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Longevity Library · Lab reference

Written by Daniel Tagge, MD
Updated October 23, 2026
Reviewed October 24, 2026
47 sources · Measured in sessions per week

System: Mitochondria & Cellular Energy

Heat and saunaSauna bathing · Passive heat therapy · Heat exposure

In one Finnish cohort of 2,315 middle-aged men followed about 21 years, those who reported 4 to 7 sauna sessions a week had a 63 percent lower risk of sudden cardiac death than those who reported 1 a week, with the same direction for fatal coronary disease, fatal cardiovascular disease and all-cause mortality, and the same cohort later showed lower hypertension, dementia, stroke, pneumonia and respiratory disease with frequent sauna use. The evidence is strong in direction and weak in breadth: nearly all of it is one population of Finnish men who answered a questionnaire once in the 1980s, no trial has tested sauna against any hard outcome, and the trials that exist are small and short and show lower blood pressure, better vessel function and, in a few, lower fasting glucose.

Heat is an old stressor the body is built to answer: sweating, a faster heart, more blood to the skin, and over weeks a larger plasma volume and a primed cellular stress response. The Finnish cohort data are the most consistent lifestyle association on this shelf after fitness itself, and the most narrowly sourced: one cohort of middle-aged men, one questionnaire, no trial of hard outcomes. The small trials show what a session does to blood pressure and vessels and what eight weeks does to glucose in people who cannot exercise. The safety record is good for most adults, worse with alcohol, and a session changes the blood drawn the next morning.

01 · The scale

Where the laboratory range and the evidence sit.

One Finnish cohort of middle-aged men: 4 to 7 sessions a week against 1 carried hazard ratios of 0.37 for sudden cardiac death, 0.54 for new hypertension, 0.34 for dementia and 0.59 for respiratory disease over 20 to 25 years; in its men-and-women sample, 0.23 for cardiovascular death and 0.39 for stroke. Fitness and sauna together beat either alone. No trial has measured a hard outcome; the trials show lower blood pressure, better vessel function and, in small groups, lower fasting glucose.

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  1. Range the Finnish cohort studied, by one questionnaire at baseline

    1 and above sessions per week · KIHD, 1984 to 1989 (Laukkanen 2015)

  2. None: 43 of 1,688 in the men-and-women sample, too few to estimate

    0 to 0 sessions per week · Laukkanen 2018

  3. 1 a week: the reference group in every Finnish analysis

    1 to 1 sessions per week · Laukkanen 2015

  4. 2 to 3 a week: hazard ratios 0.7 to 0.8 for most outcomes, confidence intervals usually crossing 1

    2 to 3 sessions per week · Laukkanen 2015; Zaccardi 2017; Laukkanen 2017

  5. 4 to 7 a week: hazard ratios 0.2 to 0.6 for death, hypertension, dementia, stroke and respiratory disease

    4 and above sessions per week · Laukkanen 2015; Laukkanen 2018; Kunutsor 2018

  • Laboratory range
  • Evidence supports
  • Guideline goal or unstudied
Scale in sessions per week. The Finnish cohort asked, once at baseline, how many times a week a person took a sauna, how long each sitting lasted and how hot the room was. Its authors describe the traditional Finnish sauna as dry air with a relative humidity of 10 to 20 percent and a recommended temperature of 80 to 100 °C at the level of the bather's head, with sittings that usually run 5 to 20 minutes; the mean temperature its participants reported was about 76 °C, and the authors write that their findings cannot be directly applied to steam rooms and warm water therapy, which operate at lower temperatures and do not allow the humidity changes of water on heated rocks. Infrared cabins, hot tubs and hot baths are different exposures with far less data; where this entry quotes them, it says so. Bands show where studies found something, not a recommendation for any one person.

02 · What it is

What heat and sauna does.

Sauna bathing is short passive exposure to high air temperature, typically 45 to 100 °C depending on the kind of sauna, producing mild hyperthermia and a thermoregulatory response that is neuroendocrine, cardiovascular and cytoprotective at once; repeated exposure acclimates the body to heat, a pattern the field describes as hormesis. The traditional Finnish sauna, the one the outcome data come from, is dry air at a relative humidity of 10 to 20 percent with a recommended temperature of 80 to 100 °C at head height and about 30 °C at the floor, with sittings that usually last 5 to 20 minutes and brief rises in humidity when water is thrown on the heated rocks.1,2,3Grade C

The physiology during a sitting looks like moderate exercise. In 102 adults with at least one cardiovascular risk factor, one 30-minute session at 73 °C raised heart rate from 65 to 81 beats a minute, lowered systolic blood pressure from 137 to 130 mm Hg and diastolic from 82 to 75, lowered mean arterial pressure from 99.4 to 93.6 and reduced carotid-femoral pulse wave velocity, a measure of arterial stiffness, from 9.8 to 8.6 meters a second, with systolic pressure still lower 30 minutes later. In 34 patients with heart failure studied with a catheter in the pulmonary artery, a 15-minute sauna at 60 °C raised heart rate by 20 to 25 beats a minute and the blood temperature in the pulmonary artery by 1.2 °C, raised cardiac and stroke indexes and lowered systemic vascular resistance and the filling pressures of the heart. The investigators of the hot water trials make the same comparison: the rise in core temperature, cardiac output and vascular shear stress is similar to exercise. The Finnish group's own review lists the mechanisms it postulates for the long-term associations: improved endothelium-dependent dilatation, reduced arterial stiffness, modulation of the autonomic nervous system, changes in circulating lipids and lower systemic blood pressure, each of them postulated rather than proved.4,5,6,7,8Grade C

The reason a physician cares is one cohort. The Kuopio Ischaemic Heart Disease Risk Factor Study enrolled 2,315 men aged 42 to 60 from Eastern Finland between 1984 and 1989, asked them once how often, how long and how hot they took a sauna, and followed them a median of 20.7 years. Every mortality, hypertension, dementia, stroke, pneumonia and inflammation finding on this page comes from that cohort or from its later sample of 1,688 men and women, with one further Finnish survey cohort for dementia. The direction is consistent across every outcome; the population is one country, one sex for most analyses, one decade of enrollment and one questionnaire, which is why nothing here is graded A.9,2,10Grade B

03 · Origins

Where it came from, and where it sits in the network.

Humans are the sweating ape. The evolutionary reading is that early hominins in open habitats benefited from an unusual ability to dump heat, which let them forage safely in the heat of the day when predators could not hunt, and that endurance running evolved later for scavenging and then hunting, with strong selection for heat-loss mechanisms, above all sweating, to run prey into hyperthermia; modern humans remain furless, striding bipeds adapted to shed heat rather than retain it. Beneath that whole-body story sits an older one: cells from nearly all organisms respond to heat and other stresses by rapidly making a highly conserved set of proteins, the heat shock proteins, which are needed for survival at normal as well as raised temperatures and protect against damage from ischemia, cytokines and energy depletion, which is why the same proteins are discussed in exercise, oxidative stress, metabolic challenge and aging.11,12Grade C

Repeated heat changes the body the way training does. Heat acclimation improves sweating and skin blood flow, lowers body temperature at rest and during work, reduces cardiovascular strain, improves fluid balance, alters metabolism and enhances cellular protection, with the size of each adaptation set by the intensity, duration, frequency and number of exposures and by whether the heat is dry or humid. The cardiovascular side of that adaptation is an increase in total body water, an expansion of plasma volume, a better-sustained or higher stroke volume and a lower heart rate; repeated heat exposure expands plasma volume without changing red cell volume, and dehydration does the opposite. In six competitive distance runners, three weeks of sitting in a humid sauna at about 90 °C for about 31 minutes after training, on about 13 occasions, expanded plasma volume by 7.1 percent and lengthened a run to exhaustion by 32 percent against control, a change the authors equate to about 1.9 percent in a time trial and attribute to the larger blood volume.13,14,15,16Grade C

On this shelf, heat sits beside aerobic fitness and upstream of blood pressure, the vessel wall and, in small studies, glucose. Eight weeks of hot water immersion four to five times a week, in 20 young sedentary adults with a thermoneutral sham group, doubled flow-mediated dilation of the brachial artery from 5.6 to 10.9 percent, lowered aortic pulse wave velocity from 7.1 to 6.1 meters a second, thinned the carotid intima-media from 0.43 to 0.37 mm and lowered mean arterial pressure from 83 to 78 mm Hg, with no change in the sham group; the authors call the changes on par with or greater than exercise training in sedentary people. A single hour in 39 °C water raised plasma nitrite, a marker of nitric oxide availability, from 271 to 391 nM in ten overweight men, and a two-week course of ten immersions lowered their fasting glucose from 4.44 to 3.98 mmol/L and fasting insulin from 68.1 to 55.0 pmol/L against matched controls. Serum drawn from ten people after eight weeks of that immersion, added to cultured endothelial cells, prevented the NF-κB activation and blunted the superoxide burst of a hypoxia-reoxygenation challenge, as did 24 hours at 39 °C, which is cell-culture evidence that the protection travels in the blood as well as in the temperature. Those are hot baths, not saunas, and ten and twenty people, not cohorts; they show the direction of the mechanism and the markers it touches, which is why fasting insulin, fasting glucose and hs-CRP are linked from this page.7,17,18,19Grade C

04 · The usual guidance

What the guidelines say.

