Getting Stronger

At this year’s Ancestral Health Symposium, I spoke about how exposing yourself regularly to cold temperatures can increase your tolerance for the cold. More importantly, it can also trigger deeper health benefits, including reducing inflammation, improving your immune response to colds and flus, helping burn fat and lose weight and — perhaps most surprisingly–improve your mood and increase your resilience.

This 36-minute talk covers the evolutionary background of our ability to adapt to cold climates, the physiology and psychology of cold adaptation, and some practical ways to experience the cold — including cold showers, cold baths, ice baths, open water swimming, cool sleeping and whole body cryotherapy. I end with an experiment you can try to test your ability to adapt to the cold and experience its benefits.

You can click on the above photo or HERE to watch the video.

Here is a slide-by-slide transcription of the talk, with video timestamp references. There is also a good Q&A session at the end, which I did not transcribe, but is worth hearing.

Slide 1. (0:00). Benefits of Cold Adaptation. Ancestral Health Symposium, UCLA, August 18, 2022.

What if I told you that by exposing yourself to cold temperatures you could lose some extra pounds, boost your immunity and improve your mood and resilience? I’ve been taking cold showers every morning since 2009.  When I tell people that, most people look at me like I’m crazy. Today I’d like to give you some reasons to deliberately expose your self to cold temperatures on a regular basis. And I’ll share some practical tips on the best ways to do it.

Slide 2. (0:58). I’ve now given 6 previous talks at AHS and I write a blog called Getting Stronger. My talks have covered topics as diverse as vision improvement, overcoming obesity, and improving your memory.  I like to base my talks on a combination personal experience and a look at the underlying science.

But what all my AHS talks, and my blog posts, have in common is the central theme of hormesis. That’s the judicious use of low dose and intermittent stress to improve your health.

So cold exposure is a type of hormesis. And today, I’ll try to convince you that increasing your exposure and tolerance to cold is one of the most actionable types of hormesis you can incorporate into your daily routine.

Slide 3. (1:47). Here’s an outline of my talk:

• Indoor heating is a recent innovation in human evolution 
• Human migration to colder climates drove both genetic and cultural adaptations
• Regular exposure to cold activates physical and psychological benefits
• There are several ways to embrace & benefit from cold exposure

Slide 4. (2:44). As animals moved into colder climates, their genes and metabolism changed, to help them adapt.

Slide 5. (3:01). Our early evolutionary cousins, the Neanderthals, co-existed with woolly mammoths. During the last Ice Age, both species migrated out of Africa into Europe and Asia and had to adapt to colder climates. They both evolved more body hair, and more body fat, including brown fat, which I’ll discuss later. 

Researchers at Tel-Aviv University found that Neanderthals and Woolly Mammoths actually evolved similar sets of genes and regulatory proteins. It’s a case of convergent evoSlution. These shared genetic alleles include LEPR, which codes for leptin receptor for brown fat regulation & thermogenesis, and MC1R, which codes for lighter hair & skin for vitamin D absorption.

Slide 6. (4:09). As Neanderthals and Denisovans migrated north about 350,000 years ago, they had to adapt to colder climates in Europe and Asia. Homo sapiens left Africa about 60,000 years ago and interbred with the Neanderthals and Denisovans. Excavations showed that both of these populations evolved genes that help them survive cold climates

These same or similar genes are found in modern humans who live in cold or high altitude climates, including EPASI — found in modern Tibetans –and TBX15 and WARS2 — which that increase heat from body fat – found in modern Inuits.

Slide 7. (4:58). Our species, Homo sapiens, arrived about 400,000 years ago.  We and our evolutionary cousins evolved during an Ice Age, the Pleistocene. While they invented fire, clothing and shelter, much of the day was spent outdoors. 

The ice age only ended 12,000 years ago, allowing agriculture to take root. But even then climate was variable. When we bathed, before about 1850, the water was typically not pre-heated. Only within the last century, did most people start to live indoors in climate-controlled homes and offices.

But I hope its clear that protection from the cold is a recent innovation in evolutionary time. We evolved to  tolerate the cold.  It’s hardwired into our DNA, we just need to activate the genes.

Slide 8. (5:56). But so what? We now have the ability to live indoors most of the time, in our climate-controlled homes and offices. So why not just enjoy it? 

When you think about heat and cold, what emotions do you feel? Getting cold can be uncomfortable, make you miserable, even make you sick.

So why deliberately get cold?  What are the benefits?

