Cardiovascular effects of sauna

Cardiovascular effects of sauna are the changes that sauna bathing produces in the heart and blood vessels, from the acute circulatory response of a single session to the long-term associations with heart disease, stroke and blood pressure reported in epidemiological studies. The acute effects are among the best-documented features of Finnish sauna bathing; the long-term picture is built on observational cohorts and is presented in the literature with careful language about association rather than proof of cause.

Acute effects

The immediate response to a hot room is a warm-blooded version of mild exercise. The skin vessels dilate to carry heat to the surface (see Vasodilation), cardiac output rises, and the pulse quickens: Heart rate in a sauna climbs to typical values around 100–140 beats per minute in a seated adult, while Blood pressure in a sauna shows a moderate systolic rise in the early minutes and a fall back toward, and often below, the resting level during recovery. Direct comparisons with laboratory exercise show that the pressure and pulse pattern during bathing corresponds to that of submaximal dynamic exercise of mild to moderate intensity. The acute load is graded by the room temperature, the humidity and the length of the session, and it is reversible within minutes of cooling; a cool shower, a rest in the cooling room or a swim ends the response promptly (see Contrast bathing).

These acute responses are connected, physiological processes that belong to Thermoregulation and Blood circulation rather than to disease. The body is doing real circulatory work — the same work that would build fitness if repeated — and the monotony of the stimulus is one reason researchers have proposed that regular bathing contributes to cardiovascular conditioning in the way regular exercise does. The parallel must not be overdrawn: the sauna does not activate the muscles, does not raise oxygen consumption as running does, and is not a substitute for training.

Long-term associations

The epidemiological core of the field comes from large, long-running Finnish cohorts of middle-aged men (and some later studies including women), in which habitual sauna habits were recorded and participants followed for cardiovascular outcomes. The principal findings, as summarised in reviews of the literature, are:

• Deaths from cardiovascular disease and sudden cardiac death were less frequent among men who bathed often (for example, four to seven times per week) than among those who bathed once a week or less, in analyses adjusted for age, lifestyle and major risk factors;
• Hospitalisation and death from stroke were less frequent among frequent bathers;
• The later development of hypertension was less common among frequent bathers;
• Fatal outcomes were lowest for bathing sessions of moderate length (around 15–20 minutes), rather than very short or very long sessions.

The consistency of the direction across studies and the plausible mechanisms — repeated circulatory stress, improved vascular function, lower resting blood pressure in frequent bathers — have made these findings influential. Equally central to any honest account is what they do not show: observational cohorts cannot exclude that healthier, fitter and more sociable people choose to bathe often, and the adjustments for lifestyle cannot fully remove that selection. Controlled intervention data are limited, and the reviews of the subject state explicitly that the evidence for a protective effect is suggestive but that causality is not established (see Sauna epidemiology and Clinical sauna studies for the detail). Associations of frequent bathing with lower rates of type 2 diabetes and with better markers of systemic inflammation have been reported from the same cohorts and are discussed under Diabetes and sauna and Immune system and sauna.

Risks and limits

The same acute load that underwrites the long-term associations is the source of the acute risks. Collapse with fainting, the precipitation of arrhythmias, and circulatory strain in people with established disease are the recognised dangers, and the safe use of the sauna presumes rule-following: short sessions, hydration, slow posture changes and no bathing under the influence of alcohol (see Alcohol and sauna). People with unstable angina, recent heart attack, severe aortic stenosis or uncontrolled arrhythmia are routinely advised against bathing, and those with treated hypertension, heart failure or coronary artery disease should follow their clinician's advice, especially because medication interacts with the heat response (see Medication and sauna and Sauna contraindications). There is no evidence that a sauna is a treatment for any heart condition; decisions about exercise- or heat-based therapies belong with a doctor (see Medical advice before sauna).

Measurement and research

The cardiovascular responses are measured in research with continuous ECG, beat-to-beat pressure recordings, blood-flow probes and, increasingly, the wearable sensors used in field studies; Heart rate monitoring in a sauna and Blood pressure measurement in a sauna describe the practical limits of measurement in the cabin itself. The physiological knowledge base is summarised in Sauna research, and the overall balance of beneficial and adverse effects for different groups in Sauna and health.

See also

• Heart rate in a sauna
• Blood pressure in a sauna
• Vasodilation
• Sauna epidemiology
• Clinical sauna studies

References

• Laukkanen JA, Laukkanen T, Kunutsor SK. "Cardiovascular and other health benefits of sauna bathing: a review of the evidence." Mayo Clinic Proceedings 93(8):1111–1121, 2018. doi:10.1016/j.mayocp.2018.04.008
• Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. "Association between sauna bathing and fatal cardiovascular and all-cause mortality events." JAMA Internal Medicine 175(4):542–548, 2015. doi:10.1001/jamainternmed.2014.8187
• 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. doi:10.1212/wnl.0000000000005606
• 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 30:1120–1125, 2017. doi:10.1093/ajh/hpx102
• Kukkonen-Harjula K, Kauppinen K. "Health effects and risks of sauna bathing." International Journal of Circumpolar Health 65(3):195–205, 2006. doi:10.3402/ijch.v65i3.18102
• Heinonen I, Laukkanen JA. "Effects of heat and cold on health, with special reference to Finnish sauna bathing." American Journal of Physiology – Regulatory, Integrative and Comparative Physiology 314(5):R629–R638, 2018. doi:10.1152/ajpregu.00115.2017
• Ketelhut S, Ketelhut RG. "The blood pressure and heart rate during sauna bath correspond to cardiac responses during submaximal dynamic exercise." Complementary Therapies in Medicine 44:218–222, 2019. doi:10.1016/j.ctim.2019.05.002
• Hussain J, Cohen M. "Clinical effects of regular dry sauna bathing: a systematic review." Evidence-Based Complementary and Alternative Medicine 2018:1857413, 2018. doi:10.1155/2018/1857413
• Tansey EA, Johnson CD. "Recent advances in thermoregulation." Advances in Physiology Education 39(3):139–148, 2015. doi:10.1152/advan.00126.2014