No guideline sets a dose. The Finnish cohort's own categories were 1, 2 to 3 and 4 to 7 sessions a week in a traditional sauna, recommended at 80 to 100 °C at head height, with sittings that usually run 5 to 20 minutes (Laukkanen 2015; Laukkanen 2018).

No professional society has issued a guideline on sauna frequency, duration or temperature, and the systematic review of regular dry sauna studies ends by asking for more data on the frequency and extent of adverse effects and for work to determine the optimal frequency and duration of distinct types of sauna bathing for targeted effects and the populations most likely to benefit. The categories a reader will meet everywhere, 1, 2 to 3 and 4 to 7 sessions a week, are the Finnish cohort's questionnaire groups, chosen for analysis; they are a description of how Eastern Finnish men bathed in the 1980s, not a prescription.20,9Grade C

In the original cohort of 2,315 men, 601 reported one session a week, 1,513 two to three and 201 four to seven, and sitting length was grouped as under 11, 11 to 19 and over 19 minutes. In the later men-and-women sample weekly time in the sauna was grouped as 15 minutes or less, 16 to 45 and more than 45 minutes, and the 43 participants who used no sauna at all were too few to analyze separately, so the one-a-week group is the reference in every Finnish analysis; the cohorts cannot say what no sauna at all does, because almost everyone in Finland takes one.9,2Grade B

05 · The evidence

What the studies support.

The founding analysis followed 2,315 men aged 42 to 60 for a median of 20.7 years, during which 190 died suddenly of cardiac causes, 281 of coronary heart disease, 407 of cardiovascular disease and 929 of any cause. Sudden cardiac death occurred in 10.1 percent of men who reported one sauna a week, 7.8 percent of those who reported two to three and 5.0 percent of those who reported four to seven; all-cause mortality was 49.1, 37.8 and 30.8 percent. After adjustment for cardiovascular risk factors the hazard ratio for sudden cardiac death was 0.78 (95 percent confidence interval 0.57 to 1.07) for two to three sessions and 0.37 (0.18 to 0.75) for four to seven, with a trend p of .005, and similar associations with fatal coronary disease, fatal cardiovascular disease and all-cause mortality. Sitting length mattered too: against under 11 minutes, sessions over 19 minutes carried a hazard ratio of 0.48 (0.31 to 0.75) for sudden cardiac death, with inverse associations for fatal coronary and cardiovascular disease but not for all-cause mortality. This is graded B, not A: it is one prospective cohort in one population with exposure measured once by questionnaire, and no second population or trial has reproduced the mortality finding.9Grade B

Women were added in a later sample of the same study: 1,688 participants with a mean age of 63 (range 53 to 74), 51.4 percent women, followed a median of 15.0 years with 181 fatal cardiovascular events. Cardiovascular mortality fell linearly with sessions a week with no threshold; against one session a week, the age- and sex-adjusted hazard ratios were 0.71 (0.52 to 0.98) for two to three and 0.30 (0.14 to 0.64) for four to seven, and after adjustment for established risk factors, physical activity, socioeconomic status and incident coronary disease they were 0.75 (0.52 to 1.08) and 0.23 (0.08 to 0.65). Minutes a week were inversely associated in a continuous manner, and adding sauna frequency to a risk model built from the usual factors improved its C-index by 0.0091 and reclassified 4.14 percent of participants. The mean reported sauna temperature was about 76 °C. This is still the same Finnish study, a different sample of it, so it extends the finding to women without making it a second population.2Grade B

Blood pressure is the most plausible path, and the cohort shows it. Among 1,621 men without hypertension at baseline, 251 (15.5 percent) developed it over a median of 24.7 years, defined as a physician diagnosis, a systolic pressure over 140 or diastolic over 90 mm Hg, or treatment. Against one session a week, the hazard ratio adjusted for age, smoking, body mass index and baseline systolic pressure was 0.76 (0.57 to 1.02) for two to three sessions and 0.54 (0.32 to 0.91) for four to seven, and after further adjustment for glucose, creatinine, alcohol, heart rate, family history, socioeconomic status and cardiorespiratory fitness, 0.83 (0.59 to 1.18) and 0.53 (0.28 to 0.98). The acute experiment agrees: one 30-minute session lowered systolic pressure by 7 mm Hg and diastolic by 7 in 102 adults with a risk factor, and systolic pressure was still below baseline half an hour later.21,5Grade B

Dementia was the finding that traveled furthest. In the 2,315 men, 204 were diagnosed with dementia and 123 with Alzheimer's disease over the median 20.7 years; against one session a week, the hazard ratio adjusted for age, alcohol, body mass index, systolic pressure, smoking, diabetes, prior heart attack, resting heart rate and LDL cholesterol was 0.78 (0.57 to 1.06) for two to three sessions and 0.34 (0.16 to 0.71) for four to seven, and 0.80 (0.53 to 1.20) and 0.35 (0.14 to 0.90) for Alzheimer's disease. One other Finnish cohort has looked: 13,994 men and women aged 30 to 69 from the Finnish Mobile Clinic survey, followed 39 years with 1,805 dementia diagnoses, in whom sauna bathing 9 to 12 times a month against none or fewer than four carried a hazard ratio of 0.47 (0.25 to 0.88) over the first 20 years and 0.81 (0.69 to 0.97) over the whole follow-up. Two Finnish cohorts agree in direction; the effect shrank as follow-up lengthened in the second, and a cohort cannot separate men who sauna often from men well enough to.22,10Grade B

Stroke, pneumonia and chronic lung disease followed the same pattern. In 1,628 men and women aged 53 to 74 without prior stroke, 155 strokes occurred over a median of 14.9 years; four to seven sessions a week against one carried a hazard ratio of 0.39 (0.18 to 0.83) adjusted for age and sex, 0.39 (0.18 to 0.84) after cardiovascular risk factors and 0.38 (0.18 to 0.81) after physical activity and socioeconomic status, unmodified by age or sex, similar for ischemic stroke and weaker for the 34 hemorrhagic strokes. In 1,935 men followed 25.6 years with 379 hospital-diagnosed cases of chronic obstructive pulmonary disease, asthma or pneumonia, two to three and four or more sessions a week carried hazard ratios of 0.73 (0.58 to 0.92) and 0.59 (0.37 to 0.94) against one or fewer; for pneumonia alone in 2,210 men with 375 cases, 0.72 (0.57 to 0.90) and 0.63 (0.39 to 1.00) after adjustment that included energy intake, socioeconomic status, physical activity and C-reactive protein.23,24,25Grade B

Sauna and fitness are independent in the cohort and best together. Among 2,277 men whose cardiorespiratory fitness was measured by respiratory gas analysis and followed a median of 26.1 years, with 520 cardiovascular and 1,124 all-cause deaths, high against low fitness carried hazard ratios of 0.51 (0.41 to 0.63) for cardiovascular and 0.65 (0.57 to 0.75) for all-cause mortality, and three to seven sauna sessions a week against two or fewer carried 0.74 (0.59 to 0.94) and 0.84 (0.72 to 0.97). Against low fitness with infrequent sauna, high fitness with frequent sauna carried 0.42 (0.28 to 0.62) for cardiovascular and 0.60 (0.48 to 0.76) for all-cause mortality, high fitness alone 0.50 and 0.63, and frequent sauna alone 0.72 and 0.78. For sudden cardiac death in 2,291 men with 226 events, the figures were 0.31 (0.16 to 0.63) for both, 0.49 (0.34 to 0.70) for fitness alone and 0.71 (0.45 to 1.10) for sauna alone. Fitness is the larger factor; sauna adds to it rather than replacing it, and the group's 2023 review frames frequent sauna the same way, as something that may augment protective factors such as physical activity and fitness and attenuate risk factors such as high blood pressure and inflammation, on evidence it describes as largely observational.26,27,28Grade B

