Written by Rhonda Patrik (RP), Veli-Jussi Jalkanen (VJJ sections 14 – 22) and Joseph Mercola Posted on: April 10, 2014..
Rhonda Patrick, Ph.D. (RP):
Bathing oneself in heat for the purposes of purification, cleansing, and healing is an ancient practice, dating back thousands of years and observed across many cultures. Variations of its use are seen today in the banyans of Russia, the sweat lodges of the American Indians, and, most famously, the saunas of Finland.
Sauna use, sometimes referred to as ”sauna bathing,” is characterized by short-term passive exposure to extreme heat. This exposure elicits mild hyperthermia – an increase in the body’s core temperature – that induces a thermoregulatory response involving neuroendocrine, cardiovascular, and cytoprotective mechanisms that work together to restore homeostasis and condition the body for future heat stressors.
In recent decades, sauna bathing has emerged as a means to increase lifespan and improve overall health, based on compelling data from observational, interventional, and mechanistic studies. Of particular interest are the findings from studies of participants in the Kuopio Ischemic Heart Disease Risk Factor (KIHD) Study, an ongoing prospective population-based cohort study of health outcomes in more than 2,300 middle-aged men from eastern Finland, which identified strong links between sauna use and reduced death and disease.
The KIHD findings showed that men who used the sauna two to three times per week were 27 percent less likely to die from cardiovascular-related causes than men who didn’t use the sauna. Furthermore, the benefits they experienced were found to be dose-dependent: Men who used the sauna roughly twice as often, about four to seven times per week, experienced roughly twice the benefits – and were 50 percent less likely to die from cardiovascular-related causes. In addition, frequent sauna users were found to be 40 percent less likely to die from all causes of premature death. These findings held true even when considering age, activity levels, and lifestyle factors that might have influenced the men’s health.
The KIHD also revealed that frequent sauna use reduced the risk of developing dementia and Alzheimer’s disease in a dose-dependent manner. Men who used the sauna two to three times per week had a 66 percent lower risk of developing dementia and a 65 percent lower risk of developing Alzheimer’s disease, compared to men who used the sauna only one time per week.
The health benefits associated with sauna use extended to other aspects of mental health, as well. Men participating in the KIHD study who used the sauna four to seven times per week were 77 percent less likely to develop psychotic disorders, regardless of the men’s dietary habits, socioeconomic status, physical activity, and inflammatory status (as measured by C-reactive protein).
Overview of sauna practices
The term “sauna” is a Finnish word, and it typically refers to an unpainted spruce- or pine-paneled room, with wooden benches made of aspen, spruce, or obeche. The bulk of the research related to sauna bathing has been conducted in Finland or in regard to Finnish-style sauna practices. Not all saunas are Finnish-style, however, and saunas may differ according to their heat source, relative humidity, and duration of use.
Historically, saunas were heated by wood fires – a practice still observed today in rural parts of Finland. Most modern saunas, however, are heated by conventional electric heaters or infrared heaters. Conventional heaters warm the air to a high temperature, ranging from 70°C to 100°C (158°F to 212°F), optimally at 80°C to 90°C (176°F to 194°F) at the level of the user’s face. The heat of the warmed air transfers to the body.
Infrared heaters emit thermal radiation, which heats the body directly while also warming the surrounding air. They operate at lower temperatures than traditional saunas, at 45°C to 60°C (113°F to 140°F). Infrared heaters emit either near or far wavelengths. Near infrared heaters use incandescent bulbs to produce thermal radiation of varying wavelengths, ranging from near-infrared wavelengths (primarily) to middle-infrared wavelengths (to a lesser degree). Far infrared heaters use ceramic or metallic heating elements that emit energy in the far-infrared range, which is similar to energy produced by the sun.
Saunas can be either dry or wet. In a dry sauna, the relative humidity is low (10 to 20 percent). A common practice in Finland, called löyly, is to throw water on the heater rocks to increase the humidity slightly. The term “wet sauna” is a misnomer, however, referring to a steam sauna, where the humidity is extremely high (typically greater than 50 percent), which keeps sweat from evaporating. A wet sauna may feel (subjectively) hotter than a dry sauna and is harder on the cardiovascular system, due to the reduced evaporative cooling.
Duration and temperature
Finnish-style sauna bathing involves one to three sessions of heat exposure lasting five to 20 minutes each, interspersed with periods of cooling. Some cooling methods can be rather extreme and involve rolling in snow or immersing in cold water, which further stresses the cardiovascular system. Sauna poses little risk of cardiovascular complications in healthy people, however.
The KIHD studies that found a dose-dependent reduction in cardiovascular-related mortality, all-cause mortality, and Alzheimer’s disease incidence typically involved saunas that were heated to a temperature of at least 78.9°C (174°F) for at least 20 minutes. In fact, these studies found that the amount of time spent in the sauna also affected cardiovascular-related mortalities, with a longer duration of 19 minutes or more having a more robust effect than 11 to 18 minutes on lowering mortality rate.
Another form of thermal treatment, called waon therapy, originated in Japan. Like traditional sauna, waon utilizes low humidity, but the temperatures are slightly lower, at approximately 60°C (140°F). Waon therapy is associated with improvements in multiple aspects of cardiovascular function.
Physiological response to heat stress
Exposure to high temperature stresses the body, eliciting a rapid, robust response. The skin and core body temperatures increase markedly, and sweating ensues. The skin heats first, rising to 40°C (104°F), and then changes in core body temperature occur, rising slowly from 37°C (98.6°F, or normal) to 38°C (100.4°F) and then rapidly increasing to 39°C (102.2°F).
Cardiac output, a measure of the amount of work the heart performs in response to the body’s need for oxygen, increases by 60 to 70 percent, while the heart rate (the number of beats per minute) increases and the stroke volume (the amount of blood pumped) remains unchanged. During this time, approximately 50 to 70 percent of the body’s blood flow is redistributed from the core to the skin to facilitate sweating. The average person loses approximately 0.5 kg of sweat while sauna bathing. Acute heat exposure also induces a transient increase in overall plasma volume to mitigate the decrease in core blood volume. This increase in plasma volume not only provides a reserve source of fluid for sweating, but it also acts like the water in a car’s radiator, cooling the body to prevent rapid increases in core body temperature and promoting heat tolerance.
Repeated sauna use acclimates the body to heat and optimizes the body’s response to future exposures, likely due to a biological phenomenon known as hormesis, a compensatory defence response following exposure to a mild stressor that is disproportionate to the magnitude of the stressor. Hormesis triggers a vast array of protective mechanisms that not only repair cell damage but also provide protection from subsequent exposures to more devastating stressors.
The physiological responses to sauna use are remarkably similar to those experienced during moderate- to vigorous-intensity exercise. In fact, sauna use has been proposed as an alternative to exercise for people who are unable to engage in physical activity due to chronic disease or physical limitations.
Molecular mechanisms involved in the heat stress response
The hermetic effects of heat stress are facilitated by molecular mechanisms that mitigate protein damage and aggregation and activate endogenous antioxidant, repair, and degradation processes. Many of these responses are also triggered in response to moderate- to vigorous-intensity exercise and include increased expression of heat shock proteins, transcriptional regulators, and pro- and anti-inflammatory factors.
Heat shock proteins
Heat-shock proteins (HSPs) comprise a large, highly conserved family of proteins that are present in all cells. They play prominent roles in many cellular processes, including immune function, cell signalling, and cell-cycle regulation.
Under normal conditions, cells maintain a constant, or ”basal,” level of HSPs to facilitate several aspects of the protein synthesis machinery, including assembly, folding, export, turn-over, and regulation. However, normal metabolic processes and immune function create reactive by-products (such as reactive oxygen species and reactive nitrogen species) that can damage proteins and disrupt their structure. Intrinsically disordered proteins are common features in cardiovascular diseases, and damaged, dysfunctional proteins, which can aggregate, or clump together, are strongly implicated in the pathogenesis of neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. Increased expression of HSPs prevents protein disorder and aggregation by repairing proteins that have been damaged, and, in fact, animal evidence suggests that HSPs may offer protection against neurodegenerative diseases.
