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Liam Browning, David Puder, MD A Global History Of Heat Therapy: From Ancient Finnish Saunas to Modern Medicinal UsesTimeline of Heat Therapy: A Global HistoryCirca 4000-2000 B.C.E.: Circa 2000-1000 B.C.E.: Circa 1000 B.C.E.: Traditional Chinese Medicine and Ayurveda: In China and India, heat therapy techniques like moxibustion and steam treatments are employed for improving circulation, reducing pain, and promoting detoxification.
Circa 500 B.C.E.-500 C.E: Greek and Roman Bathhouses: The Greeks began using heated baths and steam baths, referred to as laconica. Communal bathhouses became central in Roman society, with figures like Galen writing about hot baths to treat melancholia and other ailments. Ottoman Hammams: Public baths in the Middle East and North Africa, known as hammams, were common throughout the region, offering both hygienic and therapeutic benefits. It later rose to greater prominence as an integral part of Islamic culture beginning in the 7th-8th century. The buildings contained a hot room (Hararet) with underfloor heating by a furnace and also a cold room (Soğukluk) for cold water immersion. Native American Sweat Lodges: Indigenous tribes across North America developed sweat lodges, used for purification, spiritual rituals, and healing. These lodges were a staple in Native American culture and closely mirror sauna practices.
Middle Ages (Circa 500-1500 C.E.): European Bathhouses: Communal bathhouses were widespread across medieval Europe, combining hygiene with socializing and therapeutic practices. Mayan Temazcal: In Mesoamerica, the temazcal, a type of sweat lodge, was used for ritualistic cleansing and healing, particularly in the context of childbirth and illness.
19th Century C.E.: Victorian-Era Turkish Baths (Hammams): Western Europe, particularly the U.K., experienced a revival in communal heat therapy with the introduction of hammams, or Turkish baths.
1900s C.E.: “Malaria Fever Cure”: Austrian physicians Julius Wagner-Jauregg and Rudolf Rosenblum introduced heat therapy via induced fever to treat psychiatric symptoms related to syphilis, particularly neurosyphilis, and later experimented with it for other mental health disorders. Before the discovery of penicillin, this method led to significant improvement in about 30-50% of cases; however, some patients experienced worsening symptoms, and approximately 15% died from complications.
1960s C.E.: Development of Infrared Saunas: Infrared saunas, which heat the body directly using radiant heat, were introduced as a modern alternative to traditional saunas, allowing for lower ambient temperatures.
21st Century C.E.: Present Day:
How Physical Health Conditions Elevate Depression Risk: Unveiling The Mind-Body ConnectionThere is a strong link between physical health and mental health.
Increased risk of depression with these diseases:
Key Findings From The Kuopio Ischemic Heart Disease Study: The Long-Term Benefits Of Sauna UseThe strongest literature on sauna is from a longitudinal observational study in Finland, called the Kuopio Ischemic Heart Disease (KIHD) Risk Factor Study. 2,327 middle-aged men (mean age 53 y/o) Grouped participants by sauna frequency: Most participants used a dry sauna at an average temperature of 80°C (170°F) for an average of 14 minutes (range 2-90 minutes) One of the first publications of this study looked at cardiovascular outcomes, stroke, and all-cause mortality after 21 years (Laukkanen et al., 2015). Compared to once weekly sauna users, the 3-7x/week users had a 40% reduced risk of all-cause mortality, 50% reduced risk of fatal cardiovascular disease, 48% risk of fatal coronary artery disease, and a 63% decreased risk of sudden cardiac death. This is after adjusting for age, BMI, SBP, LDL, smoking, previous MI, T2DM, activity, and SES. In the unadjusted analyses, the 2-3x/group had a significantly reduced risk of these outcomes, suggesting a dose-response relationship. The dose-response effect was also seen with sauna session duration. Compared to sauna users with sessions less than 11 minutes, the HR for sudden cardiac death was 0.93 (95% CI, 0.67-1.28) and 0.48 (95% CI, 0.31-0.75) for sauna users with average sessions of 11-19 minutes and >19 minutes respectively, supporting this dose-response relationship.
