The more TV a 3-year-old watches, the more likely he or she is to behave aggressively, a new study shows.

Just having the TV on when the child wasn't watching it was also linked to aggressive behavior, although the relationship wasn't as strong, Dr. Jennifer A. Manganello of the University at Albany, State University of New York, Rensselaer, and her colleagues found.

She and her colleagues looked at 3,128 women from 20 US cities who had a child between 1998 and 2000. While there was some diversity of education among the study participants, one-third hadn't graduated from high school.

Two-thirds of the mothers said their three-year-old watched more than two hours of TV a day, and the average viewing time for kids was around three hours. On average, the TV was on for about five additional hours on a typical day.

After accounting for factors known to be associated with aggressive behavior, such as living in a violent neighborhood or having a mother who suffers from depression, TV watching and household TV time were both still significantly associated with aggressive behavior, such as hitting others, having angry moods, being disobedient, and screaming a lot.

The American Academy of Pediatrics recommends no TV at all for children two and younger, and two hours a day or less for older kids, Manganello and her team note in their report.

There are a number of ways that excessive TV viewing could contribute to a child's degree of aggressive behavior, the researchers add. Children may see violence on TV, and time spent watching TV may mean less time for behaviors that help kids develop positively, such as reading or playing.

We really don't know what's going on for certain, Manganello said. Future research needs to look both at TV content and at what's going on in a child's home when the TV is on, she added.

The findings show, Manganello said, that parents have to consider the overall TV environment of the home, as well as how much TV their child is watching.

Parents should be smart about TV use, Manganello told Reuters Health. They should limit the time that children use TV, pay attention to the content of TV programs, and consider how TV is used throughout the home.

SOURCE: Archives of Pediatrics & Adolescent Medicine, November 2009.

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