When cells are stressed due to changes in their environment, cellular proteins can unfold or become damaged, impairing their normal function and further increasing their vulnerability to change. During exposure to stress from temperature extremes, reduced nutrient levels (as in fasting), or hypoxia (reduced oxygen), cells increase expression of HSPs to stabilize unfolded proteins and repair or re-synthesize damaged proteins.
Heat stress, in particular, robustly activates HSPs. For example, after healthy men and women sat in a heat stress chamber for 30 minutes at 73°C (163°F), their levels of HSP72 increased by 49 percent. In a different study, in which healthy men and women were exposed to deep tissue heat therapy for six days, participants’ levels of HSP70 and HSP90 increased 45 percent and 38 percent, respectively. In addition, their biomarkers of mitochondrial biogenesis improved, and their mitochondrial function increased by 28 percent compared to baseline levels. The activation of HSPs is sustained over time, suggesting that heat acclimation induces whole-body adaptations that increase heat tolerance, resulting in protective cellular adaptations.
Nrf2 is a transcription factor commonly found in a cell’s cytoplasm. Upon activation, Nrf2 travels to the nucleus, leading to the orchestrated regulation of a vast network of genes with cytoprotective, antioxidant, and anti-inflammatory functions and providing protection against oxidative stress, electrophilic stress, and chronic inflammation – the underlying causes of most chronic diseases.
Heat exposure activates Nrf2, thereby upregulating a HSP called heme oxygenase-1, or HO-1, an enzyme that breaks down heme (a powerful pro-oxidant) to generate carbon monoxide (an anti-inflammatory gas) and bilirubin (an antioxidant). The downstream effect of HO-1 upregulation includes inhibition of the expression of several pro-inflammatory molecules involved in the pathophysiology of cardiovascular disease, including E-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1.
FOXO3 proteins are members of the FOX family of highly conserved transcriptional regulators. They play important roles in human lifespan and healthy aging. FOXO3s regulate a vast number of genes that combat elements of cellular aging, such as damage to DNA, proteins, and lipids, and loss of stem cell function. They also increase the production of genes that regulate DNA repair, tumor suppression, stem cell function, immune function, and protein aggregation to further mediate the deleterious effects of aging. FOXO3s participate in autophagy, but when autophagic mechanisms are disturbed, FOXO3s confer cellular sensitization to apoptosis, a type of programmed cell death.
Following heat stress, FOXO3 proteins form a complex with sirtuin 1, or SIRT1, an enzyme that influences aging and longevity via multiple molecular pathways. Sirtuins regulate a variety of metabolic processes, including release of insulin, mobilization of lipids, response to stress, and modulation of lifespan. SIRT1 enhances FOXO3’s resistance to oxidative stress and its ability to induce cell cycle arrest, but it also inhibits FOXO3’s ability to induce apoptosis, shifting FOXO3 activities away from cell death and toward stress resistance.. Read more about FOXO proteins.
Interleukin-6 (IL-6) & Interleukin-10 (IL-10)
Inflammation is a fundamental cause of chronic disease processes. Maintaining the appropriate balance of pro- and anti-inflammatory factors is crucial for the development and subsequent resolution of an inflammatory response. IL-6 is a pro-inflammatory cytokine that plays an important role in the regulation of central homeostatic and immunological processes. However, IL-6 also dampens the inflammatory response through its activation of IL-10, a potent anti-inflammatory cytokine. Hyperthermia induces a large increase in circulating IL-6 and, potentially, a reciprocal release of IL-10. The role of IL-6, which can be robustly activated by muscle in the context of exercise, may be more complex than simple inflammatory mediator: as a ”myokine,” it is also necessary for the insulin-sensitizing effects of exercise. Listen to discussion by scientist Dr. Charles Raison at 46:15 of this episode.
Heat exposure induces protective responses against the deleterious biological processes that drive cardiovascular disease and related disability. Some of these responses recapitulate those experienced during exercise. For example, heart rate may increase up to 100 beats per minute during moderate-temperature sauna bathing sessions and up to 150 beats per minute during hotter sessions, similar to the increases observed during moderate- to vigorous-intensity physical exercise. Furthermore, in a study involving 19 healthy adults, the effects of a single 25-minute sauna session were comparable to moderate physical exercise with respect to cardiovascular measures. During sauna use or moderate exercise, the participants’ heart rate and blood pressure increased immediately, but after the sauna or exercise session, participants’ blood pressure and heart rate began to drop below baseline levels measured pre-sauna or -exercise. Like exercise, long-term sauna use generally improves blood pressure, endothelial function, and left ventricular function, and reduces inflammation.
The World Health Organization estimates that nearly 18 million people die each year from cardiovascular diseases, roughly one-third of all deaths worldwide. Cardiovascular disease is largely preventable with lifestyle behaviors such as sauna use.
As described above, large prospective studies conducted in eastern Finland have shown that compared to men who never use the sauna, moderate sauna users (two to three times per week) are 27 percent less likely to die from cardiovascular-related causes, and frequent users (four to seven times per week) are 50 percent less likely to die from cardiovascular-related causes. In addition, the frequent sauna users were found to be 40 percent less likely to die from all causes of premature death, regardless of age, activity levels, and lifestyle factors. Learn more about the role of sauna use in the prevention of cardiovascular disease in this podcast with author Dr. Jari Laukkanen.
Congestive heart failure
Congestive heart failure, or CHF, represents the culmination of all forms of cardiovascular disease. It leads to impaired blood flow to the heart and peripheral tissues with subsequent functional losses, shortness of breath, fluid retention, and left ventricular hypertrophy. Treatment is often limited to pharmaceutical, dietary, or palliative care.
Findings from a prospective, multicentered, randomized controlled trial involving 149 patients with advanced CHF demonstrated that two weeks of waon therapy improved the patients’ endurance, heart size, and disease status compared to those who received standard medical care. In a different randomized controlled trial involving 30 CHF patients with frequent premature ventricular contractions, or PVCs, a type of abnormal heartbeat, researchers found that two weeks of infrared dry sauna (waon therapy) reduced the number of PVCs the patients experienced in a 24-hour period (from a baseline of ~3097 to ~848). A control group that received conventional medical therapy showed no changes.
Ischemic heart disease
Ischemic heart disease, also known as coronary artery disease, is characterized by reduced blood supply to the heart. It is the most common cause of death in most western countries. A randomized controlled trial examined the effects of sauna use in 24 patients with ischemic heart disease with chronic total coronary artery occlusion (full blockage of one or more of the arteries that supply the heart) who had not responded to non-surgical procedures and were not candidates for surgical interventions. The findings demonstrated that 15 waon sessions given over a three-week period improved the patients’ vascular endothelial function. No improvements were observed in the control group that received standard medical care.
Peripheral artery disease
Peripheral artery disease, or PAD, is a painful and debilitating condition in which the arteries that supply the head and extremities narrow. A pilot trial involving 20 patients with PAD who received 50 waon sessions over a period of 10 weeks demonstrated improvements in pain levels, walking endurance, and lower extremity blood flow. A similar randomized controlled trial involving 21 patients with PAD showed comparable improvements.
Dyslipidaemia, or abnormal blood lipid levels, is a strong predictor of cardiovascular disease risk. Two small studies have shown that regular sauna use modulates serum cholesterol and lipoproteins in healthy adults. Women who were exposed to seven 30-minute sauna baths over a period of two weeks exhibited reduced total cholesterol levels (from ~4.47mmol/L to ~4.25mmol/L) and reduced low-density lipoprotein, or LDL, levels (from ~2.83mmol/L to ~2.69mmol/L). Similarly, men who were exposed to ten 45-minute sauna baths over a period of three weeks exhibited reduced total cholesterol levels (from ~4.50mmol/L to ~4.18mmol/L) and reduced LDL levels (from ~2.71mmol/L to ~2.43mmol/L).
Hypertension, defined as a systolic pressure of 130 mm Hg or higher, or a diastolic pressure of 80 mm Hg or higher, is a chronic elevation of blood pressure. It is a robust predictor of future incidence of stroke, coronary heart disease, heart attack, heart failure, and cardiovascular-related death. Central to the pathophysiology of hypertension is the loss of arterial compliance, or elasticity, which can have far-reaching effects on multiple organ systems, including the brain and kidneys. A common element among sauna users, however, is lower incidence of hypertension through improvements in arterial compliance. For example, men who used the sauna two to three sessions every week were found to have a 24 percent lower risk of developing hypertension, and men who used the sauna four to seven times per week had a 46 percent lower risk for hypertension, compared to men who used the sauna only once per week.  Just a single sauna session has been shown to lower blood pressure and improve arterial compliance.  As such, sauna use may serve as a non-pharmacological means to address, or even prevent, hypertension.
