Kidney disease and sauna

Kidney disease and sauna is one of the clearer "ask first" subjects of this encyclopaedia, because the kidneys are the everyday casualty of both the heat and the misinformation that surrounds it. In the hot room the kidney's blood supply is temporarily reduced as the circulation is sent to the skin, its water-conserving work is doubled by the sweat's demands, and every dose of Dehydration the session causes is paid for in renal currency; for a person whose kidneys are damaged — chronic kidney disease (CKD) — those ordinary bills arrive without the surplus that a healthy kidney carries.

The kidneys in the heat

Two facts anchor the subject. First, during heat exposure the share of cardiac output delivered to the kidneys falls as blood is redirected to the skin; a healthy kidney copes with the reduction, and the nephrons conserve water and sodium under hormonal instruction (see Electrolyte balance). Second, the water bill of a session — the half litre or more of sweat — must be balanced by intake, and the balancing organs are precisely the kidneys: the fluid is drunk in and processed by them, and the urine clears the day after. The functional message is simple: a sauna visit is a renal workload even for healthy people, made larger by the diuretic effects of alcohol (Alcohol and sauna) and of many medicines (Medication and sauna), and the workload is imposed on top of whatever scarcity the person's condition has already created.

For the person with CKD the same session costs more. The damaged kidney concentrates urine less well, so water and salts are harder to conserve; blood-pressure regulation and cardiovascular control are less robust, with the heat load and orthostatic dips of the hot room weighed against damaged vasculature (Low blood pressure and sauna, Fainting in a sauna); medicines are almost always involved — blood-pressure tablets, diuretics, and the medications that define sauna interactions; and complications such as anaemia reduce heat tolerance further. NHS summarises the paired realities of CKD: often silent in early stages, commonly caused by the same hypertension and diabetes that affect sauna bathers, and accompanied by an increased cardiovascular risk that makes the whole subject a medical decision rather than a lifestyle question (see Medical advice before sauna and Sauna contraindications).

The "sweat away the waste" myth

The myth-laden corner of this page is the detoxification claim, which runs in the opposite direction of the physiology: the person with kidney disease is sometimes told that heavy sweating "relieves" the kidneys. The measured content of waste substances in sweat (see Detoxification claims about sauna and the metal-in-sweat review literature) is small; the kidneys are the actual elimination organ; and anything that dehydrates the patient raises the concentration work of those kidneys rather than lightening it. A session that produces a litre of sweat is not a dialysis session; it is a bill. The wise reversal of the myth is the one this article leaves standing: for kidney health, water, blood-pressure control and diabetes management are the levers, and the sauna is a pleasant optional extra within the nephrologist's rules, not a renal therapy.

Practical rules

The practical rules for the renal patient: clearance from the treating clinician or renal team before any bathing; clear understanding of the fluid allowance — some CKD patients are told to restrict fluids, others to maintain them, and the nephrology instruction takes precedence over the general "drink more" advice of this encyclopaedia (see Hydration during sauna); short, mild sessions only; no alcohol; no bathing with fever or infection (Fever and sauna, Infection and sauna); meticulous attention to medication (Medication and sauna); a companion; and the knowledge that the session's mild cardiovascular stimulus (Cardiovascular effects of sauna) is useful to the general health context of CKD only when the renal team has signed it off. Dialysis patients add the specific cautions of their treatment — vascular access, fluid and electrolyte limits, and the fragility of the post-session balance — which, again, are questions for the dialysis unit, not for the cabin's thermostat (see Older adults and sauna for the overlapping group and Sauna safety for the room's own rules).

See also

• Dehydration
• Electrolyte balance
• Medication and sauna
• Detoxification claims about sauna
• Medical advice before sauna

References

• National Health Service. "Chronic kidney disease." NHS, UK. nhs.uk/conditions/kidney-disease (page reviewed 22 March 2023)
• 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
• Cheuvront SN, Kenefick RW. "Dehydration: physiology, assessment, and performance effects." Comprehensive Physiology 4(1):257–285, 2014. doi:10.1002/cphy.c130017
• Sears ME, Kerr KJ, Bray RI. "Arsenic, cadmium, lead, and mercury in sweat: a systematic review." Journal of Environmental and Public Health 2012:184745, 2012. doi:10.1155/2012/184745
• 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
• 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
• 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