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	N	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 (p < 0.05), reduced CTR on CXR (p < 0.05), improved NYHA classification (p < 0.05) 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 (p < 0.001); reduced BNP levels (p < 0.001); increased nitric oxide metabolites (p < 0.05)	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 (p < 0.05) 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 (p < 0.05), increase in 6 MWD (p < 0.01), improved ABI (p < 0.01), 2-fold increase in mRNA CD34/GAPDH gene expression levels (p = 0.015), increases in serum nitrate and nitrite levels (p < 0.05, p < 0.05) 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 p < 0.01, p < 0.001; control p < 0.05, p < 0.05). Body wt decreased (p < 0.0001); LVEF on ECHO increased (p < 0.0001); plasma BNP decreased (p < 0.001) 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 (p < 0.01), fewer couplets (p < 0.05), fewer episodes of VT (p < 0.01), decreased CTR (p < 0.05), increased HRV variability (p < 0.01), lowered serum levels of BNP (p < 0.01) 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 (p < 0.05) and urinary 8-epi- prostaglandin F2α levels (p < 0.001) 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, p < 0.001)	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 (p < 0.01); extended treadmill times (p < 0.01), improved flow-mediated dilation of brachial artery (p < 0.05) 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 (p < 0.05), increase in 24 h urine nitrite and urine nitrate levels (p < 0.05, p < 0.05); 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), p = 0.023; reduced levels of norepinephrine and BNP, p = 0.015 and p = 0.035; increased 6 MWT, p < 0.001; improved FMD, p < 0.001; increased CD34+ counts, p = 0.025	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 (p = 0.042), fatigue (p = 0.014), general health (p = 0.037) 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 (p < 0.01); 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 (p < 0.01 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 (p < 0.05), improved CTR (p < 0.05), improved LVEF on ECHO (p < 0.05), increased 6 MWT (p < 0.05), decreased plasma norepinephrine and epinephrine levels (p < 0.01, p < 0.05) with sauna intervention. Reduced number of hospitalisations (p < 0.01) 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 (p < 0.05), SBP and DBP (p < 0.01, p < 0.05), FBG (p < 0.05); Improved flow mediated dilation of brachial artery (p < 0.001) 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 (p = 0.019), decreased CTR on CXR (p = 0.002), decreased LVEDD (left ventricular end-diastolic dimension) on ECHO (p = 0.047), decreased plasma BNP levels (p = 0.005), improved flow-mediated dilation of brachial artery on Doppler USS (p = 0.0006) 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 (p < 0.01, p < 0.05); body wt reduced (p < 0.05); fasting glucose levels decreased (p < 0.05); % flow mediated dilation of brachial artery improved (p < 0.001) 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.