A study of children in the U.S has shown that limiting children's recreational screen time to less than two hours a day, sleeping sufficiently and engaging in physical activity is associated with better cognition, compared with not meeting these recommendations.
Overall, only 5 percent of the children in the study met all three recommendations on sleep, screen time, and physical activity while 30 percent met none of the recommendations. Sixty-three percent of children spent more than two hours a day staring at screens, failing to meet the screen-time limit.
Less than two hours of screen time a day was the one factor most linked to better performance in the test.
According to Dr. Shawna Newman, an attending psychiatrist at Lenox Hill Hospital in New York City, the study "clearly demonstrates the specific benefit of exercise for children, in addition to that of good sleep hygiene and the limitation of screen time contributing positively to cognitive development".
The study, published Wednesday in the Lancet Child & Adolescent Health, found that 51% of US kids met the sleep guidelines; 37% stayed within screen time parameters; and 18% reached the exercise recommendation.
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In the study, data were analyzed from 4,520 children from 20 sites across the US. "This study is showing that less than two hours of recreational screen time is beneficial for children". Children and parents completed questionnaires and measures at the outset of the trial to estimate the child's physical activity, sleep and screen time.
The researchers found that as each recommendation was met by a participant, there was a positive association with global cognition, which includes memory, attention, processing speed and language.
"I think that the overarching goal here is that parents should consider the whole 24-hour day of their children and put realistic rules or limits in place for how long they are on their screens for, having bedtime rules, and making sure to encourage physical activity", Walsh said.
"We really had an opportunity here to look at how meeting each of these guidelines and meeting all of the guidelines relate to cognition in a large sample of American children". Dr Walsh said more research was needed to examine the potential impact of different online activities.
And of course, the study was an observational one which meant a causal relationship could not be established. "In the case of evening screen use, this displacement may also be compounded by impairment of sleep quality".