Slide 9. (6:29). Let’s take a closer look what happens to you when you are exposed to the cold — either mild or extreme cold.
It’s important to distinguish three phases:

• the immediate physiological responses, from a single exposure
• the secondary response, once you step out of the cold, from that single exposure
• Longer term adaptive responses, from multiple exposures

These effects can be quite different.  The aftermath and adaptive responses are often opposite to the initial response.

Slide 10. (6:43). If you are not cold adapted, you’ll experience a number of immediate effects.

• Your skin vasoconstricts (in the video, I misspoke “vasodilates”) and blood moves to the core to preserve heat.
• You start shivering.
• Your sympathetic system kicks in  – that’s your flight or fight response – with noradreline and insulin to produce energy.

Slide 11. (7:12). Then, there are secondary responses that kick in. After a few minutes, your shivering may start to warm you up – that’s thermogenesis. And you feel more comfortable, or at least less uncomfortable.

When you step out of the cold your parasympathetic system kicks in to calm you. That’s your “rest and digest system system” that acts as a balance to the sympathetic system. This also activates some anti-inflammatory cytokines that can reduce swelling or injury.

Blood rushes back to your skin and it may appear reddish. And you may experience some elevation in mood that lasts for hours.

Slide 12. (7:48). Now when you repeat this process a number of times, it’s a signal to the body that this could become a routine and some adaptation is required.  Adaptation or acclimation is a process that can take days, weeks or months. 

In the case of cold exposure, there are three adaptive responses I’d like to talk about, responses that occur over time

• Your brown fat is activated, allowing you to warm up without shivering
• You get certain metabolic benefits like improved insulin sensitivity, weight loss
• Your immune system gets a boost
• Sustained mood enhancement and resilience

Let’s go into some of these main effects.

Slide 13. (8:30). We’ll start with thermogenesis — how your body warms itself up when exposed to the cold. Your body needs to maintain a core temperature around 37C or 98.6 F. If it drops to low, you risk hypothermia

When you are exposed to the cold, this activates cold thermoreceptors in your skin, relaying the signal through nerve fibers to the hypothalamus, your brains master thermostat.

Slide 14. (9:07). This activates your sympathetic nervous system to release noradrenaline in your skeletal muscles. The skeletal muscles to rapidly contract or shiver. And that generates heat in in your core, as a primary response to the cold.

Slide 15. (9:26). But your shivering muscles then also produce a hormone called irisin, which stimulates your brown fat to produce heat. Your brown fat is rich in mitochondria, and a protein called thermogenin or uncoupling protein 1. It’s activated when the norepinephrine from your muscles bind to receptors in the brown fat. Brown fat also produces a protein called  FGF21 that enables non-shivering thermogenesis. 

Instead of slowly burning your fatty acids and glucose using the TCA cycle to produce ATP for metabolism,, to help you move, or digest or think, thermogenic quickly and inefficiently burns fuel to dump heat.  This is sometimes called a “futile cycle”, because no work is accomplished, just heat. This inefficiency can have other benefits like speeding your metabolism by 20% and helping with weight loss.  

If you have a lot of brown fat, this non-shivering thermogenesis warms you up fast and you don’t have to rely as much on shivering.

Slide 16. (10:39). Babies have a lot of brown fat, which allows them to keep warm without shivering. As we age, we lose brown fat.

Where is your brown fat? The photo at the top left shows a young, fit person with a lot of brown fat. There isn’t much, but when its found, it tends to be localized around the shoulders and neck. The photo at right shows a less fit person without much brown fat.

However, it was recently discovered that conversion of white fat to brown fat can be induced by exposure to the cold! This induced brown fat is called beige fat or brite fat. At the bottom you see white fat on the left, dense brown fat on the right – it’s smaller and richer in mitochondria. The middle shows the beige fat brown fat that is partly converted to brown fat.

What is really promising is that cold exposure can cause “beigeing” of white fat.

Slide 17. (12:05). Now we can zoom out and put cold stimulation of brown fat into a bigger picture. Cold exposure is one of several hormetic stressors – like exercise, calorie restriction and hypoxia at high altitude -that activate a master regulator called PGC-1α.

This activates the production of irisin in the skeletal muscle. And the beigeing of inflammatory white fat to anti-inflammatory brown fat. The more irisin, the more of your white fat is converted to brown fat. And as I said, enables non-shivering thermogenesis, making it easier for you to tolerate the cold. But the inefficiency of non-shivering thermogenesis also speeds your metabolism by 20% and helps you lose weight

The PGC-1α  master switch also has other metabolic effects:

• It increases BDNF in the brain, which benefits mood and cognition
• It inhibits mTOR, reducing systemic inflammation
• It increases insulin sensitivity
• It inhibits NPY receptors in your hypothalamus, which suppress appetite, increase sthe urge to exercise, and activates autophagy, making it easier to lose weight.

