A long-running Australian study has found that higher cardiorespiratory fitness in childhood is linked to a lower risk of developing clinical depression decades later, with the association appearing stronger in women. The research tracked more than 1,000 Australians over roughly 32 years, from a 1985 national fitness survey to adulthood in the mid-to-late 2010s, and analysed whether childhood endurance and muscle performance predict depression in later life.
Depression remains a major public health challenge. While physical activity is widely promoted for well-being, scientists have sought to understand how fitness itself, as an objective measure of the body’s capacity, relates to mental health across the lifespan. This study distinguishes fitness from mere activity, examining how the body’s ability to sustain work relates to later depression risk.
The investigation draws on data from the Childhood Determinants of Adult Health (CDAH) Study, led by researchers at the Menzies Institute for Medical Research and the University of Tasmania. The team analysed the 1985 Australian Schools Health and Fitness Survey, which tested 8,498 schoolchildren aged 7 to 15. A subset was followed into adulthood, with up to 1,080 participants (519 men and 561 women) attending follow-up clinics between 2014 and 2019, aged 36 to 49, and completing a clinical mental health interview.
Childhood fitness testing included a timed 1.6-kilometre run or walk to gauge cardiorespiratory fitness, converted to average running speed. A smaller subset completed a submaximal cycling test. The study also measured muscular power via standing long jump and muscular strength via handgrip tests, with adjustments made to account for lean body mass. In adulthood, depression was diagnosed using a standard WHO interview reflecting major depressive disorder and dysthymia, applying criteria from the DSM-4.
Over the follow-up, 190 of the 1,080 participants developed depression, about 17.6 per cent, including 117 women and 73 men. The researchers used survival analyses to see how a one-standard-deviation increase in childhood fitness related to depression risk, controlling for early life factors such as age, sex, BMI, and neighbourhood socioeconomic status, and accounting for dropout with statistical weights.
For the overall sample, a one-standard-deviation increase in childhood 1.6-kilometre running speed was linked with a 15 per cent lower rate of developing depression in adulthood. That reduction remained at 15 per cent after adjusting for standing long jump performance, neighbourhood SES, and childhood BMI, though it lost statistical significance in full models.
When the data were examined by sex, the association was more pronounced among women. A one-standard-deviation rise in childhood running speed was associated with a 19 per cent lower rate of depression in women, and a 28 per cent lower rate with cycling fitness in age-adjusted analyses. After full adjustment, these estimates remained similar in size but were not statistically significant; among men, the corresponding reductions were smaller (about 10 per cent for running speed and 6 per cent for cycling) and did not reach significance.
Experts emphasised that while the patterns were intriguing, they should not be read as proof of causation. “One of the major strengths of this study is the long follow-up period,” said Fraser, a postdoctoral research fellow at the Menzies Institute and Adelaide University affiliate. “Few studies have objectively measured fitness in childhood and then assessed depression more than 30 years later.”
Fraser added: “We know that being physically active is good for mental health, and previous research has shown that fitter adults are less likely to develop depression. However, much less is known about whether fitness during childhood and adolescence is related to depression decades later.”
External expert Mohsen Joshanloo, a psychology professor at Keimyung University in South Korea who was not involved in the study, termed the finding as extending prior work: “Higher cardiorespiratory fitness in childhood and adolescence was associated with a lower risk of depression in adulthood. This pattern was clearest for fitness measured by 1.6-km run speed.”
Fraser cautioned that the study cannot determine why these associations occur, noting that “the biggest misconception would be to conclude that fitness prevents depression or that low fitness causes depression.” She stressed that the research is observational and that fitness is only one contributing factor among biological, psychological, and social influences on mental health, with other aspects of physical fitness delivering broad health benefits.
The researchers point to several possible biological pathways, including the release of endorphins and brain-derived neurotrophic factor during aerobic exercise, alongside reduced inflammation and regulated cortisol. They also suggest psychosocial pathways—such as improved self-esteem, body image, and social support networks—could share responsibility for the observed patterns, even after adjusting for reported exercise levels in 1985.
Limitations include substantial attrition over the decades and the smaller sample for the cycling and handgrip tests, which reduces the power of those particular analyses. Adult onset of depression relied on recall over many years, which can introduce memory errors, and the study design cannot establish causality.
Fraser urged caution, stating: “Further research is needed to determine whether the observed associations between childhood and adolescent fitness and later depression are causal and to better understand the biological, psychological, and social mechanisms that may underpin these relationships.”
Joshanloo echoed the call for further work, saying: “Future studies using different research designs could help determine whether improving fitness in childhood can reduce the risk of depression later in life and, if so, why.”
The study’s authors include Kylie J. Smith, Costan G. Magnussen, Cristina Cadenas-Sanchez, Grant R. Tomkinson, Leigh Blizzard, Kristy Sanderson, Terence Dwyer, Alison J. Venn, and Brooklyn J. Fraser.
