Aim for two hours outdoors each day to help prevent myopia
Adding 40 minutes of outdoor school activity a day for first-graders reduced new myopia over three years from about 40% to about 30% in one randomized trial. Chinese health guidance recommends at least two daylight hours outdoors daily or 14 hours weekly. Cloudy days count, as does spending breaks outside.
What it takes
Nothing, but outdoor time needs a place in the daily schedule, often competing with homework and online classes. Consistency matters.
What you may gain
A cluster-randomized trial in 12 Guangzhou primary schools included 952 intervention and 951 control pupils, average age 6.6 years. Intervention schools added a 40-minute outdoor class each school day, and parents were encouraged to provide more outdoor time. Three-year myopia incidence was 30.4%, 259 of 853 eligible children, versus 39.5%, 287 of 726 controls: a difference of −9.1 percentage points, 95% CI −14.1 to −4.1, P<0.001. Spherical equivalent changed by −1.42 D versus −1.59 D, a difference of 0.17 diopters, P=0.04. Axial elongation, growth in the eye's front-to-back length, did not differ significantly, P=0.07. China's Ten Key Facts on Preventing and Controlling Myopia in Children and Adolescents recommends at least two daylight hours outdoors daily or 14 hours weekly, notes benefit even in cloudy weather, and advises avoiding intense afternoon heat and sun.
Context & considerations
The trial lasted three years and began around age six. A 9.1-percentage-point difference reduces incidence but does not guarantee prevention. The official guidance also recommends reading posture with roughly one Chinese foot, about 33 cm, between eyes and page, a fist between chest and desk, and an inch between fingertips and pen tip; looking into the distance for at least 20 seconds after 20 minutes of near work; and limiting recreational screens for schoolchildren to 15 minutes per session and one hour daily. Outdoor time is not the same as a physical education lesson: going outside during breaks also counts. The original calls this the only randomized-trial-supported prevention measure; the cited trial establishes its benefit, not the exclusivity of that claim.
Research & references
He M et al. (2015). Effect of Time Spent Outdoors at School on the Development of Myopia Among Children in China: A Randomized Clinical Trial. JAMA. https://doi.org/10.1001/jama.2015.10803; General Office of the National Health Commission (2023). Ten Key Facts on Preventing and Controlling Myopia in Children and Adolescents, Guoweiban Fuyouhan [2023] No. 278. https://www.gov.cn/zhengce/zhengceku/202307/content_6894284.htm