Who is the Iceman?

Wim Hof, alias the Iceman, is a very passionate person. I first met him when he came to our laboratory for the measurement of brown fat. He immediately started to talk about his achievements of withstanding extreme cold, about how good this is for our health and mentality, but also that his skill is nothing special; most people can do it. He loves to share his ideas and embraces scientific research.

I must say, my students and I really liked to work with him and we got hooked on his enthusiasm. After the first measurement day, we had a dinner with Wim. That evening, he played the guitar and we had fun. The next morning after the breakfast, I practiced breathing techniques and Wim convinced me to take cold showers. Since then, for several years now, I do take a cold shower every day. Did I become healthier? I don't really know. I was already quite healthy. What I liked was that I overcame my fear and reticence for cold. After some time you just take the cold as it is, have the shower in your routine just as tooth brushing. I also noted changes in my body. No strong aversive shock feelings anymore as soon as I switch from warm to cold water. I just stay relaxed showering. Is that healthy?

The Dutchman Wim Hof is famous for being able to withstand extreme cold. As a young man he already felt attracted to the cold, until he could not resist it anymore and took a winter dive in the pond of the Vondelpark in Amsterdam. From then onward he got addicted. Cold is his warm friend. He holds several world records for staying in a tub filled with ice cubes up to his neck for almost 2 h. Moreover, he ran a half marathon barefoot in the snow and swam under the polar ice from ice hole to ice hole.

He claims that a combination of cold exposure, meditation, and breathing techniques can strengthen your inner nature and prevent disease. More specifically, through his method you should be able to make consciously contact with your autonomous nervous system and your immune system. All over the world, he organizes workshops and travels to extreme environments. The core activities of his workshops are breathing techniques, meditation, and cold exposure. Often physical exercise is included as well.

Who is this man? How can he withstand radical cold? What is known about his claims? What are the facts, what is fiction and are his claims worth to be studied?

In this editorial, I will not provide a complete scientific picture of the scientific ins and outs of cold, meditation, and hyperventilation. Instead, I will explore the potential of the claims with a slight overexposure of thermophysiological aspects.

Because of my interest in cold exposure, more specifically in non-shivering thermogenesis and brown fat activation, I asked Wim Hof to join our experiments. We expected him to have an overload of brown adipose tissue. Earlier, other Dutch scientists of the Radboud University studied Wim and reported that he maintained his core body temperature and increased energy expenditure up to 100% of his resting metabolic rate, without shivering, while surrounded with ice cubes.

The main function of brown adipose tissue is to convert chemical energy into heat, so-called non-shivering thermogenesis. It can be made visible during cold exposure with a glucose tracer (fluorodeoxyglucose, FDG) using a Positron emission tomography–computed tomography (PET/CT) scan (Fig. 1). Most young adults do have substantial amounts of brown adipose tissue, while it is significantly reduced in elderly and overweight people. To test Wim, we used an individualized cooling protocol, developed to measure maximal non-shivering thermogenesis. Under these conditions, brown adipose tissue activity was measured. We observed a rise of 40% of his resting metabolic rate, which is the highest value we measured thus far.¹ In a group of young adults, we normally observe non-shivering thermogenesis levels up to a maximum of 30%. However, after analyzing the PET/CT scans, the amount of brown adipose tissue was not very high compared with young adults, although it was high compared with his age group. Interestingly, the amount of brown fat measured was not enough to explain the high levels of non-shivering thermogenesis observed.

During the measurements, we noted that as soon as the cooling protocol started, Wim changed his breathing. From just ‘normal’ breathing he started to inhale deeply and kept his breath relatively long before exhaling. In fact, he was practicing his meditation technique, which is linked to Tummo meditation. Tummo meditation involves vigorous respiratory muscle activity. We decided to have a closer look at the PET/CT scans and indeed found increased metabolic activity (uptake of FDG) of the long respiratory muscle that contributed to explaining the high non-shivering thermogenesis at least to some extent.

The conclusion must be nothing miraculous occurred. Although a non-shivering thermogenesis of 40% is considered as high, it is not that extreme. I think Wim Hof withstands the cold in the ice cubes through a combination of several factors: an increased heat production (non-shivering thermogenesis, brown fat activation, contraction respiratory muscles), efficiently increasing body tissue insulation (vasoconstriction) thereby reducing heat loss and conserving the body core heat content, and finally, possibly not unimportantly, he used his well-trained mental ability to endure the cold (change of mindset, as he calls it). As soon as he steps out of the ice, he starts shivering just as everybody else, due to the redistribution of the cooled blood from his limbs to the body core – also known as the afterdrop effect.

So is that it? Wim is just slightly more adapted and resilient to extreme cold, and above all that, he makes people enthusiastic about his method. He makes them feel good to do more than what they thought they were capable of. So should we forget about the health claims? I don't think so.

