MONDAY, Sept. 12 (HealthDay News) -- A new study suggests that
testosterone levels drop after men become fathers, perhaps because
they don't need to compete with other males for mates anymore and
instead focus on bonding with their children.
The findings don't prove that fatherhood directly affects
testosterone levels, and it's not clear how the hormonal systems in
men may detect that they've become fathers in the first place.
Still, researchers found that men had "a really dramatic drop"
in testosterone levels once they became fathers, said study author
Lee T. Gettler, a graduate student at Northwestern University.
"There's something that's going on in their first months that's
helping them transition to their role as fathers."
Humans are unusual among mammals because the males actually
assist with raising offspring, Gettler said. Only 5 percent of
other mammals do that. In contrast, males help out in 90 percent of
bird species, he said.
Gettler was inspired to launch the study in part because of his
own childhood experiences. He and friends were scrawny kids while
growing up in Minnesota but had strong fathers, he recalled. "We
thought that when men became fathers, they got their man strength,"
The study, however, suggests something a bit different, at least
when it comes to levels of testosterone.
The researchers examined results of blood tests of 624 young men
in the Philippines who were followed over 4.5 years. About
one-third of them got married or found long-term girlfriends and
became fathers; those men were more likely to have higher
testosterone levels before becoming fathers, perhaps because it
helped them attract women.
However, once they became fathers, their testosterone levels
dipped between 26 percent and 34 percent, depending on what time of
day it was measured. That's roughly twice as much as testosterone
levels dropped in the single men who didn't become fathers.
What do these lower testosterone levels mean for the men? It's
hard to say. "I don't think it makes them less tough or less
masculine," Gettler said. "It might make them more attuned to the
needs of their kids and less oriented toward competing with other
men outside of the family context, whether that means competing
with other men for the attention of women or engaging in risky
Testosterone levels dipped even lower in men who directly helped
take care of their kids. "Our assumption is that there's something
about physically interacting with their kids, whether it's through
sight or smell or physical touch, that activates something in the
brain of men and has this trickle-down effect," Gettler said.
Richard G. Bribiescas, chair of anthropology at Yale University,
said lower testosterone levels could "be a side effect of
increasing bonding hormones such as oxytocin and prolactin.
Lowering one's testosterone may also bolster a male's immune system
and thereby decrease the possibility of passing along pathogens and
infections to newborns whose immune systems are still
Robert J. Quinlan, an associate professor of anthropology at
Washington State University, said the study raises the question of
whether testosterone levels don't drop in men who end up having
poor relationships with their children. "One might manipulate the
system by encouraging fathers to get the early experience with
children that lowers testosterone levels, and then perhaps family
stability and child outcomes would improve," he said.
The study appears in this week's online edition of the
Proceedings of the National Academy of Sciences.
For more about
testosterone, try the U.S. National Library of Medicine.
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