Exposure to some forms of entertainment is a corrupting influence on children, leading teens who watch sexy programs into early pregnancies and children who play violent video games to adopt aggressive behaviour, researchers said.

Researchers at the RAND research organization said their three-year study was the first to link viewing of racy television programming with risky sexual behavior by teens.

"Our findings suggest that television may play a significant role in the high rates of teenage pregnancy in the United States,'' said Anita Chandra, a behavioural scientist who led the research at RAND, a nonprofit research organization.

"We're not saying we're establishing causation, but we are saying this is one factor that we were able to prospectively link to the teen pregnancy outcome,'' Chandra said.

The researchers recruited adolescents aged 12 to 17 and surveyed them three times between 2001 and 2004, asking about television viewing habits, sexual behaviour and pregnancy.

In findings that covered 718 teenagers, there were 91 pregnancies. The top 10th of adolescents who watched the most sexy programming were at double the risk of becoming pregnant or causing a pregnancy compared to the 10th who watched the fewest such programs, according to the study published in the journal Pediatrics.

The study focused on 23 free and cable television programs popular among teenagers including situation comedies, dramas, reality programs and animated shows. Comedies had the most sexual content and reality programs the least.

"The television content we see very rarely highlights the negative aspects of sex or the risks and responsibilities,'' Chandra said. "So if teens are getting any information about sex they're rarely getting information about pregnancy or sexually transmitted diseases.''

Teen pregnancy rates in the United States have declined sharply since 1991 but remain high compared to other industrialized nations. Nearly 1 million girls aged 15 to 19 years old become pregnant yearly, or about 20 percent of sexually active females in that age group. Most of the pregnancies were unplanned, the report said.

Young mothers are more likely to quit school, require public assistance and live in poverty, it said.

"Television is just one part of a teenager's media diet that helps to influence their behaviour. We should also look at the roles that magazines, the Internet and music play in teens' reproductive health,'' Chandra said, acknowledging still other factors can influence teen sex habits.

Living in a two-parent family reduced the chances of a teen getting pregnant or causing a pregnancy. Black teenagers, and those with discipline problems, had higher risks.

The report suggested broadcasters provide more realistic portrayals of the consequences of sex and that parents limit their children's access to sexually explicit programming.

A second study in the journal added to existing evidence that youths who play violent video games -- a worldwide trend with American children averaging 13 hours of video gaming a week -- led to increased physically aggressive behaviour.