"Families, Resources and Adult Health: Where Do Sexual Minorities Fit?" is one of the first studies comparing the health of married couples, cohabitating opposite-sex couples and cohabiting same-sex couples. The study appears in the March 2013 Journal of Health and Social Behavior.

"Previous studies have indicated there are health disadvantages to living together versus being married, but almost no previous research has focused on same-sex couples," said Justin Denney, assistant professor of sociology, associate director of the Kinder Institute Urban Health Program at Rice and the study's lead author. "This study is one of the first to show that the mental and physical health disadvantages of unmarried couples living together may extend to same-sex couples."

Denney said the findings were somewhat surprising given that previous research documents a strong positive relationship between higher socio-economic status and good health. The study showed that cohabitating same-sex couples have greater socio-economic resources than both married couples and cohabiting opposite-sex couples. Same-sex couples have average household incomes of $10,000 more per year than married couples and approximately $18,000 more per year than cohabiting opposite-sex couples, and they have approximately one more year of education.

Denney said that their research showed that health disadvantages between the two types of cohabiting couples occur for different reasons. For opposite-sex cohabiters, health disadvantages are partially the result of lower socio-economic status; for same-sex couples, the causes of the health disadvantages are undetermined but are not tied to socio-economic status, he said.

"Our research shows that cohabitating opposite-sex couples have fewer resources than married opposite-sex couples and are less likely to share the resources that they do have (such as health insurance and bank accounts) that can be leveraged toward better health," Denney said. "However, the study shows that cohabitating same-sex couples are socio-economically advantaged and similar to married opposite-sex couples in their tendencies to share resources within a relationship that can positively impact health."

Bridget Gorman, professor of sociology at Rice and the study's co-author, said that given the socio-economic advantages of cohabiting same-sex couples, it's unclear why they report equally poor health as cohabiting opposite-sex couples and worse health than married opposite-sex couples. However, she theorizes that there are factors not measured in their study that could have a negative impact on the health of cohabiting same-sex couples.

"Based on previous research linking health to socio-economic status, one might expect cohabitating same-sex couples to report the best health," she said. "However, our survey has no direct measures of stress from discriminatory experiences and that may be playing a part that we can't assess."

Gorman said that previous studies have determined that being a racial minority can have a negative impact on health because of discrimination and other undesirable experiences, and it is reasonable to assume that these experiences would extend to sexual minorities.

Denney and Gorman hope future research will continue to include sexual minorities in discussions of relationships and health. Both authors noted that there is little research available on the health of same-sex couples, and they hope this study will encourage further studies of this population. The authors believe that research on different living environments is timely, given the current debate on same-sex marriage.

"If there are actual health benefits to being married, how can we justify excluding a population from marrying?" Denney said.

The study is based on survey responses of self-rated health from the National Health Interview Survey, which monitors the country's health by collecting data on a broad range of health topics through personal household interviews. The data was collected between 1997 and 2008 and comes from interviews with approximately 3,200 unmarried individuals living in cohabiting same-sex relationships, 20,000 unmarried individuals in cohabiting opposite-sex relationships and 400,000 individuals in married opposite-sex relationships.