The new research, published in Psychoneuroendocrinology, investigated the link between maternal mood and the oxytocin pathway during breastfeeding, in mothers with and without symptoms of postnatal depression.

Oxytocin is a hormone that is released in both the brain and body. It plays a central role in childbirth and breastfeeding, and is involved in social relationships, especially intimacy, and the attachment process during infancy.

In breastfeeding, oxytocin triggers the ‘let-down’ reflex that releases the mother’s milk and is stimulated in both mothers and their baby by skin-to-skin touch.

Oxytocin release also interacts with specific brain regions to reduce stress and stimulate reward associated with this, facilitating mother-infant bonding and early infant development.

Mothers experiencing postnatal depression report increased stress during breastfeeding and early weaning. Although the social context related to a mother’s depression likely contributes to this, it has not been known whether the oxytocin system may also be affected.

In the UK, postnatal depression affects more than one in every 10 women within a year of giving birth, symptoms include persistent low mood, feeling agitated or irritable, and trouble sleeping,

For the new study, 62 new mothers aged between 23 and 44 years old, who had an infant between three and nine months old, were each given a nasal spray prior to breastfeeding, containing either oxytocin or a placebo.

Breast milk samples were collected during breastfeeding and analysed for oxytocin. The team found that oxytocin levels in breast milk were not affected by mothers’ mood at baseline.

However, while oxytocin was seen to increase in the breast milk of women without postnatal depression after using a nasal spray containing the hormone, this effect was reduced in mothers experiencing postnatal depression.

Lead author, Dr Kate Lindley Baron-Cohen (UCL Psychology & Language Sciences) said: “Our findings indicate that the oxytocin system is affected by postnatal depression in new mothers in the context of breastfeeding. Since higher levels of oxytocin in mothers are associated with positive outcomes in a child’s social development and in their mental health, these results point to a possible pathway through which infants of mothers experiencing postnatal depression may be at greater risk of later mental health vulnerabilities.”

These findings indicate a new direction for research, to further explore how oxytocin is affected in postnatal depression, and what the most effective treatment could be to support mothers who would like to breastfeed but are experiencing challenges.

The research was supported by the National Institute for Health and Care Research ARC North Thames, the Lord Leonard and Lady Estelle Wolfson Foundation, Wellcome, the University of York, the Fund for Psychoanalytic Research through the American Psychoanalytic Association, the International Psychoanalytical Association, the Michael Samuel Charitable Trust, the Denman Charitable Trust, and the Galvani Foundation.