The endothelium, the cell layer that lines the blood vessels, secretes substances that regulate blood vessel dilation (vasodilators) and constriction (vasoconstrictors). Endothelial dysfunction is characterized by decreased secretion of vasodilators and/or increased secretion of vasoconstrictors. This imbalance leads to impaired endothelium-dependent vasodilation, which is common among people who have CHF. Two weeks of sauna therapy, however, improved endothelial and cardiac function in patients with CHF.
Left ventricular dysfunction
Dysfunction of the heart’s left ventricle sets in motion a cascade of compensatory mechanisms that promote organ-level structural changes and elicit system-level hormonal adaptations. It is widely recognized as the end-stage of heart failure. Both single-session and long-term (five days per week for four weeks) sauna use improved ventricular function in men with CHF and may have therapeutic value for treating late-stage cardiovascular disease.
Inflammation is a critical element of the body’s immune response that involves immune cells, cell-signaling proteins, and pro-inflammatory factors. Acute inflammation occurs after minor injuries or infections and is characterized by local redness, swelling, or fever. Chronic inflammation occurs on the cellular level in response to toxins or other stressors and is often “invisible.” It plays a key role in the development of many chronic diseases, including cancer, cardiovascular disease, and diabetes.
C-reactive protein, or CRP, one of several blood proteins often referred to as acute phase reactants, participates in the body’s inflammatory cascade. Elevated CRP is associated with the development of atherosclerosis, loss of arterial compliance, and incidence of cardiovascular events. Sauna use, however, reduces blood levels of CRP. In a study of more than 2,000 men living in Finland, CRP levels were inversely related to the frequency of sauna bathing in a dose-response fashion, with lower levels linked to greater frequency.
As described above, IL-10 is a potent endogenous anti-inflammatory protein. In a study involving 22 healthy male athletes and non-athletes who received two 15-minute sauna sessions at 98.2°C (208°F) separated by a 5-minute cool shower, the men’s resting IL-10 levels increased, and this adaptation occurred faster in the athletes. A slight increase in some of the HSPs was also observed.
Cognitive & mental health
Heat stress and exercise increase the expression of brain-derived neurotrophic factor, or BDNF, a protein that acts on neurons in the central and peripheral nervous systems, to promote the growth of new neurons. BDNF modulates neuronal plasticity and ameliorates anxiety and depression from early-life stressful events. It is active in the hippocampus, cortex, cerebellum, and basal forebrain – areas involved in learning, long term memory, and executive function. BDNF is also produced in exercising muscle tissue, where it plays a role in muscle repair and the growth of new muscle cells.
Normal cognitive function relies on sufficient blood flow to the brain and peripheral nervous system, so cardiovascular diseases and cognitive decline often go hand-in-hand. For example, hypertension alters the structure of cerebral blood vessels and impairs blood flow to the brain. Poor cerebral blood flow is commonly observed in mice and humans and may contribute to impaired amyloid-beta clearance, thereby accelerating the progression of Alzheimer’s disease.
In addition, heat exposure increases the production of BDNF to promote neurogenesis – the growth of new neurons in the brain (as described above). Findings from a large observational study of middle-aged men living in Finland demonstrated that men who used the sauna four to seven times per week had a 65 percent reduced risk of developing Alzheimer’s disease, compared to men who used the sauna only one time per week.
Elevated biomarkers of inflammation are commonly observed in people who have depression. Chronic activation of the body’s inflammatory response system promotes the development of depressive symptoms and induces changes in brain and neuroendocrine function. Sauna use has been shown to reduce symptoms of depression.
In a randomized controlled trial involving 28 people diagnosed with mild depression, participants who received four weeks of sauna sessions experienced reduced symptoms of depression – such as improved appetite and reduced body aches and anxiety – compared to the control group, which received bedrest instead of sauna therapy.
In a randomized, double-blind study of 30 healthy adults diagnosed with depression, participants who were exposed to a single session of whole-body hyperthermia in which core body temperature was elevated to 38.5°C (101.3°F) experienced an acute antidepressant effect that was apparent within a week of treatment and persisted for six weeks after treatment.
Similarly, in a double-blind randomized controlled trial in which core body temperature was elevated by 1.5°C (2.7°F), IL-6 levels in participants increased markedly, and participants with the highest IL-6 levels had the lowest levels of depression one week later (see discussion with Dr. Charles Raison at 44:18). Some of these benefits may be due to the effects of heat stress on circulating levels of pro-inflammatory IL-6 and the reciprocal effects of IL-10 (as described above).
Beta-endorphins and the opioid system. Another factor that may play a role in mental or cognitive effects from sauna use may depend on the opioid system. Beta-endorphins are endogenous opioids that are part of the body’s natural painkilling system. They are produced and stored primarily in the anterior pituitary gland of the brain and play important roles in pain management and reward circuitry. Evidence suggests that beta-endorphins are responsible in part for the ”feel-good” response to exercise. The binding of beta-endorphins to mu-opioid receptors on nerve cells suppresses the release of pain-promoting substances in the brain. Sauna use promotes robust increases in beta-endorphins.  
The body also produces an opioid called dynorphin, which is generally responsible for dysphoria, a profound sense of unease or dissatisfaction. Dynorphin also mediates the body’s response to heat, helping the body to cool. Dynorphin is produced in many different parts of the brain, including the hypothalamus, the striatum, the hippocampus, and the spinal cord. The binding of dynorphin to kappa-opioid receptors triggers cellular events that promote pain and distress.
Sauna use (or intense exercise) promotes dynorphin release, which may be responsible for the general sense of discomfort experienced during heat exposure. Interestingly, in a biological feedback response that occurs after dynorphin binds to the kappa-opioid receptor, the brain produces more mu-opioid receptors, sensitizing them to endorphin and future endorphin exposure.
Mental focus and attention span
Two key players in cognitive and mental function are norepinephrine, a hormone and neurotransmitter produced in the brain, and prolactin, a hormone released by the pituitary gland. Norepinephrine enhances focus and attention, while prolactin promotes myelin growth, which makes the brain function faster, a critical feature in repairing nerve cell damage.
When young men stayed in a sauna that was heated to 80°C (176°F) until subjective exhaustion, their norepinephrine levels increased by 310 percent and their prolactin levels increased by 900 percent. Levels of cortisol, a hormone commonly associated with the stress response, were slightly decreased. Similarly, in a study involving women who participated in 20-minute sessions in a dry sauna twice a week experienced a 86 percent increase in norepinephrine and a 510 percent increase in prolactin after the session.
These findings suggest that since the norepinephrine response to exercise is blunted in children with attention deficit hyperactivity disorder, or ADHD, and norepinephrine reuptake inhibitors are frequently prescribed to treat ADHD, use of heat stress and its acclimation may one day be a useful alternative therapeutic approach employed by clinicians within some yet-to-be-established age-appropriate protocol.
Hormonal and metabolic function
Sauna use promotes growth hormone release, which varies according to time, temperature, and frequency. For example, two 20-minute sauna sessions at 80°C (176°F) separated by a 30-minute cooling period elevated growth hormone levels two-fold over baseline, but two 15-minute sauna sessions at 100°C (212°F) dry heat separated by a 30-minute cooling period resulted in a five-fold increase in growth hormone.
Interestingly, repeated exposure to whole-body heat treatment through sauna use has an even more profound effect on boosting growth hormone immediately afterward: Seventeen men and women who were exposed to two one-hour sauna sessions at 80°C (176°F) dry heat (typical Finnish-style sauna) per day for seven days exhibited a 16-fold increase in growth hormone levels by the third day. The growth hormone effects generally persisted for a few hours post-sauna. It is noteworthy, however, that sauna use and exercise can synergize to significantly elevate growth hormone when used together.
