Previous research has shown that youngsters who spend hours in front of the television are more likely to have these problems, but this is the first study to show that such health problems can extend into later life.

Investigators from the University of Otago in Dunedin studied 1000 people born in 1972 and 1973 until they reached 26 years of age, to see if a link exists between television viewing and cardiovascular health.

The children's parents were asked to estimate how long their child spent watching television on weekdays at several age points between 5 and 11 years. At the ages of 13, 15 and 21 years, the adolescents reported their viewing themselves.

Health evaluations of the participants at 26 years old revealed that those who watched more than 2 hours of television a day as children and adolescents had an increased body mass index, raised cholesterol, poor cardiovascular fitness and were likely to smoke. However, television viewing was not associated with high blood pressure.

Reporting in this week's issue of The Lancet, the team notes that among all 26-year-olds, watching too much television is probably responsible for patients being overweight in 17% of instances, 15% of cases of raised cholesterol, 15% of cases of poor fitness and 17% of such people becoming smokers.

Lead researcher Dr Robert Hancox said: "Our results suggest that excessive television viewing in young people is likely to have far-reaching consequences for adult health."

Ideally children should watch television for a maximum of 1 hour per day, he recommended.

"Adults are likely to obtain health benefits themselves if they lead by example and turn off the television," added Dr Hancox. "We believe that reducing television viewing should become a population health priority."