Inflammation moves with sauna frequency in the cohort and seems to mark who benefits. Among 2,269 men, four to seven sessions a week against one went with hs-CRP 0.84 mg/L lower (95 percent confidence interval 0.14 to 1.55 lower) and a leucocyte count 0.28 billion per liter lower at baseline after adjustment, and 1.66 mg/L and 0.49 billion per liter lower when remeasured 11 years later, with fibrinogen lower at 11 years and no association with GGT, the oxidative-stress marker. In 2,575 men followed a median of 27.8 years with 1,618 deaths, an hs-CRP above 3 mg/L carried a hazard ratio of 1.27 (1.13 to 1.44) for all-cause mortality and frequent sauna 0.86 (0.76 to 0.97); men with high hs-CRP who used the sauna two or fewer times a week had a hazard ratio of 1.28 (1.12 to 1.47), and men with high hs-CRP who used it three to seven times a week 1.06 (0.81 to 1.40), which the authors read as frequent sauna offsetting the mortality risk of inflammation. Both are associations in the same men; hs-CRP has its own entry on this shelf.29,3Grade B

The only randomized trial of a Finnish sauna against a hard-ish endpoint is small and recent. Forty-seven sedentary adults aged about 49 with at least one cardiovascular risk factor were randomized to eight weeks of guideline-based exercise followed by a 15-minute sauna, exercise alone, or control; the sauna started at 65 °C and rose 5 °C a fortnight at 10 to 20 percent humidity. Exercise alone raised cardiorespiratory fitness by 6.2 mL/kg/min (4.2 to 8.3) against control and reduced fat mass without changing blood pressure; adding the sauna raised fitness a further 2.7 mL/kg/min (0.2 to 5.3), lowered systolic pressure by 8.0 mm Hg (1.4 to 14.6) and lowered total cholesterol against exercise alone. The authors call for dose-response work on duration and frequency, which has not yet been done.30Grade B

Heat as therapy has been studied longest in heart failure, where it began as a contradiction. The Kagoshima group showed in 1995 that a 15-minute sauna at 60 °C improved hemodynamics in 34 patients with chronic heart failure, most in New York Heart Association class III or IV with a mean ejection fraction of 25 percent, by lowering preload and afterload, with plasma norepinephrine rising during the sauna and returning to baseline by 30 minutes after it. In 20 patients in class II or III, two weeks of daily 60 °C dry sauna for 15 minutes followed by 30 minutes under blankets improved symptoms in 17, increased flow-mediated dilation of the brachial artery without changing nitroglycerin-induced dilation, and lowered plasma brain natriuretic peptide, with none of these changing in 10 matched untreated patients. The same regimen in 25 young men with coronary risk factors raised flow-mediated dilation from 4.0 to 5.8 percent against 8.2 percent in healthy controls, again without changing nitroglycerin dilation, which places the effect in the endothelium. These are 60 °C cabins, some far infrared, used under supervision in sick people, and they are the origin of the vascular mechanism, not evidence about a hot Finnish sauna in a healthy adult.6,31,32Grade C

In people who cannot or do not exercise, hot water does some of what exercise does to the markers on this shelf. In 18 women with obesity and polycystic ovary syndrome (mean age 27, body mass index 41), 30 one-hour hot tub sessions over 8 to 10 weeks lowered fasting glucose from 105 to 89 mg/dL, lowered the glucose and insulin areas under a two-hour tolerance test, increased insulin signaling in fat biopsies and lowered serum testosterone from 51 to 34 ng/dL, with no change in body mass index and no change in the time controls; in the same women it lowered muscle sympathetic nerve activity from 20 to 13 bursts a minute, systolic pressure from 124 to 114 and diastolic from 77 to 68 mm Hg, C-reactive protein, total cholesterol and carotid wall thickness, and improved flow-mediated dilation after an ischemia-reperfusion challenge from 5.6 to 9.5 percent. Nine treated women and nine controls, assigned rather than randomized, in one laboratory: a mechanism and a direction, graded accordingly.33,34Grade C

06 · What moves it

The levers with evidence behind them.

What is listed here has been tested. The size of each effect, and the size of the study, are in the sentence, so a small effect reads as a small effect.

  • Frequency, as the cohort describes it

    the cohort's risk fell with each step from 1 to 2 to 3 to 4 to 7 sessions a week; no trial has tested a dose

    Every Finnish analysis uses the same three groups, and in every one the middle group sits between the reference and the frequent group: hazard ratios of 0.78 and 0.37 for sudden cardiac death, 0.76 and 0.54 for new hypertension, 0.78 and 0.34 for dementia, 0.73 and 0.59 for respiratory disease, in each case for two to three and four to seven sessions a week against one. In the men-and-women sample cardiovascular mortality fell linearly with sessions a week with no threshold, and minutes a week were inversely associated in a continuous manner. That is a dose-response in a questionnaire, which strengthens the association without proving it; the one randomized trial used a single 15-minute sauna after each exercise session for eight weeks and its authors say the dose-response work remains to be done.9,21,22,24,2,30Grade B

  • Sitting length and temperature, as the cohort describes them

    sittings over 19 minutes carried lower cardiac mortality than sittings under 11 in the men; the sauna itself ran about 76 to 80 °C

    In the 2,315 men, sessions of 11 to 19 minutes carried a hazard ratio of 0.93 (0.67 to 1.28) for sudden cardiac death against sessions under 11 minutes, and sessions over 19 minutes 0.48 (0.31 to 0.75), with the same direction for fatal coronary and cardiovascular disease and no association with all-cause mortality. The room was a traditional Finnish sauna: a recommended 80 to 100 °C at head height, about 30 °C at the floor, 10 to 20 percent relative humidity, a reported mean of about 76 °C and, in the authors' words, an average of approximately 80 °C, with sittings that usually run 5 to 20 minutes. The acute experiments used 73 °C for 30 minutes; the one trial started at 65 °C and rose to 80. Nobody has tested whether hotter or longer is better; the cohort describes what Finnish men did, and the trials describe what was tolerable for sedentary people with risk factors.9,2,3,5,30Grade B

  • After exercise

    adds to fitness and lowers systolic pressure beyond exercise alone in one trial; expands plasma volume and endurance in runners

    A 15-minute sauna after each guideline-based exercise session for eight weeks raised cardiorespiratory fitness by a further 2.7 mL/kg/min and lowered systolic pressure by a further 8.0 mm Hg against exercise alone in 47 sedentary adults with a risk factor. In six distance runners, three weeks of about 31 minutes in a humid 90 °C sauna straight after training expanded plasma volume by 7.1 percent and lengthened a run to exhaustion by 32 percent, with the performance gain tracking the plasma volume gain (correlation 0.96). In the cohort, men with high fitness who also used the sauna often had the lowest cardiovascular and all-cause mortality of any group. Heat is the cheapest addition to a training program with trial evidence behind it, and the evidence is for adding it, not substituting it.30,16,26Grade B

  • Hot water immersion, where there is no sauna

    the better-studied substitute in trials: vessel function, blood pressure and fasting glucose in sedentary people

    Nearly all of the controlled trial evidence for heat is hot water, not sauna: a 40.5 °C bath holding rectal temperature at or above 38.5 °C for 60 minutes, four to five times a week for eight weeks, in 20 young sedentary adults; 39 °C water for an hour, ten times in two weeks, in ten overweight men; 30 one-hour hot tub sessions over 8 to 10 weeks in 18 women with polycystic ovary syndrome. Those regimens improved flow-mediated dilation, arterial stiffness, blood pressure, fasting glucose and insulin in groups of ten to twenty, and the investigators present them as an option for people with limited exercise tolerance. A bath where you live reaches the physiology the trials measured; it is not the exposure the Finnish cohort measured, and its outcome data are none.7,17,33,19Grade C

  • Infrared cabins

    a lower-temperature exposure with its own small literature; the outcome data do not transfer

    Far infrared cabins run far cooler than a Finnish sauna: 60 °C in the Japanese heart failure and coronary-risk-factor studies, 43 °C in a recovery study of basketball players. A 2009 summary of nine papers found limited moderate evidence that far infrared saunas lower blood pressure and help heart failure, fair evidence from one study each for chronic pain and weak evidence for chronic fatigue and obesity, and consistent fair evidence refuting manufacturers' cholesterol claims. In 16 basketball players, 20 minutes of infrared sauna at about 43 °C after heavy resistance exercise, against passive rest in a randomized crossover, attenuated the fall in jump performance 14 hours later, reduced muscle soreness and raised perceived recovery, with heart rate variability lower during the session and no difference overnight. None of the Finnish mortality, dementia or stroke data were collected in infrared cabins, and the cohort authors say their findings cannot be directly applied to lower-temperature exposures.35,32,36,2Grade C

  • Hydration and the blood drawn the next morning

    a session concentrates the blood for hours; repeated sessions expand plasma volume over weeks

