Time spent outdoors in childhood related to myopia among young adults in the Swedish ABIS cohort

Purpose: Elucidate the prevalence of myopia among young adults from a birth cohort of Swedish children and its relationship to possible risk factors during their childhood. Methods: Five thousand two hundred young adults, mean 23.4 years and 58% females, participating in the prospective birth cohort All Babies in Southeast Sweden (ABIS) answered a questionnaire including questions regarding health and physical activity, spectacle use, myopia and age at first optical correction. Questionnaires at previous follow-ups at ages 2-3, 5-6 and 8 years included information on type of housing, time outdoors, screen time and hours of reading. Myopia prevalence and associations with potential risk factors were analysed in univariate and multivariate regression models with Bonferroni's correction of p-values. Results: In the ABIS Swedish birth cohort of young adults, the prevalence of myopia was 29%. A univariate logistic regression showed a higher odds ratio for myopia with female gender (OR 1.59; p < 0.05) and a completed and started university education (OR 1.52; p < 0.05). Significantly lower odds ratios were found for hours spent outdoors at 8 years of age (OR 0.82; p < 0.05). Multivariate logistic regression showed a higher odds ratio for myopia in females (OR 1.52-1.57; p < 0.05) and completed and started university education (OR 1.34-1.49; p < 0.05) in all models. In a model including accommodative effort, measured in diopter hours at 8 years of age, hours spent outdoors were associated with a lower odds ratio for myopia (OR 0.86; p < 0.05). No association could be detected between myopia and the type of housing or near work. Conclusion: The prevalence of myopia among young adults in a Swedish birth cohort was lower or unchanged compared to previous data. Female gender, higher education and less time spent outdoors in childhood were associated with an increased risk of developing myopia. Recommendations from child health services and schools should be given to stimulate children to spend enough time outdoors.