007: Burn Fat, Think Clearly, and Live Longer by Becoming Best Friends with the Cold

Episode Notes:
From icing ankle sprains to whole-body cryotherapy chambers, cold therapy has been therapeutic procedure used for many years to resolve many issues. As scientific literature has increased, both excitement and skepticism for the effectiveness of the cold has increased. What hasn’t changed, is the fact that cold exposure is often uncomfortable and undesirable.

In this episode, you’re going to learn why the discomfort of the cold is more than worthwhile. From improving brain performance and reducing neurodegenerative diseases to increasing fat burning potential and adding years to your life, forcing yourself to be cold has incredible powers. I’ll also share my experience with daily cold showers, years of ice baths as an athlete, and a regular cryotherapy practice, and most importantly, how you can begin to leverage the cold for an optimized life.

Topics:
[1:58] The cold activates mitochondria-rich brown adipose tissue
[5:13] Sirtuins and the survival circuit
[7:03] Vasoconstriction for better brain health
[8:16] Relationship between the blood-brain barrier, the vagus nerve, and cold exposure
[12:03] How cold showers have changed my life
[14:17] Cryotherapy: Results of exposure to -180°C (-300°F)
[15:44] Best and easiest ways to implement cold exposure

Thank you all for joining me on this journey to lifelong health, happiness, and higher performance. And remember, always be grateful, love yourself, and serve others.

Teaser
In this episode… Three minutes surrounded by liquid nitrogen gas reaching temperatures below -180°C, which is close to -300°F. It was quite a rush, and I have continued doing weekly treatments and have noticed some significant benefits.

Episode Intro
Learn II Perform: Practical lessons so that you can immediately learn to optimize your health, happiness, and performance.

Gratitude
For today’s gratitude shout out, I want to express gratitude to the Ice Man – Wim Hof! [1]. A man who has accomplished superhuman feats including swimming underneath an iceberg the length of a football field on one breath, Wim Hof has used the cold to conquer mental diseases, control his nervous system, and trailblaze scientific research in the benefits of cold exposure. I first learned of him while watching an episode of Impact Theory with Tom Bilyeu, and was captivated by his passion, his story, and firm belief that the cold can be your best friend [2]. My journey into the cold started with Wim, so thank you to him, and also Tom Bilyeu for hosting an incredible educational platform with Impact Theory.

Topic Introduction
Alright, so cold therapy, often used interchangeably with cryotherapy or cold thermogenesis, is the application of cold temperatures to induce physiological benefits [3]. Very often, cold therapy is associated with acute injuries and inflammation, such as icing a sprained ankle or taking an ice bath following intense athletic activity. However, on a broader scale, cold therapy can apply to any form of exposure to cold temperatures that our body is forced to adapt to. This can range from walking outside in a t-shirt on a cold winter day to receiving whole-body cryotherapy treatment in a cryotherapy chamber.

So What’s the Bottom Line
Cold therapy will increase your brain health and performance, longevity, and fat-burning capabilities through three primary channels:

1. Increasing brown and beige fat
2. Activating the survival circuit
3. Improving health of the Blood-Brain Barrier

1. Increasing brown and beige fat
When I first began learning about the benefits of cold therapy, I encountered literature on brown adipose tissue, but never really understood its implications. Turns out, adipose tissue is just a fancy way of saying fat and there are actually different types of fat. Most notably, there is white fat, also known as bad fat, and there is brown fat, known as the good fat. And somewhere in between, we have what is called beige fat. One resource that helped to clear this up for me was David Sinclair’s Book, Lifespan [3]. In it, he notes that brown fat is unique because it is extremely rich in mitochondria – what everyone will remember from high school biology as the powerhouses of the cell. Sinclair notes that while brown fat is commonly observed in infants, it tends to decrease as we get older.

In Boundless, Ben Greenfield does a great job summarizing the role of brown fat and white fat [4]. Essentially, white fat is simply just stored energy waiting to be used. This is the type of fat commonly associated with obesity. But the mitochondria-dense brown fat functions by utilizing the energy stored in white fat and creating heat; it induces the metabolic effect of cold thermogenesis: the ability generate heat without shivering. Beige fat cells are interesting because they are simply the result of the browning of white fat cells. Although they do not share the exact same appearance as brown cells, their metabolic function is the exact same of brown fat.

