Couples show linked-up levels of the stress hormone, cortisol, which the body produces in response to threat.
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 that find 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 be a sign that the couple’s relationship is in trouble.
We know that infants coordinate their heart rhythms, temperature, and arousal with their parents. But do adult partners also sync up? Working with my advisor, Rena Repetti, I sought to test 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 repeatedly over several days.
We found that couples were, in fact, in hormonal sync – when one partner’s cortisol was higher the other partner’s was more likely to be 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 of each sample, we found a strong positive correlation between each partner’s cortisol levels.
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 I thought when we started this study, but we actually discovered the opposite.
When we looked at partners’ mood ratings we found they were in sync too – if one partner rated their mood more negatively, the other partner’s mood at that same time was more likely to be negative too.
Couples whose cortisol and negative mood states were more tightly linked actually reported worse relationship satisfaction. Although at first we were surprised by this result, it made sense when we considered that cortisol is a stress hormone. Partners in unhappy couples might be more reactive to each other’s stress states, perhaps exacerbating everyday stressful experiences. Happy couples might be better at calming each other’s stress states. When one partner comes home in a lousy mood, they want their partner to talk them down, not pile on.
Since that first study, I’ve examined how couples and families sync up their cortisol in several other studies. For example, in a sample of parents of an adolescent, I found that all three members of the family triad showed positive correlations in cortisol during a laboratory discussion. In another study of couples with a young child, I again found that partners showed linked patterns of cortisol. That study also looked at intimate partner aggression between the couples. We found that cortisol levels were more strongly correlated in couples with more of a history of 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.