Ben Greenfield on health: what the evidence says · JRE #1069
“your spleen compresses and you produce more erythropoietin, more red blood cells. Same thing that you produce, actually, if you sauna, like if you do a workout and you get really hot and then you go in the sauna after, they've done studies on this and they found that 30 minutes of heat therapy after you've already gotten the body hot, you produce EPO, the same as if you were to use the performance enhancing drug.”
What the evidence says
Greenfield claims that 30 minutes of sauna use after exercise raises erythropoietin (EPO) to the same degree as using EPO as a doping drug. The specific protocol he describes has been directly tested: a randomized cross-over trial in which cyclists did 30 minutes of post-exercise sauna bathing three times weekly for four weeks found that total hemoglobin mass increased only marginally and the change was within the range of normal measurement error, providing no meaningful hematological advantage over exercise alone. A 2025 systematic review of 14 randomized/cross-over trials on post-exercise heat exposure similarly found inconsistent, low-to-moderate-quality evidence, with acute studies split between no effect, benefit, or even harm, and concluded that no definitive claims about performance or hematological adaptation can currently be made. Exogenous EPO doping, by contrast, directly and substantially raises red blood cell mass and hematocrit through pharmacological receptor activation, an effect of far greater magnitude and reliability than anything documented from sauna-induced heat stress. Current evidence does not support the claim that post-workout sauna use produces an EPO or red-blood-cell response comparable to EPO doping; the comparison significantly overstates the size and certainty of the sauna effect.