cold adaptation
When it comes to improving your health, some of the simplest strategies can have a tremendous impact. For example, did you know that exposure to extreme temperatures can serve as a catalyst to improve your health?

In a previous interview, biological scientist Rhonda Patrick, Ph.D. discussed the importance of mitochondrial function — a topic she expands on in this interview. As it turns out, exposure to extreme temperatures, be it hot or cold, actually improves mitochondrial function.

Mitochondria are the energy generators in your cells. While you have about 35 trillion bacteria and as many cells in our body, you have about 500 to 1,000 times more mitochondria. Estimates suggest you may have anywhere from 15 to 50 quadrillion mitochondria.

When your mitochondria are not working properly, your body's ability to generate energy is impaired. The key is to get the old ones out and to create new ones — a process known as mitochondrial biogenesis. There are a number of strategies that can do that, including:
  • Exposure to extreme hot and cold temperatures
  • Exercise
  • Intermittent fasting or time-restricted feeding
  • Certain supplements, such as resveratrol
All of these strategies stimulate the peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1 alpha), which is the primary driver for mitochondrial biogenesis. And when it comes to maintaining biological functioning and good health, the more mitochondria you have the better.

Mitochondrial Biogenesis Benefits From Hormesis

According to Patrick, exposure to extreme cold is likely the most effective way to boost mitochondrial biogenesis, followed by exposure to heat, and exercise.

All of the strategies listed above place stress on your body, and while stress is generally viewed as a detriment to health, short bouts of stress actually produce benefits by way of hormesis.

Hormesis refers to a process of exposing your body to a very short burst of stress, be it exercise, heat, cold, fasting, or antioxidants like resveratrol.

Because it's a short burst of stress, your body reacts to this stress by activating a variety of stress response pathways that are hardwired and encoded in your genes. As explained by Patrick:
"It turns them on because they're thinking, 'I've got to prepare for war. This is stress. I need to make sure I fight this off.' Not only does it activate all these really good pathways to fight off the stress you're dealing with immediately, but it is preparing for future war.
[Your body] is basically thinking to itself, 'I may encounter this stress again. I have to activate all these good pathways that can help me deal with stress. That way, the next time I encounter it, I'm ready to fight it off.'
That's really one of the main reasons why short bursts of stress are so good for you, because we have so many amazing genes in our body that are so powerful. The problem is that as we age, they don't become activated as often. We need to find ways to activate them more ..."
Benefits of Heat Stress

Exercise is one form of heat stress, as you're elevating your core temperature. Other ways of raising your core temperature include taking a hot bath, or using a steam room or sauna. The heat stress generated helps activate genes that are important for optimizing heat shock proteins (HSP) inside your cells.

This is important, as these proteins get damaged with time and need to be renewed. Accumulation of damaged HSP can lead to plaque formation in your brain and/or vascular system.

Heat stress helps prevent this adverse chain of events. HSP are also involved in longevity, so it's really good to have a lot of HSP. They're also important for preventing your skeletal muscle from atrophying, because they prevent proteins from being degraded.
"[A]nimal studies have shown that when mice are exposed to the sauna they increase their protein synthesis by 30 percent compared to the mice that are not being exposed to the sauna.
This was shown to be dependent on the heat shock proteins, HSPs, in the muscle. [T]he important thing here is the actual heat stress. You want to feel uncomfortable. You want to feel hot. That's when you know that these good pathways are getting activated.
The other thing that happens in terms of mitochondrial biogenesis and the reason why it occurs when you're exposed to heat, is that heat itself is a stressor on the body and it creates reactive oxygen species (ROS).
[ROS are also] generated when you exercise; when you're causing your body to work more. These ROS act as a signaling molecule to make more mitochondria.
If you exercise and take a supplemental vitamin E or something that can sort of soak up the ROS, you can negate some of the positive benefits from exercise because you are now not getting those signaling molecules saying, 'Hey, we've got stress here. Let's make more mitochondria to deal with the stress.'
It's really important that you actually have some of that stress. That's part of the mechanism by which it increases mitochondrial biogenesis."
How Heat Stress Benefits Athletic Performance

Heat stress can also help boost endurance in athletes—a topic she covers more in-depth in her Hypothermic Conditioning Report, available for free download here.

In one study, athletes who spent 30 minutes in the sauna after their workouts, two times a week for three weeks, were able to increase the time it took for them to run until exhaustion by 32 percent, compared to baseline. As noted by Patrick in her report: "In other words, hyperthermic conditioning through sauna use doesn't just make you better at dealing with heat; it makes you better, period."

