As the country awaits two important Supreme Court decisions involving state laws on same-sex marriage, a small but consistent body of research suggests that laws that ban gay marriage — or approve it — can affect the mental health of gay, lesbian and bisexual Americans. When several states passed laws to prohibit same-sex marriage, for example, the mental health of gay residents seemed to suffer, while stress-related disorders dropped in at least one state after gay marriage was legalized.

Here's the research trail:

Beginning around 2004, several states banned gay marriage. Just before that series of bans, the National Institutes of Health happened to conduct a massive survey of 43,093 Americans. The questions elicited detailed information about respondents' mental health. (To validate what people reported about themselves, psychiatrists also interviewed samples of the people in the survey, and their medical diagnoses closely matched the findings of the survey.)

Soon after the wave of state bans on gay marriage, in 2004 and 2005, the NIMH conducted a second round of interviews, managing to reach 34,653 of the original respondents. (That's a high rate compared with most polls and surveys.)

Mark Hatzenbuehler, a psychologist at Columbia University who studies the health effects of social policies, analyzed the data gathered before and after the bans to determine how the mental health of people who identified themselves as gay, lesbian or bisexual had changed in those states.

Hatzenbuehler and his colleagues Katie McLaughlin, Katherine Keyes and Deborah Hasin published their analysis in 2010 in the American Journal of Public Health.

"Lesbian, gay and bisexual individuals who lived in the states that banned same-sex marriage experienced a significant increase in psychiatric disorders," Hatzenbuehler says.

"There was a 37 percent increase in mood disorders," he says, "a 42 percent increase in alcohol-use disorders, and — I think really strikingly — a 248 percent increase in generalized anxiety disorders."

To put those numbers in perspective, although Hatzenbuehler did find more than a doubling in the rate of anxiety disorders in states that eventually banned gay marriage, in absolute numbers he found that anxiety disorders went from being reported among 2.7 percent to 9.4 percent of gay, lesbian and bisexual people.

The million-dollar question is whether the laws, and the debates around them, were responsible for the change in mental health. To help answer that question, Hatzenbuehler and his colleagues looked at comparable groups and experiences.

"We showed the psychiatric disorders did not increase in lesbian, gay and bisexual populations in states that didn't debate and vote on same-sex marriages," Hatzenbuehler says. "There were also no increases — or much smaller increases — among heterosexuals living in the states that passed same-sex marriage bans."

Hatzenbuehler has also found, in a study conducted in Massachusetts, that gay men experienced fewer stress-related disorders after that state permitted gay marriage.

In a study tracking the health of 1,211 gay men in Massachusetts, Hatzenbuehler found that the men visited doctors less often and had lower health treatment costs after Massachusetts legalized same-sex marriage. When the researchers examined the diagnostic codes doctors were giving the men, they saw a decrease in disorders that have been linked to stress, such as hypertension, depression and adjustment disorders.

Hatzenbuehler says he thinks stress associated with gay-marriage debates was the "X factor." He says the quantitative data is backed by what gays, lesbians and bisexuals told the surveyors. "They reported multiple stressors during that period," Hatzenbuehler says. "They reported seeing negative media portrayals, anti-gay graffiti. They talked about experiencing a loss of safety and really feeling like these amendments and these policies were really treating them as second-class citizens."

Today, about three-dozen states ban gay marriage and about a dozen have passed laws that approve it. Some states have laws that permit civil unions but ban gay marriage.

It's unclear how or whether the upcoming Supreme Court decisions involving the constitutionality of same-sex marriage will affect the mental and physical health of gays and lesbians nationally.

It's likely that many gay, lesbian and bisexual people would see an upholding of same-sex marriage bans as an example of prejudice. But it's also possible the debate around the Supreme Court decisions could have different effects on gays than a local debate involving friends and neighbors.

Hatzenbuehler says his larger point is really that policymakers, judicial leaders and ordinary citizens need to remember that social policies are also health policies.

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