Overweight, Obesity and Risk of Adult Attention-deficit/Hyperactivity Disorder: A Nationwide Cohort Study in Korea

Objective: Overweight and obesity are frequently comorbid with attention-deficit/hyperactivity disorder (ADHD), particularly in adults.However, limited evidence exists on whether they function as antecedent risk factors for adult ADHD.Clarifying this temporal relationship may improve understanding of shared mechanisms linking metabolic dysfunction and ADHD.Methods: This nationwide retrospective cohort study used data from the Korean National Health Screening Program linked to the National Health Insurance Service database.Adults aged 20-39 years who underwent health screening between 2009 and 2012 were followed through 2023.Individuals with prior ADHD or missing baseline data were excluded.Body mass index (BMI) was categorized using Korean obesity criteria.Incident ADHD was defined as an as International Classification of Diseases, 10th Revision diagnosis (F90.0)occurring at age 18 years or older.Cox proportional hazards models estimated hazard ratios (HRs) with adjustment for demographic, lifestyle, and metabolic factors.Results: Among 6,535,197 participants, higher BMI was associated with increased ADHD risk, with a dose-response relationship across BMI categories: overweight (23.0-24.9kg/m 2 ; HR 1.039, 95% confidence intervals [CIs] 1.002-1.077),class 1 obesity (25.0-29.9kg/m 2 ; HR 1.079, 95% CI 1.041-1.119),and class 2 or higher obesity (≥ 30.0 kg/m 2 ; HR 1.162, 95% CI 1.087-1.242),whereas underweight (＜ 18.5 kg/m 2 ; HR 0.939, 95% CI 0.898-0.982)was associated with reduced risk.Associations were more pronounced in male and those with metabolic comorbidities.Conclusion: Overweight and obesity were associated with an increased risk of adult ADHD.Although causal inference is limited, these findings suggest a potential link between metabolic dysfunction and ADHD, warranting further investigation.