    One sauna sitting at room-temperature recovery cost nine men a mean of 544 g in sweat and 5.6 percent of their plasma volume, and more (7.2 to 8.0 percent) when followed by ice water or a cold shower. In 102 adults, plasma creatinine rose slightly from the end of a 30-minute session through 30 minutes of recovery while sodium and potassium held, and in a subset of 20, NT-proBNP rose 12 percent immediately after and 14 percent at 30 minutes, with no overall change in hs-CRP, creatine kinase or troponin and a 3 percent rise in creatine kinase in men. In 16 young men, plasma volume fell after each session and then showed an adaptive increase after a series of ten, the same expansion the runners and the heat-acclimation literature describe. Over decades the cohort found no association between frequent sauna and eGFR, creatinine, sodium or chronic kidney disease (hazard ratio 0.84, 0.46 to 1.53, for four to seven sessions a week against one over 25.7 years in 2,071 men). The practical reading is that a hematocrit, creatinine or sodium drawn within hours of a sauna reads the sweat, not the kidney; the same markers have their own entries here.37,5,38,39,40Grade C

  • Cooling between rounds

    cold after heat is traditional and dropped plasma volume further in the one measurement; the cohort did not record it

    The Finnish habit of a cold plunge or shower between sauna rounds has almost no outcome data of its own. In the nine-man fluid-balance study, sauna followed by head-out ice water or a 15 °C shower reduced plasma volume by 7.2 and 8.0 percent against 5.6 percent for sauna with room-temperature recovery, which the author attributed to transient fluid shifts in the skin, and cold water alone changed it by 1.3 percent, not significant. The Finnish cohort questionnaires asked about the sauna, not what followed it, so none of the hazard ratios on this page can be credited to or against cooling.37,2Grade C

  • What it does to lipids

    small, transient falls in total and LDL cholesterol in a few studies; not a lipid treatment

    In 16 physically active men aged 20 to 23, ten sessions in a 90 °C Finnish sauna over about three weeks, each three 15-minute rounds with two-minute cool-downs, lowered total and LDL cholesterol during the series and the week after, with a transient fall in triglycerides and a small nonsignificant rise in HDL, and the levels returned toward baseline over the following two weeks. The eight-week trial found lower total cholesterol with exercise plus sauna than with exercise alone. The infrared review found consistent evidence against cholesterol claims for that modality. Read beside the ApoB and LDL entries, this is a marker that moves a little while the habit continues, not a reason to take up the sauna.39,30,35Grade C

  • Sleep

    widely reported, barely measured

    In a global online survey of 482 regular sauna users, half of them men, who bathed about once or twice a week, 83.5 percent reported sleep benefits after sauna use, and relaxation was the leading reason given for bathing; in a 1988 survey of 1,600 middle-aged Finns, sauna, shower and bath were among the factors people named as helping sleep, behind exercise, reading and music. Both are self-report from people who already like the sauna. No cohort or trial on this page measured sleep with a recorder after sauna; the one infrared recovery study found no difference in overnight heart rate or heart rate variability.41,42,36Grade D

07 · Reading it well

Caveats, and what belongs with a physician.

Nearly all of the outcome evidence is one cohort in one population. The mortality, hypertension, dementia, stroke, pneumonia and inflammation findings come from the Kuopio Ischaemic Heart Disease Risk Factor Study, men aged 42 to 61 from Eastern Finland enrolled in 1984 to 1989, with sauna habits reported once on a questionnaire and never remeasured, or from its later sample of 1,688 men and women; the only independent cohort is a second Finnish survey, for dementia alone. The investigators themselves note that self-administered questionnaires are prone to misclassification and recall bias. A habit this woven into one culture is also woven into everything else about a person there, and a cohort cannot fully unpick that; the consistency of direction across outcomes earns a B, and the single population is why no claim here is an A.9,2,10Grade B

Reverse causation is the specific worry. Men who are already ill, breathless, frail or unable to tolerate heat take fewer saunas, and the same men die sooner, develop dementia sooner and are admitted with pneumonia sooner. The cohort analyses adjusted for measured disease and risk factors and the one-a-week reference group is itself made of sauna users, which softens but does not remove the problem; the dementia effect in the second Finnish cohort weakened from a hazard ratio of 0.47 over the first 20 years to 0.81 over the whole follow-up, a pattern consistent with either a real but fading effect or with early reverse causation. The mortality findings have not been reproduced in any population outside Finland, and the one randomized sauna trial was eight weeks long and measured fitness and blood pressure, not events.10,9,30Grade B

The trial evidence is small, short, mostly hot water, and mostly from two laboratories. The vascular trial was 20 young sedentary adults, the glucose study ten overweight men, the polycystic ovary studies nine treated women and nine controls assigned rather than randomized, the heart failure study 20 patients with 10 matched controls, the runner study six men, and the sauna-plus-exercise trial 47 people for eight weeks; the systematic review of regular dry sauna found 40 studies with 3,855 participants, of which only 13 were randomized and most enrolled fewer than 40. The review of heat and vessels adds that beneficial findings are not unanimous and that methods vary too much to pool. These studies show what heat can do to a marker; they have not shown that it prevents anything.7,17,33,31,16,30,20,19Grade C

A session changes the blood drawn afterwards. Plasma volume fell 5.6 to 8.0 percent after one sitting in the fluid-balance study, plasma creatinine rose slightly through 30 minutes of recovery in 102 adults, NT-proBNP rose 12 to 14 percent, and creatine kinase rose 3 percent in men; hematocrit, hemoglobin, creatinine, sodium, albumin and anything else reported as a concentration will read high in blood drawn within hours of a sauna, and the longer-run adaptation is the opposite, a larger plasma volume that can read as slight dilution. A result that looks like dehydration or a kidney in trouble deserves the question of when the last sauna was before it earns a label; over 25 years the cohort found no effect of frequent sauna on kidney function.37,5,38,40Grade C

Death in the sauna is rare and usually involves alcohol. In Finland, with about 2 million saunas for 5.2 million people, deaths occurring in a sauna in 1990 to 2002 ran at under 2 per 100,000 inhabitants a year; 51 percent were natural deaths, heat was the cause in 25 percent, and 50 percent of the deceased were under the influence of alcohol. In Sweden, 77 sauna deaths in 1992 to 2003 were 82 percent men, mostly middle-aged, 71 percent of those tested were positive for alcohol, often at high concentrations, 44 percent were attributed to alcohol and 23 percent to cardiovascular disease, and all but two of those found dead were alone. The Finnish review states the rule: alcohol during sauna bathing increases the risk of hypotension, arrhythmia and sudden death and should be avoided. The alcohol entry on this shelf is the place to read about the rest.43,44,45Grade C

Some people need a conversation first. The Finnish medical review lists unstable angina, a recent heart attack and severe aortic stenosis as contraindications, and calls sauna safe for most people with stable coronary disease or an old heart attack; it reports very few heart attacks and sudden deaths in saunas. The heart failure work shows that even severe heart failure tolerated a 60 °C sauna under monitoring, which is an argument for supervision, not for independence. Anyone who feels faint standing up, is on medicines that lower blood pressure or drive fluid out, or has a condition that limits the heart's response to a faster rate and a lower pressure, is the person the acute hemodynamic data (heart rate 65 to 81, systolic pressure 137 to 130, diastolic 82 to 75 in 30 minutes) describe a risk for, and the cohort does not speak to them.45,6,4Grade C

Pregnancy and fertility are two different answers. A systematic review of 12 studies and 347 pregnant women found that none exceeded a core temperature of 39.0 °C, the threshold proposed for harm to the fetus, under any exposure studied; the highest mean end-of-session temperature in a sauna was 37.6 °C and the authors concluded that sitting in a 70 °C, 15 percent humidity sauna for up to 20 minutes, or a 40 °C bath, did not reach the threshold at any stage of pregnancy. The Finnish review likewise calls sauna safe in uncomplicated pregnancies of healthy women. The Finnish review also states that sauna does not influence fertility, but in 10 men with normal semen, two 15-minute sessions a week at 80 to 90 °C for three months strongly impaired sperm count and motility and sperm DNA packaging without changing sex hormones, and everything reversed within six months of stopping; the systematic review counts that as the one adverse effect reported across 40 studies. A couple trying to conceive has a reason to pause the sauna for the man, with a documented path back.46,45,47,20Grade C

Self-reported adverse effects are common and minor. In the global survey, 93.1 percent of reported reactions were minor, chiefly dizziness, dehydration and headache, and two respondents (0.3 percent) reported hospital visits for chest pain and eye irritation. The literature is sparse enough that the systematic review asks for more data on the frequency and extent of adverse effects before anything stronger can be said.41,20Grade C

See a physician

  • Chest pain or pressure, a racing or irregular heartbeat, faintness or a near-blackout in the sauna or in the hour after it; this is an evaluation before the next session, not a reason to sit nearer the door.
  • Known coronary disease with angina that is new, changing or occurring at rest, a heart attack in the last few months, heart failure, a heart valve problem (especially aortic stenosis), or an implanted device, before starting or resuming a sauna habit; most stable heart disease can sauna, and the plan should be made with someone who knows the heart in question.
  • Blood pressure medicines, water pills, nitrates, or any medicine that lowers blood pressure or causes dizziness on standing; the dose, the timing and the hydration around a session need adjusting, and that is a prescription conversation.
  • Pregnancy, when there is any question about fitness for heat, when the pregnancy has complications, or when the sauna is hotter or the sittings longer than the ones the evidence describes.
  • Trying to conceive, on the man's side, since three months of regular sauna measurably lowered sperm count and motility in the one study that looked, with recovery after stopping.
  • A hemoglobin, hematocrit, creatinine or sodium result that reads high or a kidney filtration estimate that reads low in someone who took a sauna within a day of the draw; the repeat timing matters more than the number.
  • Any sauna use with alcohol, or by someone who cannot be relied on to leave the heat when they should, including the very old, the very young and anyone who bathes alone.