A 2013 study by Yoneshiro etal found that spending two hours a day at 17 C (63F)  for 6 weeks, activated BAT, increased energy expenditure, and decreased body fat.

Slide 18. (13:23). Speaking of cold exposure – anyone recognize this gentleman emerging from Arctic waters?

Wim Hof has probably done more than anyone else to popularize the interest in cold exposure. He holds world records for sitting in a tub of ice for hours, running a barefoot and shiftless half marathon above the Artic Circle, and swimming 50 meters under the ice. He’s hiked up Kilimanjaro in his shorts, and he’s also run through the hot desert, showing that he can tolerate heat as well as cold. 

Wim Hof now has a whole organization that conducts nature experiences and retreats, and he has developed the popular Wim Hof breathing technique, which involves cycles of hyperventilation and breath holding.  The breathing technique can be used on its own or as a preamble to get warm before you get cold. It’s a modified version of Tummo breathing that activates the sympathetic nervous system and helps prepare you for the cold

I could talk about Wim for an hour, but I’d like to focus just on one of his claims that generated a lot of interest and controversy. Namely, Wim’s claim that he can voluntarily control his immune system, that he can enhance his immune response to better resist infection

Is this true?

Well anecdotally, many who take cold showers and swim in the open water report a marked reduction in colds and flus. In my own case, I have not had a cold or flu since I started taking cold showers in 2009.  Maybe that’s just a coincidence, or due to some other reason, or just good luck. As a scientist, I know that anecdotal experiences and correlations do not establish causation.

Slide 19. (14:49). So let’s turn to an interesting study that was done to attempt to test Wim’s remarkable claim. First, Wim asked a medical team to inject him with endotoxin and monitor his reaction, while he practiced his breathing method and sat in ice water. He showed no ill effects beyond a mild headache, he maintains.  Monitoring of his cytokine levels showed significantly reduced pro-inflammatory markers.

So maybe he is a freak of nature, a superhuman?

But Wim believes his methods can work for anyone, so in 2019  he challenged a Dutch organization to a study. He recruited 48 healthy male volunteers randomized into 4 groups to test the breathing & cold exposure. They practiced his methods for 4 days before being injected with LPS, a bacterial endotoxin that typically elevates inflammatory cytokines and you quite ill.

There were 4 treatment groups

1. Cold exposure

• standing barefoot in snow 20 min
• laying in shorts on snow, 30 min
• ice bath 3 min
• cold shower  1 min

2. Breathing exercises

• 30 hyperventilation breaths
• Exhale and hold breadth 2 min
• Deep inhalation 10 s
• 2 cycles

3. A combination of the cold and the breathing

4. And a control group.

The voluntees were monitored over 2 1/2 hours for symptoms and numerous pro- and anti-inflammatory cytokines.

What did they find?

First of all, flu-like symptoms were markedly reduced in all the trained legs. In all treatments, there is a surge in the release of sympathetic system hormones like noradrenaline, and a rise in both pro- and anti-inflammatory cytokines. But the magnitude of the spikes varied between treatments.

The group that practiced only the breathing method showed a 34% reduction in IL-6, an inflammary cytokine, relative to control. The cold exposure group had reduced symptoms, but no significant change in cytokines.

The combination of breath and cold was the only group that showed a significant increase in anti-inflammatory cytokines, like IL-10

But this is still what I would consider a short term study.  Is there any evidence to show that more prolonged adaptation to the cold can strengthen the immune system?

Slide 20. (16:22). What about long term effect on the immune system?

The is a good study by Buijze et al. (2018): “The Effect of Cold Showering on Health and Work: A Randomized Controlled Trial.” PLOS ONE 13(8): e0201978. https://doi.org/10.1371/journal.pone.0201978 

This was a Dutch study of 3018 healthy people ages 18-65 (I misspoke “18-25” in the video) with no prior routine experience of cold showering were randomized to cold showering or control groups during 30 consecutive days.  The cold showering groups started with a hot shower, and ended with 30-90 seconds cold shower, followed by 60 days of showering cold at their own. The average cold water temp in the Netherlands during the study period was 10-12 C (50-54 F).

What were the results?

