For a decade, the legislative push for "abstinence only" sex education has suggested that nonmarital sex negatively affects a teen's mental health. But a new study shows that the negative mental side effects of a teen's loss of virginity are confined to a small proportion of those who have sex -- specifically, young girls and both boys and girls who have sex earlier than their peers and whose relationships are uncommitted and ultimately fall apart.

Using data from the National Longitudinal Study of Adolescent Health, Ann Meier, University of Minnesota assistant professor of sociology, studied 8,563 seventh- through 12th-graders over an 18-month period, measuring for depression and low self-esteem. Meier compared the mental health of teens who didn't have sex to teens who were virgins at the beginning of the study, but who lost their virginity during the 18-month period.

She found that while the majority of teens did not experience depression as a result of first-time sex, some did -- those being the youngest teens (girls who had sex before age 15 and boys who had sex before 14) and whose relationship was not emotionally close and dissolved after sex. Girls in this group were particularly vulnerable to depression.

Meier believes it's the combination of these factors that make young teens most vulnerable to depression or low self-esteem after first-time sex. "Being female or younger than the average age at first-time sex among your peers increases the chance of depression, as does a lack of commitment or intimacy within the relationship and what happens to the relationship after first-time sex," said Meier. "For girls in uncommitted relationships, ending a relationship with sex has more of an impact on mental health than ending that same relationship if it did not involve sex."

The risk of suffering mental health problems from having sex as a teen is relatively low, but Meier said low risk still represents a large group of teens affected, as half the teen population is having sex. She cautioned that the study does not suggest that positive effects result from first-time sex among teens and said she hopes it will help policy-makers focus help on those most vulnerable rather than promoting a one-size-fits-all approach.

Meier's study, "Adolescent First Sex and Subsequent Mental Health," will be published in the May issue of the American Journal of Sociology.