Booting your children outside to play can not only boost their physical fitness - it can cut the chances of their developing shortsightedness, researchers say.
Shortsightedness, or myopia, has become increasingly common over the last four decades, both in the US and elsewhere - indeed, in parts of Asia, more than 80 percent of the population is nearsighted.
And a new University of Cambridge analysis of recent eye health studies indicates that the reason may be that children are spending too much time indoors, possibly because of a lack of light or too little time spent looking at distant objects.
The data included in the analysis was drawn from eight carefully selected studies on outdoor time and myopia in children and adolescents, representing 10,400 participants in total.
And the team found that for each additional hour spent outdoors per week, the chance of myopia dropped by approximately two percent. Nearsighted children spent on average 3.7 fewer hours per week outdoors than those who either had normal vision or were farsighted.
Though the reasons aren't yet clear, the protective effect appears to result from simply being outdoors rather than performing a specific activity. Two of the eight studies examined whether children who spent more time outdoors were also those who spent less time performing near work, such as playing computer games or studying, but no such relationship was found.
"Increasing children's outdoor time could be a simple and cost-effective measure with important benefits for their vision and general health," says Dr Anthony Khawaja.
"If we want to make clear recommendations, however, we'll need more precise data. Future, prospective studies will help us understand which factors, such as increased use of distance vision, reduced use of near vision, natural ultra violet light exposure or physical activity, are most important."
It also appears that boosting outdoor time may stop nearsightedness from getting worse. A separate Chinese study of 80 nearsighted children between the ages of seven and 11 found that those that were given more outdoor time each week for a two-year period were less nearsighted on average than the control group.