Table 1: Cardiovascular disease- (CVD-) related sauna studies.

Study Characteristics Study sample Intervention ComparatorsHealth effectsAdverse side effects
Author & yearLevel of evidenceDesignPop/countrySauna typeDurationComparator/
controls
Outcome
measures
Positive/negative/negligibleNone/mild/
moderate/
severe

2016
Tei et al. [31]
IRCT-
multicentre
Advanced CHF/Japan149FIR2 weeksControl group, standard medical care6 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]
IRCTCHF/Japan40FIR4 weeksControl group, standard medical careBody weight, BP, cardio-thoracic ratio (CTR) on chest X-ray, LVEF on ECHO, fasting plasma levels of BNP, uric acid, hydro-peroxide, nitrate, nitritePositive,
sauna group with reduced concentration of hydroperoxide (); reduced BNP levels ();
increased nitric oxide metabolites ()
None

2011
Kuwahata et al. [33]
IRCTCHF/Japan54FIR4 weeksControl group, standard medical careBody weight, BP, HR, CTR on chest X-ray, standard ECHO parameters, fasting plasma levels of catechol-amines and BNP; and HRV (heart rate variability) parametersPositive,
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]
IRCTPAD/Japan21FIR6 weeksControl group, standard medical careLeg 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, nitritePositive, 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 RCTCHF/Japan188FIR2 weeksControl group-
standard medical care
BP, HR, body weight, body temp, CTR (cardio-thoracic ratio) on chest X-ray, usual ECHO parameters, fasting plasma BNPPositive,
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 RCTCardiac arrhythmias,
CHF/Japan
30FIR2 weeksControl 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 RCTIncreased CVD Risk/Japan28FIR2 weeksControl 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 F2αPositive,
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 studyMiddle-aged males/Finland2315Finnish20.7 yearsFrequency 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 outcomesPositive,
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 studyMiddle-aged males/Finland2315Finnish20.7 yearsFrequency 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]
IIControlled clinical studyIHD with total coronary occlusion/Japan24FIR3 weeksControl group, standard medical careMyocardial perfusion scintigraphy with adenosine, flow-mediated vaso-dilation of brachial artery, treadmill exercise stress testing and expression of CD34-positive bone marrow-derived cellsPositive,
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]
IISingle group clinical studyInfants-
VSD and CHF/Japan
12FIR4 weeksNo control groupCore body temp, HR, BP, usual ECHO parameters including VSD measurements with colour Doppler, 24 h urine nitrate and nitrite levelsPositive,
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]
IIISingle group clinical studyCHF/Japan41FIR3 weeksNo control group6 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]
IIISingle group, sequential, longitudinal, interrupted time seriesType 2 diabetes/Canada15FIR3 monthsNo control groupSF-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 studyCHF/Japan129FIR5 yearsControl group, standard medical careEpisodes of cardiac death, cardiac events, rehospitalisations due to CHFPositive,
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]
IIISingle group clinical study/pilot trialPAD/Japan20FIR10 weeksNo control groupLeg 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]
IIISingle group clinical study/pilot trialCHF/Japan15FIR4 weeksNo control groupBody 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 interventionPositive,
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]
IIIClinical study with control groupObesity,
T2DM, smoking, hypercholesterolaemia,
HTN/Japan
35FIR2 weeks10/35 control group without any lifestyle diseasesBody 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 levelsPositive,
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]
IIIClinical study with control groupCHF/Japan30FIR2 weeks10/30 control group, standard medical careSelf-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]
IIIClinical study with control groupIncreased CVD risk/Japan35FIR2 weeksControl group 10/35 without any CVD risk factorsBody 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.