Banning fast-food advertising on television in the United States could reduce the number of overweight children by as much as 18 percent, researchers said on Wednesday.

But the team at the National Bureau of Economic ResearchFinland have done. questioned whether it would be practical to impose that kind of government regulation -- something only Sweden, Norway and

"We have known for some time that childhood obesity has gripped our culture, but little empirical research has been done that identifies television advertising as a possible cause," said economist Shin-Yi Chou of Lehigh University in Pennsylvania.

"Hopefully, this line of research can lead to a serious discussion about the type of policies that can curb America's obesity epidemic."

For their study, funded in part by the federal government, Chou and colleagues used data on nearly 13,000 children from the 1979 Child-Young Adult National Longitudinal Survey of Youth and the 1997 National Longitudinal Survey of Youth, both issued by the U.S. Department of Labor.

"The advertising measure used is the number of hours of spot television fast-food restaurant advertising messages seen per week," they wrote in the Journal of Law and Economics.

"Our results indicate that a ban on these advertisements would reduce the number of overweight children ages 3-11 in a fixed population by 18 percent and would reduce the number of overweight adolescents ages 12-18 by 14 percent."

The U.S. Centers for Disease Control and Prevention estimates that 13.9 percent of children aged 2 to 5 are overweight, 18.8 percent of those aged 6 to 11 are and more than 17 percent of those 12 to 19.

The percentages have been steadily rising.

Television watching is also known to raise obesity rates, both because children exercise less and because it can interfere with sleep.

The Institute of Medicine reported in 2006 that there was compelling evidence linking food advertising on television and increased childhood obesity.

One study suggested that children viewed an average of about 20,000 commercials aired on television per year in the late 1970s, rising to 30,000 per year in the late 1980s and more than 40,000 per year in the late 1990s.