Insulin and glucose
Insulin regulates glucose homeostasis, primarily by promoting the uptake of glucose into muscle and adipose tissue. Repeated treatment with a far-infrared sauna has been shown to significantly lower fasting blood glucose levels. When insulin resistant diabetic mice were subjected to 30 minutes of heat treatment three times a week for 12 weeks, they experienced a 31 percent decrease in plasma insulin levels and a significant reduction in blood glucose levels, suggesting re-sensitization to insulin. The heat treatment specifically targeted the skeletal muscle by increasing the expression of a type of transporter known as GLUT 4, which is responsible for transporting glucose into skeletal muscle from the bloodstream. Decreased glucose uptake by skeletal muscle is one of the mechanisms that leads to insulin resistance.
Physical fitness and athletic performance
Heat stress from using the sauna may modulate improvements in physical fitness and athletic performance by increasing endurance and maintaining or promoting gains in muscle mass.
One small intervention study looked at the effects of repeat sauna use on athletic performance and other physiological effects in six male distance runners. The findings showed that one 30-minute sauna session twice a week for three weeks post-workout increased the time that it took for the study participants to run until exhaustion by 32 percent compared to their baseline. These performance improvements were accompanied by a 7.1 percent increase in plasma volume and a 3.5 percent increase in red blood cells (RBCs). During exercise, RBCs transport oxygen from the lungs to the body’s tissues (especially working muscles) and deliver carbon dioxide to the lungs for expiration. Increases in RBC levels may facilitate these processes and improve performance.
During exercise, core body temperature increases, attenuating endurance and accelerating exhaustion. Heat acclimatization and acclimation, however, induce complex physiological adaptations that improve thermoregulation, attenuate physiological strain, and enhance athletic performance in hot environments. These adaptations are mediated via improved cardiovascular and thermoregulatory mechanisms that reduce the deleterious effects associated with elevated core body temperature, optimizing the body for subsequent increases in core body temperature during future exercise.
Whereas ”acclimatization” refers to the body’s response to heat exposure in natural environments, ”acclimation” refers to the response in controlled environments, such as a sauna or heat stress chamber. The adaptations are the same in either scenario.
In a small study involving nine female athletes who sat for 20 minutes a day for five days in a hot environment (50°C [122°F], in low humidity) wearing a sauna suit to replicate sauna conditions, the women experienced improvements in thermoregulatory, cardiovascular, and perceived strain compared to a control group.
As described above, heat acclimation increases plasma volume and blood flow to the heart (stroke volume). This results in reduced cardiovascular strain and lowered heart rate for the same given workload. These cardiovascular improvements have been shown to enhance endurance in both highly trained and untrained athletes.
Heat acclimation also increases blood flow to the skeletal muscles, fueling them with glucose, fatty acids, and oxygen, reducing their dependence on glycogen stores. Endurance athletes often “hit a wall” due to depletion of their liver and muscle glycogen stores. Heat acclimation has been shown to reduce muscle glycogen use by 40 to 50 percent compared to before heat acclimation, presumably due to increased blood flow to the muscles.
Improvements in thermoregulatory function are also observed following heat acclimation. Heat exposure activates the sympathetic nervous system, increasing peripheral blood flow and the sweat rate to dissipate core body heat. After acclimation, sweating occurs at a lower core temperature and the sweat rate is maintained for a longer period.
- Muscle mass maintenance
Muscular atrophy, the shrinking or wasting away of muscle tissue, commonly occurs with muscle immobilization or disuse following sports injuries. Atrophy causes substantial strength losses, especially during the first week of immobilization or disuse, due to reduced protein synthesis and increased protein degradation.
Maintaining muscle mass requires a balance of new protein synthesis and existing protein degradation. While new protein synthesis accompanies muscle use during exercise, protein degradation can occur during both muscle use and disuse. Of critical importance, therefore, is net protein synthesis.
Heat acclimation, which can be achieved through sauna use, may reduce the amount of protein degradation that occurs during disuse by increasing HSPs, reducing oxidative damage, promoting release of growth hormone, and improving insulin sensitivity. Maintaining positive net synthesis has special relevance for recovery from injury since injury can tip the balance towards protein degradation and away from protein synthesis in the muscles, which can promote muscle atrophy.
A small intervention study in humans found that daily heat treatments applied locally to muscle during 10 days of immobilization prevented the loss of mitochondrial function, increased HSP levels, and attenuated skeletal muscle atrophy by 37 percent compared to a sham control group. These results have been replicated in animal studies. For example, when rats received whole body hyperthermia at 41°C (105.8°F) for 30 minutes or 60 minutes, hindlimb muscle atrophy during disuse decreased by 20 percent or 32 percent, respectively.
In another rodent study of the effects of heat stress, a 30-minute intermittent hyperthermic treatment at 41°C (105.8°F) for seven days induced a robust expression of HSPs (including HSP32, HSP25, and HSP72) in muscle, correlating with 30 percent more muscle regrowth than a control group subsequent to a week of immobilization. This HSP induction can persist for up to 48 hours after heat shock. Heat acclimation causes a higher basal expression of HSPs (even when not exercising) and a more robust induction upon elevation in core body temperature (such as during exercise).
Heat shock proteins, described above, can prevent muscle protein damage by directly scavenging reactive oxygen species and by supporting cellular antioxidant capacity through their effects on maintaining the endogenous antioxidant glutathione. In addition, HSPs can repair misfolded, damaged proteins, thereby ensuring proteins maintain their proper structure and function.
Sweating facilitates the excretion of certain toxicants that bioaccumulate in the muscle, adipose tissues, and organs of humans. As described above, sauna use induces substantial sweat losses, with the average person losing approximately 0.5 kg of sweat while sauna bathing.
Heavy metals are naturally-occurring metallic elements that are toxic or poisonous at low concentrations. Exposures to heavy metals in everyday products such as arsenic in agricultural products, cadmium in cigarette smoke and automobile exhaust, lead in toys, and mercury in dental amalgam and certain types of fish, are common occurrences. Some heavy metals are excreted in sweat, and sauna use may facilitate their excretion. In a study in which the presence of various compounds (including heavy metals) in the blood, urine, and sweat of 20 adults was measured, markedly higher excretion of aluminum (3.75-fold), cadmium (25-fold), cobalt (7-fold), and lead (17-fold) was observed in sweat versus urine.
Bisphenol A, or BPA, is a chemical used during the production of polycarbonate plastics and epoxy resins. It is ubiquitous in the environment and can be found in plastic beverage bottles and food packaging, metal food and beverage can linings, dental composites and resins, and other products. BPA is an endocrine disruptor that can mimic naturally occurring hormones in the body like oestrogens, androgens, and thyroid hormones, potentially altering normal hormonal signals. High levels of urinary BPA are associated with increased risk for cardiovascular disease and diabetes.
Bisphenol A bioaccumulates primarily in adipose tissue in humans, but some evidence indicates that it is excreted via sweat and, to a lesser degree, urine. Sauna bathing may serve as means to facilitate BPA excretion via the skin to eliminate this toxicant from the human body.
Polychlorinated biphenyls, or PCBs, are organochlorine compounds historically used in industrial and chemical applications such as coolants, transformer insulators, capacitors, motors, paints, and electrical wire coatings. Although PCBs were banned in the 1970s, they still persist in the environment, and many freshwater and farmed fish are contaminated with PCBs. Adverse human health effects associated with PCB exposure are related primarily to endocrine disruption, particularly in a developing fetus, as well as increased risk for developing hypertension, cutaneous malignant melanoma, and non-Hodgkin’s lymphoma. PCBs bioaccumulate in human muscle and adipose tissue, brain, liver, and lungs and have long elimination half-lives, ranging from 10 to 15 years. Some, but not all, PCBs are excreted in sweat.
Phthalates are synthetic compounds that are used to create plastic products that are soft and malleable. They are used in other consumer goods including fragrances, paints, nail polish, and food and beverage packaging, and are a ubiquitous component of soft plastic toys as well as various other products, including vinyl floor tiles, shower curtains, synthetic leather, cosmetics, shopping bags, and pharmaceuticals.
Urine samples analysed from populations worldwide have found phthalates in up to 98 percent of participants, including pregnant women. Phthalates have a relatively short half-life of less than five hours, which means the widespread detection likely indicates chronic exposure rather than accumulation within the body. Phthalates have been shown to lower testosterone levels and block the effects of testosterone on organs and tissues. Phthalates can pass from mother to fetus through the placenta and may result in abnormal sexual development. Some phthalates but not all are readily excreted through sweat.
