HEAT THERAPY

There is a long cultural history of sauna use, but recently it has been gaining popularity as a way to improve physical health, mental health and longevity. Unfortunately, when it comes to hard outcomes, most of the research stems from observational data. That said, there are many reasons and potential benefits to incorporating sauna sessions or other forms of whole-body hyperthermia (e.g. hot tub, jacuzzi, etc.) into your weekly routine.

Here are a few: 

1. Improved cardiovascular health: when we sauna our heart rate can increase up to 100-150 bpm, similar to what you would expect with moderate intensity exercise. We also start pumping more blood from the heart (cardiac output), and blood flow is redistributed to the skin’s surface to help dissipate heat through increased sweating, which also has the bonus of removing toxins and heavy metals from the body. The cardiovascular benefits of sauna use are similar to that of a cardiovascular workout. In a very large on-going prospective study following over 2000 middle-aged men in Finland, those who report sauna bathing 2-3 times per week had a 27% lower risk of cardiovascular disease than those reporting only once weekly, and those reporting 4-7 times per week had a 50% lower risk than the latter. Additionally, sauna use can lower blood pressure. The reductions in cardiovascular risk factors with regular sauna use are interesting as a really cool intervention for those who may be unable to perform regular exercise. The research performed in sedentary populations shows a lowering of blood pressure that isn’t seen in trained participants, so it’s unclear what effect sauna use has on those already living healthy lifestyles. Dom has seen a 5-10% drop in morning blood pressure after consistently using heat therapy 2-4x/week for 1yr. 
2. Improved sleep: when timed appropriately, sauna can help dissipate heat before bed supporting our natural rhythms of body temperature. The heat from a sauna activates mechanisms that effectively lowers body temperature, which paradoxically help you cool down when your session is over. This is great for sleep, since a lowering of body temperature is needed to reduce sleep latency and transition quickly into deep sleep. In a survey of nearly 500 adults who used the sauna 1-2 times per week, over 80% reported sleep benefits after sauna use.  
3. Muscle health: the increased blood flow with heat exposure can help deliver nutrients and oxygen to our muscles, which may aid in repair and serve as a post-workout recovery tool. Additionally, one study found that whole-body hyperthermia increased the activity of the Akt-mTOR pathways which are key for growing and maintaining muscle mass, in addition to increased expression of markers of mitochondrial biogenesis, which also plays an important role in regulating muscle mass. Heat stress may be influencing several pathways that could be protective against muscle wasting which is particularly relevant to aging or situations of disuse. Heat therapy, applied using hot-water immersion also helped with muscle recovery post-exercise. However, another study found that sauna use (3 × 8 min of 80-85°C) following high-intensity training in competitive swimmers reduced next day performance. So, if using it for recovery, it may not be ideal to use the sauna after intense training prior to competition. In this context, whole-body hyperthermia may represent a stress that impairs the adaptive response to intense training. 
4. Cellular stress-resistance: on a molecular level, 30 minutes of heat stress at 70 degrees celsius has been shown to significantly increase heat shock proteins in young healthy adults. Heat shock proteins are a family of proteins that increase our cellular resilience and protection against cellular stress. Part of this response is adaptive and over time, heat stress may help train the body to better cope with future stressors. Another cellular response to heat stress includes the upregulation of a protein called Nrf2, which plays a role in augmenting our antioxidant and anti-inflammatory responses. The expression of this gene was found to increase in skeletal muscle following 60 minutes of whole body heat stress where core body temperature increased to ~39 degrees celsius. These findings were also in concert with increased expression of HSPs.

Are the benefits of sauna mostly because of elevating body temperature? 

The literature suggests that many of the benefits of sauna use are due to the elevation in core body temperature, which would suggest that there are alternatives to sauna that would elicit similar effects (e.g., hot baths and jacuzzis). An increase in core body temperature triggers thermoregulatory responses to dissipate heat in an attempt to lower body temperature – the body likes balance or in science, better known as homeostasis. 

