London ? Children who watch more than two hours of television a night seem to be at higher risk of becoming smokers or being fat, out of shape or having high cholesterol as adults, according to a new study.

Watching TV in childhood and adolescence has long been linked to adverse health indicators, including obesity, poor fitness and high cholesterol, but the study published today in The Lancet was the first to track a group from birth to adulthood.

Dr. David Ludwig, director of the obesity program at Children’s Hospital in Boston, and Steven Gortmaker, a sociology lecturer at the Harvard School of Public Health, said the data indicated television viewing in childhood had “serious long-term consequences” and strengthen “the case for a ban on food advertisements aimed at children.” Neither was connected with the study.

The researchers from the Dunedin Multidisciplinary Health and Development Research Unit assessed some 1,000 people born in Dunedin, New Zealand, in 1972-73, at regular intervals until age 26. They investigated associations between childhood TV viewing and body-mass index, or BMI, cardio-respiratory fitness, cholesterol level, smoking status and blood pressure.

They found that even an average weeknight viewing of one to two hours between the ages of 5 and 15 was associated with higher body-mass indices, lower cardio-respiratory fitness, increased smoking and raised cholesterol.

This was the case even after they adjusted for such factors as family economics, the smoking habits and weight of the parents, and the children’s size at age 5.

The study found that among 26-year-olds, 17 percent of overweight, 15 percent of raised cholesterol, 17 percent of smoking and 15 percent of poor fitness could be attributed to watching television for more than two hours a day during childhood and adolescence.

The researchers noted that, as in any observational study, they couldn’t prove TV viewing caused health problems.

“Television viewing might be a marker for some unidentified determinant of adult health, and individuals who have a natural tendency to obesity and poor physical fitness might prefer to watch television than do other activities,” they wrote.