Recovery from sauna bathing favorably modulates cardiac autonomic nervous system

The multifaceted benefits of passive heat therapies for extending the healthspan: A comprehensive review with a focus on Finnish sauna

Passive heat therapy is characterized by exposure to a high environmental temperature for a brief period. There are several types of passive heat therapy which include hot tubs, Waon therapy, hydrotherapy, sanarium, steam baths, infrared saunas and Finnish saunas. The most commonly used and widely studied till date are the Finnish saunas, which are characterized by high temperatures (ranging from 80-100°C) and dry air with relative humidity varying from 10-20%. The goal of this review is to provide a summary of the current evidence on the impact of passive heat therapies particularly Finnish saunas on various health outcomes, while acknowledging the potential of these therapies to contribute to the extension of healthspan, based on their demonstrated health benefits and disease prevention capabilities. The Finnish saunas have the most consistent and robust evidence regarding health benefits and they have been shown to decrease the risk of health outcomes such as hypertension, cardiovascular disease, thromboembolism, dementia, and respiratory conditions; may improve the severity of musculoskeletal disorders, COVID-19, headache and flu, while also improving mental well-being, sleep, and longevity. Finnish saunas may also augment the beneficial effects of other protective lifestyle factors such as physical activity. The beneficial effects of passive heat therapies may be linked to their anti-inflammatory, cytoprotective and anti-oxidant properties and synergistic effects on neuroendocrine, circulatory, cardiovascular and immune function. Passive heat therapies, notably Finnish saunas, are emerging as potentially powerful and holistic strategies to promoting health and extending the healthspan in all populations.

The influence of extreme thermal stress on the physiological and psychological characteristics of young women who sporadically use the sauna: practical implications for the safe use of the sauna

Background

Many individuals who use the sauna at a temperature of 120°C of higher are not aware of the negative consequences of extreme thermal stress. Despite extensive research into sauna use, the impact of extreme thermal stress on the physiological and psychological characteristics of sauna users have not been examined to date.

Aim

The aim was to determine the effect of 20 min sauna sessions with a temperature of 80°C and 120°C on the physiological and psychological characteristics of women who sporadically visit the sauna.

Methods

The study was conducted on 22 full-time female university students. Physical activity (PA) levels were evaluated with the Polish short version of the International Physical Activity Questionnaire (IPAQ). Anthropometric characteristics were measured before the first sauna session by the InBody270 body composition analyzer. Physiological parameters, including heart, energy expenditure, physical effort, and blood pressure (systolic blood pressure - SBP, and diastolic blood pressure - DBP), were assessed indirectly using Polar V800 heart rate monitors and the Omron M6 Comfort blood pressure monitor. The participants' wellbeing was assessed with the Profile of Mood States (POMS) questionnaire. The presence of significant correlations between heat exhaustion and heat stress variables and syncope during the second sauna session was examined with the use of classification and regression trees (CRT) and the cross-validation technique.

Results

Twenty-minute sauna sessions with a temperature of 80°C and 120°C induced a significant (p < 0.001) decrease in the values of SBP (excluding the temperature of 120°C), DBP, and body mass, as well as a significant increase in HR and forehead temperature. Exposure to a temperature of 80°C led to a significant (p < 0.001) increase in vigor with a simultaneous decrease in tension, depression, anger, fatigue, and confusion. In turn, sauna bathing at a temperature of 120°C had an opposite effect on the above mood parameters. Vomiting and confusion were the main predictors of syncope that occurred in some of the surveyed women.

Conclusion

Excessive air temperature can induce symptoms characteristic of heat exhaustion and heat stress nausea, heavy sweating, fast weak or strong HR, high body temperature, and confusion. Therefore, sauna bathing at a temperature of 80°C can be recommended to women who sporadically use the sauna, whereas exposure to a temperature of 120°C is not advised in this group of sauna users. The present findings provide highly valuable inputs for managing wellness and SPA centers.

Correlation analysis of heart rate variations and glucose fluctuations during sleep

OBJECTIVE

The body's glucose concentration is influenced by carbohydrate intake, insulin-induced carbohydrate reduction, and hepatic glycogen breakdown induced by stress hormones. This study investigated the potential of employing glucose fluctuations as a measure of stress by examining the relationship between heart rate variability (HRV) data and glucose levels during sleep in healthy subjects.

