There are a few reasons to consider including sauna use as part of your personal health and longevity strategy.
What is a sauna?
The word sauna comes from the Finnish language, and it means an earth or snow pit. While Finnish saunas today are typically log-walled, wooden paneled, or even tiled structures, these modern forms evolved from the more ancient pits. Traditionally, a sauna has wooden benches, often made from spruce, aspen, or other types of wood common to the region.
While saunas can be found around the world, a significant amount of health research on sauna use has been done in Finland due to their popularity there. Sauna design does vary, as does the heat source, humidity, and typical usage time.
Sauna use can be described as a short-duration passive exposure to high levels of heat. The result of this exposure is essentially a mild form of hyperthermia, in which the core temperature of the body rises, triggering a thermoregulatory response that attempts to restore homeostasis (balance) to the body. This process also acclimates the body to better deal with future events involving heated environments.
How are saunas heated?
The historical heat source for saunas was wood, something that continues to this day in rural areas of Finland and other countries. However, modern saunas are normally heated using electric or infrared heaters.
An electric heater will typically warm the air to between 70 – 100°C, or 158°F – 212°F. The heat then transfers from the warm air into the body.
In the case of infrared heaters, these give out thermal radiation, which not only heats the body directly but also warms the surrounding air. Infrared saunas are cooler than their electric and wood-burning counterparts, generally reaching 45°C to 60°C (113°F to 140°F).
There are two kinds of infrared sauna heaters – near- and far-infrared heaters. Near-infrared heaters use incandescent bulbs to generate thermal radiation, and they mostly produce near infrared and a little middle-wavelength infrared. Far-infrared heaters employ metallic or ceramic heating elements that mostly produce energy in the far-infrared range, which is closer to that produced by natural sunlight.
There are essentially two kinds of saunas: wet and dry. A wet sauna is really a steam sauna; it has very high humidity, often exceeding 50%, which prevents sweat from evaporating. This is why a wet sauna can often feel hotter than a dry sauna. The heart also has to work harder in a wet sauna because of the absence of evaporative cooling provided by sweat.
Dry saunas have a fairly low humidity in the 10 to 20% range, though in saunas that include heater rocks, water can be poured on them to increase that humidity somewhat.
How long do you use a sauna for?
The traditional Finnish method is to have between 1-3 individual sessions in the sauna, which typically last about 20 minutes each. These sessions are divided by a cooling period with the aim of triggering the thermoregulatory response.
This cooling period can take some well-known extreme forms, such as immediately leaving the sauna to roll around in the snow or drenching with cold water. A comparison might also be made with the ancient Romans and their practice of taking heated baths and then diving into a cold plunge pool afterwards, again aiming to activate the thermoregulatory response.
This rapid cooling taxes the cardiovascular system more so than regular cooling, forcing the heart to work harder [1]. However, doing so holds little risk of a heart attack or similar cardiac event in a healthy person.
A 2015 study discovered that there was a dose-dependent reduction of cardiovascular associated mortality, all-cause mortality, and occurrence of Alzheimer’s disease associated with sauna use [2]. This specifically related to saunas of at least 78.9°C (174°F) that were used for 20 minutes or longer.
What happens when our bodies are exposed to heat stress?
High temperature causes stress to the body, which triggers a thermoregulatory response that seeks to restore homeostasis. For example, during warm weather or in a hot environment, the hypothalamus reacts to the increased heat and sends signals to the blood vessels, instructing them to dilate.
This allows the movement of warm blood, salts, and other fluids to the skin. The blood is cooled, and the other fluids evaporate. In fact, between 50-70% of blood flow is rerouted away from the body core to the skin surface to optimize cooling via sweating.
How hard the heart works also increases as a response to heat stress. When exposed to high temperatures, cardiac output can increase by 60% or more to supply the body with oxygen. The heart rate also increases, though the amount of blood pumped with each stroke remains the same.
Finally, during severe exposure to heat, there is an increase in total plasma volume to compensate for the decreased volume of blood in the body core. The increased plasma volume acts as a backup source of fluid for use in sweat production. It also helps the body to cool and keeps the core temperature from increasing too quickly, which aids heat acclimation.
Regular sauna use triggers hormesis
Regular sauna use allows the body to acclimate to the heat and helps the body optimize its thermoregulatory response. This results in the body being better prepared for handling heat stress in the future and is likely due to hormesis.
Hormesis is a biological phenomenon in which a harmful stress-causing stimulus conveys a beneficial effect when given in small doses. Various sources of stimuli, such as exercise, exposure to low doses of toxic substances, dietary modifications, and environmental stressors such as heat or cold, can trigger hormesis.
The body responds to hormetic stressors such as heat with a compensatory defense response. Hormesis causes a wide range of protective systems to kick in, which boosts cell repair and starts the development of acclimation. This is in anticipation of future stress from the same source and may even help against an increased level of the same stressor.
