Are the Hormones of Couples in Sync?
Read the full article at Psychology Today.
We know that family members can get under each other’s skin, but can they actually influence each other’s hormones? 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 threat or challenge. And this synchrony might actually signal a relationship in trouble.
We know that infants coordinate their heart rhythms, temperature, and arousal with their parents. But do adult partners also sync up? 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 sampled their saliva and told us about their mood repeatedly over several days. We collected cortisol and mood ratings four times a day for three days, 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, during which levels peak in the morning and decline 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 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.
So that’s 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 when we started this study, but we actually discovered the opposite.
Couples whose cortisol and negative mood states were more tightly linked actually reported worse relationship satisfaction. Although this result surprised us at first, 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.
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. 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 their baby’s birth.