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Aim To examine early adolescent physical activity and risk of later depressive symptoms at age 16 years in a prospective cohort study. Methods Participants were children and parents enrolled at birth of the child. Approximately half the children enrolled in the Auckland Birthweight Collaborative Study were small for gestational age at birth (SGA ≤10th percentile for sex and gestation) and half were appropriate for gestational age (AGA >10th percentile). Maternal demographic data were collected at birth, and children were followed through to age 16 years. Depression at 16 was assessed using the Center for Epidemiological Studies Depression Scale for Children. Accelerometer measures of physical activity and sleep were measured at 11 years of age. Results Moderate to severe depression was present in 15.6% of the 467 16-year-olds. Objectively measured physical activity and sleep at 11 years were not significantly associated with depressive symptoms at 16 years of age. Conclusion Prospectively collected objective measures of physical activity levels and sleep were not predictive of depressive symptoms later in adolescence in a healthy community cohort. While interventions to promote increased physical activity and sleep in adolescents who are depressed may be effective, physical activity and sleep in the general population of adolescents does not protect against future depression.

Aim There may be a link between disruption to the gut microbiota in early life and later neurocognitive outcomes. We hypothesised that antibiotic use in early life is associated with a detrimental effect on later neurocognitive outcomes. Methods Eight hundred and seventy-one European mothers and their children enrolled in the Auckland Birthweight Collaborative Study at birth. Information on antibiotic use during the first year of life and between 12 months and three-and-a-half years of age was gathered via maternal interview. Intelligence test scores and measures of behavioural difficulties were obtained when children were three-and-a-half years, seven years and 11 years of age. Results Antibiotic use in the first year of life was reported in 70% of the 526 children with antibiotic data assessed at age three-and-a-half years. Those who had received antibiotics had more behavioural difficulties and more symptoms of depression at follow-up. Results were consistent across all standardised psychologist administered tests, as well as parent rated, teacher rated and self-report measures. Conclusion This study demonstrates an association between antibiotic use in the first year of life and subsequent neurocognitive outcomes in childhood. If confirmed by further research, these findings could have implications for the use of antibiotics for minor illnesses in infancy.