“The Wim Hof breathing method boosts immunity”

Two questions hide inside this claim, and only one has been tested.

Start with the tested one. In 2014 researchers split 24 healthy volunteers by chance into two groups of 12 [1]. One group spent ten days learning the method: cyclic hyperventilation followed by holding the breath, meditation, and immersion in ice-cold water. The other group did nothing. Everyone was then injected with endotoxin, a fragment of E. coli bacteria that reliably brings on a short bout of fever and aching, at 2 nanograms per kilogram of body weight [1].

The trained 12 released much more adrenaline, produced more of the body's main calming immune signal and less of the three signals that drive inflammation, and reported fewer flu-like symptoms than the untrained 12 [1]. The breathing did it. Hyperventilating on purpose and then holding the breath shifts the blood's acid balance and briefly lowers its oxygen, and that stress is what released the adrenaline [1].

The finding was a surprise, because this reaction had been assumed to sit outside conscious control. It is also not what the claim says. Turning inflammation down on command is close to the opposite of boosting immunity, since inflammation is part of how the body clears an infection.

Now the untested question, which is the one people actually ask: do you get ill less often? No trial has followed trained and untrained people through a winter and counted who fell ill. The closest anyone has come is a questionnaire. A 2024 case-control study compared 77 people who practised cold-water immersion together with breathwork against matched groups doing cold water alone or neither, all of them filling in forms online [3]. The breathwork group reported shorter infections of the nose and throat, and better mental health, than the cold-water-only group, who in turn reported shorter infections than people doing neither [3]. Nobody was assigned to a group and everyone reported on themselves, so people who take up ice baths may simply differ from people who do not. The authors say more research is needed [3].

The largest trial of the method shows the size of the gap. It put 404 healthy adults, average age 37, through 29 days of the method in person, the method at home, or mindfulness meditation [2]. It tracked energy, mental clarity, sleep, thinking tests and the ability to handle stress. None of those measures touch immunity or infection [2]. On what people said about themselves the method beat meditation in the moment, and that gap widened over the month, while changes in their steadier traits stayed small [2]. Assignment to the groups was only partly random [2].

Who this evidence does not describe:

• anyone with a long-term illness, since all three studies used healthy volunteers [1][2][3]
• older adults: the largest trial averaged 37 years of age, and the 2014 trial gives no age range [1][2]
• anyone hoping for protection against a particular infection, which no study here measured [1][2][3]

A safety note, since the mechanism is the risk. The breathing deliberately produces brief spells of low blood oxygen [1], so it should never be done in or under water, or anywhere that passing out would be dangerous.

The method has one good trial showing people can quieten their own inflammatory response on demand, and nothing showing they catch fewer colds. Anyone practising it for the second reason is ahead of the evidence.