With traditional dry saunas, core body temperature reaches around 38-39°C or 100-102°F. Dom’s nightly routine is to use a hot tub (set to 104°F) to elevate core temperature to 102°F (39°C) for 15-20 min before a quick swim in cool water. Increasing body temperature to this level using hot water baths has been shown to significantly increase brain-derived neurotrophic factor (BDNF) and lower plasma cortisol levels when immersed for 20-minutes.

It is very likely that you can get many of the benefits from sauna use by hot-water immersion, as many of the mechanisms are linked to increased core body temperature. It is this mild heat stress that regulates the expression of heat shock proteins and other stress proteins. 

Unfortunately, this means that infrared saunas likely either don’t elicit the same benefits as dry saunas (or other heat therapies), or they are operating through different mechanisms. Infrared saunas induce a lower temperature change than traditional dry saunas. That is not to say they are not potentially beneficial, but that the benefits of dry saunas may not be transferable to that of infrared and vice versa. If you do have access to an infrared sauna, then because of the lower temperature, the duration may have to be increased (e.g., ~45 minutes as compared to 20 minutes). 

COLD THERAPY

Similar to sauna where you can likely get the benefits just from increasing core body temperature using other heat methods, the potential benefits of cold therapy may not depend on how you are cooling the body, just that you are. A good sign is that you have started shivering, you feel tense, and that you’re uncomfortable. How long you expose yourself to cold will depend on the mode of cold exposure. 

Many would likely agree that cold exposure is not enjoyable in the moment, but the euphoric effect after is what people love most. This is likely due to increased levels of dopamine, serotonin, and beta-endorphins released during cold water immersion and elicits a mood boosting effect for hours after. The sympathetic response to cold exposure can also enhance focus, energy, and attention which has obvious benefits in daily living, especially when timed during certain parts of the day.

In response to cold, the body tries to mitigate heat loss through vasoconstriction and reduced blood flow. This is an attempt to mitigate heat loss through our extremities and keep our core body temperature as warm as possible. This vasoconstriction is mostly due to the increased sympathetic neurotransmitter, norepinephrine. Because our vasoconstrictive response to NE may be attenuated with age, older individuals may have a lower tolerance for cold, but they may also experience greater health effects from the adaptive response. 

The body tries to heat itself up by shivering, which is just involuntary muscle contractions, but also nonshivering thermogenesis which is the heat produced from non-contracting tissues (i.e., not muscle). This nonshivering thermogenesis comes from brown adipose tissue, the “healthy” fat tissue that keeps the body warm, is metabolically active, and rich in mitochondria. You can actually improve both the amount of BAT on your body and its activity through cold exposure. 

Because women tend to have less lean body mass, with similar surface area, they may experience a more rapid drop in core body temperature than men. Essentially, the larger your surface area to mass ratio (smaller individuals), the greater the decline in body temperature during cold exposure. And, the greater your body fat percentage, the slower you will experience changes in body temperature and longer periods may be required to activate the shivering response. Worth noting is that cold tolerance may even fluctuate across a woman’s menstrual cycle as well. It appears that during the luteal phase, the shivering response is lower compared to the follicular phase, suggesting that cold tolerance may be lower during the luteal phase.

Many people will use cold therapy as a way to lower inflammation, recover from injury, and recover from exercise training. Cold water immersion immediately post resistance training may blunt the response we are training for – muscle growth. In one study comparing cold water immersion to active recovery following strength training, greater changes in muscle mass and strength were achieved with the active recovery group compared to the cold exposure group. It is best practice to use cold exposure away from resistance training (hours) if your goal is hypertrophy. Whether or not you use cold therapy post exercise will depend on your goals, as you may feel good after an ice bath that follows training. Endurance training seems to be a different conversation, as cold exposure following endurance exercise may actually enhance these endurance adaptations like mitochondrial biogenesis which support greater aerobic capacity and performance. Ultimately, however, this research is very slim and using cold water immersion to optimize aerobic capacity probably won’t go a long way. It is interesting and deserving of more research nonetheless, especially for muscle health applications. 