In 2012, researchers from the Radboud University of Nijmegen (The Netherlands) performed a study on the Wim Hof method, focusing on immune responses. In short, they compared a group of volunteers that were trained by Wim Hof and a control group. The training consisted of 10 d of meditation, breathing techniques (cyclic hyperventilation followed by breath retention), and exposure to cold (immersions to ice cold water).² The investigators studied the effect of the intervention on the autonomic nervous system and the innate immune response. The outcome parameters consisted of, among others, plasma epinephrine (as a measure of the sympathetic nervous system) and experimental endotoxemia. The latter is an experimental approach to study the effects of an acute and transient immune activation. Interestingly, they observed profound differences between the two groups. The trained group had significantly increased epinephrine levels, increased levels of anti-inflammatory cytokine, decreased levels of pro-inflammatory mediators, and less pronounced fever. Also flu-like symptoms were lower in the trained group compared with the untrained group.

The set-up of the research, however, did not allow discrimination between the acute and the acquired responses, because during the experiment itself, the volunteers from the intervention group were allowed to hyperventilate and the control group was not. Therefore, the investigators concluded that hyperventilation can temporally activate the sympathetic nervous system and suppress the innate immune response. Long-term training effects were not addressed. Therefore, it still needs to be sorted out if the training itself (hyperventilation, cold, and/or meditation) caused the observed effects.

I think it would be interesting to study the different techniques (hyperventilation, meditation, cold exposure) separately first and then the combined effects. Hyperventilation has earlier been shown to affect our sympathetic nervous system, as increases in (nor)epinephrine have been linked to both the hyperventilation and hypoxia due to breath retention. The meditation Wim Hof practices is, as mentioned above, linked to Tummo Meditation and Pranayama (yogic breathing). Tummo meditators are believed to be able to dry wet sheets that are wrapped around their naked bodies while they are practicing the mediation in the freezing cold Himalayas. This meditation technique is not so much characterized by relaxation, but involves both somatic and neurocognitive components. The somatic components involve special breathing techniques as well as isometric exercises that may cause a rise in heat production (as we were able to show for the respiratory muscles, see above). The other component involves meditative visualization revealing intense sensations of bodily heat in the spine, which are reported to aid in sustaining temperature increases for longer periods.

Finally cold may exert health effects. First of all, cold may increase energy expenditure by shivering, but also by non-shivering thermogenesis, as mentioned above. In the recent past, quite a few studies from several laboratories showed that humans are able to increase their non-shivering thermogenesis capacity due to cold acclimation. This mirrors numerous studies in rodents. However, the effects in humans are of a smaller magnitude compared with these animals. The increase in non-shivering thermogenesis goes hand in hand with increases in brow fat presence and activity. Brown fat is thought to be healthy, as animal studies show positive effects on obesity and on glucose and lipid metabolism. In humans, white adipose tissue mass was reduced after six weeks of mild cold exposure (2 h/d, 17°C) with a concomitant rise in active brown adipose tissue.³ Brown fat is also believed to play a role in the etiology of diabetes. Activated brown adipose tissue can take up large quantities of glucose and lipids in rodents, and in humans, its activity has been negatively associated with diabetic status. In search for the effect of cold acclimation in patients with type-2 diabetes, we were happily surprised to find out that insulin sensitivity was markedly increased after only 10 d of mild cold acclimation.⁴ Probably, skeletal muscle is the main tissue involved in the increased glucose handling.

These studies show that mild cold can have profound effects on our health, at least with respect to the metabolic syndrome. Whether more extreme cold, as Wim practices, may have comparable effects, still needs to be investigated. Extreme cold air (4°C for 20 min a day) does increase the capacity of non-shivering thermogenesis.⁵ Studies showing the often-circulated effects of cold showers or winter swimming on health parameters are, however, very scarce. As far as I know, only one study in cold water swimmers suggests that regular cold exposure may stimulate insulin sensitivity.

Apart from the metabolic effects, Wim Hof's method may increase vasomotion, thereby training our blood vessels and the cardiovascular system.

It is interesting to note that many of the effects of cold on our metabolic health (energy, glucose, and lipid metabolism) and cardiovascular system show parallels with the effects of exercise training. However, as indicated above with the Radboud University study, it remains unknown whether regular cold exposure on its own positively affects our immune system.

Finally, I think mental health may be influenced by the Wim Hof method – not only by the meditation. Many of Wim Hof's pupils become extremely enthusiastic, experiencing their bodily feelings during almost bioenergic hyperventilation sessions that they never experienced before. They are also pushing boundaries and feeling relaxed after extreme body challenges.

There is, however, a string attached to the Wim Hof Method, that is the risk that people may think the method is scientifically valid. Wim is a wholehearted speaker, but his scientific vocabulary is galimatias. With conviction, he mixes in a non-sensical way scientific terms as irrefutable evidence. Many less scientifically literate people believe what he says and several seriously diseased people have used his method as the final straw. Stories of believers circulate on the Internet, in popular magazines and are broadcasted as well. The scientific investigations are often presented with a biased view.

When practicing the Wim Hof Method with a good dose of common sense (for instance, not hyperventilating before submerging in water) and without excessive expectations: it doesn't hurt to try. Although the effects on our health wait to be proven, people may feel healthier.

All in all, I think it is worthwhile to sort out whether and which of the training aspects of Wim's method affect our immune system and metabolism. And, with respect to the extreme challenges, is Wim special? Or are we all, as he himself proclaims, ice(wo)men?

Figure 1. The Iceman Wim Hof released after the PET/CT scan for the measurement of brown adipose tissue activity.