About 40 per cent of three-month-old babies and 90 per cent of two-year-olds regularly watch television, regardless of health implications.

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CHICAGO: Most parents let their babies watch television despite warnings that it can negatively affect brain development, according to a new study.

About 40 per cent of three-month-old babies and 90 per cent of two-year-olds regularly watch television or videos and the median age for introducing babies to television was nine months.

At three months babies were watching an average of less than an hour a day. This rose to more than an hour and a half by 24 months, the study said.

Health implications

"The public health implications of early television and video viewing are potentially large," wrote lead author Frederick Zimmerman, of the University of Washington in Seattle, U.S.. "The effects of media exposure on children's development are more likely to be adverse before the age of about 30 months than afterward."

The authors conducted a telephone survey of 1,009 parents of children aged two to 24 months in February 2006. They found that most parents thought their children watched less television than other infants and said they watched television with their child more than half the time.

Just 21 per cent said they used television "as a babysitter" while 29 per cent said they thought the programs were educational or good for their child's brain.

A separate study, published yesterday, showed that teenagers who watch even an hour's television a day have a higher risk of poor school performance while those who watched three hours or more a day were at an elevated risk of persistent attention and learning difficulties.

And as they got older, those who watched more television were significantly less likely to do well at school than those who cut back on their viewing hours. Researchers followed 678 families over 20 years, asking them about television habits and school problems as teenagers and then about their academic achievements as adults.

Poor performance

The length and breadth of the study allowed researchers to control for low socio-economic status and pre-existing learning problems, which are often blamed for poor school performance and increased television viewing. While teens with family or learning problems were more likely to watch more television than those without, researchers found this was not enough to explain away the "significant" links between attention and learning problems and frequent television viewing.

Television viewing at age 14 was "associated with elevated risk for subsequent frequent attention difficulties, frequent failure to complete homework assignments, frequent boredom at school," wrote lead author Jeffrey Johnson, of Columbia University and the New York State Psychiatric Institute, in New York City, U.S..

Both studies were published in the Journal of the American Medical Association's Archives of Paediatrics and Adolescent Medicine.