Watching TV more than two hours a day early in life can lead to attention problems later in adolescence, according to a new study.

The roughly 40% increase in attention problems among heavy TV viewers was observed in both boys and girls, and was independent of whether a diagnosis of attention deficit/hyperactivity disorder was made prior to adolescence.

The link was established by a long-term study of the habits and behaviours of more than 1,000 children born in Dunedin, New Zealand, between April 1972 and March 1973. The children aged 5 to 11 watched an average of 2.05 hours of weekday television.

From age 13 to 15, time spent in front of the tube rose to an average of 3.1 hours a day.

“Those who watched more than two hours, and particularly those who watched more than three hours, of TV per day during childhood had above-average symptoms of attention problems in adolescence,” Carl Landhuis of the University of Otago in Dunedin wrote in his report, published in the journal Pediatrics.

Young kids who watched a lot of TV were more likely to continue the habit as they got older, but even if they did not the damage was done, the report said.

“This suggests that the effects of childhood viewing on attention may be long lasting,” Landhuis wrote. Landhuis offered several possible explanations for the association.

One was that the rapid scene changes common to many TV programmes may overstimulate the developing brain of a young child, and could make reality seem boring by comparison. “Hence, children who watch a lot of TV may become less tolerant of slower-paced and more mundane tasks, such as school work,” he wrote.

It was also possible that TV viewing may supplant other activities that promote concentration, such as reading, games, sports and play, he said. The lack of participation inherent in TV watching might also condition children when it comes to other activities.

The study was not proof that TV viewing causes attention problems, because it may be that children prone to attention problems may be drawn to watching TV.