People of all sexual orientations who have ever had a same-sex sexual partner are more likely to develop post-traumatic stress disorder, researchers at the Harvard School of Public Health say.

The findings, published online last week in the American Journal of Public Health, showed that sexual minorities—gay men, lesbians, bisexuals—and heterosexuals who have had same-sex partners are at a greater risk for developing PTSD than the general population.

Maltreatment and interpersonal violence—such as non-consensual sex, domestic violence, and kidnapping—of sexual minorities leads to the increased rate of PTSD in this population.

For the most part, these traumatic events occur at a younger age than what the general population experiences—another cause of the higher levels of PTSD within the group.

“It’s known that sexual minorities have high exposures to violence” and “high rates of mental health,” said the study’s lead author, Andrea L. Roberts ’88, a postdoctoral fellow in epidemiology at HSPH.

Using data from the National Epidemiologic Survey on Alcohol and Related Conditions, which represents 34,653 U.S. residents, the researchers found that many of the sexual minority subjects who developed PTSD experienced their most traumatic event before reaching the age of 12.

Although these children are not aware of their sexual orientations at this age, they may exhibit atypical behaviors for their gender—for example, a boy may exhibit some feminine qualities, according to Roberts.

These tendencies can lead to bullying and other traumatic events, in which the parents do not intervene or provide adequate protection for their children, Roberts said.

In addition, the researchers found that heterosexuals who have had same-sex sexual partners have the same risk of developing PTSD as self-identifying homosexuals. But heterosexuals who are merely attracted to the same sex do not display as high of a risk.

The study, Roberts said, demonstrates that doctors, particularly pediatricians, need to recognize that their sexual minority patients may face victimization in the future, or have faced such experiences in the past.