Similarities between heat shock (sauna) and cold shock (ice dipping) (RP):
- Both are thermal stresses on the body and both can induce heat shock proteins (HSPs). This is because cold shock is also a hermetic stress that induces the expression of genes involved in stress response. However, the cold shock does not induce as robust of an increase in HSPs.
- Cold shock causes a massive release of norepinephrine (heat can also induce) from the locus cerulean, which helps with focus and attention. A burst of NE also makes you feel really good… norepinephrine-reuptake inhibitors are also a class of drugs used to treat ADHD.
- This increase in norepinephrine from cold shock regulates thermogenesis through the expression of uncoupling protein 1. The function of ucp1 is to uncouple the mitochondria—explain this and how it ramps up mitochondrial metabolism and stimulates lipolysis. Also, repeated norepinephrine release has been shown to cause white adipose tissue to express UCP1 and become more like brown adipose tissue.
- Some of the other effects (like dimorphic release and the effects on the opioid system) aren’t the same for cold shock, however.
Useful practical issues in real sauna bathing (Veli-Jussi Jalkanen, VJJ)
When people bathe together in safe, relaxed and caring atmosphere, it makes people approach automatically each other, even become friends. Social atmosphere in a mixed group also supports various hormone production in each member.
Effect of self – esteem and body awareness in nude bathing (VJJ)
The most healthy and natural way of having sauna is to bathe nude. Nude body is physically more relaxed and feels better all stimulants of from the water, heat, herbs and treatments. Also bathing nude in a safe company (same sex or mixed group) increases own body approval and quickly makes people take human body as natural without (culture combined) fears and shames. Usually people are surprized how quickly they relax in a mix group and become liberated in this sense. Also doing all sorts of treats like mud or clay coating, herbal oils etc. cannot be done well with any clothes on. Bathing nude also gives people an experience of comfortable and healthy nudeness, when nothing is pressing or limiting movements or the freedome of the skin and sweating. Cooling swimming nude in the pool after each sauna heat session, gives people an experience of very enjoyable water “touch” which also has some of the same effect as lymphatic massage generated by the water turbulence on the skin.
Health and relaxation treats in Sauna (VJJ)
Sauna is excellent place to feed many kind of reviving natural biochemical into the body in sauna because the skin is open and receptive. Such things are sauna birch “whip” treatment, herbal oil treatment, mud (treatment peat actually) and clay coating, herbal juice (numerous choices) treatments etc. There is maybe no better place to do these treatments than sauna and this way maximize the whole effect by getting these vitalizing biochemical in the body when it is very active anyway.
Important Quality of Air (VJJ)
If sauna is heated with traditional normal electricity stove, the quality of air is not too good. the glowing steel in the stove destroys the negative ions from the air. This is why sauna experts, who have experienced better saunas, do not like e-saunas. The difference is that its easy to bathe and enjoys in sauna with good air for hours but most of us come out from e-saunas after minutes. Wood heated saunas are so better in this respect. The best is if sauna is heated with the steam that comes out from the burning process. This is so called traditional Finnish smoke sauna. New Finnish wood pellet burning technology is offering here a way to burn wood totally smoke free (only CO2 and H2O come out) and thus avoid all bad sides traditional wood stove heating.
Other important issue is also ventilation. Sauna must be well ventilated to get safely the health benefits. Many materials, people etc. evaporate gasses when they heat up and they need to be ventilated out and fresh oxygen in. this is often neglected.
Powerful Welfare Treatments by Touching (VJJ)
When we touch the other person or get safely touched in a relaxing and safe way, the person we touch, produces “happy hormones” like dopamine, serotonin and oxytocin. These important health, happy feeling and relaxing hormones are known to degrease loneliness, depression, and increases relaxation and happiness. Particular thing is that also the person who touches, also produces these hormones in his/her body. In sauna massages, back/body wash, yoga, pair stretching etc. offer natural and fluent way to benefit also this powerful tool for health, stress relief and relaxation.
Ice dipping after Sauna Heat Sessions (VJJ)
Heat regulation and hormonal stimulation is greatly accelerated if cooling down after sauna sessions happens in the snow or cold water. People know by experience that after going to icy water the body produces so much heat that it stays warm 5- 15 minutes wet and nude even in frosty air (not in the wind). The wonderful feeling of warmth that takes over the body after ice dipping is a sign of powerful hormonal process for the balancing, heat production and adaptation. This is a maybe a superior way to produce the healthy brown fat (BAT) that turns into energy when a person enters cold conditions. I am excited to support having sauna in a social group when it´s easy even for a beginner to go into the cold water. If one needs to walk on ice, special ice dipping shoes are handy (but not necessary if you are experienced) to keep the toes from getting cold. Bathing clothes are uncomfortable because they hold the icy water from leaving the skin after coming out. It takes 2-4 times to get comfortably used to this “shocking” treatment. Many people, who have practical possibility, also adopt this super healthy habit and do it daily even without sauna. They all have a common feature: they very seldom have a flue. Surely this cold shock also has strong hormonal impacts and it’s a good way to train one’s micro circulation effectively.
The most effective way doing the cold dipping is to stay in the cold water also with your head under the surface from 1-2 up to 30 – 40 seconds but only when you are truly experienced and know how your body behaves and can do that comfortably without mental pressure.
About Useful and Practical Sauna Habits and Performance that Enforce Sauna Health Impacts (VJJ)
In some cultures (Germany) there is often very strict order of doing things according to the instructions of the sauna “master”. Our bodies however are very different and so the heat level (how high on the benches you are if there is a choice), how much you add water/snow on the stones to produce steam, and how long you can comfortably stay in the heat, are details, which are very individual.
Likely the best practice is that everybody listens to her/his own body and decide the length of the stay inside, drinking water, number of heats and cool downs (outside, shower, snow or in the water) as they feel best and most suitable to themselves. With more experience and with the hints of more experiences sauna enthusiasts all learn to make the sauna more and more fitting to her/his body and get more and more health benefits out from it.
Alcohol is not a good drink in sauna. We need to drink a lot of liquid there if we sweat a lot as we should. If it is alcohol, many health-, social and accident dangers increase, and safety and comfort of the neighbours likely diminish.
Cultural differences (VJJ)
Germany may be the leader in public saunas. There are several spas with pool area where people ware bathers and sauna areas where all are nude, but one must have a towel under their butts and feet while sitting on the benches. The atmosphere is relaxed, social, calm, and safe.
In Finland, the original and traditional sauna country of the North, the bathing in the saunas used to be for the whole farm staff together. Even villages had village saunas with all people bathing together without bathers etc. Such practices where common 1600 – 1900.
Unfortunately this traditional and valuable culture has somewhat degenerated due to unfortunate Anglican heritage of puritan (…”pure”) and inhibited values which has also spread out from UK to British colonies and to US and through their entertainment media to other countries too.
In Arabic and catholic culture people in the same sex do not show the bodies to each other. In Asian cultures men and women bathe also separately. Still in some traditional and famous spas in Japan, all people are told to bath nude and mixed in the thermal spas, which is like exception in their culture. In Asia the word sauna, unfortunately, is often linked with prostitution.
How to Avoid Getting Tired in Sauna (VJJ)
Many people have experience that they get tired in sauna. Some things are wrong their bathing. In high quality bathing one should be energized and relaxed after sauna. The most common reasons to get tired in sauna are
- Not drinking water enough (alcohol dries up the body, sugar, or carbon drinks not good at all)
- Overheating the body that is insufficient cooling between the heat periods
- Lack of oxygen / poor ventilation.
- Poor quality of air. Glowing steel wires abolish the negative ions from the air. This happens in electric saunas if the wires are not covered with ceramics coating. Forest after rain with its super rich air is good example of air full of negative ions. Wood burning stoves (varies between the brands) save better the negative ions in the air.
If these 4 mistakes are avoided, sauna enjoyment / treatment / therapy can last up to 3-4 hours in all.
