Abstract
<title>Abstract</title> <p>The "outdoor activity hypothesis" suggests a protective effect of outdoor time against myopia, primarily evidenced in children and implied for adolescents. However, the associations of different physical activity types and intensities with myopia in adult populations remain unclear. This cross-sectional study examines the association between physical activity and myopia in U.S. adults (≥ 12 years), challenging the pediatric "outdoor activity hypothesis." Using NHANES data (1999–2008, n = 8,947), myopia was defined as spherical equivalent ≤-1.0 D. Activities were self-reported and analyzed via survey-weighted logistic regression, adjusting for demographics, socioeconomic status, and health factors. Contrary to pediatric evidence, outdoor activities (OR = 1.18, 95% CI: 1.03–1.37) and high-intensity activities (OR = 1.17, 95% CI: 1.00–1.36) were linked to a modestly increased myopia risk, while moderate-intensity showed no association (OR = 1.03, p = 0.634). Subgroup analyses revealed distinct patterns: outdoor activity risk was significant only in middle-aged adults (40–59 years: OR = 1.32), and high-intensity risk in older adults (≥ 60 years: OR = 1.50). Notably, no associations were observed in youth (< 20 years). These findings suggest the activity-myopia relationship differs by age and intensity. The observed positive associations in adults can be attributed to behavioral confounding (e.g., the correlation between high activity levels, educational attainment, and near-work) or limitations in exposure measurement (binary self-report). Unlike children, where outdoor time is protective, adult activity patterns appear unrelated to myopia prevention. Longitudinal studies with detailed activity assessments are needed to clarify causality and lifespan differences.</p>