METHODS

In this cross-sectional study, a chest-worn electrocardiogram (ECG) and continuous glucose monitoring device (CGM) were respectively used to monitor the heart rate intervals and glucose fluctuations of five subjects (two males, three females) during sleep. A time-series correlation analysis was performed on the HRV data extracted from heart rate intervals and the corresponding glucose fluctuation data.

RESULTS

The time-series analysis of ECG and CGM data collected from subjects during sleep (n = 25 nights) revealed a moderate negative correlation between glucose levels and HRV, with a cross-correlation coefficient of r = -0.453.

CONCLUSION

Similar to HRV, changes in stress levels can be detected by observing glucose fluctuations, particularly during sleep when the impact of food intake can be eliminated. Our findings highlight a significant correlation between glucose levels and HRV, indicating that glucose fluctuations can be used as an indicator of autonomic nervous system activity in an exploratory study.

Effects of whole-body cryotherapy and static stretching are maintained 4 weeks after treatment in most patients with chronic fatigue syndrome

In the previous study, whole-body cryotherapy (WBC)+static stretching (SS) has been shown to reduce the severity of some symptoms in Chronic Fatigue Syndrome (CFS) noted just after the therapy. Here we consider the effects of treatment and explore the sustainability of symptom improvements at four weeks (one-month) follow-up. Twenty-two CFS patients were assessed one month after WBC + SS programme. Parameters related to fatigue (Chalder Fatigue Questionnaire (CFQ), Fatigue Impact Scale (FIS), Fatigue Severity Scale (FSS)), cognitive function (Trial Making test part A and B (TMT A and TMT B and its difference (TMT B-A)), Coding) hemodynamic, aortic stiffness (aortic systolic blood pressure (sBP aortic)) and autonomic nervous system functioning were measured. TMT A, TMT B, TMT B-A and Coding improved at one month after the WBC + SS programme. WBC + SS had a significant effect on the increase in sympathetic nervous system activity in rest. WBC + SS had a significant, positive chronotropic effect on the cardiac muscle. Peripheral and aortic systolic blood pressure decreased one month after WBC + SS in comparison to before. Effects of WBC + SS on reduction of fatigue, indicators of aortic stiffness and symptoms severity related to autonomic nervous system disturbance and improvement in cognitive function were maintained at one month. However, improvement in all three fatigue scales (CFQ, FIS and FSS) was noted in 17 of 22 patients. In addition, ten patients were treated initially but they were not assessed at 4 weeks, and are thus not included in the 22 patients who were examined on follow-up. The overall effects of WBC + SS noted at one month post-treatment should be interpreted with caution.

Does the Combination of Finnish Sauna Bathing and Other Lifestyle Factors Confer Additional Health Benefits? A Review of the Evidence

Sauna bathing, a tradition deeply rooted in the Finnish culture, has been used for thousands of years for leisure, relaxation, and wellness. Sauna bathing is linked with substantial health benefits beyond its use for leisure and relaxation. Several observational and interventional studies suggest that regular or frequent sauna bathing reduces the incidence of vascular and nonvascular diseases, such as hypertension, cardiovascular disease, dementia, and respiratory conditions; may improve the severity of conditions such as musculoskeletal disorders, COVID-19, headache, and influenza; and increases the life span. The beneficial effects of sauna bathing on adverse outcomes have been linked to its blood pressure-reducing, anti-inflammatory, antioxidant, cytoprotective, and stress-reducing properties and its synergistic effect on neuroendocrine, circulatory, cardiovascular, and immune function. Evidence suggests that frequent sauna bathing is an emerging protective risk factor that may augment the beneficial effects of other protective risk or lifestyle factors, such as physical activity and cardiorespiratory fitness, or attenuate or offset the adverse effects of other risk factors, such as high blood pressure, systemic inflammation, and low socioeconomic status. This review summarizes the available epidemiologic and interventional evidence linking the combined effects of Finnish sauna bathing and other risk factors on vascular outcomes including cardiovascular disease and intermediate cardiovascular phenotypes, nonvascular outcomes, and mortality. We also discuss the mechanistic pathways underlying the joint contributions of Finnish sauna bathing and other risk factors on health outcomes, the public health and clinical implications of the findings, gaps in the existing evidence base, and future directions.