Many Health Benefits of cold exposure (Cryotherapy) By Dr. Mercola (M)
While living in a climate-controlled environment has its benefits in terms of keeping us comfortable, it can actually have surprising impacts on health. There’s a compelling body of evidence showing exposure to harsh conditions can be highly beneficial. In fact, extreme temperature variations appear to help optimize many biological functions.
Any of us can take full advantage of the many magnificent benefits that regular cold exposure can have to improve your health. One of the mechanisms by which cold exposure or cold thermogenesis aids weight loss and reduces your risk of diabetes and other chronic disease is by inducing brown adipose tissue (BAT) = brown fat.
BAT, which is incredibly mitochondrial-dense, helps improve your mitochondrial function. One of the physiological functions of body fat is to be used as fuel to heat your body if you have active BAT metabolism. This is accomplished by uncoupling the mitochondria from producing ATP and actually producing heat instead. By regularly exposing yourself to cold, you build up a mitochondria-rich tissue in brown fat and help your body generate heat, which actually lowers your blood sugar and decreases insulin resistance.
Beige fat is a derivative of brown fat and is recruited through your white fat, which can then be used to heat your body and maintain a more active-passive metabolism. Indeed, the conclusion I reached after many decades of studying health is that burning fat as your primary fuel is a key to preserving and maintaining your health. There are a number of ways to reach this goal. You can do it through diet, and in my new book, “Fat for Fuel,” I explain how to do that. But there’s also a tremendous synergy with cold thermogenesis.
Cold Exposure Increases Whole-Body Metabolic Rate (M)
A recent study1 in Bioscience Reports looked at the impact of cryotherapy — exposure to cold — on the mitochondrial structure in BAT and skeletal muscle, both of which are thermogenic sites. As explained in this study:
“Mitochondria are very dynamic organelles that undergo dramatic remodeling in response to increase in local energy demand within a cell. The mitochondrial architecture (including cristae density, compactness, length, shape, and size) is a reflection of their level of activity, and thus it is also an indicator of cellular energy status. It is believed that organs involved in thermogenesis within the mammalian body elevate their metabolism in response to cold adaptation.”
While BAT and muscle both generate heat, they do so by using different mechanisms. In BAT, heat generation is based on mitochondrial metabolism. In muscle, mitochondrial metabolism plays only a secondary role by supplying energy to the muscle. In other words, mitochondrial metabolism is directly responsible for BAT-based thermogenesis, but only indirectly linked to thermogenesis in skeletal muscle.
Together, these differing thermogenic processes allow your body to maintain a constant core body temperature. As your body adapts to increasingly colder temperatures, several things happen, which together results in an increase in your overall metabolic rate:
|Oxygen consumption increases||Enzymatic activity in the mitochondria of your muscle is upregulated|
|Fibroblast growth factor 21, IL1α, peptide YY, tumor necrosis factor α and interleukin 6 are induced, and appear to play an important role in coordinating the various physiological adaptations to cold, and in the cross-communication that occurs between BAT and muscle||Insulin and leptin are downregulated|
|BAT becomes browner||The number of mitochondria increases|
Health Benefits of Cryotherapy (M)
The fact that cold thermogenesis increases the number of mitochondria and improves their overall function accounts for many of the health benefits associated with cryotherapy. For example, cold thermogenesis has been shown to:2,3,4
|Strengthen joint tissue||Support weight loss efforts by increasing metabolism|
|Increase blood circulation||Reduce symptoms of depression and anxiety by at least 50 percent5|
|Speed rate of recovery following joint or muscle injury6||Provide temporary relief lasting about 90 minutes from pain associated with arthritis7|
|Reduce pain and swelling following injury||Reduce your risk of developing cognitive decline and dementia by reducing inflammation and oxidative stress8|
|Reduce inflammation||Improve symptoms of eczema9|
|Enhance benefits of physical therapy||Reduce pain associated with migraines when applied to the back of the neck for about 30 minutes10|
|Improve muscle function and strength||Boost mental focus and attention by increasing production of norepinephrine in your brain.
Norepinephrine can be increased twofold just by getting into 40 degree F water for 20 seconds, or 57 degree water for a few minutes11
In addition to increasing norepinephrine, cold thermogenesis also forces your body to produce cold shock protein, known as the RNA-binding motif 3 or RBM3, in your brain. 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, and research shows that by increasing RBM3, Alzheimer’s onset can be significantly delayed — at least in rodents.12
Studies have also been done on human cells, showing that RBM3 does get activated when your 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 cold thermogenesis could have a neuroprotective effect.
Common Cryotherapy Methods (M)
There are a number of different cold thermogenesis methods available. Some high-end spas and gyms will have cryotherapy booths, along with saunas. But you can also take advantage of cold thermogenesis at home by:
|Applying an ice pack or cold gel pack||Applying an iced towel (simply wet a towel and freeze it) or massaging the area with ice cubes|
|Taking a cold shower or alternating between cold and hot in your shower||Taking an ice bath|
|Exercising in cold weather wearing few articles of clothing||Jumping into an unheated pool following sauna or exercise|
|Bathing in any nature water when temperatures are low||Turning down the thermostat in your house in the winter to about 60 F|
Keep in mind that cold thermogenesis treatment should not last for more than a few minutes, to 10 or 20 minutes after you have acclimated, and is contraindicated for pregnant women, young children, those with high blood pressure and/or a heart condition. Cold causes acute vasoconstriction, which can be potentially dangerous if you have high blood pressure or heart failure. A quick cold shower would probably be OK, but avoid ice baths or other extreme cold water immersion techniques.
As a general rule, 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. That said, over time you will become acclimated to the cold, which will allow you to withstand colder temperatures for longer periods of 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.
Again, the ability to generate more heat is a direct result of increased BAT and, secondarily, improved thermogenesis in your skeletal muscle. The more mitochondria you have in your fat tissue, the more fat you’re able to burn and the more heat your body can generate, which translates into an increased ability to withstand cold for longer periods of time.
One of the simplest ways to improve your BAT metabolism is taking cold showers, which you can do on a daily or near-daily basis. The initial tensing you experience is part of your body’s attempts to heat itself back up. Try to suppress this initial instinct and relax instead. Just how long it takes to build up BAT is still unknown, but we do know that BAT is generally a seasonal tissue.
In the winter, your body generates more of it as a way to boost its ability to stay warm. In the summer, you have less. A primary issue is, how often do you activate it? Without environmental stimuli, meaning exposure to various temperature extremes, your body will not create this metabolically or energy-rich tissue since it has no reason to do so. Taking an ice-cold rinse each day, year-round is a simple way to consistently activate your BAT metabolism.
When to Avoid Cryotherapy (M)
There is one important caveat worth mentioning. When you’re doing strength training, the oxidative stress generates reactive oxygen species (ROS) that actually 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 Rhonda Patrick, Ph.D., in a previous interview:
“This is what’s important to understand: Exercise is a stress on the body. You’re making ROS. 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].”
Cold Thermogenesis Is a Simple Way to Optimize Your Health (M)
When it comes to improving your health, many of the simplest strategies can have a significant impact. Regularly exposing yourself to cold temperatures can catalyse a wide variety of beneficial changes in your biology that can go a long way toward optimizing your health.
One of the things I do regularly, nearly every day when I am home, is to take a 30-minute 170 degree far-infrared sauna and then jump in an unheated pool and swim five laps. In the summer the water is in the 80s but it can go down to the 40s in the winter. It is absolutely amazing how good you feel after coming out of the pool when it’s winter. It’s incredibly invigorating.
Regularly exposing yourself to these kinds of extreme temperature variations will help improve your mitochondrial function, which we have now come to realize is a foundational aspect of good health, disease prevention and longevity.
Remember, mitochondria are the energy generators in your cells, and if they are not functioning well, or if damaged ones are not efficiently replaced by new, healthy mitochondria, any number of health problems are sure to ensue. Cryotherapy is one effective form of mitochondrial therapy.