Essentially, hormesis causes our cells to enter a defensive mode, a bit like how a spaceship in a sci-fi movie might raise its shields. Each time the cells encounter the same source of stress, such as heat in the case of sauna use, it gets better at protecting itself and is more resilient. Some researchers in our field are studying the effects of these hormetic stress responses and how they may influence aging and longevity.
This is also why sauna use is often recommended to people who cannot exercise due to a disability or have a medical condition that prevents it. Indeed, sauna use is similar to exercise in how it produces some of the same physiological responses [3].
Is it OK to sauna everyday?
Sauna use may lower blood pressure, so people with low blood pressure should talk to their doctor prior to using one. People who have recently had a heart attack should also consult their doctor first. That being said, if you are healthy with no underlying medical issues, it is generally considered safe to use a sauna every day.
The heat shock response protects our cells
Heat stress responses include the activation of heat shock proteins, the production of various transcription factors, and the production of both inflammatory and anti-inflammatory factors such as certain interleukins.
The heat shock proteins
Heat shock proteins are a family of proteins that are produced by our cells as a response to stressful conditions, such as excessive heat. They are important in a number of cellular processes, such as regulation of the cell cycle, cellular signaling, and functioning of the immune system.
Healthy cells always have a standing or basal level of heat shock proteins to support the day-to-day operation of protein production, export, and regulation. Unfortunately, even during healthy functioning, cells produce harmful waste and byproducts. Chief among them are the reactive oxygen and nitrogen species produced by the mitochondria as a byproduct of energy metabolism [4].
These harmful species then bounce around the inside of the cell and can damage proteins and alter their structure as well as damaging mitochondrial DNA [5]. This damage to the mitochondrial DNA is believed to be one of the nine reasons we age.
The presence of large amounts of misfolded proteins is also a feature of neurodegenerative diseases. These damaged proteins can aggregate together to form clumps and are associated with Alzheimer’s and Parkinson’s disease [6]. Misfolded proteins are also believed to be another reason we age.
Increasing our heat shock proteins may potentially protect us from neurodegenerative diseases. Animal studies suggest that additional heat shock proteins help to repair damaged proteins and may protect us from diseases such as Alzheimer’s and Parkinson’s [7].
The heat shock proteins in action
When our cells are exposed to environmental stressors, it can cause new proteins to misfold or existing ones to unfold, which impairs their function. During exposure to extreme heat and other sources of stress, our cells increase the production of heat shock proteins in an attempt to repair the damaged proteins. This damage control process is known as the heat shock response and heat shock proteins are the first line of defence.
Multiple studies have shown that heat shock proteins increase in response to heat exposure in people as they do in animals. A 2012 study showed that people who stayed in a heat chamber at 73°C (163°F) for thirty minutes saw a 49% increase of heat shock protein HSP72 levels [8].
A 2018 study using deep tissue heat therapy over a period of six days also appeared to increase the levels of heat shock proteins [9]. The researchers found that the levels of the heat shock proteins HSP70 and HSP90 rose by 45 and 38%, respectively.
They also noted that mitochondrial function also improved around 28%, and they observed an increase in mitochondrial biogenesis, a process by which cells increase mitochondrial mass and can produce more energy.
The heat shock proteins play an important role in responding to stressors such as high temperatures and are a key part of the defences our cells use. Regular sauna use is going to activate the heat shock proteins more often making our cells more robust and resistant to damage and stress.
The interleukins
In transient and tightly controlled amounts, inflammation can help to facilitate wound healing and rouse the immune system to attack invading pathogens. However, chronic or uncontrolled inflammation is a known contributing factor in many age-related diseases.
To remain healthy, it is essential that the body maintains a balance between inflammatory and anti-inflammatory factors. Too much inflammation, and cellular dysfunction and age-related diseases can occur; too little inflammation, and healing processes and immune responses are impaired. Therefore, balance is the key for the body to effectively trigger inflammatory responses, regulate them appropriately, and to resolve them when no longer required.
Interleukins are a group of naturally occurring proteins that were first discovered being expressed by white blood cells. There are over fifty interleukins in the human genome, and they can be divided into four major groups based on their structural features [10].
The immune system relies greatly on the presence and activity of interleukins, and deficiencies in some of them are associated with autoimmune diseases or immune deficiency. Most interleukins are produced by immune cells, chiefly T helper cells (helper CD4 T lymphocytes), though monocytes, macrophages and endothelial cells also produce them.
Interleukins also encourage the development and differentiation, a process by which a more generic cell changes to become specialized in form and function, of T and B lymphocytes and hematopoietic cells.
While there are many interleukins, we are concerned with interleukin 6 (IL-6) and interleukin 10 (IL-10) in the context of sauna use and heat stress.
Interleukin-6 and Interleukin-10
Sauna use increases the expression of IL-6, a pro-inflammatory cytokine that has a key role in regulating immunological functions as well as helping the body to maintain homeostasis. It has a critical role in the final differentiation of B cells maturing into immunoglobulin-secreting cells as well as in supporting nerve cell differentiation.