Evidence suggest that the best way to activate brown fat is through cold exposure. A 2015 review of the physiological roles of brown and beige fat found that “cold exposure stimulates brown adipose tissue expansion through activating the proliferation and differentiation of brown adipose precursor cells” [5]. Meanwhile, the best way to convert white fat into beige fat is also through cold exposure. The same study concluded that beige fat cells “are only readily detected in the white adipose tissue of animals that have been exposed to cold or other inducers” [5]. In support of this claim, a 2016 study found that beige fat cells “develop in white adipose tissue in response to certain stimuli — notably, exposure to cold” [6].

The benefits of brown and beige fat activation are more than improved energy metabolism and thermogenesis, as one mice study found that enhanced brown adipose tissue function was observed in mice with “remarkably extended longevity” [7]. Two other studies came to similar conclusion. A 2014 study found that animals that either had large amounts of brown fat or were subjected to shivering for three hours daily experience “significantly reduced rates of diabetes, obesity, and Alzheimer’s disease” [8]. This was attributed to the role brown fat plays in energy metabolism which drastically increases the ability to burn fat to generate heat. The other study, conducted in 2005, also found that cold exposure activates the mitochondrial functions that enable thermogenesis in brown fat [9].  

To summarize this section, we know that brown and beige fat are healthy fats capable of mobilizing stored fat and generating heat and energy. More importantly, we have discovered that the best way to increase and activate these fat cells is through cold exposure. In numerous studies, it has been shown that frequent cold exposure increases metabolic function, helps to increase fat burning, and is directly linked to disease prevention and increased lifespan. Those reasons are enough to motivate me to stay cold, but as we will find out, there are even more benefits.

2. Activating the survival circuit
Building off the last two studies referenced, they both determined that increased mitochondrial functions and longevity are suspected to be attributed to the activation of a SIRT3, which is a sirtuin that functions as part of the survival circuit [3, 8, 9]. These studies found SIRT3 is “expressed in brown adipose tissue and is localized on the mitochondria inner membrane” [8]. So this leads us to the discussion of how cold exposure up-regulates the survival circuit in a similar manner to exercise and fasting.

At this point, you may be asking what sirtuins are. In short, sirtuins are enzymes that are produced by all cells in the body [3]. They function by altering the packaging of the DNA, enabling them to turn genes on and off. In addition, they also regulate processes related to cell survival including DNA repair. The concept of sirtuins is quite confusing, and is still something I stumble over all the time, but Dr. Sinclair provides a nice metaphor, describing sirtuins as emergency responders. When cellular damage occurs in the body, the sirtuins are the first responders that relocate to assist in DNA repair and healing. So basically, sirtuins are used to regulate gene expression, and when needed, can be called upon for DNA repair. 

Regarding cold exposure, Sinclair states that “Sirtuins are switched on by the cold, which in turn activates protective brown fat in our back and shoulders” [3]. This further confirms what we have already covered, that cold exposure increases brown fat which improves metabolic functioning, fat burning, and lifespan. In terms of the survival circuit, existing literature points to the conclusion that cold exposure activates the survival circuit in a similar manner to fasting, caloric restriction, and exercise. One example of supporting evidence for cold exposure and longevity comes from a 2006 study that observed that genetically engineered mice that lived their entire life half a degree Celsius cooler than the baseline observed a 20% longer lifespan in females, the equivalent of seven healthy human years [10].

Beyond sirtuins, there is another survival adaptation worth noting. When exposed to a cold environment, the body responds by constricting blood vessels below the skin in a process called vasoconstriction [11]. This reduces heat lost through the skin and preserves the core temperature of the body and all essential organs. Initially, non-shivering thermogenesis is instigated to generate heat – this is the process enabled by brown fat cells. And if necessary, shivering begins to generate additional heat. The important takeaway is that vasoconstriction enables the body to prioritize the most important organs – the brain in particular. As blood flow to extremities is reduced, the brain receives a massive increase in nitric oxide and essential nutrients [4].

Before we move on – here’s some bonus content for you! Vasoconstriction is observed in another survival process, called the mammalian dive reflex. Think about when you jump into a pool or splash cold water on your face – do you feel an immediate rush of energy or increased alertness? Upon water submersion or breath holding, the body responds by constricting blood flow to peripheral regions to redistribute blood to vital organs and reducing oxygen consumption, giving mammals the greatest chance of surviving while underwater [12]. This enables us to hold our breath much longer underwater in a survival situation than we would be able to in a relaxed setting.

