The ‘big T’

The Philippines made it to the front page of the New York Times this week, and for the most unexpected of reasons: a journal article reporting on something called “T” among men in Cebu.

This T is the hormone testosterone, and the study involved monitoring of this hormone in 624 men, with the conclusion that “dad duty” (caring for children) brings down levels of that hormone.

I thought I’d add some more information, and comments, on this study, based on the full report, which appeared in the Sept. 12 issue of the prestigious journal Proceedings of the National Academy of Science, or PNAS for short. (My pun-loving brain was going, wow, ’pinas in PNAS! The full citation is at the end of this article.)

Let me start with the observation that the New York Times article was picked up by many more American newspapers, and given interesting headline variations.  The original New York Times article title was “In study, fatherhood leads to drop in testosterone,” but one American newspaper in Minnesota revised it to “Study says kids sap their dad’s testosterone level.” Many newspapers picked up the title of a website report from Northwestern University, which played the lead role in the study: “Fathers wired to provide offspring care.” Inquirer, which also used the article for the front page, titled it, “Drop in testosterone helps men do dad duty.”

Tongue-twisting testosterone is abbreviated to T in the journal article, but I’ll refer to it occasionally as the “big T” because many men take this hormone seriously.  The big T is often called the “male hormone,” which isn’t quite accurate because women also produce T, albeit in lower amounts.

Biomedical research has long established that T is responsible for the development of the male reproductive system as well as various secondary male characteristics which you see from puberty onwards: the moustache and other body hair, the lowering of the voice, the body getting more muscular, and a growing libido (the Tagalog term also starts with “lib”). In more recent years, there has been interest in looking at the relationship between T and behaviors, like aggressiveness and competitiveness.

From bachelors to fathers

This just published study is the first to look at hormonal changes across time, from bachelor or single non-fathers into men in a relationship and on to fatherhood.  It was conducted as part of a Cebu Longitudinal Health and Nutritional Survey which many Filipinos are unaware of but which has been going on since 1983, starting out with a main focus on maternal health, but now branching out to all kinds of health issues. In longitudinal studies, researchers keep returning to a community or a population group to look for changes and to correlate these with lifestyle and behavior.

As a medical anthropologist with a focus on gender and sexuality issues, I was particularly interested in the study because it was conducted by biological anthropologists.  People tend to identify this biological aspect of anthropology with the study of bones and fossils and are less aware of studies like this “T” project that looks at living people as well.

In this study, the researchers took a cohort or a group of males who were born in 1983-1984.  They established a baseline in 2005, measuring saliva T levels in the men and asking questions about “partnering” (meaning married or in a live-in relationship), fathering (being the biological father) and time devoted to child care (no contact, less than one hour, one-three hours, and more than three hours).

In 2009, the researchers went back to this cohort and again interviewed the men and measured T levels. They then compared the 2005 and 2009 T level results, and looked for correlations with partnering, fathering and child care.

The results?  Men with higher T levels in 2005 were more likely to have become partnered by 2009, which researchers said supported the hypothesis that T’s competitive function is meant to enhance “reproductive success” or the chances that men will end up reproducing.

What’s so intriguing though is that once the men become fathers, and get involved in child-rearing, their T levels drop.  The decline is most significant when comparing single non-fathers to men who devote more than three hours a day to child care.

Why does this happen?  The researchers say that reproductive success isn’t just a matter of mating.  Reproductive success, they say at the end of the article, involves both fathering and caregiving. Ensuring the survival of the offspring is also important, a task made more challenging in humans because of the prolonged dependency offsprings have on their parents.

You can imagine a kind of physiological loop here: fathers who don’t get involved in child care continue to have high T levels, which keep them in a “chase” mode looking for more “mating” opportunities, at the cost of neglecting children already born.

Healthier dads?

There’s more. T may be important for the “chase” but men exposed to high T levels during their reproductive age also have higher risks for prostate cancers, high cholesterol and risk-taking behaviors, named by the researchers as “drug and alcohol use and promiscuity.”  Put another way, the lowered T levels from child care don’t “sap” the father but increase chances for a longer and healthier life, part of which, we hope, is put into nurturing their children.

I am sure there will still be male readers who are worried that the lower T levels might mean less virility.  But older research has established you don’t need high T levels for “normal” male anatomy and physiology.  The extra T seems to be useful only in getting a mate, and even there I will argue that among humans, culture has changed the playing field and reduced the need for the big T.

An earlier report from this Cebu longitudinal study which was done in coordination with the University of San Carlos and published in 2009 in the journal Hormones and Behavior, found that T levels begin to decline once men “pair-bond,” meaning, when they settle down with a partner.  Tie that finding to studies showing the adverse effects of high T levels and you can understand why there’s also research showing men who are married or in a relationship live longer than those who are not.

A final point: the researchers say they only looked at men caring for their own biological children. I suspect, admittedly from an unscientific sample of one (guess who?), that even for men caring for children who are not biologically their own, intensive involvement does bring about hormonal changes. The changes aren’t just about a T decline but also about a surge in the hormone oxytocin, described alternatively as a “feel-good” and “falling-in-love” hormone because it’s also released in lactating women, and in men and women in love. When you’re having your oxytocin rush caring for kids, who cares about chasing, or being chased?

For the full article, go to pnas.org and type in either the authors’ names or part of the article’s title: Lee T. Gettler, Thomas W. McDade, Alan B. Feranil and Christopher W. Kuzawa, “Longitudinal evidence that fatherhood decreases testosterone in human males.”

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