Children who spend more than two hours a day at a computer or watching television are more likely than others to have psychological problems, scientists claim.
Researchers found that 11-year-olds who clocked up several hours in front of a screen each day scored worse on questionnaires designed to measure psychological health, regardless of how much physical exercise they got.
Angie Page, who led the study at the University of Bristol, said that as a precaution parents might consider limiting how long their children spend in front of a screen to no more than two hours a day.
The study of 1,013 children in the Bristol area found no evidence that sitting in front of a screen actually causes mental health problems. Alternatively, the findings might be a result of children with psychological difficulties, such as extreme shyness, being more likely to choose TV or computer games over more sociable activities.
"There's no evidence one way or the other and it could be either," Dr Page told the Guardian. But she added that some healthy children might be at greater risk of developing psychological problems if they increased their viewing time.
In the study, children were asked whether they agreed, disagreed or partially agreed with a list of statements, including, "I generally play alone or keep to myself" and, "I am often unhappy, downhearted or tearful". They then added details of how much exercise they took and how long they spent at a TV or computer screen. Their levels of exercise were verified by activity monitors worn on their belts for a week.
Writing in the journal Pediatrics, the team explain that while children who did little exercise fared well on the psychological assessments, those who filled their inactive time watching television or at a computer scored badly.
According to the study, children who spent more than two hours a day at a screen had a 60% higher risk of psychological problems than children who clocked up fewer viewing hours. The risk was only slightly higher in children who did little or no exercise.
"You can't rely on physical activity to compensate for long hours of screen viewing. Physical activity is good for health in many ways, but parents should consider restricting their children's screen viewing," Page said. "We don't have any guidelines on screen viewing in the UK, but this paper would support the two-hour limit as a reasonable threshold."
Previous studies have raised concerns that watching too much television can affect children's behaviour in later life. In May, a study of 1,300 children by Linda Pagani at the University of Montreal found that those who watched most TV as toddlers performed worse at school and consumed more junk food.
A study in 2004, by Dimitri Christakis at the Children's Hospital in Seattle, found that levels of attention deficit hyperactivity disorder (ADHD) in children increased in line with television viewing.
Australia and the US have adopted guidelines that advise parents to restrict the viewing time of children under two to no more than two hours a day, but there is no similar recommendation in Britain.