The presence of IL-6 is greatly increased by muscles during exercise, is pro-inflammatory, and appears to be required for the insulin-sensitizing benefits of exercise
However, while IL-6 itself is pro-inflammatory in nature, it also serves to dampen the inflammatory response by triggering IL-10, which is a powerful anti-inflammatory cytokine [11]. IL-10 plays an important role in limiting the host immune response to pathogens. This limiting function prevents damage to the host due to excessive immune responses and helps to maintain homeostasis.
FOXO3
The gene FOXO3 (Forkhead Box O3), which encodes the transcription factor FOXO3, is one of the genes associated with longevity in humans [12]. FOXO3 proteins regulate a wide range of genes that protect us against damage to DNA, proteins, and lipids along with genes that aid efficient stem cell function [13].
FOXO3 increases the expression of genes that facilitate tumor suppression to help keep us safe from cancer [14]. It also plays a role in healthy immune function [15] and is a key regulator or cellular quality control, regulating both proteostasis and autophagy [16]. FOXO3 is also a regulator of the controlled cell death known as apoptosis.
After heat stress is experienced, FOXO3 proteins make a complex with sirtuin 1 (SIRT1), an enzyme associated with longevity due to its influence with various pathways associated with aging. The sirtuins have long been referred to as “longevity genes”, and their proteins regulate cellular health via controlling the release of insulin, ensuring that lipids are working correctly, responding to stressful stimuli, and modulating lifespan in multiple species.
The presence of SIRT1 boosts FOXO3’s ability to resist oxidative stress and shifts its focus from apoptosis to resisting stress instead. This means when it combines with SIRT1 as a complex, it helps our cells to better resist heat stress and become more resilient [17].
Nrf2
NF-E2–related factor 2 (Nrf2) is an essential transcription factor that regulates the expression of more than 1000 genes in the cell, both during stressful conditions and normal operation. Nrf2 is typically triggered by oxidative stress, electrophilic stress, or chronic inflammation.
Once activated, it travels from the cytoplasm to the cell nucleus, where it regulates an array of genes with antioxidant, anti-inflammatory, and cytoprotective properties. Heat stress from a sauna is enough to activate Nrf2, which then increases the production of the heat shock protein, heme oxygenase-1 (HO-1).
This HO-1 then goes on to break down heme, a pro-oxidant, into carbon monoxide and bilirubin, which are anti-inflammatory and antioxidant, respectively [18]. The increased presence of HO-1 also suppresses the expression of a number of inflammatory molecules associated with cardiovascular disease [19].
Health benefits of using a sauna
There are multiple potential health benefits associated with regular sauna use.
Cardiovascular health
Exposure to heat triggers a number of protective responses; some of these may help protect the cardiovascular system and protect us from heart disease. Exercise is an excellent way to support a healthy cardiovascular system, and again, sauna use appears to trigger many of the same responses that exercise does.
Like exercise, sauna use can increase heart rate to around 100 beats per minute in moderate heat or at higher temperatures to as much as 180 beats per minute, which is similar to what is seen during moderate to more vigorous exercise [20-21].
Research suggests that regular sauna use may be useful in improving blood pressure and circulation while reducing inflammation. Sauna use may be particularly useful for people who cannot engage in regular exercise perhaps due to injury, frailty, or another medical condition. As always, if in doubt, consult your doctor before using a sauna.
Cardiovascular disease
The World Health Organization (WHO) suggests that around 18 million people a year die as the result of cardiovascular disease. This makes it the number one killer worldwide, and sauna use combined with lifestyle changes may help to reduce your risk.
A Finnish study compared people who used the sauna only once a week, people who used it 2-3 times a week, and people who used it 4-7 times a week. The moderate 2-3 per week people were 22% less likely to have a heart attack, and the frequent users at 4-7 times a week were an impressive 63% less at risk [2]. The frequent sauna users also saw a 37% reduction in premature death.
Cognitive Decline
Healthy brain function requires proper blood flow to deliver oxygen and nutrients to the brain. Therefore, it is no surprise that during aging, the progression of cardiovascular disease is often accompanied by cognitive decline and even neurodegenerative diseases.
High blood pressure can damage brain structure and reduce the blood flow to the brain, causing loss of cognition. This reduction in blood flow may also impair the ability of our brain to remove accumulated misfolded proteins and could also speed up the onset and progression of Alzheimer’s, Parkinson’s, and other dementias.
The Finnish study showed that men who used a sauna 4-7 times a week saw a 65% reduced risk of developing Alzheimer’s disease compared to people who use a sauna only once a week [2].
Conclusion
There are many reasons to consider using a sauna regularly, and while we have focused mostly on the cardiovascular and cognitive benefits, there are many other studies that suggest plenty of other benefits.
Regular heat stress via a sauna to activate the heat shock proteins and other hormetic response could be a useful way to increase your resilience and condition your cells to become more robust in the face of oxidative stress and other stressors that drive aging. Regular use of a sauna, therefore, may offer a viable approach to delaying aging.
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