3. Improving the health of the blood-brain barrier (BBB)
First things first, what is the blood-brain barrier? In short, the blood-brain barrier is a single-cell membrane that forms a wall between the brain and the blood [13]. What is interesting is that it has selective permeability, meaning that it only allows certain compounds to pass through. This is a key consideration, because to function properly, the brain must receive particular compounds such as glucose, ketones, and amino acids. For those coffee lovers out there, caffeine is a compound that easily crosses the blood-brain barrier, which is why drinking coffee can spark mental cognition and alertness rather quickly [4].

Now, the blood-brain barrier is also responsible for preventing toxins, pathogens, and other alien cells from entering the brain – an important task because invading cells can cause significant damage. What is concerning, is that the permeability can increase, resulting in what is referred to as a ‘leaky brain’ [13]. Much like a ‘leaky gut’ – a topic for another episode – a ‘leaky brain’ is associated with numerous neurological disorders, including: Alzheimer’s, Multiple Sclerosis, Depression, Brain Fog, sleep problems, and many more.

The potential list of contributors to a ‘leaky brain’ is long, but in Boundless, Ben Greenfield concludes the three most common are sleep deprivation, alcohol consumption, and high blood pressure. Other factors may include chronic stress, inflammation, brain trauma, infections, obesity, and many others [14].

The good news is that it is possible to increase the integrity of the blood-brain barrier and reduce permeability. The critical link appears to come from the vagus nerve, which is a major component of the autonomic nervous system [15]. With nerve fibers capable of sending information from the brain to the body, and vice versa, the vagus nerve is a critical part of the gut-brain connection that helps to regulate many bodily processes, particularly in the parasympathetic nervous system [16].

Vagus Nerve Stimulation, as you might expect, is the process of stimulating the vagus nerve. This is where we can discover how we can fix a leaky brain. A 2012 study found that vagus nerve stimulation has been shown to reduce permeability, even following traumatic brain injury, indicating that vagus nerve stimulation can assist with brain recovery and function [17]. As separate study in 2018 exploring the impact of a stroke in rats demonstrated that non-invasive vagus nerve stimulation was found to have neuroprotective properties by protecting the integrity of the blood-brain barrier [18].

Now to tie this back to cold exposure, research indicates that cold exposure serves as a non-invasive form of vagus nerve stimulation. In a 2018 study on cold stimulation, it was observed that the cardiovascular reactivity to the cold resulted in an increase in cardiac-vagal activation [19]. Meanwhile, a separate study in 2009 on cold water immersion (an ice bath for example) was found to restore vagal-related functioning after highly intense exercise [20]. Their conclusion was that cold-water immersion “may serve as a simple and effective means to accelerate parasympathetic reactivation during the immediate period following supramaximal exercise.” In other words, in a stressed state, cold exposure can help to quickly activate the parasympathetic nervous system through the vagus nerve, which we now know corresponds with improved blood-brain barrier health.

Here’s my takeaway. Our brain’s health and performance is largely dependent on the integrity of the blood-brain barrier. One way to strengthen it is through vagus nerve stimulation, and one of the easiest ways to do that, is cold exposure. In short, cold exposure may contribute to the reduction of brain fog and neurodegenerative diseases while promoting increased focus, sleep, and positive moods. And to tie it back to the start, it turns out that vagus nerve actually modulates brown fat activation… everything is interconnected. How cool is that? [21].

Personal Experience
So now, I am going to share how I’ve implemented cold exposure into my. First of all, I’d like to note that I am writing this episode on a cold Fall day with my window open while only wearing shorts and a t-shirt. No blankets, no socks, no extra heat. I have had goosebumps for the last four hours… so I am trying to practice what I preach!

As for regular implementation, I have found the easiest way is to take cold showers. In the spring of 2020 when beginning to experiment with regular cold exposure, I would crank the water as cold as it got at the end of every shower. I started off with 15-30s for a few days, and then I quickly worked my way up to 2-3 minutes. I found that after the initial shock during the first 5-10s, it was quite tolerable. Typically, I would allocate 3-5 mins at the end of every shower with the water as cold as it gets.

