Potential social-environmental factors affecting ADHD symptoms of 55,528 children from Longhua district, Shenzhen, China

Abstract

Objective: Attention-deficit/hyperactivity disorder (ADHD) is one of the most prevalent neurodevelopmental disorders in childhood, frequently persisting into adolescence and adulthood. It is associated with a wide range of comorbid psychiatric and behavioral conditions. While emerging evidence suggests that social and environmental factors may influence the development and expression of ADHD symptoms, large-scale studies incorporating longitudinal data on early-life environmental exposures remain limited. Given the cross-sectional design of this study, we aimed to investigate the frequency and duration of outdoor activities among preschool children during infancy (0–1 years) and toddlerhood (1–3 years), and to examine their associations with ADHD symptoms. Methods: A retrospective observational study was conducted using data collected from parents of children enrolled in 250 kindergartens across Longhua District, Shenzhen, China. A total of 59,600 questionnaires were distributed, assessing sociodemographic characteristics, outdoor activities frequency and duration. ADHD symptoms were evaluated using the hyperactivity/inattention subscale of the Strengths and Difficulties Questionnaire (SDQ). Results: A total of 55,528 valid questionnaires were included in the final analysis. The overall prevalence of ADHD symptoms was 6.9%. Boys exhibited significantly higher ADHD symptom scores compared to girls (3.76 ± 1.96 vs. 3.42 ± 1.87, P < 0.001). Children from households with lower monthly income demonstrated higher ADHD symptom scores than those from higher-income families (F = 261.478, P < 0.001). There was a significant association between higher frequency and duration of outdoor activities and lower ADHD symptoms scores (P < 0.001). Conclusion: Increased frequency and duration of outdoor activities during early childhood were associated with reduced ADHD symptoms in children. These findings suggest a potential association between early exposure to outdoor activities and lower levels of ADHD symptoms, particularly in densely populated urban areas where access to green spaces is limited. However, additional research is needed to explore the underlying mechanisms and long-term associations of early childhood outdoor activities with ADHD symptoms and other developmental outcomes.