Is She the One? Your Hormonal Profile Knows

How do you know if the person you’re dating is “the one”? Astrologers, magazine quizzes and mothers are time-tested sources of answers. But none of them are exactly peer-reviewed.

Now, brain scientists at Israel’s Bar-Ilan University have found a more reliable prognostic for relationship success – hormones. It turns out that the way new lovers’ hormone levels relate predicts how they will get along and whether they will stay together or break up.

“When you’re falling in love, your hormones and behaviors adjust to those of your partner,” said Professor Ruth Feldman, who led the research at Bar-Ilan’s departments of brain science and psychology and is an adjunct professor at Yale University. “By looking at certain hormone levels in you and your partner, we can get an idea of how the process is going and even where it’s headed.”

The findings, published in the journal Social Neuroscience in March, reveal how biology and behavior interact to create romance and could be used to create new therapies for couples.

The good, the bad and the lovey

Feldman, along with Dr. Inna Schnedierman and Dr. Orna Zagoory-Sharon of Bar-Ilan, looked at the powerful “love hormone” oxytocin and several other hormones known to be involved in mammalian bonding. They found that levels of three of the hormones – oxytocin, cortisol and testosterone – predicted how well male-female couples that had been together between six weeks and three months resolved conflicts.

On average, the new lovers had almost twice as much oxytocin – which is associated with intimacy and cooperation – in their blood as a singles (and even more than Feldman previously found in parents of newborns). Interestingly, the lover experiencing this oxytocin rush was not affected by it. Rather, his or her partner tended to be more empathetic when discussing a problem in their relationship.

What do one person’s hormones have to do with someone else’s behavior, you ask? Well, Feldman thinks the effects of oxytocin flow from one partner to the other as part of a bio-behavioral feedback loop. So higher oxytocin in one partner, say a woman, causes her to be nicer to her boyfriend, boosting his oxytocin and making him nicer to her, which in turn further elevates her oxytocin.

Cortisol and testosterone appear to drive similar feedback loops. When both partners in a couple had higher cortisol – a stress hormone that reduced empathetic behavior in individuals – they tended to show less empathy toward each other and were more likely to break up in the next six months.

In the case of testosterone – which was associated with less empathy in women – higher levels in both partners tended to make them more hostile to each other. But when only one partner had higher testosterone, they tended to be less hostile to each other. Score one for the theory that opposites attract.

Have you taken your empathy today, honey?

The study shows, for the first time, that bio-behavioral synchrony takes place early in romantic relationships. The behaviors and hormones of new lovers apparently interact in self-reinforcing cycles that can either bind a couple together or cause them to drift apart.

To some extent, it’s fair to conclude that biology is destiny in relationships, says Feldman. Two people with high cortisol or testosterone may just be too stressed or aggressive to sustain a relationship together, she says. But the study also offers hope. Couples adjust to each over time, and the changes can be lasting. In a follow-up six months after the initial blood tests, the scientists found that lovers’ hormone levels were unchanged.

“When you open your heart and soul to another person, your hormonal systems become very plastic,” said Feldman. “This creates a window in which you can shape and be shaped by the person, potentially forming a lasting bond.”

In addition to advancing understanding of romantic relationships, which are central to human health and well-being, the study paves the way for new treatments for relationship problems, Feldman says.

With the help of therapists, couples can learn to control subtle cues – even unconscious nonverbal ones, like eye contact, tone of voice and touching – that can set off hormonal-behavioral chain reactions for good or bad. Intimacy-enhancing drugs may one day help. An oxytocin nasal spray has already been shown in clinical trials to reduce cortisol levels and improve negative communication between couples.