ADHD and physical health: comorbidity and risk factors

Abstract

Research has shown that ADHD is associated with several different physical health conditions, spanning a range of physiological mechanisms. The relationship between ADHD and physical health is complex and research is often cross-sectional or overlooks the impact of many environmental factors associated with ADHD. As ADHD is highly heritable, understanding these associations whilst considering genetic and environmental influences is crucial. The papers in this thesis utilised Millennium Cohort Study data to explore longitudinal and cumulative relationships between ADHD and physical health conditions in childhood. Paper 1 (Chapter 2) examined associations between cumulative numbers of similar physical conditions across childhood and ADHD symptoms in adolescence, adjusting for cumulative environmental risk. Cumulative sensory and neurological, but not atopic, conditions were significantly associated with ADHD symptoms. Cumulative cardiometabolic conditions were largely driven by higher obesity prevalence in the sample. This cluster of conditions was not associated with ADHD symptoms once environmental risk was adjusted for. Building on these findings, Paper 2 (Chapter 3) explored how the relationship between ADHD and weight changes throughout childhood from birth to adolescence. Cohort members with an ADHD diagnosis/high symptoms were typically lighter at birth, then more likely to have obesity from age 5. Path analyses, adjusted for environmental risk, showed that ADHD symptoms at ages 7-14 predicted BMI at the subsequent time point (age 11-17). In males, this association appeared only in early adolescence. Both Papers 1 and 2 found significant results after adjusting for environmental risk indicating a role of genetic liability. Paper 3 (Chapter 4) found associations between ADHD polygenic scores and obesity, epilepsy and asthma. Polygenic scores were also associated with earlier onset of epilepsy and asthma and with BMI from age five. Genetic nurture effects were explored by analysing the relationship between noninherited parental genetic liability and children’s physical health outcomes, but no significant associations were found. Together, the findings presented in this thesis highlight the complex relationship between ADHD and physical health and demonstrate the interplay of numerous genetic and environmental influences across development.

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Identifiers

ORCID for Claire Louise Reed: orcid.org/0000-0003-1385-4729

ORCID for Valerie Brandt: orcid.org/0000-0002-3208-2659

ORCID for Dennis Golm: orcid.org/0000-0002-2950-7935

ORCID for Samuele Cortese: orcid.org/0000-0001-5877-8075

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