Co-Sleeping with Baby Drops Men’s Testosterone Levels

A new study shows that it's not only women's bodies that adapt to parenthood: fathers who sleep next to their tot show dips in their levels of testosterone, which researchers say is good for the baby.

In prior research, study author Gettler (currently of the University of Notre Dame in the US state of Indiana) and his colleagues found that when men become fathers, their testosterone levels drop and the more involved dads were in caring for their children, the more significant their drops in the hormone.

A new study suggests that men's bodies make adjustments to better adapt to child rearing. AFP/Relaxnews

After taking saliva samples before and after sleep, they found those who shared a bed with junior had dips in their testosterone levels in the evening. The researchers also took testosterone samples in 2005 and 2009, and they found that dads who dozed next to their child had a third less testosterone than before, compared to dads who slept separately.

While high testosterone levels have been linked to aggression, extroversion, and risk-taking, lower testosterone levels are good for parenthood. Drops in testosterone have been connected to a fathers responsiveness to their children, wrote the study authors.

The researchers aren't sure that sleeping next to the baby causes the decline in testosterone, and that more work needs to be done. But research also shows that disruptions in a man's sleep -- a baby's cry, for example -- are known to cut testosterone production, said the researchers.

Bed sharing is seen as a controversial practice in some countries due to infant safety, but in the study, even dads sleeping in the same room with their children showed lower testosterone levels than men who slept separately.

Though the study is by no means conclusive (nor are researchers entirely sure their work applies to dads outside of the Philippines), blogger Jezebel writes, it does suggest that our traditional concept of arm-wrestling, water-buffalo-tackling masculinity is in for a thorough evolutionary biology revision.

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Co-sleeping with baby drops men's testosterone levels