Impact of physical activity on the incidence of psychiatric conditions during childhood: a longitudinal Swedish birth cohort study.

BACKGROUND Emerging evidence supports the importance of physical activity (PA) and behaviours that build resilience to prevent childhood psychiatric disorders. OBJECTIVE To investigate associations between parent-reported PA, time spent outdoors and participation in organised sports and later incidence of psychiatric conditions in children. METHODS A birth cohort of 17 055 Swedish children was followed up until age 18 years. Data on parent-reported PA, time outdoors and participation in organised sports were collected for children at ages 5, 8 and 11. Diagnoses of psychiatric conditions were obtained from a national registry. Longitudinal interactions were analysed with two-way analysis of variance, and hazard ratios for incidence until 18 years were calculated with Cox proportional hazard models, adjusting for mothers' education and use of psychotropics, children's adverse life events and sex. RESULTS PA declined from 4.2 to 2.5 hours per day between 5 and 11 years of age. PA at 11 years was negatively associated with the incidence of any psychiatric conditions among all participants (HR=0.88, 95% CI 0.79 to 0.98) until 18 years. PA at 11 years showed a trend for reducing depression among girls (HR=0.82, 95% CI 0.67 to 1.00) and boys (HR=0.71, 95% CI 0.47 to 1.06) and protected against anxiety (HR=0.61, 95% CI 0.42 to 0.90) and addiction (HR=0.65, 95% CI 0.45 to 0.95) for boys, but not for girls (anxiety: HR=0.96, 95% CI 0.81 to 1.13, addiction: HR=1.04, 95% CI 0.68 to 1.58). Time outdoors showed no protective associations, while participation in organised sports showed significant protective effects on anxiety and addiction for both boys and girls, and on depression for boys. CONCLUSIONS This study provides evidence that PA and participation in organised sports may have sex-specific protective effects against several childhood psychiatric conditions.