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," he said.
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 t
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