Phase-change material cooling blanket: A feasible cooling choice during transport after exercise-induced hyperthermia

BACKGROUND

Exercise-induced hyperthermia preceding the onset of exertional heatstroke requires a rapid reduction in the body core temperature (T_core) to ensure safety. In recent years, phase-change material (PCM) cooling devices have been increasingly used for rapid cooling after hyperthermia due to their superior capacity for heat absorption.

OBJECTIVES

This study aimed to evaluate the cooling performance and effectiveness of a PCM cooling blanket on heart rate (HR) and heart rate variability (HRV) recovery after exercise-induced hyperthermia.

DESIGN

Randomized cross-over.

METHODS

The study participants were 12 male volunteers who were engaged in professional training and completed an endurance exercise for approximately 30 min in a hot and humid environment (temperature ≈ 30 °C; relative humidity ≈ 66%). The participants underwent a 30-min cooling trial after exercise, receiving either treatment with a PCM cooling blanket (PCM group) or natural cooling (CON group). The T_core, HR, and HRV time-domain indices were used for analysis.

RESULTS

The T_core values were significantly lower in the PCM group during cooling. Reductions in the T_core from precooling to 20 min of cooling were significantly greater in the PCM group than in the CON group. The HR in the PCM group was lower than that recorded in the CON group at 10 and 20 min of cooling. The reduction in HR during cooling from precooling was also significantly greater in the PCM group. HRV time-domain indices during cooling in the PCM group were significantly lower compared with the CON group while elevations in some HRV time-domain indices from precooling to postcooling were significantly greater in the PCM group than in the CON group.

CONCLUSIONS

The PCM cooling blanket had good cooling performance and the ability to hasten recovery of both HR and HRV. It may serve as a feasible cooling choice during transport after exercise-induced hyperthermia.

Mild Water-Filtered Infrared-A Whole-Body Hyperthermia Reduces Pain in Patients with Fibromyalgia Syndrome-A Randomized Sham-Controlled Trial

The challenging treatment situation of patients with fibromyalgia syndrome (FMS) requires additional therapy options. The effects of water-filtered infrared-A whole-body hyperthermia (WBH) versus sham hyperthermia on pain intensity were investigated in an outpatient setting within a two-armed randomized sham-controlled trial. n = 41 participants aged between 18 and 70 years with a medically confirmed diagnosis of FMS were randomized to WBH (intervention; n = 21) or sham hyperthermia (control; n = 20). Six treatments with mild water-filtered infrared-A WBH over a period of three weeks with at least one day in between treatments were applied. On average, the maximum temperature was 38.7 °C for a duration of approximately 15 min. The control group received exactly the same treatment except that an insulating foil between the patient and the hyperthermia device blocked most of the radiation. Primary outcome was pain intensity measured by the Brief Pain Inventory at week 4. Secondary outcomes included blood cytokine levels and FMS-related core symptoms and quality of life. Pain intensity at week 4 was significantly different between the groups in favor of WBH (p = 0.015). A statistically significant pain reduction in favor of WBH was also found at week 30 (p = 0.002). Mild water-filtered infrared-A WBH effectively reduced pain intensity at the end of treatment and follow-up.

Cardiovascular autonomic modulation during passive heating protocols: a systematic review

Objective.To conduct a systematic review of the possible effects of passive heating protocols on cardiovascular autonomic control in healthy individuals.Approach.The studies were obtained from MEDLINE (PubMed), LILACS (BVS), EUROPE PMC (PMC), and SCOPUS databases, simultaneously. Studies were considered eligible if they employed passive heating protocols and investigated cardiovascular autonomic control by spontaneous methods, such as heart rate variability (HRV), systolic blood pressure variability (SBPV), and baroreflex sensitivity (BRS), in healthy adults. The revised Cochrane risk-of-bias tool (RoB-2) was used to assess the risk of bias in each study.Main results.Twenty-seven studies were included in the qualitative synthesis. Whole-body heating protocols caused a reduction in cardiac vagal modulation in 14 studies, and two studies reported both increased sympathetic modulation and vagal withdrawal. Contrariwise, local-heating protocols and sauna bathing seem to increase cardiac vagal modulation. A reduction of BRS was reported in most of the studies that used whole-body heating protocols. However, heating effects on BRS remain controversial due to methodological differences among baroreflex analysis and heating protocols.Significance.Whole-body heat stress may increase sympathetic and reduce vagal modulation to the heart in healthy adults. On the other hand, local-heating therapy and sauna bathing seem to increase cardiac vagal modulation, opposing sympathetic modulation. Nonetheless, further studies should investigate acute and chronic effects of thermal therapy on cardiovascular autonomic control.

