Secondly, by promoting erythropoietin synthesis in the kidney. Testosterone enhances intestinal iron absorption from small intestine (jejunum-ileum), iron incorporation in red blood cells and hemoglobin synthesis. This is the main reason why men do have higher hematocrit-hemoglobin-myoglobin values than women. Androgens are a major stimulus for erythropoiesis, while estrogens are not. As a result of it, males do have greater stamina and endurance in sports (marathon, triathlon) More
The Effects of Steroids on Bone Marrow and Erythropoiesis