TL;DR: Heat and cold exposure can improve health and longevity through boosting cardiovascular health, glucose sensitivity, and bone health. For athletes, there is evidence that sauna use can improve endurance, protein synthesis, and growth hormone production, resulting in increases in performance and muscle growth. HSPs increase during heat exposure, resulting in repair of aggregates implicated in a multitude of diseases. Heat and cold exposure also boosts hormones and neurotransmitters vital to brain and nerve health.
It was a chilly Sunday morning at Beatrixpark in Amsterdam. The park was quiet. It was early, the city was still asleep. Seventeen-year-old Wim Hof was wide awake, walking through the park in existential angst. In recent years, Wim had embarked on a journey to find deeper connection and meaning in his life. He explored karate, kung fu, yoga, and various spiritual disciplines. Each promised to offer what Wim was seeking, but each left him unsatisfied. As Wim followed the path alongside the canal, he noticed a thin layer of ice had formed on the surface. Suddenly, he felt an urge to jump in. “I felt attracted to the ice”. He undressed and entered the water. As his body reacted to the cold, he felt his mind focus inwards, towards a deeper part of himself. He felt a true connection with himself, his reptilian brain. He had found it. “This is it”.
Wim would return the next day, the day after, and the day after that. Cold had become his master and he a willing disciple. Wim has since gone on to develop his signature breathing technique and cold therapy program. He has broken numerous records, including the longest under ice swim (57.5 m) and the longest time in direct, full-body contact with ice (1:53) (both since broken).
Wim Hof was not the first to discover the power temperature has to change our state. There are records from as early as 1112 of Finnish sauna bathers who spent time in hot wooden saunas and “beat themselves with branches and finally pour[ed] cold water over themselves”. Roman baths contained multiple rooms that the bathers would graduate through, starting in the Tepidarium (warm room) and eventually finishing in the Frigidarium (cold pool). As far back as we see into history, we have willingly subjected ourselves to the stress of heat and cold. But it’s only recently we’ve begun to understand the science behind our drive towards temperature extremes.
Ice
Brown adipose tissue (BAT or “brown fat”) is a mitochondria-rich substance previously thought to only exist in infants. We’ve recently discovered adults have it too, though stores decrease as we age. Research suggests cold exposure can activate this fat and stimulate the conversion of white fat to brown fat through mitochondrial biogenesis. Activated brown fat produces heat through non-shivering thermogenesis, and consumes white fat to do so (ice pack weight loss vest anyone?). Brown adipose tissue activation also improves insulin sensitivity, bone health, increased adiponectin and irisin levels. Adiponectin has been shown to decrease inflammation in the body and is involved in glucose regulation. Irisin is a hormone heavily involved in building lean muscle mass and reducing obesity through white to brown fat conversion. Irisin is also linked to longevity. Healthy centenarians were found to have increased serum irisin levels, suggesting irisin may play a key role in increasing life span.
BAT activation is regulated through a chemical released in the brain called norepinephrine. Norepinephrine increases alertness and enhances focus and memory. The release of this stress hormone and neurotransmitter may explain Wim Hof's deep feeling of connection upon entering the icy waters of the Beatrixpark canal. Heat and cold stress also cause increased endorphin sensitivity, leading to increased feelings of well-being and euphoria. In my personal experience, the release of norepinephrine and the increase in opioid receptor sensitivity is the most pleasurable part of the entire process, it’s the reason I’m addicted to ice baths and sauna sessions. Entering icy waters or enduring an intense sauna session comes with a feeling of calmness and positivity.
There is also evidence that mitochondria biogenesis occurs in muscle tissue as well when exercise is combined with cold exposure. This has been shown to improve performance in endurance athletes.
Fire
Research on heat exposure through a variety of modalities is quite robust. One study looked at Finnish sauna bathers and found an increase in frequency of sauna bathing to be associated with a reduced risk of cardiovascular disease and all-cause mortality.
Heat exposure has also been shown to increase lifespan in lower organisms through an increase in heat shock proteins (HSPs) HSPs play a vital role in refolding and stabilizing proteins. Maintaining the 3d structure of proteins is key to preventing aggregates (clumps of misfolded proteins). Aggregates are implicated in numerous diseases, including Alzheimer’s and Parkinson’s.
Norepinephrine and prolactin have been shown to increase with sauna use. Prolactin promotes an increase in myelin production which is important for nerve health and repair.
Heat exposure can also provide significant improvements in endurance athletes, increasing plasma volume and red blood cell count. There is also evidence it can improve muscle hypertrophy by improving protein synthesis through an increase in growth hormone, improved insulin sensitivity, and the HSP increase mentioned previously. One study found that two sauna sessions per day for a week showed a 16x increase in growth hormone (one-hour duration at 176F).
Dosage
Note: As always, this post is for informational purposes only. Consult your doctor before subjecting yourself to cold or heat exposure.
Dosage can be tricky when approaching frequency, duration, and temperature. Hypothermia, shock and possible sudden cardiac death are risks with cold exposure. For saunas or hot pools, the risks include hyperthermia, heatstroke, and heart problems in those with preexisting conditions. By monitoring duration and temperature, as well as gradually increasing dosage, we can mitigate these risks.
My personal exploration into cold exposure started with 30-second long cold showers. After my usual shower, I gradually shifted the temperature until it was as cold as possible (works better during winter). I maintained that temperature for 30 seconds before ending my shower. This led to ice baths which then eventually led to a freezer on my back patio filled with 35F ice water. My only tool was breathwork. Wim Hof’s breathing method and box breathing were key to my progression.
With heat, my practice has primarily been through sauna bathing. Gradually increasing temperature and duration has allowed my body to adapt without negative side effects. I currently use a far infrared sauna at home but try to use a Finnish dry sauna whenever possible (there is little research on the efficacy of infrared saunas). I sauna 3-5x per week for 20-40 min at 160F (infrared saunas don’t get as hot). Before my home sauna, I would use the sauna at the gym or sweat it out in a hot bath.
Determining your own dosage can be tricky. Finnish sauna-goers generally recommend sauna bathing 2-7x per week at 176-212 F (80-100 C) for 10-20 minutes (repeated several times, cooling off in-between rounds). Be kind to yourself. Work up slowly. A good place to start is ending your daily shower with a 30-second cool period, where you adjust the temperature so it’s uncomfortable, but you aren’t experiencing cold shock. For heat, a hot bath 1x or 2x per week is a gentle introduction to heat exposure. The goal is to nudge yourself out of your comfort zone, becoming confident in your capability of adapting to a wide range of environmental temperatures.
Conclusion
Our hormetic response to heat and cold stress can improve athletic performance and muscle building. It can also improve glucose response, heart and bone health, as well as give a boost to our brain and nervous system. The minimum effective dose has not yet been determined for both hot and cold exposure, but through the wisdom of tradition and studies at different dosages, we can make an educated guess of an acceptable dose. Similar to an exercise regimen, the key is a gradual progression. With time the body and mind will adapt. The heat will torment less, the cold won’t bite as hard, and you’ll be stronger, healthier, and more prepared to face life’s stressors.