Cardiorespiratory fitness (CRF) strongly influences health, but very little is known about the childhood determinants of adult CRF. Our longitudinal study investigated whether childhood psychopathology and socioeconomic status (SES) were related to adult CRF in 1647 Finnish male military conscripts.

Childhood psychopathology was assessed at the age of eight using the Rutter and Children's Depression Inventory questionnaires. Parental education and family structure were used to assess childhood SES. In late adolescence, depressive symptoms were assessed with the Beck Depression Inventory and smoking with a questionnaire. CRF in early adulthood was examined with the Cooper's 12-minute run test.

General linear models showed that low parental education (p=0.001), depressive symptoms in childhood (p=0.035) and late adolescence, smoking, underweight, and overweight/obesity (all p<0.001) independently predicted lower CRF. The interaction between depressive symptoms in childhood and adolescence was significant (p=0.003). In adolescents with depressive symptoms, childhood depressive symptoms (p=0.001) and overweight/obesity (p<0.001) predicted lower CRF. In adolescents without depressive symptoms, conduct problems in childhood predicted lower CRF in the initial models, but the effect disappeared after taking into account smoking and body mass index. Mediational analysis confirmed these results.

We lacked data on physical activity and only studied males at three time-points.

Recurrent depression in childhood and adolescence and low SES in childhood predict lower adult CRF. Conduct problems in childhood predict lower CRF, but the effect is mediated by overweight/obesity and smoking. Psychiatric treatment for children and adolescents should promote physical activity, particularly for children with low SES.