But how exactly does heat boost athletic endurance? First of all, heat stress causes a number of adaptations that reduce the adverse effects associated with elevated body temperatures. This includes:
  • Reduced heart rate
  • Lower core body temperature during exercise
  • Higher sweat rate and increased thermoregulatory control
  • Increased plasma volume, which optimizes blood flow to your heart, muscles, skin, and other tissues
  • Reduced rate of glycogen depletion due to improved blood flow to skeletal muscle
In short, being heat acclimated helps enhance endurance, and there are three different mechanisms at work here:
  1. By increasing plasma volume and blood flow to your heart, it reduces cardiovascular strain and lowers your heart rate during exercise
  2. By increasing blood flow to your muscles, more nutrients such as glucose and oxygen are delivered, thereby reducing fatigue. According to Patrick, hyperthermic conditioning can reduce muscle glycogen use by as much as 50 percent
  3. By improving thermoregulatory control and increasing sweat rate, your core body heat can remain lower even during high exertion. Once you're heat acclimated, sweating occurs at a lower body temperature than previously, and you sweat longer
How Heat Stress Benefits Your Brain

Heat also has very robust and profound effects on your brain. Your body responds to heat by cooling itself down, and it does that by increasing production of dynorphin—the chemical opposite of endorphins. However, dynorphin sensitizes your brain to endorphins, which can have a mood boosting effect. Dynorphin is responsible for that dysphoric feeling when you're hot, when you're lying in the sun, or when you're exercising.
"I think what's really important for people to understand is everyone's always trying to avoid stress. They want to be comfortable. I think the reason for that is people are aware of the fact that chronic stress is bad. When you're constantly having a stressor, you don't have this positive hormetic response to it ...
But the short burst of stress is really good ... It has this feedback mechanism where it increases the expression of a receptor that binds to endorphin, called the mu opioid receptor. You make more of these receptors. That way, the next time you produce endorphin, you're more sensitive to it ... So you actually can relieve anxiety," Patrick says.
The ROS generated when you're exposed to heat also benefits your brain by increasing production of growth factors, such as brain-derived neurotropic factor (BDNF), which in turn promote the growth of neurons. With age, neurons are lost in many brain regions, and sauna bathing can be an important strategy to slow down or prevent brain aging.

Sauna Bathing Is Good for Your Heart

Heat also has a profound effect on your heart and cardiovascular health. A Finnish study published last year found that men who used the sauna two to three times a week had a 27 percent lower death rate from heart disease and a 24 percent lower all-cause mortality rate compared to those who only used the sauna once a week.

Men who used it four to seven times a week had a 50 percent reduction in death from heart disease, and a 40 percent reduction in all-cause mortality. So there's a clear dose-dependent response, meaning the more frequently you use the sauna, the greater the beneficial effect. These heart and cardiovascular benefits are related to the fact that when you get hot:
  • Your heart rate increases, just as during exercise
  • Your blood vessels dilate
  • The smooth muscle cells that line your blood vessels relax
Temperature matters, of course. In this study, they used the traditional hot, dry Finnish sauna. The temperature averaged 79 degrees Celsius (174 degrees Fahrenheit), which is extremely hot by most standards. The duration was typically 20 minutes or longer. Infrared saunas and steam rooms operate at lower temperatures, so the outcomes might not be identical were you to compare them. Still, heat that isn't as extreme will provide similar benefits.

Benefits of Cryotherapy

As with heat, the rationale for exposing yourself to very cold temperatures also has to do with the benefits associated with hormesis. You may have heard that cold temperatures can help you burn more body fat, and mitochondrial biogenesis is directly involved in this process.

When you're exposed to cold, your body increases production of norepinephrine in the brain, which is involved in focus and attention. It also improves mood and alleviates pain, partly because it lowers inflammation. You can increase norepinephrine two-fold just by getting into 40-degree water for 20 seconds, or 57-degree water for a few minutes.

While best known as a neurotransmitter, norepinephrine also acts as a hormone. One of its functions is causing vasoconstriction, which helps your body conserve heat. Norepinephrine also acts as a signaling molecule to make more mitochondria in your fat tissue (your main energy reserves), and a byproduct of energy production is heat.

This also helps prepare you for the next time you're exposed to cold. The more times you're exposed to cold, the more mitochondria you make in your fat cells and the better you can withstand lower temperatures. This is a topic Dr. Patrick covers more in-depth in her cold shock report, available for free download here.

So yes, you do "get acclimated" to colder temperatures with time. Wim Hof, aka. "The Iceman," is a perfect example of this. He's exposed himself to cold on a daily basis for decades. As a result, he's now able to withstand the cold for much longer periods than one might consider normal, because his body can generate more heat. As explained by Patrick, "The more mitochondria you have in your fat, the more fat you're burning, the more heat you can make, the longer you can stay in the cold."

