Becoming a Dad Can Lower Men’s Testosterone for Years — and That Might Actually Make Them Better Fathers

New evidence shows that testosterone drops may last long after the baby years.

Men’s bodies change when they become fathers, but not in ways most people expect.

A new study from researchers at the University of Notre Dame reveals that fatherhood reshapes men’s biology for years, even decades, after their children are born. The research, published in Psychoneuroendocrinology, shows that men living with school-aged or teenage children have lower testosterone levels than single men or partnered men without kids.

Previous research suggested that new fathers experience a drop in testosterone. However, it wasn’t clear whether this decline persists as children grow older.

That decline, the authors stress, isn’t a sign of poor health. While a man’s testosterone may be lower when he is a partner or a father, it does not significantly increase his risk for clinically low testosterone, known as androgen deficiency, the researchers wrote.

Hormones of the Household

Men face a fundamental life history trade-off in how they invest their limited bio-energetic resources. High testosterone is generally linked to mating effort, which involves competition with other males to find a mate. Lower testosterone is thought to facilitate nurturing behaviors and long-term pair-bonding, which is better for raising offspring.

That trade-off — known as the “Challenge Hypothesis” — has been observed in birds, primates, and humans alike. As fathers invest more time and energy in parenting, their bodies appear to redirect hormonal resources away from mating competition and toward social cooperation.

In this framework, when a man transitions into a committed relationship or fatherhood, his body adapts to support these new cooperative roles. Previous longitudinal research has already demonstrated that men experience a decline in testosterone when they transition into marriage and again when they become fathers to newborns.

However, “Most prior studies of human paternal psychobiology have focused on families with infants and young children, often with relatively small sample sizes,” leaving crucial questions unresolved, according to the authors of the new study, biological anthropologists Lee T. Gettler and Sarah Hoegler Dennis from the University of Notre Dame.

Different Values

To get a clearer picture across a broader age range, the researchers turned to the National Health and Nutrition Examination Survey (NHANES). This massive undertaking by the U.S. Centers for Disease Control (CDC) provides a U.S. population representative sample of health and nutritional data.

The study combined three survey waves from 2011 to 2016, ultimately analyzing a large sample of 4,903 men between the ages of 20 and 60. The researchers used serum total testosterone data that was analyzed using liquid chromatography tandem mass spectrometry — the “gold standard” for hormone measurement. They were also careful to adjust for factors like age, time of blood sampling (due to the hormone’s diurnal rhythm), sleep, physical activity, and body fat.

Ultimately, the researchers found that partnered men living with two or more children between ages six and seventeen had the lowest testosterone levels of any group studied. However, across the board, partnered men had lower testosterone than single men who were not living with children.

One of the more intriguing findings was that partnered men living with younger children (0–5 years old) did not show a significant additional drop in testosterone compared to partnered men who did not live with children. The lower testosterone in men with young families appeared to be primarily driven by the state of being partnered.

The Changing Role of the Father

This pattern echoes a long line of research showing that men’s hormones adapt to the demands of family life. The phenomenon first gained major attention in 2011, when a longitudinal study in the Proceedings of the National Academy of Sciences followed over 600 men in the Philippines. The men with higher testosterone were more likely to become fathers. And, when they did, their testosterone levels fell by about a third over four years. Those who spent the most time in childcare showed the steepest declines. Another study of first-time American fathers found that prenatal declines in testosterone predicted more hands-on caregiving after birth.

Then, a 2019 meta-analysis published in Neuroscience & Biobehavioral Reviews found that, on average, partnered men had lower testosterone than single men, and fathers had lower testosterone than childless men.

But most of those studies focused on the early years of fatherhood. Gettler and Dennis’s new work suggests that biology doesn’t simply “reset” after infancy. Instead, it continues to adapt to the evolving social landscape of family life.

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“Partnering and the parenthood transition are conceptualized as adaptive physiological responses,” the authors explain, “reflecting the salience of male-female cooperation in raising children in the evolutionary past.”

Not a Deficiency, but an Adaptation

Lower testosterone often raises red flags since it’s linked to fatigue, weight gain, and metabolic risk. But the Notre Dame study found no evidence that family-linked declines are pathological. Average testosterone levels in partnered fathers remained well above the clinical threshold of 300 ng/dL.

“Variation in U.S. men’s testosterone based on family characteristics does not significantly affect their risks for clinically low testosterone,” the study’s authors wrote.

Future studies could also test whether everyday parenting behaviors, like helping with homework or attending sports games, correlate with subtle hormonal shifts.

For now, the finding that partnered men with older children have the lowest testosterone is novel and suggests a continuing psychobiological response as family needs change.

“In contrast, our results for partnered men residing with older children suggest the possibility that paternal psychobiological responses, including for testosterone, remain dynamic as family circumstances shift,” the authors state.