Researchers found that compared with teens who spent much of their free time in front of the TV, those who were active often had higher self-esteem, better grades and were less prone to risky behavior like taking drugs, smoking, drinking or having sex.

　　The findings, based on a national survey of nearly 12,000 middle and high school students, are published in the journal Pediatrics.

　　"Across the board, children who engaged in any kind of activity were better off than kids who watched a lot of TV," said study co-author Dr. Penny Gordon-Larsen of the University of North Carolina, Chapel Hill.

　　Other studies have linked certain content of television programs, such as violence and sex, to children's behavior. But beyond this issue, Gordon-Larsen told Reuters Health, kids who spend hours watching TV "miss opportunities" to socialize, develop skills, learn teamwork and have other experiences that their more active peers benefit from.

　　That doesn't mean, however, that kids have to be on the football team. The study found that "alternative" activities like skating and skateboarding -- which adults sometimes frown upon -- were also related to better self-esteem and less risk-taking.

　　That skaters were better behaved than TV watchers might come as a surprise to some adults who see these teens as a nuisance, according to Gordon-Larsen. Skateboarding is banned in many public areas, and some communities oppose building skating parks.

　　But if kids who like to skate have nowhere to do it, "it's a shame," said Gordon-Larsen.

　　Not only should parents encourage their kids to engage in the physical activities they enjoy, she said, but schools and communities should also do more to create opportunities for children to be active.

　　In other findings, teenagers who played sports with their parents were less likely than TV lovers to engage in any of the behaviors the study considered -- from drinking and drug use to delinquency.

　　This finding, write the study authors, underscores the "important role" parents play in their children's activities, or lack thereof.

　　Overall, Gordon-Larsen said, the study results also highlight the fact that exercise is not only about weight control. "This study makes clear that there are other benefits as well," she said.