“The Wim Hof Method lets you control your immune system.”

The research found this

The experiment behind the claim ran in 2014. Dutch researchers randomly assigned healthy young men to train in the Wim Hof Method or to a control group, and 12 trained and 12 untrained men went through the test day.1Source 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 ↗ Hof and three instructors ran ten days of training that mixed meditation and cold exposure with a breathing drill. In each round of the drill the men took about 30 deep, fast breaths and then held their breath for two to three minutes.

Bacterial endotoxin brings on fever and flu-like symptoms, and on test day each man got a dose of it straight into a vein.1Source 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 ↗ The trained men did the breathing for about three hours with Hof coaching them. Before the injection their adrenaline stood at 1.02 nmol/L, against 0.35 in the untrained men. During the breathing it climbed to 2.08, and their blood oxygen saturation fell to about 50% at the end of the breath holds.

TNF-α and IL-6 are messengers that drive inflammation, and in the trained men they came out 53% and 57% lower. IL-10, which calms inflammation, ran 194% higher.1Source 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 ↗ The trained men also reported fewer flu-like symptoms, and their fevers settled faster. The authors concluded that the breathing appeared to drive most of the adrenaline rise and the dampened immune response.

A 2022 follow-up from the same group tested the parts one at a time. It randomly assigned 48 healthy men to cold exposure training, breathing training, both or neither, and then gave everyone the same endotoxin.2Source 2 · 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 ↗ Breathing alone dampened the response. Men who did only the cold training responded much like untrained men, and the combination had the strongest effect.

A 2024 review gathered nine papers from eight Wim Hof trials. Its most consistent finding was a drop in inflammation driven by higher adrenaline, and effects on exercise performance and breathing measures were mixed.3Source 3 · Systematic reviewDoes the Wim Hof Method have a beneficial impact on physiological and psychological outcomes in healthy and non-healthy participants? A systematic reviewAlmahayni O, Hammond L. PLOS ONE, 2024.Read the paper ↗PubMed ↗