Could There Be a Blood Test for Lasting Love?

By now, we've all heard of the powers of oxytocin, the much-vaunted "cuddle hormone" that makes people fall in love and hamsters kill each other. Well, now there's something else oxytocin can do: predict which couples will stay together.

Miller-McCune reports on a study published in the tongue-twisting journal Psychoneuroendocrinology, in which researchers tested the oxytocin levels of 163 twentysomethings, 120 of whom had recently started relationships. They found that "new lovers had substantially higher plasma levels of oxytocin, as compared to non-attached singles." No surprise there: "These findings are consistent with those reported for other mammals, particularly monogamous rodent species in which oxytocin has shown to play a critical role in the formation of pair bonds." But then they tracked down the coupled subjects six months later: 36 couples were still together. And here's the really interesting part:

Couples who stayed together showed higher oxytocin levels at the initial period of romantic attachment. These findings suggest that oxytocin in the first months of romantic love may serve as an index of relationship duration.

So basically, high oxytocin at the beginning of a relationship predicts its longevity — at least up to the six-month mark. This suggests the intriguing and sort of Philip-K.-Dickish idea of a relationship blood test — you get tested for oxytocin right when you first meet, and then the doctor tells you whether you should keep dating or just throw in the towel now. This sounds kind of awful, but also a little appealing — it could save you a lot of time. And maybe there's a part of you that knows when your oxytocin levels are high enough to give a relationship legs — could oxytocin be the source of butterflies? The researchers did not explore this question.

However, they did note that it's not clear which way the arrow of causation goes here. Even at the very start of a relationship, they found that couples with high oxytocin also touched each other a lot and were very affectionate. Maybe the hormone makes you act all lovey-dovey, or maybe those who act that way just have higher levels. And maybe it's that constant touching and cuteness that lays the groundwork for a longer relationship. So maybe if Dr. Love tells you your 'tocin levels are too low, she can give you a prescription for handholding and make it all better. Until then, all we have is the cruelly imperfect guesswork of the human heart. Happy Valentine's Day!

Oxytocin Levels Predict Longevity of Love Affairs [Miller-McCune]

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