Hormone Oxytocin May Help Keep Men Faithful

Love, trust, cuddling … those are words not only associated with successful relationships but also with the hormone oxytocin, which, according to a new German study, may help encourage fidelity in men who are in committed relationships.

For the study, published Tuesday in the Journal Neuroscience, 57 men were given a sniff of oxytocin, and 29 were given a placebo, and were then introduced to a female experimenter whom they later described as "attractive." The men were asked when the experimenter was at an ideal distance from them and when she moved to a "slightly uncomfortable" distance during the rendezvous.

Men in monogamous relationships kept their distance regardless of whether they made eye contact with the female experimenter. And the hormone had no effect on the distance maintained by single men.

"Because oxytocin is known to increase trust in people, we expected men under the influence of the hormone to allow the female experimenter to come even closer, but the direct opposite happened," lead researcher Dr. Rene Hurlemann of the University of Bonn said in a statement.

"Previous animal research in prairie voles identified oxytocin as major key for monogamous fidelity in animals," Hurlemann said. "Here, we provide the first evidence that oxytocin may have a similar role for humans."

Past studies have found that oxytocin in the human brain promotes trust, friendly behavior, bonding between parents and children, and even helps bickering couples argue less. Earlier this year, a study conducted in Israel found that couples exposed to high levels of the "love hormone" during the early stages of a relationship were more likely to still be together six months later than couples exposed to lower levels of the chemical.

Cuddling, kissing, orgasm produces oxytocin in the body. Sometimes even the mere touch or close physical presence of a significant other is enough to set off the hormone. In women, oxytocin is also released during childbirth and breastfeeding.

The researchers said it wasn't clear how often the hormone could or should be administered, and future studies were needed to pinpoint exactly how oxytocin can affect behavior.