Using data collected in the 2000s, researchers found that single young women experienced a similar decline in emotional distress when they moved in with a romantic partner or when they went straight to marriage for the first time.
Men experienced a drop in emotional distress only when they went directly to marriage, not when they moved in with a romantic partner for the first time.
But for young adults who moved on from that first relationship, both men and women received similar emotional boosts whether they moved in with their second partner or got married to them.
The findings suggest an evolving role of marriage among young people today, said Sara Mernitz, co-author of the study and a doctoral student in human sciences at The Ohio State University.
As recently as the early 1990s, young people still received emotional health benefits when they went from living together to getting married, Mernitz said.
"Now it appears that young people, especially women, get the same emotional boost from moving in together as they do from going directly to marriage," she said. "There's no additional boost from getting married."
The study appears online in the Journal of Family Psychology and will be published in a future print edition.
Claire Kamp Dush, co-author of the study and associate professor of human sciences at Ohio State, said the results may reflect the fact that cohabiting today does not carry the same stigma as in previous generations. Nowadays, about two-thirds of couples live together before marriage.
"At one time marriage may have been seen as the only way for young couples to get the social support and companionship that is important for emotional health," Kamp Dush said.
"It's not that way anymore. We're finding that marriage isn't necessary to reap the benefits of living together, at least when it comes to emotional health."
Another significant finding was that the emotional benefits of cohabitation or marriage aren't limited to first relationships. The study found that young adults experienced a drop in emotional distress when they moved from a first relationship into cohabitation or marriage with a second partner.
"The young people in our study may be selecting better partners for themselves the second time around, which is why they are seeing a drop in emotional distress," Kamp Dush said.
The researchers used data from the National Longitudinal Survey of Youth 1997. This study included 8,700 people who were born between 1980 and 1984 and were interviewed every other year from 2000 to 2010.
The NLSY97 is conducted by Ohio State's Center for Human Resource Research for the U.S. Bureau of Labor Statistics.
In addition to asking about their relationship status at each interview, participants were asked five questions assessing their levels of emotional distress. They reported on a scale of 1 (all of the time) to 4 (none of the time) how often in the past month they had felt 'downhearted and blue' and other symptoms.
This study has advantages over studies that simply compare groups of people who are single, married and cohabiting.
"We are able to look at people over a 10-year period and see what happens to them individually as they make these various transitions in their relationships," Mernitz said.
The study did find some gender differences, at least for first unions of marriage or cohabitation. For those entering a first union, men experienced a decrease in emotional distress only if they went directly into marriage. There was no change in distress for men who cohabited with a female partner.
That may be because men are more likely than women to report cohabiting as a way to test a relationship, which has been linked in other research to subsequent relationship problems.
Also, Kamp Dush noted that this study assessed only emotional distress. Other research suggests that behavioral indicators of health -- such as alcohol use or violence -- may be more accurate for men than emotional indicators.
In any case, the gender differences were visible for only first unions. There were no differences in emotional health changes for men and women entering their second union, whether they were marriage or cohabitation.
The study also found that individuals who gave birth (or whose partner gave birth) showed significant decreases in emotional distress compared to those who did not have a child.
That may seem surprising, given the stress associated with having a child, Kamp Dush said. But she noted that this study looked only at emotional distress. There may be other ways in which the stress of raising a child is manifested in these couples.
Kamp Dush said that marriage may provide some benefits over cohabitation that were not measured in this study, such as stability. But these findings provide evidence of a changing landscape in the United States.
"It's not commonly known that couples can get emotional benefits from moving in together without being married. That's something we should be talking about," she said.