'Bonding hormone' Linked to Postpartum Depression

Low oxytocin levels may predict later postpartum depression.

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By Tina Hesman Saey, Science News

Women with lower levels of the hormone oxytocin in their blood during late stages of pregnancy are more likely to develop postpartum depression, new research suggests. The finding, published online May 11 in Neuropsychopharmacology, may be a first step toward identifying pregnant women who are at risk of becoming depressed after the birth of their babies.

While the link is intriguing, “there’s a lot of steps to go between a correlation and using it as a biomarker,” says Ziad Nahas, a psychiatrist and mood disorders researcher at the Medical University of South Carolina in Charleston who was not involved in the study.

Oxytocin helps stimulate contractions and lactation in pregnant women. The hormone has also been implicated in facilitating emotional bonds between people, including mothers and children. Some earlier studies have linked oxytocin to depression, but not to postpartum depression.

Of 73 women who volunteered blood samples for the study, 14 later developed postpartum depression. Oxytocin concentrations in the women’s blood varied widely, from 14.4 to 245.7 picograms per milliliter. Although the researchers found a great deal of overlap in oxytocin levels between the two groups, women who got depressed tended to have lower levels.

The link is too preliminary for doctors to use oxytocin levels to predict which patients are likely to develop postpartum depression, says Gunther Meinlschmidt, a psychobiologist at the University of Basel in Switzerland who led the study. Even if a woman has low levels of the hormone, there’s no guarantee she will get depressed. “This is not a yes, no, one-or-zero factor. It’s one of several factors” that determine a woman’s risk for the condition, he says. It’s also unclear whether treating women with oxytocin would have any effect on depression.

Low oxytocin levels might be a symptom or a cause of both depression and poor bonding between depressed moms and their babies. “It’s difficult to untangle,” Meinlschmidt says. “It might go in both directions, sort of a vicious circle.”

And measuring oxytocin levels in the blood may not indicate what is going on in the brain, where the hormone affects emotions and behavior, Nahas says.

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