This article originally appeared on Real Simple.
While the research isn’t entirely one-sided (there’s the weight issue, for one), several studies have suggested that married couples reap more health benefits than those who are single, divorced, or widowed. Now, a new study points to a potential reason why: Married people have lower levels of cortisol—a stress hormone that, when produced in excess, can contribute to inflammation and chronic disease.
The finding suggest that married people face less psychological stress than their single counterparts, say researchers from Carnegie Mellon University—and provide the first biological evidence to explain how committed partnerships can directly impact health.
To compare cortisol levels in married and unmarried people, researchers collected saliva samples from 572 adults, ages 21 to 55, multiple times a day on three non-consecutive days. All participants were in good health, and the researchers adjusted their analysis for personality traits—like extraversion, neuroticism, and agreeableness—that might influence their findings.
Overall, married people had lower cortisol levels than those who had never been or had previously been married. Their cortisol levels also tended to drop faster throughout the afternoon, compared to those who had never been married. (Cortisol naturally tends to be highest in the morning, but quicker declines have been linked to lower rates of heart disease and other positive health outcomes.)
Consistently high cortisol levels, which can be caused by ongoing stress, can interfere with the body’s ability to regulate inflammation, the authors say. Inflammation has been linked to many health conditions, including heart problems, lower immunity, diabetes, and cancer.
The study, published in the journal Psychoneuroendocrinology, only identified a link between marriage and cortisol levels; the authors can merely speculate—based on other research—what that might mean for their long-term health. And in the end the answer might be less than they think: In another study using the same participants, marriage did not affect people’s risk of catching a cold.
The researchers also say that, because their sample size was relatively young and healthy, the findings may not apply to older or sicker adults. And they acknowledge that marital status may mean different things different people. “For example, being divorced, separated or bereaved may be more acceptable (and normative) for a 60-year-old than a 30-year-old,” they write.
But overall, the authors say their findings suggest a pathway that could be responsible, at least in part, for marriage’s often-touted health perks. In a press release, co-author and psychology professor Sheldon Cohen, PhD, summed up the results in this way: “These data provide important insight into the way in which our intimate social relationships can get under the skin to influence our health.”