particularly relevant given that women are more likely to experience depression during their lifetimes. The reasons for this gender difference are not yet fully understood, but it underscores the potential value of targeted physical activity programmes for girls and young women.
A growing mental health crisis
The study arrives as mental health conditions have nearly doubled globally over the past three decades, driven largely by sharp rises in anxiety and depression. An estimated 322 million adults—one in 20 people worldwide—currently live with depression. In Europe, the burden is equally significant, with countries like Spain facing a shortage of psychologists and long waiting times for treatment.
As rates continue to climb, researchers are increasingly focusing on modifiable lifestyle factors that could help prevent or delay the onset of depression. “Importantly, fitness is something we can change; it may be an important target for improving long-term mental health,” said Grant Tomkinson, a researcher at Adelaide University.
The findings have implications beyond Australia. In Europe, where physical education curricula vary widely across the 27 member states, the study adds weight to arguments for prioritising cardiorespiratory fitness in schools. Countries like Finland and the Netherlands already lead in youth fitness, while others struggle with rising sedentary behaviour among adolescents.
While the study is observational and cannot prove causation, it offers a compelling case for investing in youth fitness as a public health strategy. As Tomkinson put it, “Fitness may be one piece of the puzzle”—but it is a piece that societies can actively shape.
