Air date: October 30, 2011

Host: Eric Metcalf

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Time now for this week’s Sound Medicine Checkup. You may have heard of the recent study that found lower testosterone levels among new dads. Sound Medicine’s somewhat concerned contributor Eric Metcalf takes a closer look.

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So this study followed 600 guys, and it found that not only were the guys with high testosterone more likely to have a partner and a kid four years later, these new daddies had bigger declines in testosterone than the guys who didn’t become fathers.

The upshot was that these hormone-deprived daddies might be too busy updating the stick-figure families on the back window of the SUV to go out looking for opportunities to make more babies. But not so fast, says Abraham Morgentaler, a Harvard urologist and author of the book Testosterone for Life.

"We have this idea that is totally mistaken but seems to be assumed by even very accomplished scientists, that a man’s behavior is influenced moment by moment almost by what his testosterone level is, and it’s simply not true.

The truth is that men have wide variability in their testosterone levels every single day, even the healthiest guys, and especially younger men. As long as guys have a testosterone level within a normal range, which we talk about is somewhere between 350 to 1,000 nanograms per deciliter, you cannot tell the difference in behavior between a guy whose testosterone is 900 compared to a guy whose testosterone is 400."

So if washing baby bottles and wearing barf-stained shirts doesn’t shrink your manly testosterone levels, what could explain this finding?

"The whole issue is not whether the testosterone was lowered in some kind of evolutionary way to make these men become better fathers, which I think is the thrust of what the authors were trying to conclude. Loss of sleep, or disordered sleep, can substantially drop testosterone. As can stress. So it’s entirely possible, and in my opinion likely, that the young fathers weren’t sleeping as well and that’s why their testosterone was lower."

Of course, testosterone does decline with age, and certain medical conditions can be linked to a drop, such as diabetes. Truly low testosterone can lead to a litany of maladies. But that’s another story. So new dads, put on your fanny packs with pride, and keep wearing your “Because I’m the Daddy, That’s Why” t-shirts. We all still know you’re the man.

I'm Eric Metcalf. Become a fan of Sound Medicine on Facebook and follow us on Twitter.

Additional Resources:

• Read about the research finding that fatherhood leads to low testosterone. From the NYT.
• Dr. Morgentaler's book is Testosterone for Life.
• Do men need testosterone supplements? Find out what the Mayo Clinic has to say.