This page is education, not individual medical advice, and reading it creates no physician-patient relationship.

08 · Open questions

What the literature does not settle.

  • Whether sauna causes any of what it is associated with. Every hard outcome on this page is an association from one Finnish cohort, and no trial has randomized people to sauna and counted deaths, strokes, dementia or pneumonia.
  • Whether the findings hold outside Finland. No cohort from another country has reproduced the mortality association; the culture, climate, diet and genetics of Eastern Finland in the 1980s travel with the habit in the data.
  • What the dose is. The cohort categories (1, 2 to 3, 4 to 7 sessions a week; under 11, 11 to 19, over 19 minutes; about 76 to 80 °C) describe what men did, and the one trial used a single 15-minute sauna after exercise; whether more or hotter is better, or when it turns harmful, has not been tested.
  • Whether hot water, infrared cabins and steam rooms deliver the same thing. The trials of vessel function and glucose are almost all hot water; the mortality data are all traditional dry sauna; nobody has compared them against each other for anything that lasts.
  • What the mechanism is. Lower blood pressure, better endothelial function, a larger plasma volume, lower inflammation and a primed heat shock response are each shown in small studies; which of them matters, and whether sauna adds anything to a person who is already fit and lean, is unknown, though in the cohort fit men who used the sauna often did best.
  • Whether women respond the same way. The men-and-women analyses come from one sample of 1,688 older adults; nearly every other number here is from men aged 42 to 61.
  • Whether sauna improves sleep when it is measured rather than asked about.

09 · In practice

How Dr. Tagge reads it in his own practice.

I use the sauna and I teach it, and I want to be plain about why, because the evidence here is lopsided. Nearly everything we know about outcomes comes from one group of Finnish men who were asked once, in the 1980s, how often they took a sauna, and then followed for twenty years. In those men the people who bathed most often died least, and the same men had less hypertension, less dementia, fewer strokes and less pneumonia. That is a remarkable set of associations, it points the same way every time, and it is still one cohort, one questionnaire and one culture. No trial has tested the sauna against any of those outcomes, and I will not pretend otherwise. What the small trials show is what a sitting does: the heart speeds up as it would on a brisk walk, blood pressure comes down and stays down for a while, the vessel lining works better, and over weeks the plasma volume expands the way it does with training. That physiology is why I take the sauna seriously as a tool rather than a comfort, and it is why I place it beside aerobic fitness rather than instead of it; the Finnish men who were fit and bathed often did best, and the ones who bathed often without being fit did least well of the three. I read heat against the markers I already watch. If someone's resting blood pressure is high, their hs-CRP is up and they do not sleep well, the sauna is one lever I reach for alongside the walk and the bedtime, and I expect it to show up in those numbers, not to be taken on faith. One marker is a clue and three are a story, and heat belongs in the story, not as its own chapter. There are people I talk with before they start: anyone with unstable angina or a heart attack in the last few months, anyone with significant aortic stenosis or heart failure, anyone who gets lightheaded standing up, anyone on blood pressure medicines or water pills whose timing may need to change, anyone pregnant, and anyone who intends to drink in there, which is where the rare deaths come from. I ask people to drink water before and after, to sit down and leave the moment they feel odd rather than tough it out, and never to bathe alone when alcohol is involved, which in my practice means never. I also ask for no sauna in the day before blood work, because a sitting concentrates the blood for hours and I have seen a hematocrit, a creatinine and a sodium read high for no reason but sweat. I will not give you a number of sessions or minutes of my own; the cohort's categories are the only numbers on this page and they belong to it, not to me. Where I am ahead of the evidence is in treating the sauna as part of a plan for someone who is not Finnish, not male and not middle-aged in 1985. I act on the physiology and the association together, I say so, and I would change my mind if a trial told me to.

A practice judgment, labeled as one (Grade D): it is how one physician reads the number for the people he cares for, not a recommendation for you.

10

Questions

11 · Sources

47 sources, read in full.

Numbered in the order they appear. Each line says what this page relies on from the paper; the link opens the record at PubMed or the publisher.

  1. 1.

    Patrick RP, Johnson TL. Sauna use as a lifestyle practice to extend healthspan. Experimental Gerontology. 2021. PMID 34363927. DOI 10.1016/j.exger.2021.111509.

    Review · A narrative review describing sauna use as short passive exposure to 45 to 100 °C depending on modality, producing mild hyperthermia and a neuroendocrine, cardiovascular and cytoprotective response, with repeated use acclimating the body to heat in a pattern attributed to hormesis; summarizes the cohort, interventional and mechanistic literature.

  2. 2.

    Laukkanen T, Kunutsor SK, Khan H, Willeit P, Zaccardi F, Laukkanen JA. Sauna bathing is associated with reduced cardiovascular mortality and improves risk prediction in men and women: a prospective cohort study. BMC Medicine. 2018. PMID 30486813. DOI 10.1186/s12916-018-1198-0.

    Prospective cohort · In 1,688 KIHD participants (mean age 63, 51.4 percent women) followed a median 15.0 years with 181 fatal cardiovascular events, 2 to 3 and 4 to 7 sessions a week against 1 carried fully adjusted hazard ratios of 0.75 (0.52 to 1.08) and 0.23 (0.08 to 0.65), with a linear decrease and no threshold; full text describes the traditional sauna (80 to 100 °C at head height, sittings 5 to 20 minutes, mean reported 76 °C) and the baseline questionnaire.

  3. 3.

    Kunutsor SK, Jae SY, Kurl S, Kauhanen J, Laukkanen JA. Inflammation, sauna bathing, and all-cause mortality in middle-aged and older Finnish men: a cohort study. European Journal of Epidemiology. 2022. PMID 36255556. DOI 10.1007/s10654-022-00926-w.

    Prospective cohort · In 2,575 KIHD men followed a median 27.8 years (1,618 deaths), hs-CRP above 3 mg/L carried a hazard ratio of 1.27 (1.13 to 1.44) and 3 to 7 sauna sessions a week 0.86 (0.76 to 0.97); high hs-CRP with infrequent sauna 1.28 (1.12 to 1.47) and high hs-CRP with frequent sauna 1.06 (0.81 to 1.40); full text describes the traditional Finnish sauna as 10 to 20 percent relative humidity, median frequency 2 sessions a week.

  4. 4.

    Lee E, Laukkanen T, Kunutsor SK, Khan H, Willeit P, Zaccardi F, Laukkanen JA. Sauna exposure leads to improved arterial compliance: Findings from a non-randomised experimental study. European Journal of Preventive Cardiology. 2018. PMID 29048215. DOI 10.1177/2047487317737629.

    Laboratory method study · In the same 102 adults, a 30-minute session at 73 °C raised heart rate from 65 to 81 beats a minute, lowered mean arterial pressure from 99.4 to 93.6 mm Hg and left ventricular ejection time from 307 to 278 ms, and lowered pulse wave velocity from 9.8 to 8.6 m/s immediately and 9.0 after 30 minutes of recovery.

  5. 5.

    Laukkanen T, Kunutsor SK, Zaccardi F, Lee E, Willeit P, Khan H, Laukkanen JA. Acute effects of sauna bathing on cardiovascular function. Journal of Human Hypertension. 2018. PMID 29269746. DOI 10.1038/s41371-017-0008-z.

    Laboratory method study · In 102 adults (mean age 51.9, 56 percent men) with at least one cardiovascular risk factor, one 30-minute session at 73 °C and 10 to 20 percent humidity lowered carotid-femoral pulse wave velocity from 9.8 to 8.6 m/s, systolic pressure from 137 to 130 and diastolic from 82 to 75 mm Hg, with systolic still lower at 30 minutes; plasma creatinine rose slightly through recovery while sodium and potassium held.

  6. 6.

    Tei C, Horikiri Y, Park JC, et al.. Acute hemodynamic improvement by thermal vasodilation in congestive heart failure. Circulation. 1995. PMID 7743620. DOI 10.1161/01.cir.91.10.2582.

