The later children get to bed, the higher their risk of myopia, according to a study in the journal Scientific Reports. Investigators say bedtimes were consistently a risk factor for both myopia prevalence and progression.
To establish this, researchers followed 6295 children in Shanghai, China, for 2 years in a school-based study, analyzing the relationship between a range of demographic, environmental, and behavioral factors and myopia.
Their results suggest that a later bedtime is a risk factor for myopia prevalence at baseline (OR = 1.55, P =.04), 2-year myopia incidence (OR = 1.44, P =.02), and progression in 24 months (P =.005), even after adjusting other factors.
The participants were aged between 6 and 9 years. After the 2-year study period, data from 5355 participants showed myopia in 27.64%. A total of 4982 participants who did not have myopia at baseline attended the 24-month visit, where 1094 were discovered to have developed myopia.
Only 9.9% of those in the study went to bed at 10pm or later at baseline. That number doubled to 20% at the 24 month follow-up. By contrast, the percentage of participants who went to sleep before 9pm decreased from 20.6% to 6.6% in the same time period. Alongside previously known risk factors, including age, urban residency, family history of myopia and fewer outdoor activities, late bedtime (P =.009) and late wake-up times (P =.001) were also linked with baseline myopia.
Even after taking sleep duration and weekly outdoor time into consideration, those who went to sleep at 9:30pm or later had 1.55-fold higher odds of being myopic at baseline compared with those who slept before 9pm (P =.04).
And when researchers looked at the connection between sleep and 2-year myopia incidence, they found — even adjusting for residency area, age and gender — those who went to bed at 9:30pm or later had a 1.4-fold higher odds of developing myopia (P =.02) than those who went to bed before 9pm.
Although the study was based on a larger, younger sample of participants without high degrees of myopia, the results echo previous research in which a group of teenagers with high myopia were found to have later bedtimes compared with teenagers with either mild or no myopia.
The researchers suggest more study is needed to uncover whether later bedtimes make children more prone to myopigenic activities under poor lighting, or more susceptible to abnormal eye growth due to circadian disturbance.
Liu X, Naduvilath T, Wang J, et al. Sleeping late is a risk factor for myopia development amongst school-aged children in China. Sci Rep. 2020;10(1):17194. doi: 10.1038/s41598-020-74348-7.