Of the 79% of participants who completed the study, there was no reduction in the incidence (i.e. total number) of reports of cold, flu or illness, but there was  a 29% reduction in sickness absence for the cold showering group relative to the control, with p = 0.003.  So a 29% reduction in illnesses severe enough for you to stay home from work. 

Slide 21. (17:50). Another secondary effect of cold exposure is an anti-inflammatory effect. In fact, this is probably the one that you are most familiar with if you are an athlete. “Put ice on it” is a common recommendation to reduce swelling and pain associate with an acute injury. The localized cold temperature reduces the activity or perhaps overactivity of white blood cells and cytokines.

But cold on the skin also activates the sympathetic nervous system. It causes a quick surge in noradrenaline. And the sympathetic nervous system can be pro-inflammatory in the short term. Which helps mobilize energy and defense.  But it can also sharpen pain and inflammation.

So is this a good thing?

Well the sympathetic surge is a short term, primary response.  In its wake the parasympathetic system kicks in. And with with repeated exposures, the sympathetic surge becomes less pronounced, and the parasympathetic system is strengthened.   And this system is associated with anti-inflammatory cytokines.. The longer term anti-inflammatory effects come through the PGC-1-alpha cascade I mentioned, stimulating irisin, brown fat, and inhibiting mTOR.

Slide 22. (18:25). And now we get to what I personally think is the greatest benefit of cold exposure: the benefits to mood and resilience.

One of the very noticeable secondary effects of cold exposure, that many or most people notice, is a boost in mood. This can start shortly after you step into a cold shower or the ocean, and once you step out. It’s a sense of feeling energized, happy, even euphoric. And that benefit can last for hours, or even all day or longer

But beyond mood, it can improve your emotional resilence. Your ability to absorb the slings and arrows of life. To handle adversity without it bothering you so much.

Seneca, the famous Roman orator and Stoic philosopher wrote that he was “a great lover of cold baths”. And the Roman baths included the “frigidarium” – the cold bath.

Many cultures embrace cold swimming as a balm for the soul. But how does cold shower boost mood and resilience?

Slide 23. (19:43). I think the most persuasive explanation for the mood boost after taking a cold shower or cold swim comes a 1980 paper by Richard Solomon, a psychology at Penn, based on the idea of homeostasis. Solomon was trying to explain how we react to intense experiences. He studied the experience of of novice and experienced skydivers.

The left plot shows the skydiver before the first jump. The line in the middle is called “neutral or baseline”.  That’s homeostasis. When they jump the first time, homeostasis is disturbed — this is shown as a jump in State A – which is fright. And physiologically, that’s adrenaline and cortisol. The brain, like the body, always trys to return to a neutral state when it gets disturbed. So State B is the opponent process.  It’s the calming – parasympathetic system. And neurotransmitters like beta endorphins or serotonin. When the skydiver lands, the stress is over, and there is an Opponent Process B that calms things. There is laughing and even elation that lasts a few hours

The right plot shows what happens after many jumps. The opponent process B is well developed, and anticipates State A. So you see the Peak of A smaller and flatter. And the robust Process B continues deeper and longer

I would argue that cold exposure is like skydiving.  The initial shock and discomfort is followed by a boost in mood.  And the more you do it, the less uncomfortable and shorter the period of discomfort, and the more extended the period of well-being and euphoria. 

Slide 24. (22:09). Cold exposure improve not just psychological mood, but physical resilience. How do we know this? I mentioned that one of the primary responses to the cold is activation of the sympathetic nervous system — our fight or flight response, good for emergencies. This is associated with secretion of noradrenaline in the muscles.

Eventually, this stimulates a secondary response. The other half of the autonomic nervous system kicks in too calm you down and restore homeostasis. That is the parasympathetic nervous system:  “rest and recover”.

Repeated activation of the sympathetic nervous system, if acute and not chronic tends to strengthen the parasympathetic system. It’s the physical counterpart of the opponent process psychology. Homeostatic control is often like this — its anticipatory. The body is adaptive — if there will be a lot of stresses and emergencies, there will be a need to put out the fires.

Well biohackers have discovered heart rate variability (HRV) as a tool tool to track the balance between sympathetic and parasympathetic. A stressed heart is metronomic and shows little variability in the frequency or interval between beats. The heart of a resilient person shows flexibllity and ability to shift between rest and activity. A higher HRV reflects readiness for activity, a lower HRV indicates stress and a need for rest. Athletes use HRV to track the effect of workouts, diet, travel, and stress on their readiness to train

I experimented to find what makes my HRV go up or down. 

