Men undergo hormonal changes during the transition to fatherhood and interactions between these hormones are related to how they interact with their children, according to new research published in Philosophical Transactions of the Royal Society B. Surprisingly, however, oxytocin does not appear to be one of these hormones.
Mothers have biological connections to their infants through pregnancy and breastfeeding, which are accompanied by hormonal fluctuations. But much less is known about the hormonal changes that men experience in the transition to fatherhood. The team of scientists behind the new study sought to start filling in this gap in the research literature.
“Around half of the parents are fathers, yet research on parents focuses on mothers most of the time,” said study author Marian Bakermans-Kranenburg, a professor at the Institute of Applied Psychology in Lisbon. “The transition to parenthood is a life experience that is accompanied by huge hormonal changes in women. What happens to men’s hormone system when they become fathers for the first time? And are hormone levels related to how they interact with their babies?”
Hormones are critical regulators of many physiological processes. In humans, hormones play a role in everything from metabolism and sexual function to mood and fertility. The researchers were particularly interested in five hormones that might influence parenting behavior: oxytocin, vasopressin, testosterone, estradiol and cortisol.
Oxytocin is sometimes called the “love hormone” because it is involved in social bonding and intimate relationships. Vasopressin regulates blood pressure and water retention. Testosterone is a male sex hormone that plays a role in sexual development and muscle growth. Estradiol is a female sex hormone that is involved in the development of secondary sex characteristics and the regulation of the menstrual cycle. Cortisol is a stress hormone involved in the body’s response to emergency situations.
For their study, the researchers recruited a sample of 73 expectant fathers, who were followed from the prenatal phase to the postnatal phase. To assess changes in hormone levels, the expectant fathers provided salvia samples on the mornings and evenings of two consecutive days at 36 weeks of gestation. They again provided salvia samples at around five weeks after the birth of their infant.
Approximately two months after the birth of their infant, the participants were observed during a 10-minute free play session. The fathers were told to play with their child as they would normally do. Their interactions were recorded and the fathers’ parental sensitivity was scored by a group of five independent raters. The researchers also recruited a separate sample of 79 fathers who had recently had their first baby, who were observed in the postnatal phase only.
In line with previous research, testosterone decreased substantially from the prenatal to the postnatal period but estradiol levels remained unchanged. Testosterone and estradiol were not individually associated with parental sensitivity. But the researchers found evidence that the interplay between the two hormones played an important role. Fathers tended to have lower parental sensitivity when they had both high testosterone and high estradiol.
“Not only mothers, but also fathers show changes in their hormonal levels when their first infant is born,” Bakermans-Kranenburg told PsyPost. “And these hormonal levels in combination do correlate with fathers parenting behavior.”
Given oxytocin’s reputation to promote bonding, the researchers had expected that higher oxytocin levels would be associated with more sensitive parenting. But they found no evidence that the hormone was related to parenting behaviors. In addition, oxytocin levels did not change from the prenatal to the postnatal period.
The study authors wrote that the hormone “may be considered an oxymoron as ‘oxytocin’ is derived from the Greek words for ‘swift childbirth’, and giving birth is typically not experienced as swift and certainly does not constitute the father’s role in the couple’s transition to parenthood.”
Prenatal oxytocin did, however, predict postnatal levels of vasopressin.
“To conclude, we did not find support for the importance of oxytocin as stand-alone hormone or in interplay with other hormones in the process of men transitioning into fatherhood or in predicting the quality of their interactions with the newborn,” the authors wrote. “We may have missed changes in oxytocin concentrations during earlier phases of the pregnancy or later than two months after birth, or oxytocin might indeed be an oxymoron.”
“By contrast, testosterone decreased substantially from the prenatal to the postnatal period and the combination of lower levels of both testosterone and estradiol was associated with higher quality of paternal interactions with the newborn. We propose that the null findings should be considered preliminary and in need of replication.”
“The next question is how differences in hormonal levels can be explained, and if we can support sensitive parenting in new fathers, e.g. by increasing their prenatal involvement,” Bakermans-Kranenburg added.
The study, “Is paternal oxytocin an oxymoron? Oxytocin, vasopressin, testosterone, oestradiol and cortisol in emerging fatherhood“, was authored by Marian J. Bakermans-Kranenburg, Martine W. F. T. Verhees, Anna M. Lotz, Kim Alyousefi-van Dijk, and Marinus H. van IJzendoorn