    Laboratory method study · In 34 patients with chronic heart failure (mean ejection fraction 25 percent; NYHA class III in 19 and IV in 13) studied by pulmonary artery catheter, a 15-minute sauna at 60 °C or a 10-minute 41 °C bath raised heart rate 20 to 25 beats a minute and pulmonary artery blood temperature 1.2 °C, raised cardiac and stroke indexes, lowered systemic vascular resistance and, in the sauna, lowered filling pressures; norepinephrine rose during the sauna and normalized by 30 minutes.

  7. 7.

    Brunt VE, Howard MJ, Francisco MA, Ely BR, Minson CT. Passive heat therapy improves endothelial function, arterial stiffness and blood pressure in sedentary humans. Journal of Physiology. 2016. PMID 27270841. DOI 10.1113/JP272453.

    Randomized trial · In 20 young sedentary adults, 8 weeks of hot water immersion 4 to 5 times a week (40.5 °C, rectal temperature at or above 38.5 °C for 60 minutes) against thermoneutral sham raised flow-mediated dilation from 5.6 to 10.9 percent, lowered aortic pulse wave velocity from 7.1 to 6.1 m/s, carotid intima-media thickness from 0.43 to 0.37 mm and mean arterial pressure from 83 to 78 mm Hg, with no change in the sham group.

  8. 8.

    Laukkanen JA, Laukkanen T, Kunutsor SK. Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence. Mayo Clinic Proceedings. 2018. PMID 30077204. DOI 10.1016/j.mayocp.2018.04.008.

    Review · A review of observational, experimental and interventional studies of Finnish sauna bathing to February 2018, postulating improved endothelium-dependent dilatation, reduced arterial stiffness, autonomic modulation, lipid changes and lower blood pressure as mechanisms, and listing areas of outstanding uncertainty and implications for practice.

  9. 9.

    Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. Association between sauna bathing and fatal cardiovascular and all-cause mortality events. JAMA Internal Medicine. 2015. PMID 25705824. DOI 10.1001/jamainternmed.2014.8187.

    Prospective cohort · In 2,315 Finnish men aged 42 to 60 followed a median 20.7 years (190 sudden cardiac deaths, 929 deaths), 2 to 3 and 4 to 7 sauna sessions a week against 1 carried adjusted hazard ratios of 0.78 (0.57 to 1.07) and 0.37 (0.18 to 0.75) for sudden cardiac death, with similar associations for fatal coronary disease, fatal cardiovascular disease and all-cause mortality; sessions over 19 minutes against under 11 carried 0.48 (0.31 to 0.75) for sudden cardiac death.

  10. 10.

    Knekt P, Järvinen R, Rissanen H, Heliövaara M, Aromaa A. Does sauna bathing protect against dementia?. Preventive Medicine Reports. 2020. PMID 33088678. DOI 10.1016/j.pmedr.2020.101221.

    Prospective cohort · In 13,994 Finnish men and women aged 30 to 69 followed 39 years (1,805 dementia diagnoses), sauna bathing 9 to 12 times a month against none or fewer than 4 carried hazard ratios of 0.47 (0.25 to 0.88) over the first 20 years and 0.81 (0.69 to 0.97) over the whole follow-up.

  11. 11.

    Lieberman DE. Human locomotion and heat loss: an evolutionary perspective. Comprehensive Physiology. 2015. PMID 25589265. DOI 10.1002/cphy.c140011.

    Review · Humans are furless, striding bipeds adapted to walk and run long distances in heat; early hominins likely benefited from improved heat dumping to forage at peak heat, endurance running evolved later with strong selection for sweating to persistence hunt, and all humans remain adapted to dump rather than retain heat.

  12. 12.

    Kregel KC. Heat shock proteins: modifying factors in physiological stress responses and acquired thermotolerance. Journal of Applied Physiology. 2002. PMID 11960972. DOI 10.1152/japplphysiol.01267.2001.

    Review · Cells from nearly all organisms respond to stress by rapidly synthesizing a highly conserved set of heat shock proteins that are essential for survival at normal and raised temperatures, underlie thermotolerance and protect against damage from ischemia, cytokines and energy depletion, with roles in hyperthermia, exercise, oxidative stress, metabolic challenge and aging.

  13. 13.

    Périard JD, Racinais S, Sawka MN. Adaptations and mechanisms of human heat acclimation: Applications for competitive athletes and sports. Scandinavian Journal of Medicine and Science in Sports. 2015. PMID 25943654. DOI 10.1111/sms.12408.

    Review · Heat acclimation improves sweating, skin blood flow, fluid balance and cellular protection, lowers body temperatures and cardiovascular strain and alters metabolism, with the size of adaptation set by the intensity, duration, frequency and number of exposures and by dry or humid conditions.

  14. 14.

    Périard JD, Travers GJS, Racinais S, Sawka MN. Cardiovascular adaptations supporting human exercise-heat acclimation. Autonomic Neuroscience. 2016. PMID 26905458. DOI 10.1016/j.autneu.2016.02.002.

    Review · The cardiovascular adaptations to heat acclimation include an increase in total body water, plasma volume expansion, better sustained or higher stroke volume, lower heart rate, improved ventricular filling and myocardial efficiency, and enhanced skin blood flow and sweating.

  15. 15.

    Sawka MN, Convertino VA, Eichner ER, Schnieder SM, Young AJ. Blood volume: importance and adaptations to exercise training, environmental stresses, and trauma/sickness. Medicine and Science in Sports and Exercise. 2000. PMID 10694114. DOI 10.1097/00005768-200002000-00012.

    Review · Repeated heat exposure induces plasma volume expansion without altering erythrocyte volume; exercise training expands both; dehydration decreases plasma volume, raises plasma tonicity, elevates heat strain and reduces performance.

  16. 16.

    Scoon GS, Hopkins WG, Mayhew S, Cotter JD. Effect of post-exercise sauna bathing on the endurance performance of competitive male runners. Journal of Science and Medicine in Sport. 2007. PMID 16877041. DOI 10.1016/j.jsams.2006.06.009.

    Randomized trial · In a crossover of six male distance runners, three weeks of post-training sauna (89.9 ± 2.0 °C, 31 ± 5 minutes, 12.7 ± 2.1 occasions) increased run time to exhaustion by 32 percent (90 percent confidence limits 21 to 43), equivalent to about 1.9 percent in a time trial, and plasma volume by 7.1 percent (5.6 to 8.7), with performance change correlating 0.96 with plasma volume change.

  17. 17.

    Hoekstra SP, Bishop NC, Faulkner SH, Bailey SJ, Leicht CA. Acute and chronic effects of hot water immersion on inflammation and metabolism in sedentary, overweight adults. Journal of Applied Physiology. 2018. PMID 30335579. DOI 10.1152/japplphysiol.00407.2018.

    Randomized trial · In 10 sedentary overweight men, one hour in 39 °C water raised plasma interleukin-6 from 1.37 to 2.51 pg/mL and nitrite from 271 to 391 nM without changing monocyte heat shock protein 72; ten immersions over two weeks lowered fasting glucose from 4.44 to 3.98 mmol/L, fasting insulin from 68.1 to 55.0 pmol/L and extracellular Hsp72 by 17 percent against 8 matched controls.

  18. 18.

    Brunt VE, Wiedenfeld-Needham K, Comrada LN, Minson CT. Passive heat therapy protects against endothelial cell hypoxia-reoxygenation via effects of elevations in temperature and circulating factors. Journal of Physiology. 2018. PMID 30118148. DOI 10.1113/JP276559.

    Laboratory method study · In cultured endothelial cells, hypoxia-reoxygenation raised NF-κB activation by 106 percent, interleukin-6 release by 37 percent and superoxide by 272 percent; both 24 hours at 39 °C and serum from 10 people after 8 weeks of heat therapy prevented the NF-κB activation and attenuated superoxide, and only the serum attenuated interleukin-6, with heme oxygenase-1 rising as a possible mechanism.

  19. 19.

    Cheng JL, MacDonald MJ. Effect of heat stress on vascular outcomes in humans. Journal of Applied Physiology. 2019. PMID 30676869. DOI 10.1152/japplphysiol.00682.2018.

    Review · Heating studies show benefits for microvascular function, endothelial function and arterial stiffness, but findings are not unanimous, heating protocols and outcome measures vary, and mechanisms of acute and chronic heating are understudied; heat is proposed for aging, at-risk and exercise-limited populations.

  20. 20.

    Hussain J, Cohen M. Clinical Effects of Regular Dry Sauna Bathing: A Systematic Review. Evidence-Based Complementary and Alternative Medicine. 2018. PMID 29849692. DOI 10.1155/2018/1857413.

    Review · Forty clinical studies of regular dry sauna from 2000 onward with 3,855 participants, only 13 randomized and most under 40 participants, mostly reporting benefit; one study of 10 men reported reversible impairment of spermatogenesis; the authors ask for data on adverse effects and on optimal frequency and duration.

