(Reuters Health) - Gay, lesbian and bisexual people living in states where it’s legal to deny services to same-sex couples may have an increased risk of mental illness even when they don’t personally experience discrimination, a U.S. study suggests.

Direct exposure to discrimination based on sexual orientation, race and a range of other factors has long been linked to higher risk of psychological distress. But less is known about the impact of state laws that let providers of goods and services - whether they’re clerks issuing marriage licenses or doctors or lawyers or bakers - turn away same-sex couples.

To examine this question, researchers looked at nationally representative survey data collected from 2014 to 2016.

They analyzed data from 37,514 adults in three states - Utah, Michigan, and North Carolina - that passed laws permitting services to be denied to same-sex couples in 2015. They also had data from 71,575 individuals in six states without these laws: Idaho, Nevada, Ohio, Indiana, Virginia and Delaware.

The researchers defined mental distress as experiencing depression, anxiety and other emotional problems on 14 or more days per month.

In states that passed denial of service laws in 2015, the proportion of sexual minorities reporting mental distress rose from 22 percent in 2014 to about 33 percent in 2016. Where no such laws existed, the proportion of lesbian, gay and bisexual adults reporting psychological problems rose only about 1 percentage point during that period.

“Policies permitting the denial of services to same-sex couples are linked with broad harm to the mental health of lesbian, gay and bisexual people, even though it is unlikely most of them directly experienced service denials,” said study leader Julia Raifman of the Boston University School of Public Health.

On June 4, the U.S. Supreme Court ruled in favor of a Colorado baker who refused, based on his Christian faith, to make a wedding cake for a same-sex couple.

As of last year, 12 states had laws permitting denial of services to same-sex couples, researchers note in JAMA Psychiatry.

Increases in mental distress among sexual minorities in affected states were similar regardless of whether the state permitted denials of marriage licenses, adoption or foster parenting, Raifman said by email.

“We saw little change in the proportion of heterosexual adults in the states with policy changes reporting mental distress, suggesting that there was not something else going on in these states that was broadly affecting mental health,” Raifman added.

Across all nine states, 4,656 participants, or almost 5 percent, identified as sexual minorities.

At the start, in 2014, rates of mental distress were similar for sexual minorities across all these states at about 22 to 24 percent. In comparison, mental distress rates among heterosexuals were steady at almost 13 percent.

Lesbian, gay and bisexual residents of states with denial of service laws had higher rates of mental distress regardless of whether they were in a relationship.

The study wasn’t designed to prove whether or how denial of service laws might directly impact mental health for lesbian, gay or bisexual individuals.

Still, the results add to evidence suggesting that unequal treatment under the law can lead to significant physical and mental health problems, said Brian Powell, a sociology researcher at Indiana University Bloomington who wasn’t involved in the study.

“It is challenging to live in a state that defines you as less than equal,” Powell said by email. “It is challenging to know that you can be fired, be denied medical treatment, be denied service in a restaurant and perhaps even more challenging to know that your state allows this.”

SOURCE: bit.ly/2J8fkKm JAMA Psychiatry, online May 23, 2018.