Clinical Effects of Regular Dry Sauna Bathing: A Systematic Review

Table 1

Cardiovascular disease- (CVD-) related sauna studies.

Study Characteristics			Study sample		Intervention		Comparators		Health effects	Adverse side effects
Author & year	Level of evidence	Design	Pop/country		Sauna type	Duration	Comparator/; controls	Outcome; measures	Positive/negative/negligible	None/mild/; moderate/; severe
2016; Tei et al. [31]	I	RCT-; multicentre	Advanced CHF/Japan	149	FIR	2 weeks	Control group, standard medical care	6 MWD; (6 min walking distance), CTR (cardio-thoracic ratio) on chest X-ray, NYHA class, plasma BNP levels	Positive,; improved 6 MWD (), reduced CTR on CXR (), improved NYHA classification () compared to control group	Mild,; decreased BP, hypovolemia, polyurination, decreased body wt
2011; Fujita et al. [32]	I	RCT	CHF/Japan	40	FIR	4 weeks	Control group, standard medical care	Body weight, BP, cardio-thoracic ratio (CTR) on chest X-ray, LVEF on ECHO, fasting plasma levels of BNP, uric acid, hydro-peroxide, nitrate, nitrite	Positive,; sauna group with reduced concentration of hydroperoxide (); reduced BNP levels (); increased nitric oxide metabolites ()	None
2011; Kuwahata et al. [33]	I	RCT	CHF/Japan	54	FIR	4 weeks	Control group, standard medical care	Body weight, BP, HR, CTR on chest X-ray, standard ECHO parameters, fasting plasma levels of catechol-amines and BNP; and HRV (heart rate variability) parameters	Positive,; mean HR decreased () in sauna group compared to control group. High frequency component of HRV in setting of beta blockade improved	None
2010; Shinsato et al. [34]	I	RCT	PAD/Japan	21	FIR	6 weeks	Control group, standard medical care	Leg pain (using VAS), ABI (ankle-brachial index), 6 MWD (6-min walking distance), PCR-CD34+ progenitor gene expression levels in peripheral blood mononuclear cells, serum levels of VEGF (vascular endothelial growth factor), nitrate, nitrite	Positive, decrease in leg pain scores (), increase in 6 MWD (), improved ABI (),; 2-fold increase in mRNA CD34/GAPDH gene expression levels (),; increases in serum nitrate and nitrite levels (, ) in sauna group compared to control group	Mild,; transient leg pain during sauna but resolved after a few sessions
2008; Miyata et al. [35]	I	RCT	CHF/Japan	188	FIR	2 weeks	Control group-; standard medical care	BP, HR, body weight, body temp, CTR (cardio-thoracic ratio) on chest X-ray, usual ECHO parameters, fasting plasma BNP	Positive,; BP and CTR decreased in both groups (sauna , ; control , ).; Body wt decreased; (); LVEF on ECHO increased (); plasma BNP decreased () in sauna group compared with control group	None
2004; Kihara et al. [36]	I	RCT	Cardiac arrhythmias,; CHF/Japan	30	FIR	2 weeks	Control group placebo intervention -supine on a bed in a temp-controlled room at 24°C for 45 min.	Self-assessed quality of life questionnaire,; 24-hr ambulatory ECG recordings with HRV analysis (std deviation of mean RR intervals), CTR (cardiothoracic ratio) by chest X-ray, usual ECHO parameters, plasma concentrations of catechol-amines, ANP, BNP	Positive,; fewer PVCs (), fewer couplets (), fewer episodes of VT (), decreased CTR (), increased HRV variability (), lowered serum levels of BNP () in sauna treatment group compared to control group	None
2004; Masuda et al. [37]	I	RCT	Increased CVD Risk/Japan	28	FIR	2 weeks	Control group placebo intervention -supine on a bed in a temp-controlled room at 24°C for 45 min.	Body wt, HR, BP, HCT, fasting plasma lipid profile and glucose, urinary levels 8-epi-prosta-glandin F2α	Positive,; systolic BP () and urinary 8-epi- prostaglandin F2α levels () significantly lower in sauna group compared to control group	None
2016; Laukkanen et al. [38]	II	Prospective cohort study	Middle-aged males/Finland	2315	Finnish	20.7 years	Frequency and duration of sauna bathing: 1 time/wk,; 2-3 time/wk,; 4–7 times/wk	Incidence dementia/Alzheimer’s disease and other CVD-related outcomes	Positive,; sauna bathing 4−7 times a week associated with 66% risk reduction (hazard ratio 0.34, 95% CI) in developing dementia or Alzheimer’s compared with 1 time/week	None
2015; Laukkanen et al. [39]	II	Prospective cohort study	Middle-aged males/Finland	2315	Finnish	20.7 years	Frequency and duration of sauna bathing: 1 time/wk,; 2-3 time/wk,; 4–7 times/wk	Incidence of sudden cardiac death,; fatal coronary heart disease, fatal CVD, all-cause mortality	Positive,; sauna bathing 4–7 sessions weekly associated with 40% reduction in all-cause mortality compared with 1 session weekly, (hazard ratio 0.60, 95% CI, 0.46–0.80, )	None
2013; Sobajima et al. [40]	II	Controlled clinical study	IHD with total coronary occlusion/Japan	24	FIR	3 weeks	Control group, standard medical care	Myocardial perfusion scintigraphy with adenosine, flow-mediated vaso-dilation of brachial artery, treadmill exercise stress testing and expression of CD34-positive bone marrow-derived cells	Positive,; improved indices of defect reversibility on myocardial perfusion scans (); extended treadmill times (), improved flow-mediated dilation of brachial artery () after sauna therapy compared to control group	None