• Guess what I found causes the biggest drop?    More than 1 alcoholic drink.
• Guess what I found causes the biggest sharpest rise?  Cold shower, cold baths, and whole body cryotherapy! I’ll show you my numbers later.

A 2008 study echos my personal experience.  Cold exposure increase HRV in the short term, and repeated exposures increase baseline HRV and increase physical and mental resilience.

So now lets look at some different ways to get cold.

Slide 25. (24:32). I take a cold shower every morning.  I started taking them in 2009, and soon I was hooked. I can’t actually remember the last time I took a hot or warm shower. Most people think this is just crazy.

When I suggest it, the common reactions are:

• I could never do that!
• Oh I do that – you mean you turn down the temperature for a few second at the end of the cold shower, right?

No, I take it cold all the way through.  

But let me describe my experience, and you’ll see how well it is explained by the Opponent Process Theory. I’ll go back to very beginning of my initial experience, which I captured in a 2010 blog post:

When you start with a cold shower, you will experience cold shock, an involuntary response characterized by a sudden rapid breathing and increased heart rate. 

• I find myself involuntarily smiling or even laughing.  For waking up, this beats caffeine. I keep the water cold the whole time. It helps to brace yourself when entering by gritting your teeth and stiffening your muscles.  Go in head first and alternate from back to front to make sure you are getting cold all over, including your hands and arms and any sensitive zones.
• After about a minute, you’ll find the cold water starts to become more tolerable, and after 2 or 3 minutes you’ll feel your body getting warm by its own efforts. This is thermogenesis. I make a point of staying in the shower until I’m no longer uncomfortable.  I found that at first my hands were the most sensitive part, and now they are no longer as sensitive, so they have habituated.
• I find that cold showers are great for the mood.  Not only are they physically invigorating, they make you feel alive, vital and ready to take on the day. They stimulate thinking early in the morning.  These effects are apparent with the first cold shower. If you continue the practice for several weeks, you’ll find the psychological benefits are even greater.
• First and foremost, cold showers appear to have improved my stress tolerance, by buffering emotional reactions. What I mean by this is that bad news, surprises, arguments, or events that would have previously caused a brief surge in adrenaline or an emotional flush, no longer have that effect, or at most have a very attenuated effect. 

I think this is a consequence of becoming acclimated to the the adrenaline-producing effect of the cold shock.  The deepening and extension of the mood boost and resilience effect are explained well by the opponent process theory of emotion.

Slide 26. (25:58). I know you are thinking that you could never take a cold shower, its just too scary. But I’ll share some tips that will make it a lot easier. Frankly, the anticipation of the cold shower is worse than the actual experience. And it really gets better after a few repetitions. You’ll actually start to look forward to it once you feel the benefits.

There are two methods:

Method 1.  Cold Ending.   Start warm and end cold.  This is the approach for wimps.

Method 2. Cold Turkey. This is the better approach – cold from the beginning.  I think this is the better way, since it also boosts your confidence.

To get started, you’ll need a timer or a timing watch. A meat thermometer in a plastic cup is also helpful. It’s important to get your whole body under the cold. Especially neck, shoulders, front and back, and hands. Getting your neck and shoulders cold will help stimulate the production of brown fat 

Less than 65 is OK, less than 60 is better. Jump in with the whole body. You will be very uncomfortable. If it helps, laugh, scream and jump around. Check your watch and observe how long it takes for the discomfort to be reduced. And for you to feel any inner warmth in your core

Once you are taking a cool shower all the way through, adjust the temperature to colder. Try to aim for 50-55 F if it is possible. Try to last 5 minutes.

Slide 27. (26:46). Cold baths. This is much more efficient heat transfer in water than air. It’s also more uncomfortable than a cold shower Try to get in neck deep.  Move arms and legs to stay cold, otherwise you get a warm boundary layer around your skin. I do it for 20 minutes.  Measure the time to start to feel comfortable, or at least not uncomfortable

Observe what happens after you get out. I found that in the beginning you can be shivering even after you get out. If you sit down or lie down you can experience waves of cold. This is called the cold drop

I found it came 20 min after getting out, in waves. Also can get lobster hands, red patchy hands.

Slide 28. (27:20). A few interesting after-effects of cold baths that I’ve noticed

Some immediate effects:

1. Lobster hands.  Your skin in your hands and feet start to vasodilate, and this can create a patchy appearance as seen in the photo of my hand at the left, which I took about 10 minutes after getting out of the tub.

