Common health conditions in childhood and adolescence, school absence, and educational attainment: Mendelian randomization study
Authors: Hughes Amanda , Wade Kaitlin H , Rice Frances , Dickson Matt , Davies Alisha , Davies Neil M , Howe Laura D 
Published: November 2019

ABSTRACTObjectivesTo assess the causal relationship of different health conditions in childhood and adolescence with educational attainment and school absence.DesignLongitudinal observational study and Mendelian randomization (MR) analyses.SettingAvon Longitudinal Study of Parents and Children (ALSPAC), a population sample of children from South-West England born in 1991-1992.Participants6113 unrelated children with available GCSE records and genetic data (50% female).ExposuresSix common health conditions with known genetic markers measured at age 10 (primary school) and 13 (mid-secondary school). These were: symptoms of Attention-Deficit Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD), depression, asthma, migraines and BMI. Genetic liability for these conditions and BMI was indexed by polygenic scores.Main outcome measuresEducational attainment at age 16 (total GCSE and equivalents points score), school absence at age 14-16.ResultsIn multivariate-adjusted observational models, all health conditions except asthma and migraines were associated with poorer educational attainment and greater school absence. Substantial mediation by school absence was seen for BMI (e.g. 35.6% for BMI at 13) and migraines (67% at age 10), with more modest mediation for behavioural and neurodevelopmental measures of health. In genetic models, a unit increase in genetically instrumented BMI z-score at age 10 predicted a 0.19 S.D. decrease (95% CI: −0.28 to −0.11) in attainment at 16, equivalent to around a 1/3 grade difference in each subject. It also predicted 8.6% more school absence (95% CI:1.3%, 16.5%). Similar associations were seen for BMI at age 13. Consistent with previous work, genetic liability for ADHD predicted lower educational attainment, but did not clearly increase school absence.ConclusionsTriangulation across multiple approaches supported a causal, negative influence of higher BMI on educational attainment and school absence. Further research is required to understand the mechanisms linking higher BMI with school absence and attainment.What is already known on this topicOn average, children with common health conditions have worse educational attainmentIt is unclear whether all health-attainment and health-absenteeism associations are causal, or reflect confounding by social and economic circumstancesWe do not know how much health-related school absenteeism contributes to these associationsWhat this study addsResults support a negative influence of high BMI in secondary school on educational attainment (GCSEs) and absenteeismAbsenteeism substantially mediated BMI-GCSE associations, suggesting a target for interventionThere was less evidence for causal effects of Autism Spectrum Disorder, depressive symptoms, asthma or migraines on attainment and absenteeismContribution of absenteeism to ADHD-GCSE associations was modest, suggesting interventions should target other mechanisms