Testosterone Moves Your Hematocrit to a New Normal

Opener

Testosterone's most common side effect in clinical trials and in practice is a rise in red blood cells, which shows up on a blood panel as higher hemoglobin and hematocrit. Most lifters know the number climbs. Fewer know how it climbs, how fast it gets there, and why it doesn't drift back down on its own while testosterone stays high. A 2014 study from Shalender Bhasin's group at Boston University School of Medicine, led by Eric Bachman, tracked hemoglobin, hematocrit, the kidney hormone erythropoietin (EPO) and the iron hormone hepcidin month by month in men given testosterone. It shows that testosterone does two things at once. It raises the hormone that tells the body to make red blood cells, and it unlocks the iron needed to build them. Then the body settles at a higher level and holds it there.

---

1. Who was studied

The data come from the Testosterone in Older Men with Mobility Limitation trial, a randomized, double-blind, placebo-controlled study:

• The men were 65 or older, had low testosterone (total testosterone 100 to 350 ng/dL, or low free testosterone), and had trouble walking two blocks or climbing 10 steps.
• Most had high blood pressure, about half had heart disease, and about a quarter had diabetes.
• They used either 10 g of testosterone gel or a placebo gel every day for 6 months.
• 166 men finished the 6 months and make up the analysis. They were tested at the start, at 1, 3 and 6 months, and again 3 months after they stopped.