New research links postnatal depression to a disrupted oxytocin response during breastfeeding

A new study published in Psychoneuroendocrinology sheds light on the complex relationship between postnatal depression and oxytocin, a hormone essential for breastfeeding and bonding between mothers and their infants. The research found no significant difference in oxytocin levels in breast milk between mothers with postnatal depression and those without, but it did reveal that oxytocin administered via nasal spray increased milk oxytocin only in mothers without depressive symptoms. These findings suggest that depression may disrupt the normal oxytocin response to breastfeeding, with potential implications for maternal well-being and infant development.

The motivation behind this study comes from growing interest in how breastfeeding supports emotional bonding between mothers and babies, and how difficulties in this process may be linked to postnatal depression. Past research has shown that breastfeeding can reduce stress, improve mood, and strengthen the emotional connection between mother and infant. However, mothers with postnatal depression are more likely to report early weaning, negative experiences while breastfeeding, and difficulty forming intimate bonds. One hypothesis is that hormonal disruptions, particularly involving oxytocin, may help explain these patterns.

Oxytocin plays a central role in milk release during breastfeeding and in emotional bonding. It is released in both the brain and the body during skin-to-skin contact and when the infant suckles. In the brain, oxytocin contributes to feelings of calm, safety, and connection. In the body, it triggers the contraction of muscle cells in the breast to release milk. The researchers wanted to know whether mothers experiencing symptoms of postnatal depression produce less oxytocin in their breast milk, and whether this could help explain some of the challenges they face in breastfeeding and bonding with their babies.

“The transition to motherhood during pregnancy and the year following childbirth is a period of vulnerability for women, and approximately 10–20% of new mothers experience anxiety and depression. This causes feelings of sadness, loss, and shame for the woman, and if left untreated can also have a damaging impact on the health of her baby,” said study author Kate Lindley Baron-Cohen, a postdoctoral researcher at University College London.

“We know that breastfeeding can have a positive effect on the mother–infant relationship and on children’s development. Breastfeeding can also be protective against mental health difficulties in new mothers. But many women who experience depression after childbirth do not breastfeed, or struggle with it if they try, which can worsen their mental health and reduce their baby’s opportunities to receive the benefits that breastfeeding can offer. We were driven to explore this further to improve the support that can be offered to new mothers and their babies.”

To investigate, the researchers recruited 62 breastfeeding mothers between the ages of 23 and 42. All participants were between 3 and 9 months postpartum and were currently breastfeeding, either exclusively or alongside other foods. The mothers completed a questionnaire that assessed their symptoms of postnatal depression using the Edinburgh Postnatal Depression Scale, a widely used screening tool. Based on their scores, the researchers divided the sample into two groups: 26 mothers who met the threshold for probable postnatal depression and 36 who did not.

Each mother attended three sessions at a research lab. In the first session, breast milk samples were collected during a regular breastfeeding session to measure baseline levels of naturally occurring oxytocin. In the second and third sessions, the mothers received a nasal spray—either a placebo or one containing oxytocin—before breastfeeding. The order was randomized and double-blinded, meaning neither the participants nor the researchers knew which spray was being administered. After a resting period to allow the spray to take effect, the mothers breastfed and another milk sample was collected.

The researchers used a laboratory technique called ELISA to measure the concentration of oxytocin in the breast milk samples. They then analyzed whether oxytocin levels were related to depression scores and whether they changed after the oxytocin nasal spray was administered.

Contrary to the researchers’ predictions, there was no evidence that mothers with postnatal depression had lower oxytocin levels in their breast milk compared to those without depression. The analysis showed no significant correlation between breast milk oxytocin levels and depression symptoms. In other words, depressive symptoms did not appear to reduce the amount of oxytocin in breast milk at baseline.

“This suggested to us the possibility that lactation difficulties reported by mothers with depression may be more attributable to psychological factors than biological ones such as oxytocin, and could be best supported by psychological therapy,” Lindley Baron-Cohen told PsyPost.

However, when the researchers looked at how oxytocin levels changed in response to the nasal spray, an interesting pattern emerged. Mothers without depression showed an increase in breast milk oxytocin after receiving the nasal spray, while mothers with depression did not.

“This indicates there may be a disruption in the brain-to-breast oxytocin pathway in mothers experiencing postnatal depression during breastfeeding, and might explain why some mothers experiencing depression are able to lactate to feed their infant but do not report the calming or rewarding effects of breastfeeding related to mother–infant bonding as do mothers who are not depressed,” Lindley Baron-Cohen explained.

The authors propose that this difference might reflect a disruption in the coordination between central and peripheral oxytocin systems. Central oxytocin is released in the brain and is involved in emotional regulation and bonding. Peripheral oxytocin, released into the bloodstream, supports milk letdown. In healthy mothers, these systems appear to work in a loop that reinforces both breastfeeding and bonding. But in mothers with postnatal depression, this loop may not function as effectively, which could make breastfeeding less emotionally rewarding and more challenging.

These findings may also help explain why some mothers with depression can successfully breastfeed while others struggle. The researchers suggest that while the peripheral oxytocin system might still allow for milk production, the central system—which contributes to the calming and rewarding effects of breastfeeding—may not be working properly. This could explain why breastfeeding does not provide the same stress-reducing and bonding benefits for mothers with depression.

“Our findings show that the hormone oxytocin is affected in mothers experiencing postnatal depression during breastfeeding,” Lindley Baron-Cohen told PsyPost. “Since oxytocin plays a key role in mother–infant bonding and is responsible for the let-down reflex that releases a mother’s breast milk during breastfeeding, new treatments that target oxytocin may be able to improve the support for mothers with postnatal depression who would like to breastfeed but are experiencing challenges. This could have treatment benefits for both new mothers and their babies.”

The study has some limitations. Although the sample size was based on power calculations and was consistent with similar research, it was still relatively small. Oxytocin levels in breast milk are lower than in other fluids, such as blood or saliva, which may have made it harder to detect small differences between groups. The researchers also measured oxytocin at only one point during each feeding session, which provides only a snapshot of hormonal changes.

“Our findings have not been replicated yet and should be treated as preliminary until they have,” Lindley Baron-Cohen said. Looking forward, “we will be exploring new treatments to improve support for mothers and infants affected by postnatal depression, and will be following up mothers and their children to explore how oxytocin may be involved in the transference of mental health difficulties across development.”

The study, “Intranasal oxytocin increases breast milk oxytocin, but has a reduced effect in depressed mothers: A randomized controlled trial,” was authored by Kate Lindley Baron-Cohen, Pasco Fearon, Ruth Feldman, Paul Hardiman, Orna Zagoory-Sharon, Elizabeth Meins, and Peter Fonagy.