2003; Sugahara et al. [41]	II	Single group clinical study	Infants-; VSD and CHF/Japan	12	FIR	4 weeks	No control group	Core body temp, HR, BP, usual ECHO parameters including VSD measurements with colour Doppler, 24 h urine nitrate and nitrite levels	Positive,; decrease in VSD shunt flow ratio (), increase in 24 h urine nitrite and urine nitrate levels (, ); surgical repair not necessary for 9/12 (75%) infants	None
2012; Ohori et al. [42]	III	Single group clinical study	CHF/Japan	41	FIR	3 weeks	No control group	6 MWT (6-min walk test); standard ECHO parameters; plasma levels of BNP, norepinephrine and circulating CD34+ cells; flow-mediated dilation (FMD) of the brachial artery	Positive,; increased LVEF (left ventricular ejection fraction), ; reduced levels of norepinephrine and BNP, and ; increased 6 MWT, ; improved FMD, ; increased CD34+ counts,	None
2010; Beever [43]	III	Single group, sequential, longitudinal, interrupted time series	Type 2 diabetes/Canada	15	FIR	3 months	No control group	SF-36 (36-item short form health survey) and VAS (visual analogue scales)	Positive,; improved stress (), fatigue (), general health () on SF-36	None
2009; Kihara et al. [44]	III	Retrospective cohort study	CHF/Japan	129	FIR	5 years	Control group, standard medical care	Episodes of cardiac death, cardiac events, rehospitalisations due to CHF	Positive,; 8/64 patients died in sauna therapy group vs 12/65 patients in control group (12.5% vs 18.5% mortality rate); Rehospitalization due to worsening CHF occurred in 20/64 (31.3%) patients in sauna group vs 44/65 (68.7%) patients in control group (); 38% reduction in cardiac event rate in sauna therapy group compared to control group	None
2007; Tei et al. [45]	III	Single group clinical study/pilot trial	PAD/Japan	20	FIR	10 weeks	No control group	Leg pain using VAS (visual analogue scale), 6 MWD (6 min walking distance), ABI (ankle/; brachial index), leg blood flow with Doppler laser imaging, digital subtraction angiography	Positive,; pain scores decreased, 6 MWD improved, ABI improved, increase in visible collateral vessels in ischaemic legs with digital subtraction angiography observed after sauna therapy ( for all)	None
2005; Miyamoto et al. [46]	III	Single group clinical study/pilot trial	CHF/Japan	15	FIR	4 weeks	No control group	Body wt, BP, HR; Self-assessed quality of life questionnaire; 6 MWT (6 min walk time); peak VO2 on bicycle ergometer; CTR (cardio-thoracic ratio) on chest X-ray; usual ECHO parameters, plasma BNP, catecholamines; number of hospitalisations one-year after sauna intervention	Positive,; decreased SBP (), improved CTR (),; improved LVEF on ECHO (), increased 6 MWT (), decreased plasma norepinephrine and epinephrine levels (, ) with sauna intervention. Reduced number of hospitalisations () one-year after sauna intervention	None
2003; Biro et al. [47]	III	Clinical study with control group	Obesity,; T2DM, smoking, hypercholesterolaemia,; HTN/Japan	35	FIR	2 weeks	10/35 control group without any lifestyle diseases	Body wt, HR, BP, HCT; fasting serum lipid profile, glucose, uric acid levels; resting arterial diameter; flow mediated dilatation of brachial artery on Doppler USS; plasma ghrelin and serum leptin levels	Positive,; decreased body wt (), SBP and DBP (, ), FBG (); Improved flow mediated dilation of brachial artery () in sauna group but results compared to control not presented	None
2002; Kihara et al. [48]	III	Clinical study with control group	CHF/Japan	30	FIR	2 weeks	10/30 control group, standard medical care	Self-assessed; quality of life questionnaire; HR, BP; fasting plasma levels of catecholamines, ANP, BNP, thiobarbituric acid-reactive substances, TNF-alpha; CTR (cardio-thoracic ratio) on chest X-ray; usual ECHO parameters; brachial artery diameter and flow-mediated dilation using Doppler ultrasound	Positive,; decreased SBP (), decreased CTR on CXR (), decreased LVEDD (left ventricular end-diastolic dimension) on ECHO (), decreased plasma BNP levels (), improved flow-mediated dilation of brachial artery on Doppler USS () in sauna group compared to control	None
2001; Imamura et al. [49]	III	Clinical study with control group	Increased CVD risk/Japan	35	FIR	2 weeks	Control group 10/35 without any CVD risk factors	Body wt, HR, BP; fasting serum levels of HCT, Lipid profile, uric acid, glucose, thiobarbituric acid-reactive substances; flow mediated dilation of brachial artery using Doppler USS; nitroglycerin-induced flow mediated dilation of brachial artery using Doppler USS	Positive,; SBP and DBP reduced (, ); body wt reduced (); fasting glucose levels decreased (); % flow mediated dilation of brachial artery improved () in sauna group but no statistical report of comparisons with control group	None

CVD = cardiovascular disease; CHF = congestive heart failure; IHD = ischaemic heart disease; PAD = peripheral arterial disease; FIR = far-infrared sauna; VSD = ventricular septal defect; NYHA = New York Heart Association grading for CHF; temp = temperature; HR = heart rate; SBP = systolic blood pressure; DBP = diastolic blood pressure; wt = body weight; ECHO = echocardiogram; VAS = visual analogue scale; FBG = fasting blood glucose; BNP = B-natriuretic peptide; HCT = haematocrit.