Upon switching to cold showers, I immediately felt invigorated after stepping out of the shower. I had this incredible rush of energy and alertness that greatly improved my productivity and focus during the day. Cold showers are a terrific option because they are extremely convenient. However, plunges in cold lakes and rivers are another great option, and if accessible, ice baths are excellent as well. When the weather is cold (think winter in the northern parts of the world) you can easily implement cold exposure every day.

I will often keep my windows open and allow my room to be particularly cool throughout the day and always keep it cool at night, which also promotes improved sleep. Often, I will go for short walks in just a t-shirt or light jacket until I am at the point of shivering, indicating that I have pushed my body beyond non-shivering thermogenesis. As the weather has cooled off during this transition from summer to Fall and an early November blizzard in southern Alberta, I must admit that I have not remained consistent with cold showers daily. However, I have leveraged the cold weather to ensure that I have still exposed myself to the cold in some form every single day.

As an athlete, I also loved taking ice baths. Although I no longer believe that ice baths are optimal for post-exercise recovery, which can be explored at another time, I do believe ice baths are a terrific form of cold exposure. During the last six years of my hockey career, I would typically take an ice bath an average of three times a week, with some periods of increased or decreased use. My preferred temperature was about 45°F, which is around 7-8°C, and I’d usually stay submerged from the ribs down for about 8-10 minutes. After these ice baths, I would always feel better during the rest of the day, although it was very difficult to articulate why or how. But if you talk to most others who take frequent ice baths, many of them will say the same.

The start of the ice bath sucks, the middle and end is tolerable, but the feeling after is wonderful. On days I took an ice bath after a morning practice, I would almost always have magnificent naps, sometimes lasting for up to three hours. Practice, ice bath, lunch, nap… those were the glory days.

Being obsessed with the cold, when I discovered that there was a cryotherapy chamber at Effect Therapy in Lethbridge, I instantly knew I had to try it [22]. Quick shout out to Bryan Pachal and the Effect Therapy team – their facility is incredible, the staff is professional, and anyone in Lethbridge should check them out. In addition to cryotherapy and massage, they also have an infrared sauna which I am in love with. Again, another topic for another episode.

Back to my experience. In early August, I had my first cryotherapy treatment: three minutes surrounded by liquid nitrogen gas reaching temperatures below -180°C, which is close to -300°F. It was quite a rush, and I have continued doing weekly treatments and have noticed some significant benefits.

Beyond the subjective feeling of immediate stress relief and increased energy, the first time I did cryotherapy in the evening, just a few hours before going to sleep, I noticed a massive spike in my REM sleep that night. Using my WHOOP fitness tracker, I observed over twice as much REM sleep as my normal baseline, nearly three hours for a single night [23]. Although I do not have enough data to note any significant trends, and there are too many other variables to consider, I have frequently observed improved recovery, heart-rate variabilities and sleep efficiency following cryotherapy.

Most of all, I genuinely feel relieved and clear-minded. After a stressful day, I can feel the stress dissipate and am often in what feels like a meditative state. It’s a wonderful feeling, and for me, I’m convinced cryotherapy is helping me significantly and I intend to continue regular treatments, even if experts still can’t agree on how or if whole body cryotherapy is as beneficial as perceived [3, 24].

So What You Can Do
The science in this episode was complicated, but how to apply the science is easy. The bottom line is that you should allow yourself to be cold every day. This can come in different forms and different durations, but remind yourself that the discomfort of being cold now may have huge dividends in the future. This idea of delaying gratification for something better in the future constantly comes up, as seen in episode six about fasting.

So what’s the easiest way to implement cold exposure? Perhaps the fastest and most convenient is to take cold showers. Take your normal shower, do what you have to, and then crank the water cold at the end. Try to take deep and controlled breaths until the initial shock passes, and try to remain in there as long as possible. Start small, maybe 5-10s, and work your way up to 30s, then a minute, and then aim for 3-5 minutes.

Another great tactic that I love is to take contrast showers. Here’s a simple strategy: 20s as cold as it gets, then 10s as hot as it gets [4]. Ten rounds of this gives you five minutes. With each switch, you are shocking your body and forcing it to adapt. It’s not nearly as miserable as it sounds. To track your time, use a TABATA app to create a timer on your phone and run through your five minutes of contrast therapy. And my recommendation with any contrast therapy – always end on cold!

