Environmental influences in the global incidence of attention deficit/hyperactivity disorder and autism spectrum disorder: A longitudinal analysis of historical trends (2010-2021) across 204 countries

Introduction: The global incidence of Attention-Deficit/Hyperactivity Disorder (ADHD) and Autism Spectrum Disorder (ASD) may be shaped by social and environmental factors. Methods: Historical incidence trends from 204 countries were retrieved from the Global Burden of Disease initiative. Pearson’s correlation (for the incidence of ADHD/ASD in 2021) and multivariable regression analyses (for the rate of change in ADHD/ASD incidence between 2010 and 2021) were conducted, adjusting for key socio-economic factors (i.e. purchasing power parity, life expectancy). Results: The incidence of ADHD in 2021 was negatively correlated with indices of urbanization and industrialization (maximum r 0.359, p <0.001). whereas, the incidence of ASD showed a positive correlation with indicators of suboptimal healthcare delivery (maximum r 0.425, p <0.001). A slower increase in ADHD incidence was associated with reductions in neonaral infections (β 0.010, p 0.007), while improvements in sanitation (β 0.041, p 0.011) were associated with a faster rise in incidence for ASD. Discussion: These findings suggest that macro-level factors such as urbanization, healthcare infrastructure, and sanitation may play a role in shaping global trends in neurodevelopmental disorders. Understanding these associations may inform public health strategies aimed at early identification and support for affected populations.