Four-year-old children who watch more television than average are more likely to become bullies, research suggests.
Poor parental support can be linked to too much TV, say experts
The University of Washington team found children who went on to bully watched about five hours of TV per day - almost two hours more than those who did not.
The study of 1,266 four-year-olds also showed mental stimulation, such as outings, being read to and eating with parents reduced the risk of bullying.
It was published in Archives of Pediatrics and Adolescent Medicine.
The researchers compared assessments of the children enrolled in a national long-term study.
They gauged how much emotional support they received from their parents, their level of mental stimulation how much television they watched at the age of four.
Factors used to assess the emotional support a child received included if they ate meals with both parents, how much the parents talked to the child, and if it was spanked.
Outings, reading, playing and parental teaching were assessed to evaluate mental stimulation.
Parents were also asked how many hours of television their children watched, on average.
They then looked at reports on children from the ages of six to 11 to see which children were described as bullies.
Around 13% of children were reported as bullies by their mothers.
The study suggested both early emotional support and mental stimulation were likely to reduce the chances of becoming a bully.
But it said the risk associated with the amount of TV children watched was "clinically significant".
Children who did not go on to be bullies watched an average of 3.2 hours of TV a day.
Those who did go on to bully watched an average of five hours a day.
Writing in the journal, the team led by Dr Frederick Zimmerman said: "Our results have some important implications.
"We have provided some empirical support to theories that suggest that bullying might arise out of cognitive deficits as well as emotional ones.
"We have added bullying to the list of potential negative consequences of excessive television viewing along with obesity, inattention and other types of aggression.
"And our findings suggest some steps that can be taken with children to potentially help prevent bullying.
"Maximising cognitive stimulation and limiting television watching in the early years of development might reduce children's subsequent risk of becoming bullies."
But UK experts cast doubt on the study's findings.
Kevin Browne, professor of forensic and family psychology at the University of Birmingham, said: "We know that emotionally neglected children are more violent, so emotional neglect itself will contribute to a child becoming a bully.
"And parents who don't take a great interest in their children and what they are watching are also those parents who emotionally neglect them or physically assault them."
And Dr Andrew Burn, of the London Institute of Education, added: "It's always claimed TV causes aggression, but it is never proved.
"Parents should have a balanced approach. Don't let a small child stay up watching TV until 3am, and don't let them watch violent or sexually explicit programmes. But parents know that."