Longitudinal Associations Between ADHD and Weight From Birth to Adolescence

Objective: Attention-deficit/hyperactivity disorder (ADHD) is associated with lower birth weight, but also with obesity in childhood. Findings on the direction of this association are mixed. This study investigated the relationship between weight and ADHD from birth across development. Method: We used data from the Millennium Cohort Study (MCS), collected at 7 time points between age 9 months and 17 years. ADHD diagnosis status and scores on the Strength and Difficulties Questionnaire (SDQ) were used to create an ADHD group and a control group. Random intercept cross-lagged panel models were conducted in female individuals (n = 4,051) and male individuals (n = 3,857) to examine bidirectional associations between body mass index (BMI) z scores and SDQ scores between ages 3 and 17 years. Analyses were adjusted for common risk factors for ADHD and obesity, such as sex assigned at birth, multiple births, and ADHD medication status. Results: Children in the ADHD group were significantly lighter in weight at birth than the control group (t[5674] = 2.65, 95% CI = 0.02, 0.14, p = .008) and were significantly more likely to have obesity at age 5 years onward (odds ratio range = 1.57-2.46, relative risk range 0.98-2.29). Path analyses conducted separately for male and female individuals showed that higher ADHD symptoms in female individuals at ages 7, 11, and 14 years significantly predicted higher BMI z scores at ages 11, 14, and 17 years, respectively. In male individuals, this association was seen only between ages 11 and 14 years (β = 0.07; 95% CI = 0.04-0.10, p < .001). Conclusion: Results suggest that interventions for children with ADHD, and their parents, should begin as soon as possible, ideally prenatally. Developmental sex differences should be considered.