Potentially one of the biggest benefits to cold exposure is how much it sucks, which requires the individual to get comfortable with intense pain. Just like exercise, doing hard things makes you more physically and mentally resilient. Working against the voice inside you to get out, to seek comfort, to stop doing the hard thing can be extremely rewarding and help you face future challenges with more confidence. The more habituated you are to cold-exposure, the more tolerant you become to acute forms of stress that hyper-activate the sympathetic nervous system. This can manifest as blunted shivering or vasoconstriction due to a reduced sympathetic response over time. So, depending on what benefits you are trying to derive out of your cold-exposure, you might need to alter your protocols accordingly (increase duration, decrease temperature, mix up different methods, etc.).  

There are many different modes of cold therapy, a few options are:

Cryotherapy: Whole body cryotherapy is less common as it involves going to a facility and there is a cost to this modality. This involves exposure to very cold air for typically 2-3 minutes in a cryo “chamber” where you are wearing mits and potentially other protective gear. 

Cold-water immersion (CWI) or ice baths: This is probably the most well-studied form of cold-exposure. The temperature can vary, depending on whether it’s a controlled environment, a lake, or you’re simply putting ice in a bathtub. Dom loves inviting guests over to use his cow trough ice bath. Regardless, CWI involves submerging your body in very cold water.  

Cold showers: An accessible option to most of us. Cold showers are very uncomfortable, and can serve as a means of cold-exposure. It’s of course, not as controlled and it’s more difficult to be “submerged” in a shower, but it will make you cold!

Due to the circadian rhythms in body temperature, it is probably best to start your day with cold exposure, rather than doing it in the evening. The rebound increase in body temperature may interfere with sleep. So, just like sauna can help dissipate heat and cool the body for bed, cold exposure can counterintuitively help support the warmer body temperature that the body wants to sit at earlier in the day. However, many people will want to cycle between hot and cold in one session. In that case, while theoretical, try ending with the temperature for the time of day (end on cold if earlier in the day, end on hot if later in the day).  Lastly, according to very recent research, the optimal time for cold exposure appears to be a cumulative 11-minutes per week 

Tips & Takeaways: 

• This review suggests the optimal temperature for the sauna is around 80-90°C with repeated cycles of hot and cold. According to this study here, aiming for ~20 minutes 4-7 times per week appears to be the best general recommendation. 
• Minimize the risk of dehydration and electrolyte loss by increasing fluid intake during or after sauna, and consider supplementing electrolytes.  Note: Hot tubs also cause profuse perspiration (you just don’t notice it), so be sure to get extra hydration after this form of heat therapy too. 
• Try using the sauna or other forms of heat therapy in the evening to help prepare your body for bed. Not only is this great for winding down at the end of the day, but it will also help you dissipate heat and cool the body.
• If you are using sauna or hot tubs to objectively improve your health, track whatever biomarkers and metrics you can. What happens to your blood pressure? What about your HR and HRV? Are these things changing in a positive direction? Be your own expert! Is the time of day you sauna impacting your sleep, mood, and cognition? By understanding your personal responses to sauna use, you will learn how to best use and prescribe the sauna for yourself. Saunas and hot tubs make you feel great, so maybe the main benefit is simply improving mental health and the social time for reconnecting with your partner after a stressful day. 
• Rhonda Patrick did an amazing deep dive into the benefits of sauna we highly recommend (see here).

Caution: 

• Knowing your limits requires common sense. Don’t push yourself in either hot or cold because you saw someone do a certain protocol on social media. Being uncomfortable is different than flirting with a potentially dangerous situation. 
• There are real risks, especially to cold exposure, such as hypothermia, arrhythmias, and frostbite (wearing mits and booties may be a good idea if you are cold plunging in lakes or outdoor bodies of water)
• Cold showers, when your head is completely submerged, puts you at risk for some gnarly brain freeze (Kristi, here… talking from experience!)
• Do not sauna or cold plunge if you are pregnant.

Written by Kristi Storoschuk