Ensuring that children spend at least 2 hours outdoors each day is currently the only myopia‑prevention method backed by randomized trials.

4. Ensuring that children spend at least 2 hours outdoors each day is currently the only myopia‑prevention method backed by randomized trials.

Cost: There is no monetary cost. However, it requires setting aside time each day — often at the expense of homework or online classes. The real challenge is maintaining this routine daily, not just occasionally.

In plain terms: A randomized trial was conducted at 12 primary schools in Guangzhou: first‑grade students were given an extra 40 minutes of outdoor activity per school day. After three years, the myopia rate in these schools was 30.4 %, compared with 39.5 % in schools without the added classes — a reduction of 9.1 percentage points. The Health Commission recommends at least 2 hours of daytime outdoor time per day, or a total of 14 hours per week. Cloudy days and standing outside during recess also count.

Benefit: In this trial, first‑grade students from 12 Guangzhou schools were randomly assigned to intervention or control groups (952 students in the intervention group, 951 in the control group; mean age 6.6 years). The intervention involved adding a 40‑minute outdoor class each day and encouraging parents to take their children outdoors after school. Over three years, the new myopia rate was 30.4 % in the intervention group (259 of 853 eligible participants) versus 39.5 % in the control group (287 of 726 eligible participants). The difference was –9.1 percentage points (95 % CI –14.1 to –4.1, P<0.001), indicating a true reduction ranging from roughly 4 to 14 percentage points. The average increase in refractive error was –1.42 D in the intervention group versus –1.59 D in the control group, a difference of 0.17 D (P=0.04); the intervention thus slowed progression slightly. D is the unit used to measure refractive error. No significant difference was observed in axial eye length between groups (P=0.07). The “Ten Core Principles for Myopia Prevention” also call for at least 2 hours of daytime outdoor activity per day or 14 hours per week; they note that even on cloudy days this activity provides protection and advise avoiding peak midday sun.

Evidence grade: A

Sources: 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. (National Health Office Maternity and Childhood Letter [2023] No. 278). <https://www.gov.cn/zhengce/zhengceku/202307/content_6894284.htm>

Notes: The trial lasted only three years and involved children starting at age 6. A 9.1‑percentage‑point difference means it can help prevent myopia in some children, but it does not guarantee protection for everyone. The same guidelines also recommend maintaining a distance of “one foot, one fist, one inch” while reading or writing, taking a 20‑second break to look into the distance after 20 minutes of close‑up work, limiting non‑educational screen time to 15 minutes at a time (no more than one hour per day), and recognizing that simply standing outside during recess counts toward the daily outdoor requirement — it is not the same as attending a formal PE class.