If you’re lucky enough to live somewhere cold, take advantage of mother nature and get outside. Go for a brisk walk, open the windows to let the cold air in, and turn off the heat in your house for a few hours. But remember, everything is in moderation. If you have a hot tub, going in and out of the hot tub a few times during the winter would be a wonderful way to apply contrast therapy. But be careful with extreme cold temperatures: Hypothermia is not the goal, goosebumps and shivers are. To help motivate you, it has been found that shivering provides five to six times the metabolic rate of normal resting levels – essentially becoming a fat burning machine [11]! And for added benefits of the cold, try exercising in a cold environment, either outdoors or in a cold room. Exercise and cold exposure together may compound the activation of brown fat [25].

And if you’re really ambitious, ice baths are a phenomenal way to reap the benefits of cold therapy, albeit a very uncomfortable experience. Depending on where you live, I would also recommend that you look up cryotherapy in your region. If there are whole-body cryotherapy treatments available near you, I highly recommend that you give it a try. All places will have a lot of information and would be more than happy to discuss how cryotherapy might benefit you.

So there you have it, there are plenty of ways to implement cold exposure to improve your brain’s health, accelerate fat burning, and even add quality years to your life.

As “The Iceman” Wim Hof says, “The cold is an absolute doorway to the soul” [26].

Episode Outro
To discover more, the full transcript of this episode with all citations is available on the website and you can also contact me on social media with any questions or comments. If you found this episode useful or think that it may help someone else, I encourage you to pass it along.

Thank you all for joining me on this journey to lifelong health, happiness, and higher performance. And remember, always be grateful, love yourself, and serve others.

References
[1] Welcome to the Official Wim Hof Method Website. (2020). Wim Hof Method. Retrieved October 28, 2020, from https://www.wimhofmethod.com/

[2] Bilyeu, T [Tom Bilyeu]. (2019, January 1). This Trick Makes You Immune To Illness | Wim Hof on Impact Theory [Video]. YouTube. https://www.youtube.com/watch?v=TM6WKeZ43s4&t=2s

[3] Sinclair, D., LaPlante, M. & Delphia, C. (2019). Lifespan : why we age–and why we don’t have to. New York: Atria Books.

[4] Greenfield, B. (2020). Boundless: Upgrade your brain, optimize your body & defy aging. Las Vegas: Victory Belt Publishing Inc.

[5] Kajimura, S., Spiegelman, B. M., & Seale, P. (2015). Brown and Beige Fat: Physiological Roles beyond Heat Generation. Cell metabolism, 22(4), 546–559. https://doi.org/10.1016/j.cmet.2015.09.007

[6] Wang, W., & Seale, P. (2016). Control of brown and beige fat development. Nature reviews. Molecular cell biology, 17(11), 691–702. https://doi.org/10.1038/nrm.2016.96

[7] Justin Darcy, Samuel McFadden, Yimin Fang, Joshua A. Huber, Chi Zhang, Liou Y. Sun, Andrzej Bartke, Brown Adipose Tissue Function Is Enhanced in Long-Lived, Male Ames Dwarf Mice, Endocrinology, Volume 157, Issue 12, 1 December 2016, Pages 4744–4753, https://doi.org/10.1210/en.2016-1593

[8] Endocrine Society. (2014, June 23). Cold exposure stimulates beneficial brown fat growth. ScienceDaily. Retrieved November 1, 2020, from www.sciencedaily.com/releases/2014/06/140623091949.htm

[9] Shi, T., Wang, F., Stieren, E., & Tong, Q. (2005). SIRT3, a mitochondrial sirtuin deacetylase, regulates mitochondrial function and thermogenesis in brown adipocytes. The Journal of biological chemistry, 280(14), 13560–13567. https://doi.org/10.1074/jbc.M414670200

[10] Conti, B., Sanchez-Alavez, M., Winsky-Sommerer, R., Morale, M. C., Lucero, J., Brownell, S., Fabre, V., Huitron-Resendiz, S., Henriksen, S., Zorrilla, E. P., de Lecea, L., & Bartfai, T. (2006). Transgenic mice with a reduced core body temperature have an increased life span. Science (New York, N.Y.), 314(5800), 825–828. https://ncbi.nlm.nih.gov/pubmed/17082459

