Physical activity in childhood and adolescence and future depressive symptoms: an 11-year prospective cohort study.

BACKGROUND: Physical activity (PA) can reduce young peoples' risk of depressive symptoms. Associations between PA and depressive symptoms are often investigated over timeframes spanning minutes to weeks. Less is known about whether childhood/adolescent PA can predict depressive symptoms in early adulthood. METHODS: Using a nationally representative sample from Ireland, latent growth mixture modelling was performed to investigate the extent to which different PA trajectories existed from ages 9-17, whether gender, weight status, and socio-economic deprivation at age 9, predicted PA trajectories from ages 9-17, and whether trajectory class membership predicted depressive symptoms at age 20. RESULTS: A 4-class solution was the best fit to the data (AIC = 52 175.69; BIC = 52 302.69; ssaBIC = 52 245.49; entropy = 1.00). Classes were labelled according to their baseline PA and slope of their trajectory: 'High-Decreasers'; 'Moderate-Decreasers'; 'Moderate-Stable'; and 'Low-Increasers'. A negative linear association existed between activity trajectory and the likelihood class members were female, overweight or socioeconomically deprived at age 9. The most active class (High-Decreasers) were significantly less likely to report depressive symptoms at age 20 than other classes. CONCLUSIONS: Multiple PA trajectories exist throughout childhood and adolescence although differences in PA levels reduced over time. The most/least active children continued to be the most/least active throughout adolescence. Those most active were least at risk of depressive symptoms in early adulthood. Being female, overweight or experiencing deprivation at age 9 were all risk factors for inactivity throughout adolescence. Findings have implications for public health and PA promotion in young people.