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Researchers tied three behaviors to higher scores on tests of mental ability in children: at least 60 minutes of physical activity a day, nine to 11 hours of sleep a night, and no more than two hours a day of recreational screen time.

The new study, in Lancet Child & Adolescent Health, included 4,524 children ages 8 to 11 who were assessed with six standard tests that measure language skills, memory, planning ability, and speed at completing mental tasks.

Compared with those who met none of the three behavioral criteria, those who met all of them scored about 4 percent higher on the combined tests. Meeting the requirements for both screen time and sleep was associated with a 5.1 percent increase in scores compared with those who met neither. Only 5 percent of the children met all three criteria, and nearly 30 percent met none.

“It may be that screen time is affecting sleep,” said the lead author, Jeremy J. Walsh, a postdoctoral fellow at the University of British Columbia. “Sleep is a critical behavior for shaping our brains. Kids need to be sleeping nine to 11 hours a night for their cognitive development to be optimal.”