[11] Westerlund, Tarja & Oksa, Juha & Smolander, Juhani & Mikkelsson, Marja. (2009). Neuromuscular adaptation after repeated exposure to whole-body cryotherapy (−110 °C). Journal of Thermal Biology – J THERM BIOL. 34. 226-231. 10.1016/j.jtherbio.2009.02.004. https://www.sciencedirect.com/science/article/abs/pii/S0306456509000205?via%3Dihub

[12] Godek D, Freeman AM. Physiology, Diving Reflex. [Updated 2020 Aug 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538245/

[13] Yazdi, P. (2019, December 17). What is the Blood-Brain Barrier? + “Leaky” Brain Conditions. SelfHacked. https://selfhacked.com/blog/blood-brain-barrier-causes-tests-leaky-brain/

[14] Wannissorn, N. (2020, January 6). 11 Factors That Disrupt the Blood-Brain Barrier. SelfHacked. https://selfhacked.com/blog/factors-and-disease-states-that-disrupt-the-blood-brain-barrier/

[15] Howland R. H. (2014). Vagus Nerve Stimulation. Current behavioral neuroscience reports, 1(2), 64–73

[16] Breit, S., Kupferberg, A., Rogler, G., & Hasler, G. (2018). Vagus Nerve as Modulator of the Brain-Gut Axis in Psychiatric and Inflammatory Disorders. Frontiers in psychiatry, 9, 44. https://doi.org/10.3389/fpsyt.2018.00044

[17] Lopez, N. E., Krzyzaniak, M. J., Costantini, T. W., Putnam, J., Hageny, A. M., Eliceiri, B., Coimbra, R., & Bansal, V. (2012). Vagal nerve stimulation decreases blood-brain barrier disruption after traumatic brain injury. The journal of trauma and acute care surgery, 72(6), 1562–1566. https://doi.org/10.1097/TA.0b013e3182569875

[18] Yang, Y., Yang, L. Y., Orban, L., Cuylear, D., Thompson, J., Simon, B., & Yang, Y. (2018). Non-invasive vagus nerve stimulation reduces blood-brain barrier disruption in a rat model of ischemic stroke. Brain stimulation, 11(4), 689–698. https://doi.org/10.1016/j.brs.2018.01.034

[19] Jungmann, M., Vencatachellum, S., Van Ryckeghem, D., & Vögele, C. (2018). Effects of Cold Stimulation on Cardiac-Vagal Activation in Healthy Participants: Randomized Controlled Trial. JMIR formative research, 2(2), e10257. https://doi.org/10.2196/10257

[20] Buchheit, M., Peiffer, J. J., Abbiss, C. R., & Laursen, P. B. (2009). Effect of cold water immersion on postexercise parasympathetic reactivation. American journal of physiology. Heart and circulatory physiology, 296(2), H421–H427. https://doi.org/10.1152/ajpheart.01017.2008

[21] Chang R. B. (2019). Body thermal responses and the vagus nerve. Neuroscience letters, 698, 209–216. https://doi.org/10.1016/j.neulet.2019.01.013

[22] Effect Massage Therapy West Lethbridge. (2020). Effect Therapy. Retrieved November 1, 2020, from https://www.effecttherapy.ca/

[23] WHOOP – The World’s Most Powerful Fitness Membership. (2020). WHOOP. Retrieved November 1, 2020, from https://www.whoop.com/

[24] Bleakley, C. M., Bieuzen, F., Davison, G. W., & Costello, J. T. (2014). Whole-body cryotherapy: empirical evidence and theoretical perspectives. Open access journal of sports medicine, 5, 25–36. https://doi.org/10.2147/OAJSM.S41655

[25] May, F. J., Baer, L. A., Lehnig, A. C., So, K., Chen, E. Y., Gao, F., Narain, N. R., Gushchina, L., Rose, A., Doseff, A. I., Kiebish, M. A., Goodyear, L. J., & Stanford, K. I. (2017). Lipidomic Adaptations in White and Brown Adipose Tissue in Response to Exercise Demonstrate Molecular Species-Specific Remodeling. Cell reports, 18(6), 1558–1572. https://doi.org/10.1016/j.celrep.2017.01.038

[26] Stead, H. J. (2018, June 26). Breathe Like The Iceman: How To Use The Wim Hof Method. Medium. https://medium.com/@harrystead17/breathe-like-the-iceman-how-to-use-the-wim-hof-method-8048fe9591de