The Effect of a Sauna on Blood Oxygen Transport and the Prooxidant–Antioxidant Balance in Untrained Subjects
Authors: V. V. Zinchuk, D. D. Zhadko
DOI / Source: https://pubmed.ncbi.nlm.nih.gov/23101249/
Date: 11 April 2011
Reading level: Intermediate
Why This Matters for Freedivers
Sauna sessions can change how your blood carries and releases oxygen, and they can also trigger short-term oxidative stress. For freedivers, that matters because heat, dehydration, and altered breathing chemistry can affect recovery, training quality, and how “fresh” you feel for a session—especially if you stack sauna + hard apnea training close together.
Synopsis
This study looked at what happens to oxygen transport in the blood when untrained young men do repeated sauna sessions over several months. The researchers weren’t asking “does sauna feel good?”—they were trying to measure the underlying blood chemistry: oxygen levels, carbon dioxide levels, blood acidity (pH), how tightly hemoglobin holds oxygen, and whether heat exposure creates oxidative stress.
The participants followed a long course: one sauna session per week for five months (20 sessions total). Each session included two hot exposures (5 minutes and 10 minutes) at roughly 85–90°C with low humidity, separated by a short cool rest. Blood was taken from a vein in the arm after sauna exposure and analyzed for gases (oxygen and carbon dioxide), pH, hemoglobin values, and markers linked to oxidative stress and antioxidant defenses.
A consistent pattern appeared right away. After sauna exposure, the men showed signs of respiratory alkalosis—their pH shifted more alkaline and their carbon dioxide dropped. In plain language: they were breathing more (hyperventilating) in response to heat, blowing off CO₂. At the same time, venous blood oxygen values rose sharply. Part of this is likely “less oxygen being extracted” in that sampled region and changes in circulation distribution during heat stress, plus the fact that blood becomes more concentrated as you sweat.
The most interesting oxygen-transport change was a decrease in hemoglobin’s affinity for oxygen, measured by an increase in p50 and a rightward shift of the oxyhemoglobin dissociation curve. That shift means hemoglobin is more willing to let go of oxygen to tissues. Heat itself pushes hemoglobin in that direction, and the changes in CO₂ and pH also influence it. The authors interpret this as a heat-driven adjustment that can support oxygen delivery to tissues during thermal stress.
But there was a tradeoff: a single sauna session was associated with oxidative stress—markers of lipid peroxidation rose and some antioxidant defenses dropped (for example, lower vitamin E levels and reduced catalase activity). In other words, the heat exposure acted like a strong stressor that temporarily increased “free radical” activity.
Here’s the encouraging part: after the full five-month course, the same sauna procedure caused smaller oxidative-stress responses. The body appeared to adapt, showing a more controlled prooxidant–antioxidant balance compared with the first exposure. The study also observed higher nitrite levels after sauna sessions, suggesting increased nitric oxide production, which may be involved in blood vessel regulation and oxygen-related processes during heat stress.
Overall, this paper frames sauna as a real physiological load: it changes breathing chemistry, shifts how hemoglobin releases oxygen, and (at least at first) creates oxidative stress—while repeated exposure seems to build some adaptation.
Abstract
This study examined how repeated dry-sauna exposure influences blood oxygen transport and oxidative stress in untrained young men. A 20-session program (weekly sauna for five months) produced acute changes consistent with heat-driven hyperventilation, including lower CO₂ and higher pH, alongside increased venous oxygen measures and a reduced hemoglobin affinity for oxygen (right-shift in the oxyhemoglobin dissociation curve). A single sauna session increased markers of oxidative stress and reduced antioxidant defenses, while responses were smaller after the full course, suggesting adaptation. Increased plasma nitrite levels after sauna exposure indicated greater nitric oxide production, potentially contributing to heat-related vascular and oxygen-transport effects.