Follow-up studies from this same cohort showed that compared to once weekly users and controlling for similar confounds, the 4-7x/week users had:
Sauna vs. Other Interventions: Comparing Long-Term Health Impacts Of Exercise, Diet, and More
Cardiovascular Health Insights: Findings from the KIHD Study and Other Key Research on Physical WellnessBlood pressure: The KIHD study from Zaccardi et al., 2017 showed that sauna sessions 4–7 times weekly was associated with a 47% relative decrease in the likelihood of developing hypertension in the 25-year follow up, controlling for age, smoking, body mass index, glucose, creatinine, alcohol consumption, heart rate, family history of hypertension, socioeconomic status, and cardiorespiratory fitness. This effect was insignificant in 2-3 times/week when controlling for these confounds. Sauna acutely decreases SBP/DBP by about 5-10mmHg for minutes to hours post-sauna (Laukkanen et al., 2018). Pizzey et al., 2021 reviewed 4 RCTs of repeated (3-5d/week) immersion in hot water (38.5-40.5°C) showed an average reduction in SBP by 5.9 mmHg and DBP by 3.9 vs. sham control. This decrease was observed in healthy, obese, and heart-failure participants with hypertension. Compare to SBP decreases observed with other lifestyle modifications: And 10-15mg decreases in SBP with antihypertensive monotherapy (Paz et al., 2016) The antihypertensive effects of sauna are thought to be due to endothelium-dependent dilatation, reduced arterial stiffness, modulation of the autonomic nervous system (Laukkanen et al., 2018).
Sauna may mimic exercise: The acute changes and after-effects of sauna on cardiac load, blood pressure, and vascular hemodynamics is extremely similar to that of moderate intensity exercise (Ketelhut & Ketelhut, 2019).
Sauna will frequently bring the heart rate to over 100 BPM and even to 150 BPM in more intense settings (Laukkanen & Kunutsor, 2024).
Does sauna provide a different benefit than exercise? Lee et al., 2022 conducted a study comparing 8 weeks of exercise alone, exercise + sauna, and control participants. Both the exercise and sauna routines were progressive in nature. They found that, compared to exercise alone, exercise + sauna improved V02 max (2.7mL/kg/min), total cholesterol (-19mg/dL), and systolic bp (-8mmHg).
Limitations: Sauna + exercise group experienced more time in which they had elevated HR. If sauna acts as an exercise mimic, time should be controlled. Exercise group did not improve as expected.
Aerobic exercise in combination with frequent sauna use has a synergistic effect on lowering cardiovascular-related mortality and all-cause mortality, according to one article from the KIHD study. The strongest reductions in mortality were found in people with high cardiorespiratory fitness (>50th percentile VO2 max) and high frequent sauna bathing (>3 sessions/week) HR 0.60 (95% CI: 0.48–0.76), followed by high cardiorespiratory fitness and low frequent sauna bathing 0.63 (95% CI: 0.54–0.74), and then low cardiorespiratory fitness and high frequent sauna bathing 0.78 (95% CI: 0.64–0.96) (Kunutsor et al., 2017).
DJP: different sports and how long people live, tennis seemed to win- 1) high SES or 2) interaction with people. How much of the sauna is interaction with people? Exploring Additional Health Benefits of Heat Therapy: Insights into Heart Failure, Diabetes, Joint Disease, and MoreA meta-analysis of low-quality studies involving heart failure patients suggests that heat therapy, such as sauna use, can help improve symptoms and reduce levels of B-type natriuretic peptide (BNP), a marker of heart failure severity (Ye et al., 2020). Qualitative studies of Waon therapy, a far-infrared dry sauna treatment, show improvement in peripheral artery disease (PAD) through enhanced ankle-brachial index (ABI), increased blood flow, and the development of collateral vessels (Tei et al., 2007). Type 2 diabetes A review of five studies (Sebők et al., 2021) on Type 2 diabetes found that while there was no significant change in glucose or HbA1c levels with interventions like heat therapy, including sauna use, there was a consistent reduction in systolic blood pressure, averaging 5-10 mmHg. This improvement is important because sustained reductions in blood pressure are associated with a lower risk of cardiovascular events and complications in diabetic patients, making it a valuable adjunct in managing long-term cardiovascular health.
