On average, mothers in the study reported their children watched 1.2 hours of TV a day. (CBC)

The amount of time spent watching TV doesn't help or hinder brain development before the age of two, a study released Monday suggests.

"Contrary to marketing claims and some parents' perception that television viewing is beneficial to children's brain development, no evidence of such benefit was found," said the study's lead author, Marie Evans Schmidt of Children's Hospital Boston.

Along with colleagues from Harvard Medical School, Evans Schmidt looked at how long 872 babies watched TV or other screens before they reached two years of age, and tracked their progress at age three.

The American Academy of Pediatrics currently recommends children younger than two never watch screen media, but surveys suggest that more than two-thirds of Americans under two watch TV daily.

In the study, result of which appear in the March issue of the journal Pediatrics, children were given vocabulary, drawing, and other tests to measure their verbal and motor skills at age six months and three years.

Mothers were asked to fill in questionnaires on the TV viewing habits of their sons and daughters at six months, one year and two years.

On average, mothers reported their children watched 1.2 hours of TV a day.

After adjusting for factors — such as maternal age, income, education, marital status, presence of siblings, race, child's body mass index, sleep habits and duration of breastfeeding — the researchers found that watching TV wasn't linked to improvements on the tests.

The study did not look at the content of the programs and videos, just the amount of time spent viewing the media.

Despite the results, researchers warned that the body of evidence suggests that watching TV before the age of two is more harmful than beneficial.

"TV exposure in infants has been associated with increased risk of obesity, attention problems, and decreased sleep quality," said study author Dr. Michael Rich, a pediatrician.

"Parents need to understand that infants and toddlers do not learn or benefit in any way from viewing TV at an early age."

The Canadian Pediatric Society also warns that too much TV is linked to problems with attention, learning and aggressive behaviour.

The study's authors cited another study in which researchers found that watching an average of 2.2 hours of TV a day before the age of three was linked to less verbal ability at age six.

It's possible that the effects of TV may not become apparent until children are older than age three and are more verbal, or that TV viewing before the age of two has less of an impact on developing cognitive abilities than between the ages of two and three, Evans Schmidt and her colleagues suggested.