The Science & Health Benefits of Deliberate Heat Exposure

A recent study found that local heating of the supraclavicular region (upper shoulders/upper back) to 41°C (105.8°F) for 20 minutes, three times per week for five weeks, induced conversion of white fat to beige fat and increased metabolism through upregulation of UCP1 and heat shock factor 1 (HSF1).

“heating of a local patch of skin to 41 degrees Celsius, which is 105.8 degrees Fahrenheit...The supraclavicular fat deposits...were exposed to this thermal source, again, 41 degrees for 20 minutes...three days per week, separated by day, Monday, Wednesday, and Friday...for five weeks total”

Engaging with uncomfortable heat (but safe heat) is necessary to access endorphin and dynorphin pathway benefits for mood elevation, because the dysregulation of dynorphin is central to depression, stress, and addiction, and moderate acute stress through heat exposure upregulates the endorphin system.

“The dynorphine system is not unique to heat-induced stress. In fact, there are beautiful studies and reviews out there about the role of dynorphine in stress and depression, in stress and alcoholism... the pleasure pain balance that exists within the dopamine system... The pain molecule, however, appears to be dynorphine. And the fact that dynorphine is dysregulated in stress and depression and alcoholism... for that reason, I'm very excited about the fact that deliberate heat exposure can leverage the dynorphine system in a short term and an acute way that allows mood to improve after the sauna exposure.”

FOXO3 is a molecule involved in DNA repair and clearance of senescent cells, and sauna exposure 2-7 times per week upregulates FOXO3 levels, which contributes to improved health and potentially lifespan extension.

“FOXO3 sits upstream in a pathway related to DNA repair, and again, clearing of the senescent cells. Sauna exposure, in particular sauna exposure two to three times or ideally four to seven times per week in that 80 to 100 degree Celsius range has been shown to upregulate levels of FOXO3.”

Heat and cold are both forms of cellular stress that activate mitohormesis—adaptive responses in mitochondria (including UCP1 upregulation, increased ATP production, and metabolic elevation)—meaning the fundamental mechanism is the same whether using heat or cold exposure.

“In this paper they describe what is called mitohormesis, which is, in essence, the fact that any number of different stressful stimuli, provided they activate UCP1 and some of these other pathways that I just described, like HSF1, can induce changes in the mitochondria that lead to increases in metabolism.”

Burning skin tissue, whether through accident or intentionally (which should never be done), activates metabolic pathways that lead to sustained increases in whole-body metabolism and fat loss that can persist for years, suggesting that the molecular pathways activated by heat-induced injury can be therapeutically harnessed through non-damaging local heating protocols.

“It's long been known from clinical data. And in fact, from a bit of research data that people that experience burn on a small, or unfortunately in some circumstances, significant portion of their body experience overall decreases in body fat and increases in metabolism that can last many years.”

The human body has two distinct body temperatures: shell temperature (skin surface) and core temperature (organs and nervous system), and the brain constantly sends signals to balance these two temperatures through a thermostat-like mechanism.

“you have two distinct temperatures. One is the temperature on your skin, what scientists call your shell, and the temperature of your core, your viscera, meaning your organs, your nervous system, and your spinal cord. And as you can imagine, the temperature of your core is always higher than the temperature at your surface.”

In the 1986 growth hormone study, the 16-fold increase in growth hormone on day 1 declined to a 3-4 fold increase on day 3 and a 2-3 fold increase on day 7 of the same week, demonstrating heat adaptation that diminishes the growth hormone response.

“on day one, there was a 16-fold increase in growth hormone. On day three, however, there was still a significant effect on growth hormone as compared to before sauna, but that effect was basically cut by two thirds. So now instead of getting a 16-fold increase, it was more like a three or four-fold increase...And then on day seven, there tended to be a two, maybe a threefold increase”

Lethargy and the urge to spread out one's limbs on a hot day are controlled by the preoptic area, which modulates skeletal muscle activity and postural behavior to increase surface area for heat dissipation; this explains why physical activity feels difficult in heat and why the body instinctively adopts heat-dumping positions.

“You're probably familiar with the feeling of being somewhat lethargic, or spreading out your limbs on a hot day. Well, that is the result of neurons in your preoptic area impacting your musculature to get you to increase your surface area so you can sweat off or release more heat.”

Heat shock proteins are protective molecules deployed by the body in response to temperature changes that prevent protein misfolding and degradation, and sauna exposure activates these proteins in a beneficial manner.

“One of the more dramatic and important effects of going into a hot environment for some period of time is the activation of so-called heat shock proteins, or HSPs. Heat shock proteins are a protective mechanism in your brain and body to rescue proteins that would otherwise misfold.”

Endorphins are released in response to acute stress and bind to the mu opioid receptor, producing pain relief and mild euphoria, while dynorphins (a different class of endorphins) bind to the CAPA receptor and produce agitation, stress, and pain sensations.

“Many of you have probably heard of endorphins. Endorphins are a category of molecules that are made naturally in your brain and body and that are released in response to different forms of stressors...if you've gone out on a long run...you experience a lack of pain at some point...or you experience a euphoria during or after that exercise...the exercise-induced consequences on the stress system, which in turn trigger the release of endorphin.”

The palms of the hands, bottoms of the feet, and upper half of the face have specialized vasculature (arteriovenous anastomoses or AVAs) without intervening capillaries that allow rapid heat exchange with the environment, making them the most efficient sites for quickly cooling or heating the core body temperature.

“The palms of our hands, the bottoms of our feet, and the upper half of our face overly specific types of vasculature, meaning specific types of veins and arteries that don't have capillaries between them, and as a consequence, heat and cold can move very quickly from the palms of the hands, the bottoms of the feet, and the upper half of our face, and change our core body temperature.”

Exposure to elevated blood glucose and insulin before sauna reduces growth hormone release because high glucose/insulin suppresses growth hormone secretion, so fasting or allowing 2-3 hours post-meal before sauna maximizes growth hormone response.

“having elevated blood glucose and or insulin tends to blunt or reduce growth hormone release, and that's true for any number of different stimuli including exercise and including sauna.”

A study found that subjects doing four 30-minute sauna sessions at 80°C (176°F) with 6-minute cool-down breaks experienced a significant decrease in cortisol output, a stress hormone, making sauna an effective tool for managing stress.

“They had these men attend four sauna sessions of 12 minutes each...The temperature of those saunas was 90 to 91 degrees Celsius...they had a six-minute cool down break during which they did get into some cool water or cold water of about 10 degrees, which is 50 degrees Fahrenheit...The major effect of this study is a significant decrease in cortisol output in these subjects.”

Regular sauna use 2-3 times per week is associated with a 27% reduction in cardiovascular mortality compared to once-weekly sauna use, and 4-7 times per week is associated with a 50% reduction in cardiovascular mortality in a large prospective cohort study of 1,688 participants.

“people who went into the sauna two or three times per week were 27% less likely to die of a cardiovascular event than people that went into the sauna just once a week...those people were 50% less likely to die of a cardiovascular event compared to people that went into the sauna just once a week.”

A study found that doing sauna once followed by doing sauna again later the same day, or doing exercise followed by sauna, did not increase growth hormone additively—meaning you cannot stack growth hormone stimuli on the same day to get compounded effects.

“anytime you release growth hormone, you reduce the likelihood that you're going to release growth hormone again later that day. And this partially explains that earlier study, where if people did this growth hormone promoting protocol on day one, but then on day three they didn't see quite as big an effect”