- Hannuksela, M. L. & Ellahham, S. Benefits and risks of sauna bathing. The American journal of medicine 110, 118-126 (2001). This is actually an important review article that covers some of the benefits of sauna use including the cardiovascular advantages and hormonal changes such as the boost in GH levels. I also like it because it covers some of the risks of alcohol use before or during the sauna. [↩]
- Ricardo J. S. Costa, M. J. C., Jonathan P. Moore & Neil P. Walsh. Heat acclimation responses of an ultra-endurance running group preparing for hot desert-based competition. European Journal of Sport Science, 1-11 (2011). The sample sizes in both studies referenced here and in #4 have small sample sizes but they are two independent studies that compliment each other. This study also reinforces the endurance enhancements in #5. [↩]
- King, D. S., Costill, D. L., Fink, W. J., Hargreaves, M. & Fielding, R. A. Muscle metabolism during exercise in the heat in unacclimatized and acclimatized humans. J Appl Physiol 59, 1350-1354 (1985). This study shows that glycogen utilization is decreased in runners after heat acclimation. The sample size is small but ref #7 (another small sample) is an independent study that shows the same effect. [↩]
- Scoon, G. S., Hopkins, W. G., Mayhew, S. & Cotter, J. D. Effect of post-exercise sauna bathing on the endurance performance of competitive male runners. Journal of science and medicine in sport / Sports Medicine Australia 10, 259-262, doi:10.1016/j.jsams.2006.06.009 (2007). This study shows the effect of preconditioning the body to heat stress by using a sauna for at least 30 min directly after after training session. While the study sample is small, other studies referenced in #2, #5 reinforce and compliment this. I also have some anecdotal data. I did some serious experimentation with the sauna a couple of years ago when I had access to a sauna. I would sit in the sauna for up to 60 min. until I pushed myself to extreme physical discomfort about 4-5 times a week. I substantially (and I know this is just anecdote) increased my running PRs. [↩]
- Michael N. Sawka, C. B. W., Kent B. Pandolf. Thermoregulatory Responses to Acute Exercise-Heat Stress and Heat Acclimation. Handbook of Physiology, Environmental Physiology (2011). This is a good review article that covers many of the mechanisms that underly the endurance enhancements as a consequence of heat acclimation. [↩]
- Garrett, A. T., Creasy, R., Rehrer, N. J., Patterson, M. J. & Cotter, J. D. Effectiveness of short-term heat acclimation for highly trained athletes. European journal of applied physiology 112, 1827-1837, doi:10.1007/s00421-011-2153-3 (2012). [↩]
- Kirwan, J. P. et al. Substrate utilization in leg muscle of men after heat acclimation. J Appl Physiol (1985) 63, 31-35 (1987). The findings in this study reinforce the data in ref #3. Both small sample sizes but multiple studies showing the same effect makes the argument stronger. [↩]
- Selsby, J. T. et al. Intermittent hyperthermia enhances skeletal muscle regrowth and attenuates oxidative damage following reloading. J Appl Physiol (1985) 102, 1702-1707, doi:10.1152/japplphysiol.00722.2006 (2007). This is an important paper because it shows that intermittent hyperthermia can enhance the regrowth of skeletal muscle in rats after disuse via induction of heat shock proteins. Having a quantitative way to non-invasively measure muscle mass in humans is difficult. Even though the experiment was done in rats (N=40) this is a good study because it also shows mechanism. [↩]
- Naito, H. et al. Heat stress attenuates skeletal muscle atrophy in hindlimb-unweighted rats. J Appl Physiol 88, 359-363 (2000). This study demonstrates that HSP induction by intermittent hyperthermia in rats can prevent muscle atrophy during muscle disuse. Again, this study was in rats but it shows mechanism has has a good sample size (N=40). [↩]
- Kokura, S. et al. Whole body hyperthermia improves obesity-induced insulin resistance in diabetic mice. International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group 23, 259-265, doi:10.1080/02656730601176824 (2007). This study was done in mice (N=20) but it demonstrates a very important mechanistic finding that hyperthermia increases the expression of glucose transporters in skeletal muscle, thus improving insulin sensitivity. Exercise (which elevates core body temp.) is known to improve insulin sensitivity. This is a cool mechanism by which this can occur. [↩]
- Yamada, P. M., Amorim, F. T., Moseley, P., Robergs, R. & Schneider, S. M. Effect of heat acclimation on heat shock protein 72 and interleukin-10 in humans. J Appl Physiol (1985) 103, 1196-1204, doi:10.1152/japplphysiol.00242.2007 (2007). This study includes a relatively small human sample size (N=12) but it is a very important because it demonstrates that heat acclimation causes a higher induction of heat shock proteins upon later exercise. This is the fundamental concept behind hyperthermic conditioning. [↩]
- Moseley, P. L. Heat shock proteins and heat adaptation of the whole organism. J Appl Physiol (1985) 83, 1413-1417 (1997). This is a review article that explains some of the functions of HSPs and reinforces the data from reference #11 demonstrating that heat acclimation can increase the expression of HSPs. [↩]
- Kuennen, M. et al. Thermotolerance and heat acclimation may share a common mechanism in humans. American journal of physiology. Regulatory, integrative and comparative physiology 301, R524-533, doi:10.1152/ajpregu.00039.2011 (2011). This study is another small human sample size (N=8) but it reinforces the data from ref #11 because it demonstrates that some of the positive effects of heat acclimation are due to increased expression of HSPs. The study even shows specificity here by administering an HSP inhibitor, which ameliorates the positive effects of heat acclimation. [↩]
- Leppaluoto, J. et al. Endocrine effects of repeated sauna bathing. Acta physiologica Scandinavica 128, 467-470, doi:10.1111/j.1748-1716.1986.tb08000.x (1986). This is a very important study because it shows the profound hormonal responses to repeated sauna use in humans (N=17). By day 3, growth hormone increased 16-fold, highlighting the importance of hyperthermic conditioning. [↩]
- Kukkonen-Harjula, K. et al. Haemodynamic and hormonal responses to heat exposure in a Finnish sauna bath. European journal of applied physiology and occupational physiology 58, 543-550 (1989). Even though the human sample size in this study is small (N=8), it shows that varying temperatures and durations differentially affect hormones. Small sample or not, the fundamental chemical changes in this study are reinforced from the data referenced in #1 and #4. [↩]
- Velloso, C. P. Regulation of muscle mass by growth hormone and IGF-I. British journal of pharmacology 154, 557-568, doi:10.1038/bjp.2008.153 (2008). [↩]
- Coleman, M. E. et al. Myogenic vector expression of insulin-like growth factor I stimulates muscle cell differentiation and myofiber hypertrophy in transgenic mice. The Journal of biological chemistry 270, 12109-12116 (1995). In this study mice were engineered to constitutively express high levels of human IGF-1 in their muscle stem cells. This caused the proliferation and differentiation of myoblasts and caused muscle hypertrophy. [↩]
- Barton, E. R., Morris, L., Musaro, A., Rosenthal, N. & Sweeney, H. L. Muscle-specific expression of insulin-like growth factor I counters muscle decline in mdx mice. The Journal of cell biology 157, 137-148, doi:10.1083/jcb.200108071 (2002). [↩]
- Healy, M. L. et al. High dose growth hormone exerts an anabolic effect at rest and during exercise in endurance-trained athletes. The Journal of clinical endocrinology and metabolism 88, 5221-5226 (2003). [↩]
- Ftaiti, F. et al. Effect of hyperthermia and physical activity on circulating growth hormone. Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme 33, 880-887, doi:10.1139/H08-073 (2008). This study shows that hyperthermia SYNERGIZES with exercise to increase growth hormone levels in humans. So you can feel the burn from your routine and then jump immediately in the sauna for amplified effects. Again, small sample (N=8) but its conclusion is logical and intuitively follows the other studies. Anything that substantially increases core temperature should increase growth hormone and the effects should potentiate each other. [↩]
