Certain teenagers who watch more television are more likely to become sexually active than those who spend less time in front of the tube, a new study shows.

　　Dr. Sarah Ashby of the University of Wisconsin School of Public Health in Madison and her colleagues found that, among a group of 4,808 boys and girls younger than 16, those who said their parents strongly disapproved of sex -- nearly three quarters of the group -- were more likely to start having sex in the following year if they watched two hours or more of TV daily.

　　The findings, appearing in the Archives of Pediatrics and Adolescent Medicine, support the hypothesis that "kids who are at overall lower risk of initiating sex may be more influenced by things that they see," Ashby told Reuters Health. For teens who don't sense parental disapproval, she added, "the cat is already out of the bag."

　　Parental disapproval in itself did indeed cut the risk of kids becoming sexually active -- 12.5 percent of these teens started having sex, compared to 24.1 percent of those who didn't feel their parents disapproved of sex.

　　Among kids who sensed parental disapproval, the more TV they watched, the greater their likelihood of becoming sexually active -- up to a point.

　　Those who watched two to five hours were more than twice as likely as those who watched less than an hour daily to start having sex. But teens logging five hours of daily TV or more were at no greater risk of starting to have sex than those who watched less than two hours.

　　It's possible that these children were watching so much television that they had no time for other activities, including sex, the researchers note.

　　The researchers also found that sexual initiation was more likely among teens who sensed parental disapproval of sex if their parents made no effort to regulate their TV watching.

　　The findings show, Ashby told Reuters Health, that "it's important that parents convey very clearly their values about sexual behavior to their children." What's more, she added, they should take other steps to reduce their children's risk of having sex, including keeping an eye on their TV viewing habits.