Testosterone +/- Avodart (Dutasteride) vs Fat-Free Mass Part 1

Yeah, I gotta read more.  Not the first time I've heard that.  At least this time around, I'm only 5 days late.  It turns out a fascinating trial was published in JAMA last week demonstrating that dutasteride makes no difference in fat-free mass in men given testosterone.  In other words, it's the testosterone that's responsible for muscle, not dihydrotestosterone.  And just how did the authors manage to separate testosterone level from dihydrotestosterone?

Well, we need to take a step back and review male physiology & biochemistry.  Testosterone is manufactured in/by the testes; a small fraction of testosterone is converted into dihydrotestosterone (DHT) by 5 alpha reductase.  Testosterone itself is considered anabolic, thus an anabolic steroid, while DHT is androgenic, thus inducing male-sex characteristics; in fact, DHT is linked to hair loss and prostate enlargement.  So 5 alpha reductase inhibitors (5ARIs) such as finasteride (sold as Proscar & Propecia) and dutasteride (sold as Avodart) are prescribed to treat hair loss and prostate enlargement.

But the question that remains is whether or not DHT plays a role in muscle development.  To study this, 102 men average 38yo were given enough gonadotropin-releasing hormone agonist to suppress their own endogenous testosterone production.  They were then randomized to receive either 50mg weekly, 125mg weekly, 300mg week, or 600mg weekly of testosterone enanthate and then further randomized to receive dutasteride 2.5mg daily vs placebo.  Remember that the FDA approved dose is only 0.5mg daily so that this large dose should be expected to, and indeed did, suppress DHT levels rather completely compared to placebo.

And in the end, whether the participant was randomized to dutasteride or placebo, thus his DHT, made no difference in fat free mass after 20 weeks.  Bottom line:  if you need a 5ARI (finasteride or dutasteride) to protect your hair line or prostate, don't worry about it affecting your muscle mass.  Check out Part 2 here.

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