Baby cools down dad's testosterone

A study in the Philippines showed hormone levels drop temporarily with the duties of fatherhood.

By AMINA KHAN

Los Angeles Times
September 14, 2011 at 1:38PM
Caroline Katherine (last name witheld) was born at 12:02 am on 1/1/2000 -- the first baby of the year in the Twin Cities. She weighed 7 lbs 4 0z and measured 20.5 inches at birth. She was held in the proud arms of her father at North Memorial Medical Center in Robbinsdale, MN on 1/1/2000.
Caroline Katherine (last name witheld) was born at 12:02 am on 1/1/2000 -- the first baby of the year in the Twin Cities. She weighed 7 lbs 4 0z and measured 20.5 inches at birth. She was held in the proud arms of her father at North Memorial Medical Center in Robbinsdale, MN on 1/1/2000. (Star Tribune file/The Minnesota Star Tribune)

Hormonally speaking, becoming a father may make you less of a man, according to new research that finds testosterone levels drop in men after they become parents. But fear not for manhood -- the results show that men are evolutionarily wired to help raise their children and that testosterone may get in the way, scientists say.

Testosterone is a hormone associated with perceived hallmarks of masculinity such as libido, aggression and musculature. Those can be useful qualities when competing for a mate, but less so when raising a child -- an endeavor that requires calm, attentiveness and an even temper.

Some studies over the last decade had shown that fathers have lower testosterone levels than their childless counterparts. But it remained unclear whether fatherhood caused the decline or if men with less testosterone were more likely to settle down and become fathers in the first place.

To answer the question, scientists measured the testosterone levels of 624 Philippine men who were 21 years old and tracked them over the next 4.5 years. The data revealed that the men with higher testosterone levels at the start were more likely to become fathers. But these dads saw their testosterone levels plummet by 26 percent upon waking and by 34 percent at bedtime over the course of the study. Compare that to the bachelors, who saw modest age-related declines of 12 percent and 14 percent, respectively.

For fathers, the initial drop was abrupt: Men with newborns saw T-levels dive by 43 percent in the morning and 49 percent in the evening during the baby's first month of life. As their infants grew, their hormone levels recovered -- men with babies between the ages of 1 and 12 months took a testosterone hit of only 23 percent in the morning and 35 percent in the evening.

Overall, men who devoted the most time to child care had the lowest testosterone levels, according to the study, which was published online Monday by Proceedings of the National Academy of Sciences.

Parental care bolstered

"There's something about being an active father that's contributing to these dramatic declines," said study leader Lee Gettler, a biological anthropologist at Northwestern University in Evanston, Ill.

The results support the idea that testosterone levels aren't static but respond to a man's behavior and cues from his cultural environment, said Peter Ellison, an evolutionary biologist at Harvard University who was not involved in the study. "The real take-home message [is that] male parental care is important. It's important enough that it's actually shaped the physiology of men," Ellison said.

He pointed to a 2008 paper he co-wrote in which he and colleagues documented the different parenting styles of men in two neighboring groups around Lake Eyasi in northern Tanzania, the Hadza and the Datoga. Hadza men were ideal fathers in many ways, Ellison said: They carried, cleaned, fed and pacified their infants and slept amid the family.

The Datoga, on the other hand, considered child-rearing to be women's work, so they rarely interacted with their infants and slept and ate separately from their wives.

Those opposing views of fatherhood were mirrored in the men's hormones. The Datoga fathers' testosterone levels were no different from their childless peers. Among the Hadza, however, fathers registered levels that were 30 percent lower in the morning and 47 percent lower in the evening than for men who weren't raising children.

Draining your manhood?

"A dad with lower testosterone is maybe a little more sensitive to cues from his child, and maybe he's a little less sensitive to cues from a woman he meets at a restaurant," said Peter Gray, an anthropologist at the University of Nevada, Las Vegas, who has conducted research on testosterone in fathers.

The study was the first to show that a father's role in child care was directly linked to testosterone production.

The head-scratcher for the modern male: Does being a good parent drain the manhood right out of you?

For what it's worth, researchers suggested that a dad's testosterone is likely to bounce back as his children mature. Regardless, Ellison quashed such neuroses about fatherhood. "It makes you a man," he said. "It's what men are supposed to do."

The New York Times contributed to this report.

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about the writer

AMINA KHAN