2. The cold drop.  You’ll feel warm at first, but as your full circulation returns to normal you can experience some transient effects. You can feel surges of cold alternating with warm. I found that the cold drop came about 20 minutes after getting out of the bath, especially if was sedentary.

This can be disturbing at first, but I found that if I follow the cold bath with something active like walking around, this effect is minimized

Some people get Reynaud’s syndrome from cold exposure.  This is odd purplish coloration of the fingers and hands and it can be painful.  Obviously, you should consult with your doctor if you have Reynaud’s. But I found numerous examples of reports of people were able to reverse their Reynaud’s by gradual exposures to cold water.  Some with cold showers or cold baths.  

3. Adaptive thermogenesis.  After cold baths and showers become more routine, you find that your extremities stay warmer and you feel more comfortable in cold weather.  This photo at the right is an infrared photo taken at the SF Exploratorium You can see my wife at the left. She always has cold fingers and toes and look how black they are in the photo.  You can see how bright white my hands are and even my eyes seem to be glowing.  My wife calls me the heat generator and this is appreciated when snuggling on a cold night.   It goes without saying that I haven’t yet been successful in convincing her to try cold bathing.

Slide 29. (28:22). If you want to go all out, try ice baths. Many athletes and biohackers swear by it. I tried it once or twice. It was quite uncomfortable. I also didn’t like the idea of having to stock my refrigerator with bags of ice

But again, a lot of people swear by it. And I probably haven’t given it a fair shot But I’ve found other methods that work fine for me, with less hassle and discomfort. So let me know if you like ice baths and what they do for you.

Slide 30. (28:43). There is a somewhat more approachable way to confront ice. Tim Ferriss has a very nice chapter in his book the 4-Hour Body, called:  “Ice Age: Mastering Termperature to Manipulate Weight. He debunks the idea that you can lose significant weight just by the thermodynamic burning of calories to stay warm. Swimming in cold water for 2 hours would burn an extra 139 calories, or 15.5 grams of fat – that’s about one ounce. A lot of work for little benefit.

The real benefit turns out to be activating your brown fat. And this can be done by just putting an ice back on the back of your neck while you watch TV or work at your compute for about 20-30 minutes/day in the evening when insulin sensitivity drops. He adds a thermogenic cocktail, but that’s probably not necessary.

Slide 31. (29:04). One of my favorite ways to experience the cold is swimming in the ocean. I live about 30 minutes from the Pacific, where the water is between 50-60F, and when i vacation on the shore, I’m always going for a dip.  I typically go for 20 minutes, and find I’m comfortable after 5 min.

You can also find a fun writeup about my ocean swimming as a form of hormesis in Bill Gifford’s book Spring Chicken, in the references at the end of this talk. I’m not one of the guys in the wet suit, I just wear my swim trunks and get a lot of odd glances.

One of the benefits of open water swimming is the efficient heat transfer from moving water.

Mark Hopper’s excellent book, Chill is the bible for open water swimmers. He’s an anesthesiolgist, who got interested in how cold temperature preconditioning before surgery can be useful in helping post-op recovery after surgery. He’s started a social ocean water swim club where he lives in Bristol, in the UK. And started something called Chill Therapy, with about 20 clubs around the UK. He’s done academc studies with an exercise physiologist, Mike Tipton, whowing that cold water swimming clubs – both the water and the social aspects are effective in combatting anxiety, depression and PTSD,

Slide 32. (29:49). Whole body cryotherapy is something I’d read about, but didn’t try until a month agoIt started in Japan, spread to Europe and is now becoming popular in the US. So I had to research it and try it myself. It sounded extreme.  Immerse your whole body up to your neck in liquid nitrogen vapor at -200 degrees F or even colder.

But for only 3 minutes

It’s popular with althletes, to reduce inflammation, pain and recovery from injury. And it had reported mood benefits. So I had to try it, and even dragged my family into it… here’s my son “enjoying it”

Slide 33. (30:17). Whole body cryotherapy has a very different effect than taking a cold shower or an ocean plunge. Water transfers heat 20-25 times faster than air or gases like nitrogen. So the chill of cold nitrogen gas is only skin deep…it doesn’t penetrate the core.

This figure shows  on the left scale and the lower blue curve how the skin temp dropped quickly from 30 to 15 C. On the right scale and the upper red curve you see the core body barely changed – it actually rises slightly from 36.6 and 37.0 C.

A Finnish study of women, comparing cryotherapy and winter swimming, found in both groups a 2-3X sudden increase in norephineprhine associated with sympathetic nervous system and pain relief. Also found a localized drop in oxygen in the skin. And after several exposures a drop in resting cortisol and ACTH.

