It seems sexually charged music, magazines, TV and movies encourages youngsters into sex at an earlier age, possibly by suggesting that everyone else is doing it.

Lead author of the report, Jane Brown of the University of North Carolina, at Chapel Hill, says the study is the first to show that the more kids are exposed to sex in media the earlier they have sex.

The researchers surveyed 1,017 black and white teens when they were 12 to 14 years old and again two years later, asking them about their use of four different kinds of media and their sexual behavior.

The adolescents were from North Carolina's Durham, Orange and Granville counties.

The research team also analyzed the sexual content in 308 different television shows, movies, songs and magazines used regularly by the teens and then calculated a measure of each teen's "sexual media diet."

They found that white teens in the study who had a high sexual media diet when they were 12 to 14 years old were more than twice as likely as those with less exposure to sex in the media to have had sexual intercourse two years later.

The relationship was not as strong for black teens as it was for whites.

Brown a professor of Journalism and Mass Communication, says teenagers are looking to the media for sexual information because they are not getting such information in other places, and the media is not the best sex educator as the crucial three C's: commitment, contraception and consequences are usually absent.

Previous research has been limited to television, but this study looked at teens exposure to movies, TV shows, music and magazines, which were all analysed for their sexual content.

Brown and her colleagues found that one of the strongest protective factors against early sexual behavior was clear parental communication about sex.

White teens who reported that their parents did not approve of them having sex at this age were less likely to have engaged in pre-coital sexual behavior.

Both black and white youth who reported their parents did not want them to have sex were less likely to have engaged in sexual intercourse by the time they were 16 years old than those who perceived less parent disapproval of teen sex.

Brown said the media, schools, parents and pediatricians need to provide more accurate and timely sexual information to teens, otherwise, the media will continue to serve as a kind of sexual super peer that doesn't have the best interests of young people in mind.

As she says, it took many studies over a number of years to establish that violence in the media increased children's violent behaviour and to begin initiatives to reduce harmful effects.

Therefore, the researchers say, it may be prudent not to wait decades to conclude that the media are also important sources of sexual norms for youth.

The study was published in the April issue of Pediatrics, the journal of the American Academy of Pediatrics.