New study reveals how bonding hormone shifts across sex and age
ASU researchers uncovered that distinct oxytocin patterns occur in females and males throughout their lifespans. Stock photo courtesy of Canva
Oxytocin, often called the “love hormone," plays a central role in building attraction, trust and social bonds among humans. Yet despite its importance, much about the hormone has remained unclear.
A new study published in PNAS uses the largest dataset of oxytocin measurements ever assembled and offers unprecedented insight into this essential hormone.
Researchers note that several aspects of oxytocin’s functions were already well established.
“Oxytocin spikes during childbirth, breastfeeding and bonding, with social connections and romantic love, and during reproduction,” said Ben Trumble, professor of evolutionary anthropology at Arizona State University's School of Human Evolution and Social Change and core faculty member of ASU's Center for Evolution and Medicine.
“However, it is expensive to measure, so most people who study oxytocin only measure it in a few samples, usually as a part of an experiment. My colleagues and I ran the largest-ever study — more than 1,200 samples from 400 people — and the first-ever study of oxytocin across the lifespan in both men and women.”
Working with the Tsimane community
Ben Trumble, professor in the School of Human Evolution and Social Change at ASU, serves as the co-director of the Tsimane Health and Life History Project. The group has a long-standing relationship with the Tsimane to collect demographic and biomedical data, and helps to provide medical care for the community — a relationship that has been in effect for more than 20 years.
The study revealed distinct oxytocin patterns in females and males. For women, oxytocin is closely tied to reproduction and child care, while men don’t reach peak levels until later in life.
In order to accomplish this, researchers worked with the Tsimane, a community of forager-horticulturalists from the Bolivian Amazon. Living a hunter-farmer lifestyle, their everyday life is very similar to human life prior to the Industrial Revolution. This offers a unique glimpse into the health and aging processes for humans before modern-day influences came into play.
Previous ASU research with the Tsimane has shown that they have the healthiest hearts, lowest rates of Alzheimer’s and dementia in the world, and minimal inflammaging.
“(Our) reason for doing this study with the Tsimane people in Bolivia is because hormone levels are very sensitive to energetic status and tend to be higher in Western industrialized populations compared to more energy-limited populations like the Tsimane,” said Adrian Jaeggi, associate professor at the Institute of Evolutionary Medicine at the University of Zürich and co-author on the study.
By looking at oxytocin levels from across the samples, from people ranging from 2 to 84 years old and who were both male and female, researchers were looking to learn more about the hormone beyond the known “love” connections.
“In this study, we aimed to explore how oxytocin varies across the human lifespan and why it varies, possibly elucidating a functional role in mediating trade-offs between reproduction and health,” said Abigail Colby, lead author and PhD candidate with the Institute of Evolutionary Medicine at the University of Zürich. The study was conducted as part of Colby’s dissertation.
The study combined both the collection of urine samples to measure oxytocin levels, as well as interviews that asked a variety of questions to learn more about participants’ breastfeeding status, parent status, their involvement in child care activities and a self-rating of their health status.
The researchers found that among female participants, oxytocin levels peaked during the reproductive years, with especially high levels observed in those who were breastfeeding.
Females who had engaged in child care activities shortly before sample collection also showed significantly elevated oxytocin concentrations. Outside of this period, women exhibited low levels throughout childhood, followed by a gradual decline beginning in their 40s, with a slight increase again in their mid-60s and beyond.
For male participants, researchers found that oxytocin levels were lower in their 20s and the highest in old age. One theory was that life events, such as parenting and becoming a grandparent, may have a long-lasting impact for males, leading to those later-in-life increases — but when researchers asked about child care activities, they found no meaningful difference between fathers and non-fathers.
But what they did find was a correlation between higher oxytocin levels and a high self-rating of health.
“A higher oxytocin level in later life among males may reflect a survivor bias, especially given that our data are cross-sectional, not longitudinal, and our finding that good self-rated health is associated with higher oxytocin,” Colby said. “Perhaps males with higher oxytocin, and potentially better health, live longer in general than individuals with lower oxytocin.”
According to Jaeggi, there may be something to this finding.
“I think what is (possible) is that oxytocin levels in these men are related to its physiological rather than behavioral functions. For example, oxytocin is involved in immune function, metabolism, the cardiovascular system, muscle regeneration, etc., hence the term ‘nature’s medicine,’ and it was related to good health in this study,” he said.
While this is the largest study and the first of its kind to look at oxytocin across the life course for both sexes, many questions still remain unanswered.
“While there are a growing number of studies on oxytocin, there is still a lot we do not know. This study is observational and cross sectional — what we really need are longitudinal studies that follow the same men across their entire lives to really test this idea,” said Trumble, who is also an affiliated researcher with ASU's Institute of Human Origins.
“Oxytocin varies across the life course in a sex-specific way in a human subsistence population” was published in PNAS. Funding for this study was provided by the Swiss National Science Foundation.
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