- Louard, R. J., Fryburg, D. A., Gelfand, R. A. & Barrett, E. J. Insulin sensitivity of protein and glucose metabolism in human forearm skeletal muscle. The Journal of clinical investigation 90, 2348-2354, doi:10.1172/JCI116124 (1992). This study demonstrated that insulin stimulated BCAA uptake in the forearm (post-absorptive and insulin infusion) The sample size in this human study was good (N=39). [↩]
- Lecker, S. H., Goldberg, A. L. & Mitch, W. E. Protein degradation by the ubiquitin-proteasome pathway in normal and disease states. Journal of the American Society of Nephrology : JASN 17, 1807-1819, doi:10.1681/ASN.2006010083 (2006). This is a review article that covers the mechanism by which insulin decreases protein degradation: proteasome inhibition. [↩]
- Chow, L. S. et al. Mechanism of insulin’s anabolic effect on muscle: measurements of muscle protein synthesis and breakdown using aminoacyl-tRNA and other surrogate measures. American journal of physiology. Endocrinology and metabolism 291, E729-736, doi:10.1152/ajpendo.00003.2006 (2006). This study used multiple different methods to measure protein synthesis and degradation in 18 humans after insulin infusion. The insulin levels were raised to physiologically relevant postprandial levels. [↩]
- Guillet, C., Masgrau, A., Walrand, S. & Boirie, Y. Impaired protein metabolism: interlinks between obesity, insulin resistance and inflammation. Obesity reviews : an official journal of the International Association for the Study of Obesity 13 Suppl 2, 51-57, doi:10.1111/j.1467-789X.2012.01037.x (2012). [↩]
- Selsby, J. T. & Dodd, S. L. Heat treatment reduces oxidative stress and protects muscle mass during immobilization. American journal of physiology. Regulatory, integrative and comparative physiology 289, R134-139, doi:10.1152/ajpregu.00497.2004 (2005). This study just reinforces and compliments the protective effect that HSPs have on muscle mass during disuse. It reinforces data referenced in #9. [↩]
- Nath, K. A. et al. Induction of heme oxygenase is a rapid, protective response in rhabdomyolysis in the rat. The Journal of clinical investigation 90, 267-270, doi:10.1172/JCI115847 (1992). This reference is relevant to the mechanism by which hyperthermic conditioning may protect against rhabdomyolysis: induction of HSP32. [↩]
- Wei, Q., Hill, W. D., Su, Y., Huang, S. & Dong, Z. Heme oxygenase-1 induction contributes to renoprotection by G-CSF during rhabdomyolysis-associated acute kidney injury. American journal of physiology. Renal physiology 301, F162-170, doi:10.1152/ajprenal.00438.2010 (2011). [↩]
- Khazaeli, A. A., Tatar, M., Pletcher, S. D. & Curtsinger, J. W. Heat-induced longevity extension in Drosophila. I. Heat treatment, mortality, and thermotolerance. The journals of gerontology. Series A, Biological sciences and medical sciences 52, B48-52 (1997). This reference, as well as the two immediate ones following, back up the notion that heat shock extends lifespan in lower organisms via HSP induction. [↩]
- Lithgow, G. J., White, T. M., Melov, S. & Johnson, T. E. Thermotolerance and extended life-span conferred by single-gene mutations and induced by thermal stress. Proceedings of the National Academy of Sciences of the United States of America 92, 7540-7544 (1995). [↩]
- Tatar, M., Khazaeli, A. A. & Curtsinger, J. W. Chaperoning extended life. Nature 390, 30, doi:10.1038/36237 (1997). [↩]
- Singh, R. et al. Anti-inflammatory heat shock protein 70 genes are positively associated with human survival. Current pharmaceutical design 16, 796-801 (2010). This study was a longitudinal cohort of a Denmark population (N=168) that found a slight increase in longevity (1 year) in females that had a polymorphism in the HSP70 gene that was associated with increased HSP expression upon heat stress. [↩]
- Yenari, M. A., Giffard, R. G., Sapolsky, R. M. & Steinberg, G. K. The neuroprotective potential of heat shock protein 70 (HSP70). Molecular medicine today 5, 525-531 (1999). [↩]
- Duveau, V., Arthaud, S., Serre, H., Rougier, A. & Le Gal La Salle, G. Transient hyperthermia protects against subsequent seizures and epilepsy-induced cell damage in the rat. Neurobiology of disease 19, 142-149, doi:10.1016/j.nbd.2004.11.011 (2005). [↩]
- Lundgren, J., Smith, M. L., Blennow, G. & Siesjo, B. K. Hyperthermia aggravates and hypothermia ameliorates epileptic brain damage. Experimental brain research. Experimentelle Hirnforschung. Experimentation cerebrale 99, 43-55 (1994). [↩]
- Laatikainen, T., Salminen, K., Kohvakka, A. & Pettersson, J. Response of plasma endorphins, prolactin and catecholamines in women to intense heat in a sauna. European journal of applied physiology and occupational physiology 57, 98-102 (1988). This study reinforces ref #15 in terms of the norepinephrine response but this demonstrates it in women. Also, the smaple size is small (N=11), so it good to have multiple studies showing similar effects. [↩]
- Salbaum, J. M. et al. Chlorotoxin-mediated disinhibition of noradrenergic locus coeruleus neurons using a conditional transgenic approach. Brain research 1016, 20-32, doi:10.1016/j.brainres.2004.03.078 (2004). [↩]
- Gregg, C. et al. White matter plasticity and enhanced remyelination in the maternal CNS. The Journal of neuroscience : the official journal of the Society for Neuroscience 27, 1812-1823, doi:10.1523/JNEUROSCI.4441-06.2007 (2007). [↩]
- Christman, J. V. & Gisolfi, C. V. Heat acclimation: role of norepinephrine in the anterior hypothalamus. J Appl Physiol (1985) 58, 1923-1928 (1985). [↩]
- Wigal, S. B. et al. Catecholamine response to exercise in children with attention deficit hyperactivity disorder. Pediatric research 53, 756-761, doi:10.1203/01.PDR.0000061750.71168.23 (2003). [↩]
- Goekint, M., Roelands, B., Heyman, E., Njemini, R. & Meeusen, R. Influence of citalopram and environmental temperature on exercise-induced changes in BDNF. Neuroscience letters 494, 150-154, doi:10.1016/j.neulet.2011.03.001 (2011). This study had an N=8 (okay, tiny) but… it demonstrated that hyperthermia and exercise synergize to elevate BDNF. This is awesome. Who doesn’t want more BDNF? [↩]
- van Praag, H., Christie, B. R., Sejnowski, T. J. & Gage, F. H. Running enhances neurogenesis, learning, and long-term potentiation in mice. Proceedings of the National Academy of Sciences of the United States of America 96, 13427-13431 (1999). [↩]
- Maniam, J. & Morris, M. J. Voluntary exercise and palatable high-fat diet both improve behavioural profile and stress responses in male rats exposed to early life stress: role of hippocampus. Psychoneuroendocrinology 35, 1553-1564, doi:10.1016/j.psyneuen.2010.05.012 (2010). [↩]
- Pedersen, B. K. Muscle as a Secretory Organ. Comprhensive Physiology (2013). [↩]
- Koltyn, K. F., Robins, H. I., Schmitt, C. L., Cohen, J. D. & Morgan, W. P. Changes in mood state following whole-body hyperthermia. International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group 8, 305-307 (1992). [↩]
- Liu, X. L. et al. [Therapeutic effect of whole body hyperthermia combined with chemotherapy in patients with advanced cancer]. Zhong nan da xue xue bao. Yi xue ban = Journal of Central South University. Medical sciences 31, 350-352 (2006). [↩]
- Narita, M. et al. Heterologous mu-opioid receptor adaptation by repeated stimulation of kappa-opioid receptor: up-regulation of G-protein activation and antinociception. Journal of neurochemistry 85, 1171-1179 (2003). This study was done in mice but shows that repeated activation of kappa opioid receptor causes mu opioid receptor to become more sensitive to beta-endorphin. This study provides a mechanism by which the dysphoric feeling from exercise or heat stress can ultimately result in a better “endorphin high.” [↩]
- Xin, L., Geller, E. B. & Adler, M. W. Body temperature and analgesic effects of selective mu and kappa opioid receptor agonists microdialyzed into rat brain. The Journal of pharmacology and experimental therapeutics 281, 499-507 (1997). [↩]
- Heckmann, J. G., Rauch, C., Seidler, S., Dutsch, M. & Kasper, B. Sauna stroke syndrome. Journal of stroke and cerebrovascular diseases : the official journal of National Stroke Association 14, 138-139, doi:10.1016/j.jstrokecerebrovasdis.2005.01.006 (2005). This reference is only an N=1 where a a man had consumed several glasses of wine before he got in the sauna and was, subsequently, found dead. Alcohol consumption while in the sauna can cause severe dehydration, hypotension, arrhthymia, and embolic stroke. This is also reviewed in reference #1 [↩]