  21. 21.

    Zaccardi F, Laukkanen T, Willeit P, Kunutsor SK, Kauhanen J, Laukkanen JA. Sauna Bathing and Incident Hypertension: A Prospective Cohort Study. American Journal of Hypertension. 2017. PMID 28633297. DOI 10.1093/ajh/hpx102.

    Prospective cohort · In 1,621 KIHD men without hypertension followed a median 24.7 years (251 incident cases), 2 to 3 and 4 to 7 sessions a week against 1 carried hazard ratios of 0.76 (0.57 to 1.02) and 0.54 (0.32 to 0.91), and 0.83 and 0.53 after adjustment including cardiorespiratory fitness.

  22. 22.

    Laukkanen T, Kunutsor S, Kauhanen J, Laukkanen JA. Sauna bathing is inversely associated with dementia and Alzheimer's disease in middle-aged Finnish men. Age and Ageing. 2017. PMID 27932366. DOI 10.1093/ageing/afw212.

    Prospective cohort · In 2,315 KIHD men followed a median 20.7 years (204 dementia, 123 Alzheimer's diagnoses), 2 to 3 and 4 to 7 sessions a week against 1 carried adjusted hazard ratios of 0.78 (0.57 to 1.06) and 0.34 (0.16 to 0.71) for dementia and 0.80 and 0.35 for Alzheimer's disease.

  23. 23.

    Kunutsor SK, Khan H, Zaccardi F, Laukkanen T, Willeit P, Laukkanen JA. Sauna bathing reduces the risk of stroke in Finnish men and women: A prospective cohort study. Neurology. 2018. PMID 29720543. DOI 10.1212/WNL.0000000000005606.

    Prospective cohort · In 1,628 KIHD men and women aged 53 to 74 followed a median 14.9 years (155 strokes), 4 to 7 sessions a week against 1 carried a hazard ratio of 0.39 (0.18 to 0.84) after adjustment for cardiovascular risk factors and 0.38 (0.18 to 0.81) after physical activity and socioeconomic status, unmodified by age or sex.

  24. 24.

    Kunutsor SK, Laukkanen T, Laukkanen JA. Sauna bathing reduces the risk of respiratory diseases: a long-term prospective cohort study. European Journal of Epidemiology. 2017. PMID 28905164. DOI 10.1007/s10654-017-0311-6.

    Prospective cohort · In 1,935 KIHD men followed a median 25.6 years (379 hospital-diagnosed cases of COPD, asthma or pneumonia), 2 to 3 and 4 or more sessions a week against 1 or fewer carried hazard ratios of 0.73 (0.58 to 0.92) and 0.59 (0.37 to 0.94); for pneumonia 0.72 and 0.63.

  25. 25.

    Kunutsor SK, Laukkanen T, Laukkanen JA. Frequent sauna bathing may reduce the risk of pneumonia in middle-aged Caucasian men: The KIHD prospective cohort study. Respiratory Medicine. 2017. PMID 29229091. DOI 10.1016/j.rmed.2017.10.018.

    Prospective cohort · In 2,210 KIHD men followed a median 25.6 years (375 hospital-diagnosed pneumonias), 2 to 3 and 4 or more sessions a week against 1 or fewer carried hazard ratios of 0.72 (0.57 to 0.90) and 0.63 (0.39 to 1.00) after adjustment including energy intake, socioeconomic status, physical activity and C-reactive protein.

  26. 26.

    Kunutsor SK, Khan H, Laukkanen T, Laukkanen JA. Joint associations of sauna bathing and cardiorespiratory fitness on cardiovascular and all-cause mortality risk: a long-term prospective cohort study. Annals of Medicine. 2018. PMID 28972808. DOI 10.1080/07853890.2017.1387927.

    Prospective cohort · In 2,277 KIHD men followed a median 26.1 years (520 cardiovascular and 1,124 all-cause deaths), high against low fitness carried hazard ratios of 0.51 and 0.65, 3 to 7 against 2 or fewer sauna sessions a week 0.74 and 0.84, and high fitness with frequent sauna 0.42 (0.28 to 0.62) and 0.60 (0.48 to 0.76) against low fitness with infrequent sauna.

  27. 27.

    Laukkanen JA, Laukkanen T, Khan H, Babar M, Kunutsor SK. Combined Effect of Sauna Bathing and Cardiorespiratory Fitness on the Risk of Sudden Cardiac Deaths in Caucasian Men: A Long-term Prospective Cohort Study. Progress in Cardiovascular Diseases. 2018. PMID 29551418. DOI 10.1016/j.pcad.2018.03.005.

    Prospective cohort · In 2,291 KIHD men followed a median 26.1 years (226 sudden cardiac deaths), high against low fitness carried a hazard ratio of 0.48 (0.34 to 0.67), frequent against infrequent sauna 0.67 (0.46 to 0.98), and high fitness with frequent sauna 0.31 (0.16 to 0.63), high fitness alone 0.49 and frequent sauna alone 0.71 (0.45 to 1.10) against low fitness with infrequent sauna.

  28. 28.

    Kunutsor SK, Laukkanen JA. Does the Combination of Finnish Sauna Bathing and Other Lifestyle Factors Confer Additional Health Benefits? A Review of the Evidence. Mayo Clinic Proceedings. 2023. PMID 37270272. DOI 10.1016/j.mayocp.2023.01.008.

    Review · A review of the epidemiologic and interventional evidence that frequent sauna bathing may augment protective factors such as physical activity and cardiorespiratory fitness and attenuate risk factors such as high blood pressure and systemic inflammation, with discussion of mechanisms and gaps.

  29. 29.

    Kunutsor SK, Laukkanen T, Laukkanen JA. Longitudinal associations of sauna bathing with inflammation and oxidative stress: the KIHD prospective cohort study. Annals of Medicine. 2018. PMID 29897261. DOI 10.1080/07853890.2018.1489143.

    Prospective cohort · In 2,269 KIHD men, 4 to 7 sessions a week against 1 was associated with hs-CRP 0.84 mg/L lower (0.14 to 1.55) and leucocytes 0.28 billion per liter lower at baseline after adjustment, and 1.66 mg/L and 0.49 billion per liter lower at 11 years with fibrinogen 0.16 g/L lower; no association with GGT.

  30. 30.

    Lee E, Kolunsarka I, Kostensalo J, et al.. Effects of regular sauna bathing in conjunction with exercise on cardiovascular function: a multi-arm, randomized controlled trial. American Journal of Physiology: Regulatory, Integrative and Comparative Physiology. 2022. PMID 35785965. DOI 10.1152/ajpregu.00076.2022.

    Randomized trial · In 47 sedentary adults (age 49 ± 9) with at least one cardiovascular risk factor randomized to exercise plus a 15-minute post-exercise sauna, exercise alone or control for 8 weeks, exercise raised cardiorespiratory fitness by 6.2 mL/kg/min against control, and adding the sauna raised it a further 2.7 mL/kg/min (0.2 to 5.3), lowered systolic pressure by 8.0 mm Hg (1.4 to 14.6) and lowered total cholesterol against exercise alone; full text: sauna began at 65 °C rising 5 °C a fortnight, 10 to 20 percent humidity.

  31. 31.

    Kihara T, Biro S, Imamura M, et al.. Repeated sauna treatment improves vascular endothelial and cardiac function in patients with chronic heart failure. Journal of the American College of Cardiology. 2002. PMID 11869837. DOI 10.1016/s0735-1097(01)01824-1.

    Randomized trial · In 20 patients with NYHA class II or III heart failure given a 60 °C dry sauna for 15 minutes followed by 30 minutes under blankets daily for two weeks, symptoms improved in 17, brachial flow-mediated dilation increased without change in nitroglycerin-induced dilation and plasma BNP fell, with no change in 10 matched untreated patients.

  32. 32.

    Imamura M, Biro S, Kihara T, et al.. Repeated thermal therapy improves impaired vascular endothelial function in patients with coronary risk factors. Journal of the American College of Cardiology. 2001. PMID 11583886. DOI 10.1016/s0735-1097(01)01467-x.

    Laboratory method study · In 25 men (age 38 ± 7) with at least one coronary risk factor, two weeks of daily 60 °C far infrared dry sauna for 15 minutes plus 30 minutes under blankets raised brachial flow-mediated dilation from 4.0 to 5.8 percent (8.2 percent in 10 healthy controls) without changing nitroglycerin-induced dilation.

  33. 33.

    Ely BR, Clayton ZS, McCurdy CE, et al.. Heat therapy improves glucose tolerance and adipose tissue insulin signaling in polycystic ovary syndrome. American Journal of Physiology: Endocrinology and Metabolism. 2019. PMID 31136202. DOI 10.1152/ajpendo.00549.2018.

