The long run: Fitness during childhood and adolescence and its association with adult depression.

BACKGROUND: Lower physical fitness is cross-sectionally and longitudinally associated with depression among adolescents and adults. Whether childhood fitness predicts adult depression remains unknown. We examined associations between childhood and adolescent cardiorespiratory fitness (CRF) and muscular fitness and adult depression. METHODS: In 1985, a representative sample of Australian children and adolescents (7-15 years) completed CRF (1.6 km run speed) and muscular power (standing long jump) tests. A sub-sample (9, 12, 15 years) underwent muscular strength (average handgrip strength) and submaximal CRF (physical work capacity at 170 beats per minute estimated from a submaximal cycle ergometer test) tests. Participants were followed-up in mid-adulthood (36-49 years) in the Childhood Determinants of Adult Health study, where lifetime DSM-IV depression/dysthymia was retrospectively diagnosed using the WHO Composite International Diagnostic Interview. For each fitness measure (1.6 km run/standing long jump: n = 1062; handgrip strength/PWC170: n = 437), Cox proportional hazards regression estimated hazards of depression. RESULTS: During follow-up (mean = 32.5 years), 117 females and 73 males experienced depression. Greater childhood and adolescent CRF (1.6 km run speed) was associated with reduced hazard of adult depression (hazard ratio (HR) [95% CI]: females, 0.80 [0.65, 0.99]; males, 0.89 [0.67, 1.19]). Muscular fitness showed weaker non-significant associations. CONCLUSION: Greater childhood and adolescent CRF was linked with reduced adult depression risk, with stronger associations for females than males. Muscular strength showed weaker, later-emerging associations. 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 underlying mechanisms.