Australian children with better cardiorespiratory fitness in 1985 had a lower risk of depression three decades later, with the strongest link among girls.

Keep the kids moving. It is advice parents hear from pediatricians, teachers and public health campaigns alike, usually framed around heart health and healthy weight. A study that followed Australian children for more than three decades suggests the payoff may extend to mental health in adulthood.

The research, published in the Journal of Affective Disorders and led by the Menzies Institute for Medical Research at the University of Tasmania with researchers at Adelaide University, found that children and teenagers with better cardiorespiratory fitness had a lower risk of developing depression as adults.

“We already know that being physically active is good for our mental health,” said Professor Grant Tomkinson of Adelaide University’s School of Allied Health and Human Performance. “Previous research has shown that fitter adults are less likely to develop depression. But we know relatively little about whether being fit early in life is linked to better mental health decades later.”

A 1985 fitness test, revisited

The study drew on the Childhood Determinants of Adult Health (CDAH) study, which grew out of a national survey of Australian schoolchildren in 1985. That year, children aged 7 to 15 had their fitness measured. Cardiorespiratory fitness was assessed with a 1.6-kilometre run and muscular power with a standing long jump; a smaller group also completed cycling and handgrip strength tests.

The 1985 survey was one of the largest national studies of children’s health and fitness ever carried out in Australia, involving thousands of schoolchildren across the country. Its participants have since been traced and re-examined as adults, creating a rare dataset that links measurements taken in childhood with health outcomes decades later.

The 1.6-kilometre run is a simple field test, but it is a well-established indicator of aerobic fitness, reflecting how efficiently the heart, lungs and muscles deliver and use oxygen during sustained effort.

More than three decades later, when the participants were 36 to 49 years old, more than 1,000 of them completed a World Health Organization diagnostic interview to determine whether they had ever experienced depression.

“The data collected over 30 years has given us a rare opportunity to examine how early-life fitness relates to mental health later in life,” said Dr Brooklyn Fraser of the Menzies Institute.

Huff and puff

The clearest signal came from aerobic fitness. “We found that children and adolescents with better cardiorespiratory fitness had a lower risk of developing depression as adults,” Fraser said. “The strongest and most consistent associations in our study were observed for cardiorespiratory fitness, or fitness developed through activities that make you huff and puff.”

Links with muscular strength were weaker and less consistent, and muscle power, as measured by the long jump, showed no clear association. The relationship between aerobic fitness and later depression appeared stronger among girls than boys.

That sex difference is notable. Depression is about 1.5 times more common among women than men, according to the World Health Organization. If childhood fitness offers some protection, the girls who stand to benefit most may also be those at greater risk.

Why fitness might matter

The study cannot say why fitter children went on to have lower rates of depression, and the release does not report effect sizes. But researchers have proposed several plausible pathways. Aerobic exercise boosts levels of brain-derived neurotrophic factor, a protein that supports the growth and survival of neurons, and reduces inflammation, which has been linked to depression. Fit children may also carry active habits into adulthood, sleep better, or benefit from the social connection and confidence that sports and play can bring.

There is also growing evidence that exercise can treat depression, not just prevent it. A large 2024 analysis of randomized trials published in The BMJ found that exercise, including walking, jogging, yoga and strength training, reduced depressive symptoms, with more vigorous activity tending to produce larger effects. The new study extends that picture back into childhood, suggesting that fitness built early may echo across a lifetime.

It is also possible that something else drives both fitness and mental health. Children from more stable, better-resourced homes may have more opportunities to be active and also face fewer of the stresses that raise depression risk.

Lead author Dr Kylie Smith of the Menzies Institute was careful about the limits. “There are many contributing factors to depression, meaning no single factor explains risk on its own,” she said. “Fitness may be one piece of the puzzle. 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.”

Something we can change

The authors call for more research into the pathways linking childhood fitness and adult mental health. The study relied on a single fitness measurement in childhood and on participants’ recollection of whether they had ever been depressed, which may not capture every episode.

The World Health Organization recommends that children and adolescents get an average of at least 60 minutes of moderate-to-vigorous physical activity each day, much of it aerobic. Most young people worldwide fall short of that target.

Yet the findings arrive as children worldwide are, on average, less aerobically fit than previous generations, a decline researchers including Tomkinson have documented for decades. For Tomkinson, that is exactly why the result matters. “Importantly, fitness is something we can change,” he said. “It may be an important target for improving long-term mental health.”

---

Notes

1. Smith, K., et al. “The long run: Fitness during childhood and adolescence and its association with adult depression.” Journal of Affective Disorders, 1 December 2026. DOI: 10.1016/j.jad.2026.122372.
2. Adelaide University. “Fit for life: childhood fitness linked to lower risk of adult depression.” EurekAlert!, 30 September 2026. https://www.eurekalert.org/news-releases/1146176.