The science of sauna.
Cardiovascular mortality cut in half. All-cause mortality cut 40%. Dementia risk 66% lower. Below is the full evidence base, peer-reviewed, cited, no marketing spin.
01
Cardiovascular health
Sauna delivers the strongest cardiovascular outcome data of any wellness intervention currently studied.
The Kuopio Ischemic Heart Disease (KIHD) Risk Factor Study, led by Dr Jari Laukkanen at the University of Eastern Finland, has prospectively followed more than 2,300 middle-aged Finnish men since the 1980s. The 2015 paper in JAMA Internal Medicine remains the single most-cited piece of sauna research in the modern literature.
Compared with men who used a sauna once a week, those who used it 4–7 times per week had a 50% lower risk of fatal cardiovascular disease and a 40% lower risk of all-cause mortality across the 25-year follow-up. The effect held after adjusting for traditional cardiovascular risk factors (smoking, BMI, blood pressure, cholesterol, diabetes), physical activity and socio-economic status.
Subsequent follow-up papers showed the relationship is dose-dependent: more time per session (≥19 min) and more sessions per week each independently lower risk. A 2018 review in Mayo Clinic Proceedings (Laukkanen, Kunutsor, Khan) attributed the cardiovascular effect to repeated exposure-induced blood-pressure reduction, endothelial improvement, heart-rate-variability gains, and a reduction in systemic inflammation.
50%
lower fatal cardiovascular events at 4–7 sessions/week
Laukkanen et al., JAMA Intern Med 2015
40%
lower all-cause mortality at 4–7 sessions/week
Laukkanen et al., JAMA Intern Med 2015
−8 mmHg
average reduction in resting systolic blood pressure
Laukkanen 2018, Mayo Clinic Proceedings
02
Longevity & all-cause mortality
The mortality dose-response curve for sauna is among the steepest seen for any voluntary intervention.
Beyond cardiovascular endpoints, the KIHD cohort showed sauna use was associated with lower all-cause mortality across the full study period, and the relationship was independent of physical exercise. In other words, sauna is not just a marker of healthy people; it appears to be doing something on its own.
Mechanistically, the leading hypotheses are heat-shock protein induction (HSP70, HSP90), improved endothelial function, increased plasma volume and stroke volume, and changes to the inflammation profile. All of these overlap with the mechanisms thought to mediate exercise's longevity benefit, sauna may be partially functioning as an “exercise mimetic”.
A 2024 systematic review in Frontiers in Aging confirmed the direction across multiple cohorts and called for the same intervention to be studied in non-Finnish populations and in women, who were excluded from the original KIHD cohort.
23%
lower all-cause mortality at 2–3 sessions/week
Laukkanen et al., JAMA Intern Med 2015
Independent
effect, after adjusting for physical activity
Laukkanen 2015
03
Brain & cognition
Regular sauna use shows the strongest dementia-protection signal of any modifiable behaviour studied.
A 2017 paper in Age and Ageing (Laukkanen et al.) followed 2,315 men over 20 years and reported a 66% lower risk of dementia, and a 65% lower risk of Alzheimer's disease, in those who used a sauna 4–7 times per week compared with once weekly. The relationship survived adjustment for cardiovascular risk factors, suggesting independent benefit.
Two mechanisms are likely. First, sauna is a powerful inducer of brain-derived neurotrophic factor (BDNF), the same growth factor exercise increases, which supports neuronal survival and plasticity. Second, the cardiovascular benefits (blood-pressure reduction, endothelial improvement) flow through to cerebral blood flow.
More recent work from Rhonda Patrick's lab and others has highlighted heat's role in modulating prolactin, growth hormone, and norepinephrine, all of which influence mood, focus and resilience over time.
66%
lower dementia risk at 4–7 sessions/week
Laukkanen et al., Age Ageing 2017
65%
lower Alzheimer's risk at 4–7 sessions/week
Laukkanen et al., Age Ageing 2017
04
Heat shock proteins
Sauna is one of the most reliable, evidence-based ways to upregulate heat shock proteins in healthy adults.
Heat shock proteins (HSPs) are molecular chaperones that help cells fold proteins correctly, repair misfolded ones, and resist oxidative and proteotoxic stress. Elevated HSP70 and HSP90 levels are associated with improved exercise tolerance, slower cellular aging markers, and better resilience to ischemia (loss of blood flow).
A single 30-minute Finnish sauna session at 73°C has been shown to roughly double circulating HSP70 within 60 minutes (Selsby et al.; Kukkonen-Harjula). Repeated exposure across weeks raises baseline levels, similar to the adaptation seen with progressive exercise training.
This is one of the cleanest mechanistic links between sauna and longevity, and it's shared with cold exposure, fasting and exercise. Hormesis, in three modalities, converging on the same cellular toolkit.
~2x
circulating HSP70 after a single 30-min Finnish session
Selsby et al.; Kukkonen-Harjula
05
Growth hormone & hormones
Two 20-minute saunas at 80°C, separated by a cool-down, can raise growth hormone fivefold.
