“Lifestyle in early youth is very much associated with onset of myopia,” Dr. Caroline Klaver of Erasmus Medical Center in Rotterdam told Reuters Health in an email interview. “Not being outside, and performing lots of near work will increase risk a lot.”

While factors like being highly educated and of non-European heritage have traditionally been linked to nearsightedness, the new study suggests that how young children spend their time is likely to be the underlying source of these differences, the study team writes in the British Journal of Ophthalmology.

The researchers looked at 5,711 children in Rotterdam who have been participating since birth, along with their mothers, in a long-term study. At age 6, the children had a full medical examination and 2.4 percent were found to have myopia, or nearsightedness.

The researchers used statistical techniques to analyze a wide variety of factors, including social and economic aspects of the household, ethnicity, lifestyle, parents’ education levels, children's’ activities and any links between these and the likelihood a child would be nearsighted.

The study team found that myopic children spent less time outdoors, had lower levels of vitamin D, had a higher body mass index and were less likely to play sports than children who weren’t nearsighted. While being of non-European descent, having a mother with a low education level and low family income were also associated with myopia, the researchers found that lifestyle factors explained most of these risks.

The study was limited by the low number of children with myopia and the lack of information about parents’ nearsightedness - “a well-known myopia risk factor,” the authors note.

“Differences in myopia prevalence between ethnic groups that have commonly been assumed to be down to genetics may in fact be due to differences in lifestyle between ethnic groups,” Dr. Jeremy Guggenheim, an optometry professor at Cardiff University in the UK, told Reuters Health in an email.

“The new study and other recent work suggests that this preventative effect of time outdoors is beneficial even at very young ages, e.g. 3 - 6 years-old,” said Guggenheim, who studies the causes of myopia and sometimes collaborates with Klaver’s team, but was not involved in the current study.

“Too much close work, such as reading and using hand-held devices, may also be a risk - although the jury is still out on this question,” he added.

To help prevent myopia, Klaver said, parents should have children play outside for 15 hours a week, and limit “near work” to no longer than 45 continuous minutes.

“It’s important to keep in mind that this type of study can never pin-point the precise causes of myopia in the way that is possible using purpose-designed clinical trials,” Guggenheim said. “Nevertheless, the risk factors that were identified in the new study fit neatly with what has been learned in recent years from such trials.”

“Basically this study adds very nicely to the evidence that we already see from many other studies and many other countries that there is definitely a connection between outdoor activity and myopia in children,” said Susan Vitale at the U.S. National Eye Institute.

“The main thing to remember is that if parents have any concerns about their child’s vision it’s very important that they get a dilated eye exam from a health care professional,” Vitale said. Regular eye care is the most important thing people can do to maintain their eye health, she added.

SOURCE: bit.ly/2v8zqbW British Journal of Ophthalmology, online June 12, 2017.