Enacting policies that promote equality, like same-sex marriage laws, may ease the mental burdens on lesbian, gay and bisexual young people, a new U.S. study suggests.

Researchers found that in states where same-sex marriage became legal, there was a drop in suicide attempts by high school students, especially among sexual minority students.

"I hope policymakers and the public are aware that the social policies that govern LGBT rights can have an impact on child welfare and wellbeing," said lead author Julia Raifman, a public health researcher at the Johns Hopkins Bloomberg School of Public Health in Baltimore.

The first state to legalize same-sex marriage was Massachusetts, in 2003. Thirty five states had done so by June 2015, when the U.S. Supreme Court made it legal nationwide.

"I was really interested in how equal rights for LGBT populations affected health outcomes," Raifman told Reuters Health.

The staggered implementation of same-sex marriage in different states offered an opportunity to examine the relationship between policy changes and health outcomes, she added.

Suicide is the second most common cause of death among people between 15 and 24 years old, Raifman's team writes in JAMA Pediatrics, and lesbian, gay and bisexual (LGB) teens are at a significantly heightened risk for suicide attempts.

A participant wears a LGBT flag as people take part in the Annual Mermaid Parade in Brooklyn Thomson Reuters

In the 2015 version of the nationally representative Youth Risk Behavior Surveillance System (YRBSS) survey, 29 percent of gay, lesbian and bisexual high school students reported having attempted suicide in the past year, compared to 6 percent of their heterosexual peers.

For the new study, the researchers used data collected from U.S. public high school students in grades 9 through 12 by the YRBSS between January 1999 and December 2015.

Researchers compared rates of reported suicide attempts in 32 states before and after same-sex marriage implementation to reported attempts in 15 states without legalization.

Almost 9 percent of all respondents and nearly 29 percent of students who identified as sexual minorities reported a suicide attempt before same-sex marriage implementation, researchers found. Implementing same-sex marriage was linked to a 7 percent reduction in the number of high schoolers attempting to kill themselves.

This reduced risk was concentrated among students who identified as sexual minorities.

The researchers estimate that same-sex marriage legalization is tied to 134,000 fewer suicide attempts each year.

The new study can't say why legalizing same-sex marriage is associated with fewer suicide attempts, but Raifman said there could be a number of reasons. For example, legalization may change the outlook of gay, lesbian and bisexual teens or it may change how other people treat sexual minorities.

"We only have evidence on the relationship between state same-sex marriage policies, but I think it’s possible other policies may affect adolescent wellbeing," she said.

Currently, no comprehensive suicide prevention program backed by science exists for teens who are sexual minorities, Mark Hatzenbuehler writes in an editorial accompanying the new study.

"Although no single factor can fully explain a complex behavior such as suicide, the study by Raifman and colleagues suggests that structural stigma - in the form of state laws - represents a potentially consequential but thus far largely overlooked contextual factor underlying suicidality in LGB youth," writes Hatzenbuehler, an associate professor of sociomedical sciences at Columbia University’s Mailman School of Public Health in New York City.