Testing the role of relative age within school year on mental health in children with neurodevelopmental vulnerability

Abstract

It is important to understand the risk factors that lead some young people to develop mental health problems. The effects of potentially modifiable causal risk factors such as relative age in the school year, and their relationship with other known factors such as neurodevelopmental disorders on mental health problems throughout development were relatively unexplored epidemiologically. First, associations were examined between relative age and risk of mental health problems in childhood, adolescence, and young adulthood, in a longitudinal population cohort (ALSPAC), using general and specific measurements of mental health and depression. Young relative age was associated with poorer parent-rated general mental health in the school years (measurements taken between 7-16 years) but not before (age 4) or after (age 25). Relative age was not associated with symptoms of depression. Second, to investigate whether those with neurodevelopmental difficulties are particularly affected by relative age effects, the design was extended to test parentrated ADHD traits before school entry, and genetic risk of ADHD as moderators of associations between relative age and mental health. Relative age and ADHD risk contributed towards mental health problem risk, but there was no evidence of interactions between relative age and ADHD risk on mental health problems. Third, associations between relative age and adult (16-25 years) mental health disorder diagnoses and other related adverse clinical outcomes were investigated in cases (individuals with ADHD/ASD diagnosed in childhood) and in controls using data from a whole population electronic healthcare records cohort (SAIL databank). Relative age showed associations with outcomes in controls, but less so for cases, and there was no evidence of interactions between relative age and neurodevelopmental disorders. Relative age was associated with ADHD diagnosis. The thesis considers the implications of these findings for policy and practice, and highlights directions for future research