Children and adolescents who regularly watch television for two hours or more a day are more likely to be overweight, smoke and have high cholesterol, according to a study reported in the July 17 issue of the Lancet.

All of these factors substantially increase long-term health problems later in life, according to researchers at the University of Otago in New Zealand.

Previous research has identified associations between television viewing and poor health outcomes such as high cholesterol and obesity, but until now no study has assessed these effects into adulthood.

The researchers studied and followed about 1,000 New Zealand children born in 1972 and 1973 until they reached 26 years of age. Parents provided details of their children's weekly television viewing habits. The researchers also assessed the participants' body-mass index (BMI), blood pressure, cholesterol and cardiovascular fitness when they reached 26 years old.

A clear association was found between extensive television viewing of more than 2 hours a day among the participants and increased BMI, raised cholesterol, greater proportion of smoking and poor cardiovascular fitness at this age. No association was found between television viewing and blood pressure.

"Our results suggest that excessive television viewing in young people is likely to have far-reaching consequences for adult health," concluded the researchers. "We concur with the American Academy of Pediatrics that parents should limit children's viewing to 1-2 hours per day. In fact, data suggest that less than 1 hour a day would be even better."

In an accompanying editorial, David Ludwig, of Harvard Medical School, said the findings strengthen the case for a ban on food advertisements aimed at children.

"In an era when childhood obesity has reached crisis proportions, the commercial food industry has no business telling toddlers to consume fast food, soft drinks and high-calorie low-quality snacks, all products linked to excessive weight gain," says Ludwig. "Measures to limit television viewing in childhood and ban food advertisements aimed at children are warranted, before another generation is programmed to become obese."

Other sources: Lancet 2004; 364: 226, 257-62