Inflammatory joint disease Cozzi and colleagues (2018) reviewed several randomized-controlled trials (RCTs) that demonstrated the benefits of balneotherapy in improving the subjective clinical course of conditions like ankylosing spondylitis, enteropathic spondylitis, and psoriatic arthritis. The studies showed that patients experienced significant relief from symptoms such as pain, stiffness, and fatigue. These improvements were primarily attributed to the anti-inflammatory and pain-relieving effects of balneotherapy, which involves bathing in mineral-rich waters. The findings suggest that balneotherapy can be a valuable complementary treatment option for managing these chronic inflammatory conditions.
Sauna Use for Depression: An Evidence-Based Review Of Infrared And Whole-Body Hyperthermia StudiesThe First RCT on Sauna Use for Depression: Masuda et al. (2005)
Whole-Body Hyperthermia and Depression: A Review of Key Studies (2019)Review of depression studies up until 2019: The impact of whole-body hyperthermia interventions on mood and depression – are we ready for recommendations for clinical application? (Hanusch & Jansenn, 2019)
Infrared chambers
Randomized-Controlled Trials on Whole-Body Hyperthermia for DepressionThe most impressive of these RCTs was from Janssen et al. (2016): Whole-Body Hyperthermia for the Treatment of Major Depressive Disorder A Randomized Clinical Trial Methods 34 moderate to severely depressed patients randomized to whole-body hyperthermia (WBH) via infrared chamber (n=16) vs sham-controls who received very mild heat (n=14). Participants underwent a single infrared session in which they sat in the heated chamber until their rectal temperature reached 38.6°C (101.5°F) (avg 47 min), followed by resting in the machine for 60 min. Depressive symptoms were assessed 1, 2, 4, and 6 weeks after WBH using the Hamilton Rating Scale for Depression (HAMD).
Results Active WBH group showed significantly reduced HAMD scores across the 6-week post intervention study period (WBH vs sham; week 1: −6.53, 95% CI, −9.90 to −3.16, P < .001, d = 2.23; week 2: −6.35, 95% CI, −9.95 to −2.74, P = .001, d = 2.11; week 4: −4.50, 95% CI, −8.17 to −0.84, P = .02, d = 1.66; and week 6: −4.27, 95% CI, −7.94 to −0.61, P = .02, d = 1.66).
Limitations/Takeaways
The authors did perform a moderation analysis controlling for expectancy effects, but did not include this variable in their original analysis. The effect size following the moderation analysis was also not reported. However, it is worth noting 70% of the sham group did believe they received the active treatment. Given this is a single session and is unlikely to provide much of a physiological stimulus lasting 6 weeks, more attention should have been given to the belief in treatment efficacy.
The other RCTs used multiple sessions: Hüppe et al. (2009) randomized 36 patients to hyperthermia, sham-control, or waitlist control. Romeyke & Stummer (2014) allocated 104 patients with severe fibromyalgia and MDD to an average of 5 hyperthermia sessions or waitlist control. Pain improved more in the hyperthermia group, but both groups improved in depressive symptoms, with no trend-level differences favoring the hyperthermia group (p = .055). All patients received physical therapy, physiotherapy, acupuncture, psychotherapy.
Naumann et al. (2017) randomized 17 moderately depressed patients to 2 weekly hyperthermia baths at 40°C (104°F) for 22 minutes for 4 weeks vs. sham-control that received green light exposure.
General Takeaways and Limitations in Heat Therapy for Depression
How Heat Exposure Enhances Antidepressant Effects: Unveiling The Science Behind Sauna Use and Mental HealthHeat stress and exercise increase the expression of brain-derived neurotrophic factor (BDNF) (Kojima et al., 2018)Whole-body hyperthermia to a core body temperature of 39.5 °C (103.1 °F) via hot water bath (20-min at 42 °C [107.6 °F]) increased BDNF levels 66% for 15 minutes (Kojima et al., 2018). Inflammation and Heat ExposureSimilar to exercise, whole body hyperthermia increases plasma levels of pro-inflammatory IL-6 and anti-inflammatory IL-10 (Katchinski et al., 1999; Windsor et al., 2018). However, the impact of these changes on depression and their potential to cause long-term alterations in inflammatory markers remains uncertain (Mac Giollabhui et al., 2024). The Role of Heat Shock Proteins (HSPs) in Sauna Therapy: Mechanisms Linked to Physical and Therefore Antidepressant Effects
HSPs are a family of proteins observed in all forms of life from bacteria to humans and are crucial for a cell’s protein quality control systems. Cells are largely made of proteins, and over time, proteins will inevitably lose their function and shape. HSPs can physically change the shape of dysfunctional or misfolded proteins. They also help new proteins fold correctly, disaggregate proteins that are clumped together, and target proteins for degradation. When cells are faced with hypoxia, heat stress, nutritional stress, or other stressors, HSP are upregulated to help make new proteins and to repair damaged ones (Rosenzweig et al., 2019).
