Thursday, April 18, 2013

The Daddy Chronicles: What Happened To My Testosterone?

Zoë at two weeks
I'm not sure how many of you know this, but on March 19th of this year I became a new daddy. It's hard to describe the meaning of this event and its impact on my life, but here is a useful comparison that might put things into perspective: My dissertation was accepted for publication on the same day that my daughter was born and despite the near month passing, I still haven't filed the publication forms for the paper. Fatherhood changes the way I see the world in radical ways!

And yet, despite knowing the changes that fatherhood has brought on in my own life, I was still shocked to read about this little finding published in 2011 by Gettler and colleagues--fatherhood reduces testosterone... a lot.

The logic for decreases in testosterone following parenthood in males is fairly straightforward. Testosterone, as we have discussed on this blog, is related to a number of behaviors that can be considered aggressive and dominant. Some of these behaviors increase the likelihood that men will fight for scarce resources and contest status disputes between individuals. Physiologically, testosterone also contributes to musculature and libido, two characteristics that play a role in either the likelihood that males will seek out mating opportunities or be chosen as desirable mates by others.

In essence, testosterone seems to facilitate behaviors that conflict with the goals of fatherhood--primarily the caring for of one's offspring. A human male can't be running around getting into bar fights and having promiscuous sex with other conspecifics if he is realistically considering being a reliable caregiver. This is why many researchers have proposed that testosterone down regulation is a physiological mechanism that underlies the transition to parenting--caregiving needs in the social environment decrease the production of testosterone and thereby facilitate the reduction of behaviors that impede parenting goals.

T decreases in new fathers (source)
In the study itself, the researchers examined 624 participants from the Philippines at ages 21.5 and 26, and measured waking and before bed levels of Testosterone using saliva samples. The researchers also collected data about any changes in relationship status or parenting. The participants were then divided into different groups of people based on their parenting status (1) already in fatherhood at age 21.5, (2) not in a relationship, (3) in a relationship, (4) in a relationship and were new fathers.

Examining changes in testosterone from age 21.5 to 26 reveals that whereas participants who were already fathers (-15pg/ml) or who were not in a relationship (-22pg/ml) showed small drops in waking testestosterone, the group who showed the largest decrease in testosterone was the new fatherhood group, who dropped in waking T by an amazing 26% (-53pg/ml)!

The plot thickens considerably when the researchers examined the new fatherhood group. Caregiving needs are likely to be strongest in the first month or so of a newborn's life, and so the researchers expected testosterone to be at its lowest for fathers of newborns. A subset of the table is presented above. In comparison to participants who were never fathers, fathers of newborns show the largest decrease in testosterone of any group (waking: -105pg/ml). As infants age, the decline in testosterone tapers off for fathers.

So in summary, it seems that fatherhood causes many amazing life changes and one of those is a withdrawal of testosterone--and presumably, its associated dominance-relevant behaviors. Maybe this pattern will curb my road rage or reduce the number of crying graduate students at my office hours? Only time will tell!

Also, this is one of my favorite quotes from any paper: "Humans are one of the few mammalian specifis in which paternal care is relatively common, with fathers often helping to raise multiple overlapping offspring who are dependent well into their second decade of life." Try third decade!

Gettler LT, McDade TW, Feranil AB, & Kuzawa CW (2011). Longitudinal evidence that fatherhood decreases testosterone in human males. Proceedings of the National Academy of Sciences of the United States of America, 108 (39), 16194-9 PMID: 21911391


  1. Congrats on Fatherhood! That is actually an interesting read. They say the transition to parenthood comes with a whole new set of responsibilities as well as eventually strengthening marital bonds. The challenges of constraints, deadlines, finances and physical energy is rough enough- now lower testosterone levels? Although I see a bonus to a less amount of road rage, you probably could use a testosterone boost giving your in a house with high estrogen and hopefully a blessed baby with a good disposition and easy temperament to offset the loss. They say parenting is give and take, Id say so...You gave your testosterone for a wonderful gift! Now go file that dissertation and rest when baby rests and before you know it, you'll be feeling energized again- just about the time the testosterone levels begin to increase and baby is about 9-11 months and mobile. :) Congrats again!

    1. Like you, I was pretty shocked by the size of the reduction in T in the early months of child rearing. It's interesting to think about this physiological change as a catalyst for all the personal role changes that follow. Thanks for reading!

  2. Welcome to fatherhood. This is one of the most fulfilling moment in ones life, It all depends on the way you take it.This is an interesting finding that at being a new father your testosterone level is found to be decreasing. We all know that as ones gets old the testosterone level decreases. In your case then ,the main cause is due to your new commitment to being a father and subsequent chores that follows could be the leading factor. There were some studies done that showed men who are involved with caring for their children had the lowest level of testosterone. Research done by North western university showed that some men who had partners and no kids their testosterone levels fell some where between the two groups. This decrease in testosterone as you put it on your article will cause change in to behaviors from being more aggressive to being moderate and calm, this is because you have more to care now that you're a father.

  3. Thank you for your informative blog in terms of testosterone. Is it safe to use a health supplements to increase testosterone levels? We all know that lots of people are suffering of less interest to sex due of low testosterone levels and they are looking for the safest and effective way to increase their T-levels.

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