Slide 34. (30:40). There are a number of studies looking at potential benefits. A review by Bleakly found observational improvements in strength and pain, but no changes in enzymes or cytokines.

More interesting are the psychological benefits. A 2007 study of patients taking meds for depression and anxiety found significant improvements when cryotherapy was added, 5 times weekly for 3 weeks.

I tried this for myself, in several 3 minutes sessions. It’s very different than cold showers or open water swimming – surprisingly tolerable. I didn’t shiver or have any subsequent core cooling. It feels like you have a thin cold layer over all your exposed skin, but you stay warm inside. When you emerge, the most immediate effect…at least for me…is pleasant euphoria, more pronounced than I get from my daily cold showers.

The mood enhancement lasted all day. My HRV hit an all-time high:

• q8.8 HRV
• q86 RMSSD
• q57 HR

The explanation is a version of the opponent process theory I described earlier. An intense stimulus first generates a spike in threat hormones like noradrenaline and cortisol associated with sympathetic activation. It’s a brief experience. But then the counter-regulatory hormones kick in to restore homeostasis by activating the parasympathetic response. And this opponent process is longer lasting. The more you do it, the less pronounced the sympathetic spike and the more extended the parasympathetic reaction.

Slide 35. (31:32). Contrast baths are quite popular. They go back to the Roman baths, which had both hot and cold pools. And it is the practice at many spas. The idea is to alternate between hot and cold temperature. The Finns are famous for jumping back and forth from the ice water to their steamy sauna.

There are a number of benefits cited.

• The idea is to alternately dilate and constrict blood vessels to promote blood circulation, treat edema, and reduce inflammation of stiff or injured, joints, musces and soft tissue, decrease lactic acid build up.
• The alternation acts as a kind of “pump” that increases circulation, speeding up supply of immune cells, oxygen, nutrients and growth factor and removing toxins and damaged cellular debris.
• Athletes have found it useful to alternate between ice and heat to speed recovery after injuries.

Actually, just using ice along can slow down protein synthesis and muscle repair.  So if that’s your goal, you may want to alternate with heat. But this use of contrasting heat and cold tends to be more localized to treated an injured limb, not typically the whole body.

The Finnish sauna culture is a whole different story.  It is common for Finn’s to have a sauna in their home, and if it is located near a lake, they can cut a hole in the ice.  The love to run naked from the sauna and dip in the ice hole, then come back for more sauna.  I’ve done this myself and its fun.  But typically the amount of time in the ice is short, maybe 30 seconds.  You can see from this photo that the stairs are strategically located to make a quick sprint back into the toasty sauna. And frequently the sauna and ice ritual is combined with strong alcohol.  So it’s hard to sort out the net benefits.  

Certainly contrast baths can more comfortable and pleasureable than the pure cold. When you are getting too hot, the cold water feels delicious. And when the icy cold starts to seem unbearable and you are shivering, the warm bath or sauna is relaxing.

I’m sure some of the benefits of contrast baths are real, but the short time in the cold water is short-circuiting the secondary and long-term adaptive benefits. My concern is that the alternation between the cold and hot further dampens the acclimatization process, both in the short term and the long term.  A big part of the mood benefit of the cold is the bracing, enlivening effect, which comes only over time.  That goes away when you warm up again, and warmth can even make you a little too relaxed or sleepy.

The opponent processes from cold exposure take time to develop, so you don’t want to cut it short.

Slide 36. (32:19). It is well known that we have a circadian sleep-wake cycle. And that sleep quality improves in dark room, that we need to minimize blue light or screen time. And that we rise best with natural sunlight

But did you know that core body temperatures have a circadian rhythm too ? To successfully initiate and maintain sleep, core temp needs to drop 1 C (2-3 F) at night. Core temp drop is not the initiator, but the consequence of sleep.

The feet and hands radiate heat and help the body to lose heat faster.  Warming them helps them radiate heat faster. Detected by thermosensitive cells in hypothalamus, signals to suprachiasmatic nucleus that controls sleep

It’s easier to fall asleep in a cooler room. The Gabra in Kenya and Hazda and Sari hunter-gatherers sleep in open huts without heating or cooling, minimal bedding, no pajamas. Optimal temp for inducing and maintain sleep is 60-65, not the 70-73 that is more common in the West. It may seem uncomfortable, but you can make it more comfortable by giving your body a kick-start.

