Hands-on parenting reduces dads' testosterone levels
MedWire News: Study results show that partnered men who have children and are actively involved in parenting have significantly lower testosterone levels than men who remain single and childless.
The findings, published in PNAS, also confirm that single nonfathers with the highest waking levels of testosterone are most likely to become a partnered father 5 years later.
"Our results provide longitudinal evidence that high testosterone predicts subsequent mating success in human males," say Lee Gettler from Northwestern University in Evanston, Illinois, USA, and colleagues.
They add that the evidence of lower testosterone levels among caregiving fathers "supports the hypothesis that father-child interaction likely contributes to suppressed paternal testosterone among fathers."
The team collected morning (AM) and evening (PM) saliva samples from 624 men living in Cebu City in the Philippines - an area where paternal involvement in parenting is common - in 2005, and again in 2009. The men were aged a mean 26 years old at the time of the second sample collection.
Using the subsample of men without children at baseline (n=465), Gettler and co-workers tested the hypothesis that those with higher baseline testosterone measurements would have greater mating success, ie, would be partnered and/or a father by follow-up.
Overall, all men experienced a decrease in testosterone levels during the study period; from 192.8 pg/ml in 2005 to 162.0 pg/ml in 2009 in the AM samples, and 117.7 pg/ml in 2005 to 92.6 pg/ml in 2009 in the PM samples.
The researchers report that single childless men with the greatest testosterone levels at baseline were significantly more likely to have a partner (odds ratio [OR]=1.20), and be a new father (OR=1.21) at follow-up, compared with their counterparts with the lowest testosterone levels; a finding that supports the study hypothesis.
In addition, men who became partners as well as new fathers during the study had significantly greater declines in AM testosterone (-26%) and PM testosterone (-34%) levels compared with men who did neither (AM=-12%, PM=-14%).
Men who became partnered but remained childless showed declines in testosterone levels similar to those who remained single and childless.
The age of children had an effect on testosterone levels, with fathers of newborns aged 1 month old or less experiencing a significantly greater decline in AM and PM testosterone levels compared with fathers of children older than 1 year. This association was independent of psychosocial stress levels, sleep quality (measured according to the number of mornings awoken feeling refreshed), or involvement in caregiving.
Indeed, involvement in caregiving also impacted testosterone levels. Men reporting 1-3 hours of childcare daily had significantly lower AM testosterone levels compared with men who reported no daily childcare, while men with the greatest involvement in parenting (3 hours or more per day) had significantly lower AM and PM testosterone levels than men reporting no care.
The researchers remark upon the "considerable" interest in the health differences between fathers and single men in light of many previous studies reporting lower risks for certain diseases among men who are married and have children.
"The large reductions in circulating testosterone among the new fathers in our sample provide a strong rationale to investigate linkages between fatherhood status and risk for diseases related to testosterone exposure," they conclude.
By Sarah Guy