The study, "Sexy Media Matters: Exposure to Sexual Content in Music, Movies, Television, and Magazines, Predicts Black and White Adolescents Sexual Behavior," found that white 12-14 year-olds who had a heavier sexual media diet were more than two times likely to have intercourse when 14-16 years old than those adolescents who had a lighter sexual media diet.

This relationship was not as significant for black teens, which seemed to be more influenced than their white peers by their parents' expectations and their friends' sexual behavior than by what they hear or see in the media.

But while one of the strongest risk factors for early sexual intercourse for both black and white teens was the perception that his or her peers were having sex, the study says that one of the strongest protective factors against early sexual behavior was clear parental communication about sex.

According to the authors, parents rarely talk with their children about sex in a timely and comprehensive way, and schools are increasingly limited in what they can say. In such a context, the mass media may be powerful educators because they provide frequent and compelling portraits of sex as fun and risk free. In 2002, for example, more than 83 percent of the 20 television shows that adolescents frequently watched included sexual content; but only about 1 in 8 of those shows included any depiction of sexual risks and/or responsibilities.

This study shows that it is not only television but also other media, such as music, movies, and magazines that push adolescents toward sexual activity.

The authors conclude that media literacy education for parents and youth, partnerships with youth-oriented media, and physician education and intervention are opportunities to help reduce media's negative effects and perhaps enhance the positive.

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Because many infants receive soy milk, the impact of genistein in humans should be carefully assessed, he said. Pregnant women are exposed to hundreds of compounds in foods, prenatal vitamins and the environment that could potentially methylate susceptible genes, he said. The effects of each compound could be beneficial or detrimental, depending upon the timing of exposure, the dose and the tissue exposed, said Jirtle.

"Our study demonstrates there are highly sensitive windows early in development when environmental exposures can permanently alter the offspring's adult susceptibility to disease," said Jirtle. "Therefore, we need to examine the effect of environmental exposures during pregnancy, not just in adulthood, if we want to accurately assess their risk or benefit to humans."

His earlier research demonstrated that four common nutritional supplements fed to pregnant mice, including folic acid and vitamin B12, lowered their offspring's susceptibility to obesity, diabetes and cancer by methylating the same agouti gene. Yet how nutrients interact in combination or in extremely high doses remains unclear, he said.

"There could be additive or synergistic effects between folic acid and genistein, or any such compounds, that hypermethylate certain genes," said Dana Dolinoy, MPH, lead author of the study. "What is good in small amounts could be harmful in large amounts. We simply don't know the effects of literally hundreds of compounds that we intentionally or inadvertently ingest or encounter each day."

Of related concern, soy is a staple of almost all laboratory mouse diets. Soy could inadvertently methylate select genes and thus mask the deleterious effects of various chemicals being tested for their risk in humans, she said.

"In the future, we may be able to potentially select compounds to protect a person from being predisposed to developing a variety of conditions," said Jirtle. "There is a vast, unknown potential for studying how our environment interacts with our epigenome to determine how we developed and who we will become."

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