A recent study published in the Proceedings of the National Academy of Sciences (PNAS) provides new insight into how oxytocin, a hormone associated with social bonding and trust, varies across sex and age. The research used more than 1,200 samples from 400 individuals, making it the largest dataset of oxytocin measurements to date.
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, explained some known aspects about oxytocin: “Oxytocin spikes during childbirth, breastfeeding and bonding, with social connections and romantic love, and during reproduction.” He added that measuring oxytocin is costly, so most studies have small sample sizes. “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.”
The research was conducted in collaboration with the Tsimane community in Bolivia. Trumble serves as co-director of the Tsimane Health and Life History Project. This partnership has lasted over two decades, focusing on demographic and biomedical data collection while also providing medical care to the community.
The findings show that oxytocin patterns differ between females and males. For women, levels are closely linked to reproduction and child care activities; peaks occur during reproductive years—especially among those breastfeeding—and decline after their 40s before rising slightly again later in life. In contrast, men’s oxytocin levels are lower in their twenties but increase with age.
To gather this information, researchers collected urine samples from participants aged 2 to 84 years old. They also interviewed subjects about their health status, parenthood status, involvement in child care activities, breastfeeding (for women), and self-rated health.
Adrian Jaeggi from the Institute of Evolutionary Medicine at the University of Zürich noted why this population was chosen: “(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.”
Lead author Abigail Colby stated: “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.”
Among female participants who had recently engaged in child care activities or were breastfeeding at sample collection timepoints showed significantly elevated oxytocin concentrations. Outside these periods childhood levels were low followed by gradual decline beginning in their forties then a slight rise again after mid-sixties.
For men there was no meaningful difference between fathers’ or non-fathers’ oxytocin levels based on reported childcare activities; however higher self-rated health correlated with higher hormone levels later in life. Colby said: “A higher oxytocin level in later life among males may reflect a survivor bias… our finding that good self-rated health is associated with higher oxytocin… Perhaps males with higher oxytocin—and potentially better health—live longer…”
Jaeggi added: “I think what is (possible) is that oxytocin levels in these men are related to its physiological rather than behavioral functions… it was related to good health in this study.”
Trumble emphasized limitations remain: “While there are a growing number of studies on oxytocin there is still a lot we do not know… what we really need are longitudinal studies that follow same men across their entire lives…”
This work builds on previous ASU research involving the Tsimane showing notably healthy hearts as well as low rates of Alzheimer’s disease among other positive aging outcomes.
Arizona State University has received recognition for its innovative approaches for eight consecutive years according to U.S. News & World Report rankings (source).
Funding for this study came from the Swiss National Science Foundation.