The Hormesis of Cryotherapy

As mentioned, when you expose yourself to heat, you make heat shock protein. When exposing yourself to cold, in addition to increasing norepinephrine you also make cold shock protein, known as the RNA-binding motif 3 or RBM3, in your brain.

This is another intriguing example of hormesis. Interestingly, when you're exposed to cold, you actually degrade synapses (the connections between neurons), but RBM3 completely regenerates them. This has been shown in hibernating animals like bears and squirrels.
"There's this really great study that was published not long ago that showed when you take a mouse genetically engineered to get Alzheimer's disease and expose it to cold, so that it's increasing RBM3, it delays the onset of Alzheimer's. Even though they were genetically engineered to get Alzheimer's disease, they get it much, much later," Patrick says.
Studies have also been done on human cells, showing that RBM3 does get activated when the brain cells are exposed to cold, and that the temperature change needed is only about 1.5 degrees Fahrenheit. More research needs to be done, but preliminary work such as this suggests cryotherapy (cold treatment) could have a neuroprotective effect.

Caveat: Avoid Cryotherapy Directly Following Strength Training

There is one important caveat worth mentioning. When you're doing strengthening exercises you generate ROS that help increase muscle mass. If you expose yourself to cold within the first hour after strength training, you suppress that beneficial process, so avoid doing cold immersion (such as a really cold shower or ice bath) immediately after strength training.

On the other hand, spending some time in the sauna after exercise may actually help increase muscle mass. It'll also help with detoxification, allowing you to sweat out toxins that can wreak havoc on mitochondrial function in general. As explained by Patrick:
"This is what's important to understand — Exercise is a stress on the body. You're making reactive oxygen species. You're generating inflammation. But that's a good thing because it's a short burst, and you want it.
... There's a one hour timeframe from the time you stop exercising [in which inflammation peaks]. That is the stressful period. But then as soon as an hour hits, the stress response kicks in and you start to have a potent anti-inflammatory [response]. You start having an antioxidant response from activating all these good genes that stay activate for a long time.
What happens is that because the cold also is causing an anti-inflammatory response, it's important that you don't get that anti-inflammatory response too soon, because you need some of that exercise-induced inflammation. You want that inflammation to happen to get the anti-inflammatory response. That's important for the strength training.
The inflammation you generate during the strength training is part of the mechanism for making more proteins in the skeletal muscle. If you blunt that, then you're going to blunt the effects of the strength training. The question is then can you do it an hour or two hours later? Studies have shown, yes, you can do cold exposure, cold water immersion and actually get some performance enhancements even from doing [that]."
Listen to Your Body

While sauna bathing and cold water immersion are generally safe, if you have any sort of medical condition, discuss it with your doctor beforehand, since both hot and cold put stress on your heart and cardiovascular system. Also listen to your body. Individual tolerance for hot and cold temperatures vary widely, and if you push it too far you can do yourself harm.

Cryotherapy tends to be a bit riskier than sauna, which is typically very beneficial for people with cardiovascular-related diseases, courtesy of the vasodilation and increased blood flow. Cold causes acute vasoconstriction, which can be potentially dangerous if you have a heart condition. A quick cold shower would probably be okay, but avoid ice baths or other extreme cold water immersion techniques.
"With that said, in general it's really, really good to listen to your body. You need to recover from the stress; otherwise it's not going to be beneficial,' Patrick says. 'If you're exercising all day, every day, you're going to die. You can't constantly keep stressing your body without a recovery period, which is part of the reason why sleep is so important for recovery, you repair all this damage that you generated throughout the day.
I tend to push things to the extreme. I'm getting better with that now. But I have experienced, with myself, when I've sat in an ice bath for several minutes, I start to feel light headed. I shouldn't be feeling light headed. That's enough. I need to get out. The same with the sauna. Feeling uncomfortable is good.
You want to push a little bit past that comfort and feel a little uncomfortable. That's important for some of the hormetic benefits. But you don't want to faint. Also, never drink alcohol in the sauna."
More Information

You can learn more about hyperthermic conditioning, cryotherapy, and cold water immersion via the free reports by Patrick.She also has a podcast where she interviews health professionals and scientists on a variety of topics related to health.

I regularly listen to her programs as they're always packed with great and usable information. On her website, you can find many videos on a variety of topics in which she summarizes key information in clear and easy to understand layman's terms. You can also sign up for her newsletter, in which she publishes longer, heavily referenced articles and special reports.