Men trained by Wim Hof had a weaker inflammatory response to an injected toxin
The claim that the Wim Hof Method lets you control your immune system comes from this 2014 PNAS trial. Researchers trained Dutch men for ten days, then injected them and a group of untrained men with bacterial endotoxin.
The paper
Voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans
Kox M, van Eijk LT, Zwaag J, van den Wildenberg J, et al.. Proceedings of the National Academy of Sciences, 2014;111(20):7379-7384.
See the study at a glance
- Design
- Randomized controlled trial using injected bacterial endotoxin
- People
- 24 men tested (30 enrolled)
- Who they were
- Healthy, non-smoking young men in the Netherlands. The median ages were 24 and 22 in the two groups.
- What they did
- Wim Hof and three instructors ran ten days of training. It began with four days in Poland, and the men then practiced at home. On test day every man got 2 ng/kg of E. coli endotoxin into a vein, and the trained men did the breathing for about three hours with Hof coaching them.
- How long
- Ten days of training and home practice, then one test day
These numbers came out of it
−53%
The inflammatory signal TNF-α came out 53% lower in the trained men than in the untrained men.
+194%
The anti-inflammatory signal IL-10 ran 194% higher in the trained men.
2.08 nmol/L
The trained men's adrenaline reached 2.08 nmol/L during the breathing. The untrained men's level before the injection was 0.35.
~50%
Blood oxygen saturation fell to about 50% at the end of the breath holds.
The researchers did this
Dutch researchers randomly assigned healthy young men to train in the Wim Hof Method or to a control group.Source 1 · Randomized trialVoluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humansKox M, van Eijk LT, Zwaag J, et al.. Proceedings of the National Academy of Sciences, 2014.Read the paper ↗PubMed ↗ In each of two training blocks, the researchers drew 6 of the 9 trained men by sealed envelope for the test day. That put 12 trained and 12 untrained men through the experiment.
Hof and three instructors led ten days of training that began with four days in Poland. The men stood barefoot in snow for up to 30 minutes, lay bare-chested in snow for 20 minutes, dipped or swam daily in 0–1°C water and hiked bare-chested at −5 to −12°C.Source 1 · Randomized trialVoluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humansKox M, van Eijk LT, Zwaag J, et al.. Proceedings of the National Academy of Sciences, 2014.Read the paper ↗PubMed ↗ They learned a breathing drill in which they took about 30 deep, fast breaths and then held their breath for two to three minutes, round after round. Meditation was part of the course too. For five to nine days back home they practiced for two to three hours a day and took cold showers.
On test day each man received 2 ng/kg of E. coli endotoxin into a vein, and the trained men did the breathing for about three hours with Hof coaching them.Source 1 · Randomized trialVoluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humansKox M, van Eijk LT, Zwaag J, et al.. Proceedings of the National Academy of Sciences, 2014.Read the paper ↗PubMed ↗ Before the injection their adrenaline stood at 1.02 nmol/L, against 0.35 in the untrained men. It rose to 2.08 during the breathing, and in some men it went as high as 5.3. Oxygen saturation fell to about 50% at the end of the breath holds, while noradrenaline and dopamine stayed within normal ranges.
The trained men's inflammatory response came out smaller. Compared with the untrained men, their TNF-α was 53% lower and their IL-6 57% lower.Source 1 · Randomized trialVoluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humansKox M, van Eijk LT, Zwaag J, et al.. Proceedings of the National Academy of Sciences, 2014.Read the paper ↗PubMed ↗ IL-8 came in 51% lower, and the anti-inflammatory IL-10 ran 194% higher. The trained men also reported fewer flu-like symptoms, and their fevers cleared faster. The authors concluded that the breathing appeared to drive most of the adrenaline rise and the dampened immune response.
The study can't tell you these things
- Only young men took part, and 24 of them went through the endotoxin test.
- The training bundled cold exposure with breathing and meditation, so this trial alone can't say which part did what.
- Hof coached the trained men himself during the test.
- Endotoxin is a lab model of inflammation, and the trial did not test real infections.
- The breath holds pushed oxygen saturation down to about 50%, and the same breathing pattern can cause a blackout in water.Source 2 · ReviewThe physiology of survival: Breath‐hold shallow‐water divingBaker AH, Jones A, Mayhew A, et al.. Experimental Physiology, 2026.Read the paper ↗
People quote it like this
People cite the trial as proof that the Wim Hof Method lets you control your immune system. It measured a weaker inflammatory response to injected endotoxin, and its authors gave most of the credit to the breathing.Source 1 · Randomized trialVoluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humansKox M, van Eijk LT, Zwaag J, et al.. Proceedings of the National Academy of Sciences, 2014.Read the paper ↗PubMed ↗ A 2022 follow-up found that cold training alone didn't change the response.Source 3 · Randomized trialThe Effects of Cold Exposure Training and a Breathing Exercise on the Inflammatory Response in Humans: A Pilot StudyZwaag J, Naaktgeboren R, van Herwaarden AE, et al.. Psychosomatic Medicine, 2022.Read the paper ↗PubMed ↗
We cited these sources
- 01Kox M, van Eijk LT, Zwaag J, van den Wildenberg J, Sweep FCGJ, van der Hoeven JG, et al.. Voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans. Proceedings of the National Academy of Sciences. 2014;111(20):7379-7384. doi:10.1073/pnas.1322174111 PMID 24799686
- 02Baker AH, Jones A, Mayhew A, McAvoy C, Macleod R, Montgomery H, et al.. The physiology of survival: Breath‐hold shallow‐water diving. Experimental Physiology. 2026;111(5):2403-2410. doi:10.1113/EP093322
- 03Zwaag J, Naaktgeboren R, van Herwaarden AE, Pickkers P, Kox M. The Effects of Cold Exposure Training and a Breathing Exercise on the Inflammatory Response in Humans: A Pilot Study. Psychosomatic Medicine. 2022;84(4):457-467. doi:10.1097/PSY.0000000000001065 PMID 35213875