    Randomized trial · In 18 women with obesity and polycystic ovary syndrome (age 27, body mass index 41.3) assigned to 30 one-hour hot tub sessions over 8 to 10 weeks or time control, heat lowered fasting glucose from 105 to 89 mg/dL, the glucose and insulin areas under a two-hour tolerance test, and serum testosterone from 51 to 34 ng/dL, and raised adipocyte insulin signaling, with no change in body mass index or in controls.

  34. 34.

    Ely BR, Francisco MA, Halliwill JR, et al.. Heat therapy reduces sympathetic activity and improves cardiovascular risk profile in women who are obese with polycystic ovary syndrome. American Journal of Physiology: Regulatory, Integrative and Comparative Physiology. 2019. PMID 31483156. DOI 10.1152/ajpregu.00078.2019.

    Randomized trial · In the same 18 women (9 heat, 9 control), 30 hot tub sessions lowered muscle sympathetic nerve activity from 20 to 13 bursts a minute, systolic pressure from 124 to 114 and diastolic from 77 to 68 mm Hg, C-reactive protein, total cholesterol and carotid and femoral wall thickness, and improved flow-mediated dilation after ischemia-reperfusion from 5.6 to 9.5 percent, with no change in controls.

  35. 35.

    Beever R. Far-infrared saunas for treatment of cardiovascular risk factors: summary of published evidence. Canadian Family Physician. 2009. PMID 19602651.

    Review · From nine human studies of far infrared sauna: limited moderate evidence for normalizing blood pressure and treating heart failure, fair evidence from a single study for chronic pain, weak single-study evidence for chronic fatigue and obesity, and consistent fair evidence refuting cholesterol-reduction claims.

  36. 36.

    Ahokas EK, Ihalainen JK, Hanstock HG, Savolainen E, Kyröläinen H. A post-exercise infrared sauna session improves recovery of neuromuscular performance and muscle soreness after resistance exercise training. Biology of Sport. 2023. PMID 37398966. DOI 10.5114/biolsport.2023.119289.

    Randomized trial · In a randomized crossover of 16 male basketball players, 20 minutes of infrared sauna at 43 ± 5 °C after a heavy resistance protocol, against passive recovery, attenuated the fall in countermovement jump 14 hours later, reduced muscle soreness and raised perceived recovery; heart rate variability was lower during the sauna and no different overnight.

  37. 37.

    Kauppinen K. Sauna, shower, and ice water immersion. Physiological responses to brief exposures to heat, cool, and cold. Part I. Body fluid balance. Arctic Medical Research. 1989. PMID 2736001.

    Laboratory method study · In nine men, sauna with room-temperature recovery produced a mean weight loss of 544 ± 207 g and a 5.6 percent fall in plasma volume; sauna followed by ice water immersion or a 15 °C shower produced falls of 7.2 and 8.0 percent, and cold water alone 1.3 percent, not significant.

  38. 38.

    Kunutsor SK, Häkkinen A, Zaccardi F, et al.. Short-term effects of Finnish sauna bathing on blood-based markers of cardiovascular function in non-naive sauna users. Heart and Vessels. 2018. PMID 29971466. DOI 10.1007/s00380-018-1202-9.

    Laboratory method study · In 102 experienced sauna users after a 30-minute session at a mean 73 °C, NT-proBNP rose from 46.0 to 50.5 ng/L (12 percent) immediately and 14 percent at 30 minutes in a subset of 20, with no significant overall change in hs-CRP, creatine kinase, troponin I or CK-MB and a 2.99 percent rise in creatine kinase in men.

  39. 39.

    Gryka D, Pilch W, Szarek M, Szygula Z, Tota Ł. The effect of sauna bathing on lipid profile in young, physically active, male subjects. International Journal of Occupational Medicine and Environmental Health. 2014. PMID 25001587. DOI 10.2478/s13382-014-0281-9.

    Laboratory method study · In 16 men aged 20 to 23, ten Finnish sauna sessions (90 ± 2 °C, 5 to 16 percent humidity, three 15-minute rounds with 2-minute cool-downs) every one or two days lowered total and LDL cholesterol during and for a week after the series with a transient fall in triglycerides and a nonsignificant rise in HDL; plasma volume fell after each session and showed an adaptive increase after the ten sessions.

  40. 40.

    Kunutsor SK, Kauhanen J, Laukkanen JA. Sauna bathing, renal function and chronic kidney disease: Cross-sectional and longitudinal findings from the KIHD study. European Journal of Clinical Investigation. 2023. PMID 37029766. DOI 10.1111/eci.14001.

    Prospective cohort · In 2,071 KIHD men with normal kidney function, 4 to 7 sessions a week against 1 showed no significant difference in baseline eGFR, creatinine or sodium (potassium 0.05 mmol/L higher), no difference in sodium or potassium at 11 years, and no association with chronic kidney disease over a median 25.7 years (188 cases; hazard ratio 0.84, 0.46 to 1.53).

  41. 41.

    Hussain JN, Greaves RF, Cohen MM. A hot topic for health: Results of the Global Sauna Survey. Complementary Therapies in Medicine. 2019. PMID 31126560. DOI 10.1016/j.ctim.2019.03.012.

    Cross-sectional study · Among 482 regular sauna users surveyed online (51.3 percent men, bathing about 1 to 2 times a week), relaxation was the leading motive, 83.5 percent reported sleep benefits, 93.1 percent of adverse reactions were minor (dizziness, dehydration, headache), and two respondents reported hospital visits for chest pain and eye irritation.

  42. 42.

    Urponen H, Vuori I, Hasan J, Partinen M. Self-evaluations of factors promoting and disturbing sleep: an epidemiological survey in Finland. Social Science and Medicine. 1988. PMID 3363395. DOI 10.1016/0277-9536(88)90313-9.

    Cross-sectional study · In a survey of 1,600 middle-aged urban Finns (75 percent response), exercise was most often named as helping sleep, followed by reading and music, with sauna, shower and bath among the other factors reported to help; evening coffee, heavy or late meals and exercise, and stress were named as disturbing it.

  43. 43.

    Kenttämies A, Karkola K. Death in sauna. Journal of Forensic Sciences. 2008. PMID 18471223. DOI 10.1111/j.1556-4029.2008.00703.x.

    Cross-sectional study · In Finland (about 2 million saunas for 5.2 million people), deaths occurring in a sauna in 1990 to 2002 ran at under 2 per 100,000 inhabitants a year; 51 percent were natural deaths, heat exposure was the cause in 25 percent, and 50 percent of the deceased were under the influence of alcohol.

  44. 44.

    Rodhe A, Eriksson A. Sauna deaths in Sweden, 1992-2003. American Journal of Forensic Medicine and Pathology. 2008. PMID 19749613. DOI 10.1097/PAF.0b013e318145ae05.

    Cross-sectional study · Of 77 sauna-related deaths in Sweden in 1992 to 2003, 82 percent were men, mostly middle-aged; 71 percent of the 69 tested were positive for alcohol, 44 percent of explained deaths were alcohol-related and 23 percent cardiovascular, and all but two of those found dead in the sauna were alone.

  45. 45.

    Hannuksela ML, Ellahham S. Benefits and risks of sauna bathing. American Journal of Medicine. 2001. PMID 11165553. DOI 10.1016/s0002-9343(00)00671-9.

    Review · Sauna is well tolerated by most healthy adults and children and safe in uncomplicated pregnancy; contraindications are unstable angina, recent myocardial infarction and severe aortic stenosis; it is safe for most people with stable coronary disease; very few heart attacks and sudden deaths occur in saunas, and alcohol during bathing raises the risk of hypotension, arrhythmia and sudden death and should be avoided.

  46. 46.

    Ravanelli N, Casasola W, English T, Edwards KM, Jay O. Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis. British Journal of Sports Medicine. 2019. PMID 29496695. DOI 10.1136/bjsports-2017-097914.

    Review · Across 12 studies of 347 pregnant women, no core temperature exceeded 39.0 °C; the highest mean end-of-session temperature was 37.6 °C for sauna and 36.9 °C for hot bathing, and the authors concluded that a 70 °C, 15 percent humidity sauna or a 40 °C bath for up to 20 minutes does not reach the teratogenic threshold at any stage of pregnancy.

  47. 47.

    Garolla A, Torino M, Sartini B, et al.. Seminal and molecular evidence that sauna exposure affects human spermatogenesis. Human Reproduction. 2013. PMID 23411620. DOI 10.1093/humrep/det020.

    Laboratory method study · In 10 men with normal semen, two 15-minute Finnish sauna sessions a week at 80 to 90 °C for three months strongly impaired sperm count and motility and reduced normal chromatin packaging and mitochondrial function without changing sex hormones; all effects were completely reversed six months after stopping.

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