Exploring the Impact of Outdoor Activities and Sibling Compositions on Autism Spectrum Disorder: A Causal Mediation Analysis Using the National Survey of Children's Health in the United States

Purpose Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition influenced by both environmental and familial factors. This study examined the association between ASD risk and (1) the duration of children's outdoor activities on weekdays and weekends, and (2) sibling composition, specifically the number and gender of siblings. Methods We analyzed cross-sectional data from the 2022 National Survey of Children’s Health (NSCH), including 22,294 children aged 3 to 5 years. Propensity Score Matching (PSM) was used to reduce selection bias by adjusting for covariates such as age, sex, race, anxiety, ADHD, and depression. Weighted logistic regression estimated adjusted odds ratios (wORs), and machine learning models assessed complex interaction effects. Results Outdoor activity was inversely associated with ASD. Compared to ≤ 1 hour, 2 hours of weekend activity reduced ASD odds by 43% (wOR = 0.57; 95% CI: 0.48–0.68), and ≥ 3 hours by 63% (wOR = 0.37; 95% CI: 0.31–0.44). On weekdays, 2 hours reduced odds by 49% (wOR = 0.51), and ≥ 3 hours by 58% (wOR = 0.42; 95% CI: 0.35–0.50). Having one female sibling halved ASD odds (wOR = 0.50), while male siblings increased risk (one: wOR = 2.25; two or more: wOR = 1.87). Machine learning identified highest ASD likelihood among children with no female siblings and limited outdoor activity, and lowest among those with female siblings and ≥ 3 weekend hours outdoors. Conclusion Extended outdoor activity and the presence of female siblings are associated with reduced ASD risk and may inform early prevention efforts.