Family life lowers men’s testosterone without causing medical deficiency

New research analyzing a large, representative slice of the American population suggests that family life is linked to distinct hormonal profiles in men. The study found that men living with a partner and school-aged children tend to have lower testosterone levels than single men or partnered men without children.

These findings indicate that hormonal adjustments to fatherhood likely continue well past the infant years, though these changes do not appear to increase the risk of medically concerning hormone deficiencies. The results were published in the journal Psychoneuroendocrinology.

Biological anthropologists have studied the relationship between male hormones and behavior for decades. A leading theory in this field proposes that men have limited bio-energetic resources. They must allocate these resources between the effort required to find a mate and the effort required to raise offspring.

High levels of testosterone are generally associated with mating effort and competition with other males. Conversely, lower levels of this hormone are thought to facilitate nurturing behaviors and long-term bonding.

This theoretical framework suggests that when a man enters a committed relationship or becomes a father, his biology shifts to support these new roles. Past research has provided evidence for this idea. Studies have observed testosterone declines in men as they transition into marriage and again when they become fathers to newborns. However, the majority of this research has focused on the very early stages of parenthood.

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Researchers often concentrate on the transition to fatherhood during the first year of a child’s life. This leaves a gap in understanding how male biology functions as children grow up. Parenting an adolescent requires a different set of skills and behaviors than caring for an infant. It is not well understood if the hormonal suppression seen in new fathers persists as the demands of parenting change over time.

Lee T. Gettler and Sarah Hoegler Dennis from the University of Notre Dame conducted the study to address these unanswered questions. They sought to determine if the lower testosterone levels associated with fatherhood continue when men live with older children. They also investigated a critical health question. They wanted to know if these naturally occurring dips in testosterone place men at risk for a medical condition known as androgen deficiency.

The researchers utilized data from the National Health and Nutrition Examination Survey. This is a major program run by the Centers for Disease Control and Prevention. It collects detailed health and nutritional information from a sample of people intended to represent the U.S. population. The study analyzed data from three different waves of the survey collected between 2011 and 2016.

The final sample included 4,903 men between the ages of 20 and 60. This large sample size allowed the researchers to make robust statistical comparisons. The team categorized the men based on their relationship status and their living arrangements with children. They distinguished between men living with younger children aged five and under and those living with older children aged six to seventeen.

To measure testosterone, the survey used serum samples analyzed via liquid chromatography tandem mass spectrometry. This method is considered the gold standard for hormone measurement due to its high precision. The researchers adjusted their statistical models to account for the time of day the blood was drawn. Testosterone levels naturally fluctuate throughout the day, typically peaking in the morning.

The analysis also controlled for a variety of other factors that can influence hormone levels. These included age, body fat percentage as measured by waist circumference, sleep habits, and physical activity levels. By accounting for these variables, the researchers could isolate the specific associations between family structure and testosterone.

The findings revealed clear patterns linking partnering and parenting to hormonal variations. The first major observation was that partnered men generally had lower testosterone than single men who did not live with children. This difference was statistically significant and aligns with previous research on marriage and partnership.

A more novel finding emerged when the researchers looked at the age of the children in the home. Partnered men living with school-aged children or adolescents had significantly lower testosterone levels than partnered men who did not live with children. This suggests that the biological regulation of testosterone does not stop after the toddler years.

The effect was most pronounced in fathers of older children. Partnered men living with two or more children between the ages of six and seventeen showed the lowest relative levels. This specific group had lower testosterone than both single men and partnered men with no children in the household.

The pattern for men with younger children was somewhat different. Partnered men living with infants or toddlers did not show a significant additional drop in testosterone compared to partnered men without children. In this specific dataset, the lower levels in men with young families appeared to be driven primarily by the state of being partnered.

The study then addressed the medical implications of these findings. There is a medical consensus that clinically low testosterone can be harmful. Levels below 300 nanograms per deciliter are often classified as hypogonadism. This condition is linked to increased risks for cardiovascular disease, metabolic issues, and other health problems.

The researchers hypothesized that the lower testosterone seen in fathers is an adaptive biological trait rather than a pathology. If this hypothesis is correct, the levels should not drop low enough to be considered clinically deficient. The data supported this prediction.

The analysis showed that neither being partnered nor living with children increased a man’s likelihood of having clinically low testosterone. While the average levels were lower for fathers, they remained within a range considered healthy for physiological functioning. This distinction is significant for men’s health. It suggests that the body can downregulate testosterone to support family life without crossing the threshold into a disease state.

The study also examined whether age influenced these patterns. Men’s testosterone naturally declines as they get older. It was possible that the differences between single and partnered men would disappear in older age groups. However, the researchers found that age did not significantly alter the associations. The link between family roles and testosterone appeared consistent across the age range of 20 to 60.

These results expand the current understanding of human paternal biology. They suggest that fathers may experience a sustained or renewed biological adjustment as their children reach school age and adolescence. The authors propose that this could be related to the changing role of the father. As children age, fathers often take on roles that involve teaching, coaching, and guiding social development.

There are limitations to the study that frame how the results should be interpreted. The survey did not explicitly ask men if they were the biological fathers of the children in their homes. The researchers used residence with children as a proxy for fatherhood. It is possible that some participants were stepfathers, adoptive fathers, or other male relatives.

Another limitation is the nature of the blood testing. The study relied on a single blood sample from each participant. A clinical diagnosis of low testosterone typically requires two separate measurements taken in the morning. While the single sample is sufficient for population-level research, it is less precise than clinical diagnostic protocols.

The study is also cross-sectional, meaning it looked at different men at a single point in time. It did not follow the same men as they aged and their families grew. This design makes it impossible to say for certain that family life caused the testosterone differences. It remains theoretically possible that men with lower testosterone are simply more likely to marry and stay with their families.

Future research is needed to explore the mechanisms behind the findings regarding older children. The authors suggest that future studies should look at specific parenting behaviors. It would be informative to see if direct interaction with adolescents, such as helping with homework or emotional support, correlates with hormonal changes. This could help clarify why fathers of older children show this distinct biological profile.

The study, “U.S. men’s testosterone (T), partnering, and residence with children: Evidence from a nationally-representative cohort (NHANES) and relevance to clinically low T,” was authored by Lee T. Gettler and Sarah Hoegler Dennis.