Fatherhood Decreases Waking, Evening Testosterone Levels

High testosterone levels predict mating success; levels decline rapidly during fatherhood

TUESDAY, Sept. 13 (HealthDay News) -- Baseline waking testosterone levels are high in men who are likely to become partnered fathers, and both waking and evening testosterone levels decline significantly after men become fathers, according to a study published online Sept. 12 in the Proceedings of the National Academy of Sciences.

Lee T. Gettler, from Northwestern University in Chicago, and colleagues investigated whether fatherhood suppresses testosterone or if men with lower testosterone are more likely to become fathers. A total of 624 fathers were compared with 465 single nonfathers. Testosterone was measured in saliva samples at waking and before bed from participants when they were of average age of 21.5 years (baseline), and again when they were an average age of 26.0 years (follow-up).

The investigators found that single nonfathers at baseline were significantly more likely to become partnered fathers during follow-up of 4.5 years if they had high waking testosterone at baseline. Subsequently, there was a big decrease in the median waking and evening testosterone in men who became partnered fathers (−26 percent and −34 percent, respectively), and this decline was significantly greater than that seen in single nonfathers. As compared to fathers not involved in child care, fathers reporting three hours or more of daily child care had significantly lower testosterone at follow-up.

"Using longitudinal data, these findings show that testosterone and reproductive strategy have bidirectional relationships in human males, with high testosterone predicting subsequent mating success but then declining rapidly after men become fathers," the authors write.

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