CHICAGO - Researchers have found that every hour preschoolers watch television each day boosts their chances - by about 10 percent - of developing attention deficit problems later in life.
The findings back up previous research showing that television can shorten attention spans and support American Academy of Pediatrics recommendations that youngsters under age 2 not watch television.
"The truth is there are lots of reasons for children not to watch television. Other studies have shown it to be associated with obesity and aggressiveness" too, said lead author Dr. Dimitri Christakis, a researcher at Children's Hospital and Regional Medical Center in Seattle.
The study, appearing in the April issue of Pediatrics, focused on two groups of children - aged 1 and 3 - and suggested that TV might overstimulate and permanently "rewire" the developing brain.
The study involved 1,345 children who participated in government-sponsored national health surveys. Their parents were questioned about the children's TV viewing habits and rated their behavior at age 7 on a scale similar to measures used in diagnosing attention deficit disorders.
The researchers lacked data on whether the youngsters were diagnosed with attention deficit disorders but the number of children whose parents rated them as having attention problems - 10 percent - is similar to the prevalence in the general population, Christakis said. Problems included difficulty concentrating, acting restless and impulsive, and being easily confused.
About 36 percent of the 1-year-olds watched no TV, while 37 percent watched one to two hours daily and had a 10 percent to 20 percent increased risk of attention problems. Fourteen percent watched three to four hours daily and had a 30 percent to 40 percent increased risk compared with children who watched no TV. The remainder watched at least five hours daily.
Among 3-year-olds, only 7 percent watched no TV, 44 percent watched one to two hours daily, 27 percent watched three to four hours daily, almost 11 percent watched five to six hours daily, and about 10 percent watched seven or more hours daily.
In a Pediatrics editorial, educational psychologist Jane Healy said the study "is important and long overdue" but needs to be followed up to confirm and better explain the mechanisms that may be involved.
The researchers didn't know what shows the children watched, but Christakis said content likely isn't the culprit. Instead, he said, unrealistically fast-paced visual images typical of most TV programming may alter normal brain development.
"The newborn brain develops very rapidly during the first two to three years of life. It's really being wired" during that time, Christakis said.
"We know from studies of newborn rats that if you expose them to different levels of visual stimuli ... the architecture of the brain looks very different" depending on the amount of stimulation, he said.
Overstimulation during this critical period "can create habits of the mind that are ultimately deleterious," Christakis said. If this theory holds true, the brain changes likely are permanent, but children with attention problems can be taught to compensate, he said.
The researchers considered factors other than TV that might have made some children prone to attention problems, including their home environment and mothers' mental states.
The American Academy of Pediatrics said in 1999 that children under the age of 2 should not watch television because of concerns it affects early brain growth and the development of social, emotional and cognitive skills.
Jennifer Kotler, assistant director for research at Sesame Workshop, which produces educational children's television programs including "Sesame Street," questioned whether the results in the April Pediatrics would apply to educational programming.
"We do not ignore this research," but more is needed on variables that could affect the impact of early exposure to television, including whether content or watching TV with a parent makes a difference, Kotler said.
"There's a lot of research... that supports the positive benefits of educational programming," she said.