HSPs may be vital for preventing some of the effects of aging. The cell’s ability to counteract stress declines with age due to a variety of reasons that stem from metabolic dysfunction as a result of mitochondrial decline or accumulations of DNA mutations. Protein quality control systems also decline with age as well, as the number and efficiency of HSPs decreases. As a result, more defunct proteins are formed and our cells become less capable of handling them. Declines in particular HSPs are related to neurodegenerative disorders associated with protein aggregates such as Alzheimers, Parkinson’s, and Huntington disease, and may be related to normal cognitive decline. They also are important for recycling the proteins involved in neurotransmission and can be neuroprotective in cases of seizures and strokes (Stetler et al., 2010).
Sauna and exercise both increase the expression of HSPs, likely through the effects of hyperthermia at temperatures >38.5°C (101.3°F) (Hunt et al., 2019). To what extent elevated HSPs confer a benefit is unclear, but some passive heat exposure studies in rats and humans (serum) have observed that a 30-40% increase in HSP was associated with conserved muscle mass and greater mitochondrial function (Yoshihara et al., 2013; McGorm et al., 2018).
Hormonal Changes with Sauna Use: Short-Term Boosts in Growth Hormone, Testosterone, and CortisolSimilar to aerobic or strength training, sauna increases growth hormone concentration in the short term, often by about 2- to 5-fold (Kukkonen-Harjula et al., 1989). Some studies have also reported small increases in testosterone while others have shown mixed effects on cortisol (Laukkanen & Kunutsor, 2024).
These effects seem similar to that of exercise, as they last only a few hours and do not seem additive when combined with exercise. For instance, one study did not observe an additional increase in GH, testosterone, or cortisol with the addition of sauna following endurance, strength, or a combined workout (Rissanen et al., 2020). The Detoxifying Power of Sweating: How Sauna and Exercise Aid Heavy Metal ExcretionSweating is often touted as a method to aid heavy metal detoxification. Research suggests that sweat can enhance the excretion of certain metals like aluminum (3.75-fold), cadmium (25-fold), cobalt (7-fold), and lead (17-fold) compared to urine (Genuis et al., 2011). However, the effectiveness and composition of sweat can differ based on whether it’s induced by passive hyperthermia (sauna) or active hyperthermia (exercise).
A small study (Kuan et al., 2022) found that sweat from exercise had higher concentrations of metals like nickel, lead, copper, and arsenic compared to sauna sweat, while mercury levels were similar. This difference likely stems from the greater metabolic activity during exercise, which mobilizes more toxins. In contrast, sauna-induced sweating primarily serves thermoregulation, potentially leading to lower concentrations of some metals.
There is evidence suggesting that dementia may be associated with elevated levels of certain heavy metals in the brain. For example, studies have identified higher concentrations of aluminum, mercury, and lead in individuals with Alzheimer’s disease, pointing to a potential link between metal accumulation and neurodegeneration. While cohort studies from Finland have shown a correlation between frequent sauna use and lower rates of dementia, it remains unclear whether this benefit is directly related to heavy metal excretion or other factors, such as improved cardiovascular health and reduced inflammation. It is important to note that the majority of heavy metals are excreted through stool, with smaller amounts eliminated via urine and sweat. In cases of significantly elevated heavy metal levels, chelation therapy remains the gold standard for treatment.
Safety And Precautions Of Heat Exposure: Risks, Contraindications, And Special ConsiderationsRisks in Extreme Competition:
Death and serious health issues can occur during high-intensity competitions in hot environments, especially when participants push their physical limits.
Pregnancy:
Exposure to extreme heat during pregnancy has been linked to central nervous system birth defects, such as anencephaly and spina bifida, and the suggested teratogenic threshold for core body temperature is 39.0 °C (102.2 °F) (Graham et al., 1998).
