[mpreda]

About erythropoietin (EPO), I understand it's a hormone whose amount is regulated by the need for oxygen in the blood (i.e. a feedback loop which regulates the amount of red blood cells to be just what is needed to satisfy the oxygen needs of the body).

So EPO is not limited by the ability of the kidneys to produce it (I expect, by a large margin). So one kidney would just as well be able to produce all the EPO you may need, the kidney is not the limiting factor.

[sulam]

A tour full of competitive cyclists would beg to differ with this analysis.

[jagraff]

Cyclists who dope with EPO are raising their levels far beyond what is healthy in order to get their red blood cell count to superhuman levels. It has the side effect of massively raising your risk of stroke

[sulam]

My point is that cyclists dope with EPO precisely because the body doesn't produce enough for your oxygen needs. There is a cap, probably for good reasons as you say.