Perhaps paradoxically, warming the skin and extremities right before sleep helps the body shed heat, and achieve the cooler temp of sleep. It’s the opposite of cold showers, where a short exposure to the cold on the surface, drives sympathetic nervous system, and thermogenesis to maintain core temp. A warm shower or bath will have a similar soporific effect, help the body to dump heat through the skin.

Many people, especially women, get cold feet. You can also wear booties or gloves to induce further internal cooling, but try to leave the room cool. And minimal bedclothes or heavy blankets.

Krauchi, in a 1999 Nature article, in a study with 11 young men found that warming up their feet enhanced vasodilation and heat loss, reducing the time to fall asleep from 25 min to 10 min.

A body cooling experiment from Raymann studied older individuals and people with insomnia. They were put into a whole body thermal sleep suit that selectively warmed hands and feets by 1 deg F. Well, 58% of the control group experienced waking up during the last half of the night. This was reduced to only 4% for the intervention group with the sleep suits.

Matthew Walker, in his excellent book “Why we sleep?” cited experiment warming feed and hands dilates blood vessels, promoting core temp drop and faster sleep onset

I tried this myself, sleeping with light sheet and a blanket just on my feet, with the window open. I already sleep well, but I’d say this produced an even deeper, more restful sleep.

Slide 37. (33:10). People ask me which method is best. My answer is:  it depends on your lifestyle and what you are looking for.

I made this chart with my ratings of the methods relative to 3 potential benefits

• Metabolic – like weight loss, immunity
• Psychological – mood, sleep
• Convenience – how easy to do every day – without traveling or spending money

I don’t think you have to choose just one – you can combine them. So the easiest to do every day are cold showers and cool sleeping, and maybe the ice pack on your neck. But you should definitely try swimming in the ocean and cryotherapy.

Slide 38. (33:47). So you might think the main benefit is just getting more tolerant of the cold. But the benefits are deeper, including

• Improved energy, resilience and mood
• Enhanced immunity
• Weight loss and improved insulin sensitivity
• Improved sleep quality 

Slide 39. (34:15). There are some potential risks:

• Reynaud’s syndrome.   If you have this, proceed with caution. But actually several bloggers have found you can reduce or reverse Reynaud’s by means of gradual, progressive cold exposure. See YouTubers:  Try (2021), Lenfenstey(2020).
• Hypothermia. Mainly a risk with open water swimming and ice baths. Signs include clawing of fingers, or loss of coordination.  Avoid sudden full body immersion — do it gradually.  Body before face & head. 
• Heart attack.  This is generally a very low risk, unless you have heart disease or CVD.  If in doubt, enter the water gradually, not suddenly. Mike Tipton has some good guidelines at:
  https://www.heart.co.uk/southcoast/news/local/heart-attack-warning-over-cold-water/

Slide 40. (34:51). So I’ll try to boil it down to a few points to remember,:

• We humans evolved during an Ice Age to be able to adapt to the cold. Our modern climate-controlled indoor existence is depriving us of some of those benefits.
• Frequent exposure to cold air and water acclimates us and promotes health adaptations.
• The benefits include better exercise recovery, fewer colds and flus, and most of all, improved mood and resilience
• Challenge yourself to get comfortable with the cold. Some may want to try ocean swimming or even whole body cryotherapy. And see if your sleep quality improves by  sleeping in a cooler room, at 65F or less, with a light blanket and your feet coverd. 
• The most accessible way to take a cold shower.  You have one at home and you have one wherever you are staying tonight.
• Try it tomorrow morning, and let me know how it goes.  And try it again the Saturday morning and see if it gets a little easier.  Pay attention to how long it is before the shock goes away.  And pay attention to your mood during the morning..See if you can keep it up for a week.  Some of you will get hooked on it.  

Slide 41. (35:16). Try a cold shower tomorrow morning! You don’t need the meat thermometer, but use a watch timer if you have one. Try going Cold Turkey.  My goodness, its August here in LA.  You should try Helsinki in January.

Wear a timer watch.  Try to go the full 5 min. Write down the time at which the real discomfort ended. And see how you feel through the morning. Then try it again Saturday morning to see if you are more adapted. And let me know!

Slides 42-43. (35:37, 34:44). References for further reading.

Slide 44. (35:50). So maybe we can now see heat and cold in a different light. Heat is nice but can make you drowsy. Cold is energizing, even exhilarating!

As Wim Hof says, “make the cold your friend” Embrace the cold!

Thanks for listening.

Slide 45. (36:10). Questions?