Contraindications:
Hydration and Electrolyte Balance: Dehydration is a common risk during heat exposure, which can lead to complications like heat stroke and fainting. Adequate water and electrolyte intake is essential, especially during prolonged sauna sessions or intense exercise.
Age-Related Risks: Older adults are more susceptible to heat-related complications due to decreased cardiovascular resilience and sweat function. Additional caution is advised for this population. Children are more vulnerable to heat exposure due to their underdeveloped thermoregulation, higher risk of dehydration, and reduced sweating efficiency. They are also less aware of their physical limits, increasing the risk of heat-related illnesses like heat exhaustion or heat stroke. For young children, especially under 6, sauna sessions should be brief (5-10 minutes) at lower temperatures, with close supervision and regular hydration. Gradual acclimatization and education on hydration and rest are key to minimizing risks.
Chronic Health Conditions: Individuals with conditions such as diabetes, multiple sclerosis, or autonomic dysfunction may have reduced heat tolerance. Consultation with a healthcare provider is recommended before engaging in sauna use or intense heat exposure.
Acclimatization: Gradually increasing exposure to heat, starting with shorter sessions at lower temperatures, can improve tolerance and reduce risks, particularly for those new to saunas or hot environments.
Medication Interactions:
It is important to consider that there are life-threatening medication-related hyperthermia syndromes in psychiatry, but that these are not caused by heat exposure (Ahuja & Cole, 2018). These include: Neuroleptic Malignant Syndrome (NMS) Serotonin Syndrome Malignant (or Lethal) Catatonia (often linked to antipsychotics and mood stabilizers) Anticholinergic Toxicity Syndrome Stimulant (cocaine, amphetamine) toxicity Malignant Hyperpyrexia (typically due to anesthetic agents like succinylcholine and inhalational anesthetics) Parkinsonism–Hyperpyrexia Syndrome (can occur with withdrawal from dopamine agonists or abrupt changes in Parkinson’s medication) Thyrotoxicosis (Thyroid Storm) (exacerbated by certain medications like amiodarone)
However, other medications can impact heat tolerance and have been associated with higher risk of adverse heat events (heat exhaustion, heat stroke, dehydration) and greater morbidity in the elderly and in people with predisposing cardiovascular conditions according to a limited number of case studies and case-control studies (Bongers et al., 2020; Kalisch Ellett et al., 2016):
Cardiovascular drugs Diuretics, which increase dehydration risk. ACE inhibitors, which can impair thirst. Propranolol, a beta-blocker, increases sweating and therefore fluid replacement is essential. Vasodilators like nitroglycerin, hydralazine, isosorbide dinitrate lower blood pressure by relaxing blood vessels, which can dissipate body temperature, but can lead to hypotension and syncope.
GLP-1 inhibitors impair thirst. NSAIDs, potentially through altering prostaglandin signaling, which is known to be important for generating a fever. Anticholinergics (amitriptyline, oxybutynin, diphenhydramine, benztropine) and drugs with anticholinergic activity (tricyclic antidepressants, clozapine, olanzapine, quetiapine, chlorpromazine, and thioridazine) can impair sweating. Antipsychotics, especially first generation through their high-affinity for D2 receptors, can cause hyperthermia through neuroleptic malignant syndrome (NMS) and potentially through non-NMS mechanisms by affecting the hypothalamus, the body’s principal heat regulator. SSRIs can impair thermoregulation of the hypothalamus and increase risk of hyponatremia related to SIADH, particularly in the elderly taking fluoxetine or citalopram (Chiu et al., 2020; Kirpekar & Joshi, 2005).
AcknowledgementsWe extend our gratitude to Dr. Rhonda Patrick, Dr. Jari Laukkanen, and Dr. Setor Kunutsor for their insightful reviews on sauna and heat therapy (Patrick & Johnson, 2021;Laukkanen & Kunutsor, 2024), which played a crucial role in shaping this episode. References:Ahuja, N., & Cole, A. J. (2009). Hyperthermia syndromes in psychiatry. Advances in Psychiatric Treatment, 15(3), 181–191. doi:10.1192/apt.bp.107.005090 Anderson, R. J., Freedland, K. E., Clouse, R. E., & Lustman, P. J. (2001). The prevalence of comorbid depression in adults with diabetes: a meta-analysis. Diabetes care, 24(6), 1069– |
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