The Dad Drop

Why having kids makes testosterone crash

Becoming a father can sap you of your energy, your sleep, your income--and, it turns out, your hallmark hormone of maleness: testosterone.

In a study of 465 Filipino men, researchers measured testosterone levels when the men were single in their 20s, then again five years later, when about a third of the men had kids. The researchers found that childless men experienced only a slight, age-related drop in their hormone levels, while fathers saw their levels drop almost twice as much. Those with the least testosterone: dads who were most involved in their children's daily care.

The results suggest that it's...

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