Are the Hormones of Couples in Sync?

Source: Ivanko80/Shutterstock

We know that family members can get under each other’s skin, but can they actually influence each other’s hormones? It's been found that infants coordinate their heart rhythms, temperature, and arousal with their parents. But do adult partners also sync up? I have been working on a series of studies finding that people in close relationships can do exactly this: Couples show linked-up levels of the stress hormone cortisol, which the body produces in response to a threat or challenge. And this synchrony might actually signal a relationship in trouble.

I first tested this question in a sample of dual-income married couples, who participated in the Center for the Everyday Lives of Families study at the University of California, Los Angeles. Each member of the couple contributed a saliva sample and told us about their mood repeatedly over several days. We collected cortisol and mood ratings four times a day for three days, or 12 samples in all.

When we crunched these data, my graduate advisor Rena Repetti and I found that couples were, in fact, linked up: For each occasion that one partner’s cortisol was higher than usual, the other partner’s was likely higher, too. Cortisol has a daily rhythm, with levels peaking in the morning and declining across the day. But even after controlling for the time of day that each saliva sample was taken, we found a strong positive correlation between partners' cortisol levels.

When we looked at partners’ momentary mood ratings, we found that they were also in sync: If one partner rated their mood more negatively, the other partner’s mood at that same time was more likely to be negative, too.

This is good news, right? Couples attune to each other, which means that the better their relationship, the more linked up they’d be. That’s what we thought, too, when we started this study. But we actually discovered the opposite: Couples whose cortisol and negative mood states were more tightly linked actually reported lower relationship satisfaction. This result surprised us at first, but it clicked when we remembered that cortisol is a stress hormone. Partners in unhappy couples might be more reactive to each other’s stress states and negative moods, perhaps exacerbating their everyday stressful experiences. Happy couples might be better at calming each other down and balancing out each other's arousal. After all, when you come home in a lousy mood, you want your partner to reassure you, not to pile on additional stress.

Since that first study, I’ve examined how couples and families sync up their cortisol within several other projects. In a sample of parents of adolescents, my postdoctoral advisor Gayla Margolin and I found that all three members of the family triad showed positive correlations in cortisol during a laboratory conflict discussion. Next, I worked with UCLA collaborator Christine Dunkel Schetter and other researchers on a study of couples with a young child who sampled cortisol on the same day. Again, we found that partners showed linked patterns of cortisol. We also found that cortisol levels were more strongly correlated in couples with a history of intimate partner aggression. This finding provides additional evidence that tightly linked stress hormones may reflect an unhealthy relationship dynamic.

Since cortisol plays a role in metabolism and immune functioning, the family-level factors that cause out-of-whack cortisol may also contribute to long-term health. Knowing that unhappy couples may sync up their cortisol more strongly gives us some insight into why distressed marriages can be detrimental to health. Perhaps it’s the added stress of living with a partner whose bad moods can get on your nerves — literally.

I'm continuing to look at hormonal linkage, and have also found evidence for synchrony within partners' testosterone levels across pregnancy. University of Michigan researcher Robin Edelstein took multiple samples of fathers' and mothers' testosterone during pregnancy, and we found that the fathers whose testosterone levels were more strongly correlated reported being more invested, committed, and satisfied in their relationships with their partners after a baby’s birth. Fathers also reported more dedication to the postpartum relationship if they showed more of a drop in testosterone over the pregnancy. Women’s testosterone rises in late pregnancy, due to the influence of the placenta. In other words, men and women may show the opposite pattern of testosterone change across pregnancy. But by using a statistical model that included both the influence of time (number of weeks into the pregnancy) and the partner’s hormone level, we were able to test both the change across pregnancy and the level of synchrony within the couple.

Although I have found in several studies that cortisol synchrony appears in more distressed relationships, in this case, more correlated testosterone predicted more postpartum commitment. These differences may be due to the different function of the hormones — one plays a role in stress, the other in reproduction. The timing of our data collection, during pregnancy, may have also affected our results.

To understand these and other processes better, I’m collecting data for HATCH (Hormones Across the Transition to Childrearing), a new study that will follow couples from pregnancy across the first year of parenthood, and will sample both cortisol and testosterone from mothers and fathers. I’m hoping to again look at synchrony within couples and whether it predicts family well-being over a sensitive period, like the transition to parenthood.

Hormones Essential Reads

Contraceptives and Mental Health

How Hormones May Affect Addiction and Depression

Source: Soupstance, Creative Commons license

How can you prevent stress contagion within your own relationships?

Remember that your partner's stress can take a toll on your body, too, so work to cultivate calm when your partner gets agitated. Experiment to figure out how to help soothe your partner in the moment, and encourage your partner to return the favor when you get overwhelmed. Finding healthy ways to tackle stress will help keep not only your relationship, but also your hormones in balance.

^{Note: a version of this piece also appears on Fatherhood.Global}