Longitudinal evidence that fatherhood decreases testosterone in human males

Abstract

In species in which males care for young, testosterone (T) is often high during mating periods but then declines to allow for caregiving of resulting offspring. This model may apply to human males, but past human studies of T and fatherhood have been cross-sectional, making it unclear whether fatherhood suppresses T or if men with lower T are more likely to become fathers. Here, we use a large representative study in the Philippines (n = 624) to show that among single nonfathers at baseline (2005) (21.5 ± 0.3 y), men with high waking T were more likely to become partnered fathers by the time of follow-up 4.5 y later (P < 0.05). Men who became partnered fathers then experienced large declines in waking (median: -26%) and evening (median: -34%) T, which were significantly greater than declines in single nonfathers (P < 0.001). Consistent with the hypothesis that child interaction suppresses T, fathers reporting 3 h or more of daily childcare had lower T at follow-up compared with fathers not involved in care (P < 0.05). Using longitudinal data, these findings show that T and reproductive strategy have bidirectional relationships in human males, with high T predicting subsequent mating success but then declining rapidly after men become fathers. Our findings suggest that T mediates tradeoffs between mating and parenting in humans, as seen in other species in which fathers care for young. They also highlight one likely explanation for previously observed health disparities between partnered fathers and single men.

Fig. 1.

(A) Within-group changes in AM and PM T values between 2005 and 2009. Mean values of T, adjusted for time of saliva collection and usual wake time (AM), were compared using paired t tests. Group 1 (n = 83) comprised men who were partnered and fathers in 2005 and 2009. Group 2 (n = 257) comprised men who were not partnered in 2005 and 2009 and were never fathers. Group 3 (n = 46) comprised men who became partnered between 2005 and 2009 and were never fathers. Group 4 (n = 162) comprised men who became partnered and were first-time fathers between 2005 and 2009. *P < 0.05; **P < 0.01, ^◇P < 0.0001. Error bars indicate SEM. P, partnered. (B) Between-group changes in AM and PM T values between 2005 and 2009 based on partnering and parenting status. Group descriptions are as in A. Values were adjusted for time of saliva collection and usual wake time (AM) and are derived from regressing the change in T on changes in partnering and parenting status, with group 2 as the comparison group, controlling for sleep quality and psychosocial stress (Tables S2 and S3). Partnered fathers are included for visual comparison but were not part of the regression analyses. ***P < 0.001. Error bars indicate SEM.

Fig. 2.

Between-group changes in AM and PM T values between 2005 and 2009 with fathers stratified by child age. Values are adjusted for time of saliva collection and usual wake time (AM) and are derived from regressing the change in T on fatherhood, stratified by child age, with men who were not fathers in 2005 and 2009 as the comparison group, and controlling for sleep quality and psychosocial stress (Tables S5 and S6). Fathers of newborns were men whose youngest child was in the perinatal period [1 mo (m) old or less]. Fathers of infants were men whose youngest child was older than 1 mo (m) but 1 y (yr) old or less. ^P < 0.10; **P < 0.01; ***P < 0.001. Error bars indicate SEM.

Fig. 3.

2009 AM and PM T values among fathers varying in daily physical childcare. Values were derived from regressing T on daily paternal caregiving, controlling for time of saliva collection, usual wake time (AM), sleep quality, psychosocial stress, and number of children, with fathers who reported no involvement in childcare as the comparison group. No care (n = 34), 0–1 h (n = 37), 1–3 h (n = 139), 3+ h (n = 102). Regression models were calculated with robust SEs. ^aP = 0.020; ^bP = 0.044; ^cP = 0.015. AM model: R² = 0.047; PM model: R² = 0.046. Error bars indicate SEM.