Meta-analysis links outdoor activity to lower myopia risk in Chinese pediatric patients

A systematic review and meta-analysis found that increased outdoor activity is associated with a lower risk of myopia among Chinese children and adolescents, based on data from 31 studies involving 380,215 participants. The analysis was led by Jin Dai of the College of Physical Education, Hunan Normal University in Changsha, China.

The analysis, conducted in accordance with PRISMA guidelines, included studies identified through Web of Science, PubMed, CNKI, and Wanfang databases through October 2025. Researchers used a random-effects model to pool odds ratios and conducted subgroup and sensitivity analyses to assess exposure thresholds, study design, and geographic latitude.

Across the included studies, greater outdoor activity was consistently associated with reduced myopia risk (pooled OR = 0.75; 95% CI = 0.71–0.80), although heterogeneity was high (I² = 94%). Compared with less than 1 hour of outdoor activity per day, exposure of 1–2 hours (OR = 0.85; 95% CI = 0.79–0.92), 2–3 hours (OR = 0.86; 95% CI = 0.78–0.95), and more than three hours (OR = 0.74; 95% CI = 0.63–0.87) were all associated with lower risk. When dichotomized at 2 hours, more than 2 hours of daily outdoor exposure was associated with reduced risk (OR = 0.74; 95% CI = 0.69–0.80).

“Promoting regular outdoor activity – on the order of approximately 2 hours per day – represents a reasonable, evidence-supported public-health target derived from heterogeneous observational and interventional data,” the study authors stated. “This exposure range should be interpreted as an approximate and pragmatic benchmark rather than a rigid or universal optimum. Future longitudinal and experimental studies with standardised exposure assessment and age-specific analyses will be essential to refine exposure thresholds, clarify effect modification, and strengthen causal inference. Coordinated efforts by educators, parents, and policymakers remain critical to embedding outdoor exposure into children’s daily routines through curriculum design, recess scheduling, and school-based health initiatives.”

Findings were consistent across cross-sectional, cohort, and randomized study designs, as well as across geographic latitude strata, although the magnitude of association varied. The overall risk of bias among included studies was rated as moderate, with common limitations including reliance on self-reported outdoor activity and incomplete adjustment for confounders.

The study also examined exposure-response relationships, finding that protective associations became more consistent at approximately 2 hours of daily outdoor activity, with limited additional benefit observed at higher durations. Differences between exposure categories were not statistically significant.

The authors noted that the prevalence of myopia among Chinese youth has increased sharply in recent decades, with contributing factors including increased academic demands, reduced outdoor time, urbanization, and digital device use. While genetic susceptibility plays a role, the analysis emphasized modifiable environmental and behavioral factors, particularly outdoor exposure.

Biological mechanisms cited in the study include the effect of higher outdoor light intensity on retinal dopamine release and ocular growth, as well as the role of natural light in circadian regulation. Behavioral factors, such as reduced near work during time spent outdoors, may also contribute.

Sensitivity analyses stratified by study design and latitude showed consistent directional associations, supporting the robustness of the findings. However, substantial heterogeneity persisted, reflecting variation in study methods, populations, and exposure definitions.

The certainty of evidence was rated as moderate using the GRADE framework, with inconsistency cited as a limitation but offset by a large cumulative sample size and consistent direction of effect.

“Inconsistency was judged serious due to high heterogeneity (I² = 94%), although the association remained consistently protective. Indirectness and imprecision were not concerns, as all studies examined relevant populations and the pooled estimate showed a narrow CI (95% CI = 0.71–0.80) excluding the null,” the study authors stated. “… Considering all domains, the overall certainty of evidence was rated as moderate, reflecting upgrading for large cumulative sample size and consistency in effect direction.”

Reference:

1. Dai J, Wang J, Bao YH, Zhang Y. Exposure-response association between outdoor activity time and myopia risk in Chinese children and adolescents: a systematic review and meta-analysis. J Glob Health. 2026;16:04122. doi:10.7189/jogh.16.04122