A series of older but well-replicated studies (Kukkonen-Harjula, Acta Physiologica Scandinavica) demonstrated that two 20-minute sauna sessions at 80°C with a 30-minute cool-down between produced a roughly 5-fold acute increase in growth hormone in healthy adults. Sessions stacked on consecutive days produced larger releases.
Growth hormone supports tissue repair, muscle maintenance, and skin collagen turnover. While the acute response normalises within hours, the implication for athletes and ageing adults is consistent with the broader sauna recovery literature, sauna sits squarely alongside resistance training and quality sleep as a hormonal-status lever.
Norepinephrine and prolactin also rise substantially during sauna sessions, mediating the alertness-then-relaxation pattern members typically report.
~5x
growth hormone after twin 20-min 80°C sessions
Kukkonen-Harjula et al., Acta Physiol Scand
06
Immune function
Regular sauna use lowers the frequency of common respiratory infections and shifts immune markers favourably.
A 1990 randomised trial (Ernst et al., Annals of Medicine) showed twice-weekly sauna over 6 months halved the incidence of common colds in the intervention group. More recent observational work has shown reductions in respiratory illness incidence, lower CRP (inflammation marker) and shifts in lymphocyte populations consistent with improved immune surveillance.
Acute heat exposure also induces mild leukocytosis, circulating white blood cells rise transiently, and improves the migration capacity of neutrophils, the body's first-line immune cells.
−50%
incidence of common colds over 6 months
Ernst et al., Annals of Medicine 1990
07
Mental health & depression
Whole-body hyperthermia has now produced its first randomised controlled trial signal for major depression.
A 2016 RCT in JAMA Psychiatry (Janssen et al.) tested a single whole-body hyperthermia session (infrared heat to a core temperature of 38.5°C) in 30 adults with major depressive disorder. Six weeks post-treatment, the intervention group showed a clinically significant antidepressant response that exceeded what would be expected from a single-session intervention.
Beyond the depression literature, regular sauna use is associated with lower psychological distress scores, fewer reported episodes of low mood, and lower risk of incident psychotic disorders (Laukkanen 2018 cohort).
Mechanistically: heat acutely raises beta-endorphin, dynorphin and norepinephrine, and the regular practice appears to recalibrate the hypothalamic-pituitary-adrenal axis in ways that mirror moderate exercise.
Sustained
antidepressant response 6 weeks after a single whole-body hyperthermia session
Janssen et al., JAMA Psychiatry 2016
08
Athletic recovery
Post-exercise sauna increases plasma volume, supports protein synthesis and accelerates perceived recovery.
Sauna is a workhorse of Finnish athletic culture for reason. Heat acclimation studies in trained athletes show 4 weeks of post-training sauna (≈30 min at 80°C, four times weekly) increases plasma volume by 7–18%, raises VO₂max, and improves run-time-to-exhaustion in temperate conditions. (Scoon et al., Journal of Science and Medicine in Sport 2007.)
For recovery, post-resistance-training sauna has been linked to faster recovery of force production, reduced delayed-onset muscle soreness, and elevated post-exercise growth hormone responses. The Soeberg principle, heat at the end of a hard training day, cold earlier, is a well-supported sequencing rule that R1SE members can apply directly using our Fire & Ice room.
+7–18%
plasma volume after 4 weeks of post-training sauna
Scoon et al., J Sci Med Sport 2007
09
Skin, detoxification & sweat
Sweat is not the body's primary detoxification route, but sauna does provide a small, measurable elimination of specific toxins.
Sauna sweat contains trace amounts of heavy metals (lead, cadmium), bisphenol A, phthalates and PCBs at levels above plasma concentrations, which means the body is actively concentrating some lipophilic toxins into sweat for elimination. (Sears, Genuis et al., Journal of Environmental and Public Health 2012.) The clinical magnitude is small compared with hepatic and renal clearance, but real.
On the skin side, regular sauna use is associated with improved barrier function, faster wound healing in the infrared literature, and visible improvements in capillary tone. The cardiovascular flush leaves a measurable improvement in microcirculation that explains the “sauna glow” members notice.
Measurable
but modest excretion of heavy metals and BPA in sauna sweat
Sears, Genuis et al., 2012
Common questions
Reading is the first step. Heat does the work.
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More from the R1SE Sauna Library
Sauna Knowledge Hub
Every sauna page on the R1SE knowledge library.
ReadTypes of Sauna
Finnish, infrared, steam, smoke, hybrid, how each works.
ReadHistory of Sauna
2,000 years from Finnish löyly to modern recovery rooms.
ReadHow to Sauna
Beginner to advanced protocols, frequency, timing.
ReadSauna Safety
Contraindications, hydration, cardiac considerations.
ReadWho Saunas and Why
Bryan Johnson, Huberman, Rhonda Patrick, Hugh Jackman.
ReadTry sauna at R1SE
Knowledge is one thing, the body learns by doing. Book a Fire & Ice session, an infrared sauna, or our 8-person Finnish barrel sauna at the Kelham Urban Spa.