Poor mental health and casual sex contribute to each other over time among teen and young adults, a new study published in the Journal of Sex finds. Researchers at Ohio State University found that teens who showed symptoms of being depressed were more likely than others to have casual sex. It also discovered an inverse correlation: that those who had casual sex were more likely to be depressed later on.

“There’s always been a question about which one is the cause and which is the effect. This study provides evidence that poor mental health can lead to casual sex, but also that casual sex leads to additional declines in mental health.” said Sara Sandberg-Thoma, lead author of the study.

The findings apply to both men and women alike. The results surprosed the authors, since it seems to undermine what most consider to be the standards around male and female sexuality — that women don't have as much casual sex. “That was unexpected because there is still this sexual double standard in society that says it is ok for men to have casual sexual relationships, but it is not ok for women,” said Claire Kamp Dush, assistant professor of human sciences at Ohio State, “But these results suggest that poor mental health and casual sex are linked, whether you’re a man or a woman.”

Ten thousand adolescents from 80 high schools and 52 middle schools in grades 7 through 12 were interviewed. The teens were then interviewed again when they were aged 18 to 26. They were surveyed about their romantic relationship experiences as well as depressive symptoms and thoughts of suicide. Casual sexual relationships were reported by 29 percent of the teens interviewed. "Casual sex" was defined in the study as having sex with a partner that one was not "dating."

Overall, 29 percent of the respondents—33 percent of men and 24 percent of women—reported engaging in any casual sexual relationship. These were defined as any relationship in which the participant reported he or she was “only having sex with partner”— not officially dating. The participants who reported having casual sexual relationships when they were young adults were more likely to have thoughts of suicide or more depressive symptoms as teens. In addition, a decline in mental health was linked to casual sex. "This study provides evidence that poor mental health can lead to casual sex, but also that casual sex leads to additional declines in mental health," said Sandberg-Thoma.

The researchers are not sure why casual sex was linked to later serious consideration of suicide, but not depressive symptoms, in these participants. “It may be that depressive symptoms fluctuate during adolescence and it is hard to capture an accurate reading when measured just twice, as in this study,” Kamp Dush said.

Kamp Dush also believes that casual sexual relationships may hurt the ability of young adults to develop committed relationships at an important time in their development. She also believes that researchers need to look closely at other measures of mental health.

“'The goal should be to identify adolescents struggling with poor mental health so that we can intervene early before they engage in casual sexual relationships," said Sandberg-Thoma.