Frequent sauna bathing offsets the increased risk of death due to low socioeconomic status: A prospective cohort study of middle-aged and older men

BACKGROUND AND AIM

Low socioeconomic status (SES) and frequent sauna bathing are associated with increased and decreased risk of all-cause mortality, respectively. Whether there is an interplay among SES, sauna bathing and all-cause mortality risk is not known. We aimed to evaluate the separate and joint associations of SES and frequency of sauna bathing (FSB) with all-cause mortality risk in a prospective cohort study.

METHODS

We employed the Kuopio Ischaemic Heart Disease Study cohort comprising of 2575 men aged 42-61 years at study entry. Self-reported SES and sauna bathing habits were assessed at baseline. Socioeconomic status was categorized as low and high (median cutoff) and FSB as low and high (defined as ≤2 and 3-7 sessions/week, respectively).

RESULTS

During a median follow-up of 27.8 years, 1618 deaths occurred. Comparing low vs high SES, the multivariable-adjusted HR (95 % CI) for all-cause mortality was 1.31 (1.18-1.45). Comparing high vs low FSB, the multivariable-adjusted HR (95 % CI) for all-cause mortality was 0.86 (0.76-0.97). Compared with high SES-low FSB, low SES-low FSB was associated with an increased risk of all-cause mortality 1.35 (1.20-1.51), without significant evidence of an association for low SES-high FSB and all-cause mortality risk 1.07 (0.89-1.29). Positive additive and multiplicative interactions were found between SES and FSB.

CONCLUSIONS

There exists an interplay among SES, sauna bathing and all-cause mortality risk in a general Finnish male population. Frequent sauna baths may offset the increased overall mortality risk due to low SES.

Repeated warm water baths decrease sympathetic activity in humans

Acute whole-body heat stress evokes sympathetic activation. However, the chronic effects of repeated moderate heat exposure (RMHE) on muscle sympathetic nerve activity (MSNA) in healthy individuals remains unclear. We performed RMHE with 4 weeks (5 days/week) warm baths (~40 °C, for 30 min) in 9 healthy older (59 ± 2 yrs) volunteers. Hemodynamic variables and MSNA were examined prior, 1 day after and 1 week following 4 weeks of RMHE in a laboratory at ~23 °C. Cold pressor test and handgrip exercise were performed during the tests. Under normothermic condition, the resting MSNA burst rate (prior, post, post 1-wk: 31.6 ± 2.0, 25.2 ± 2.0, 27.7 ± 1.7 bursts/min; P < 0.001) and burst incidence (P < 0.001) significantly decreased after RMHE. Moreover, the resting heart rate significantly decreased after RMHE (62.3 ± 1.6, 59.5 ± 2.0, 58.2 ± 1.6 beats/min, P = 0.031). The low frequency to high frequency ratio of heart rate variability, an index of sympathovagal balance, also decreased after RMHE. The sensitivity of baroreflex control of MSNA and heart rate were not altered by RMHE, although the operating points were reset. The MSNA and hemodynamic responses (i.e. changes) to handgrip exercise or cold pressor test were not significantly altered. These data suggest that the RMHE evoked by warm baths decreases resting sympathetic activity and HR, which can be considered beneficial effects. The mechanism(s) should be examined in future studies.

Impact of sodium citrate ingestion during recovery after strenuous exercise in the heat on heart rate variability: A randomized, crossover study

Changes in hydration status influence plasma volume (PV) which is associated with post-exercise parasympathetic reactivation. The present study hypothesized that, after dehydrating cycling exercise in the heat (DE), stimulation of PV expansion with sodium citrate (CIT) supplementation would promote heart rate variability (HRV) recovery in endurance-trained men. Twelve participants lost 4% of body mass during DE. During subsequent 16-h recovery, participants consumed water ad libitum (CIT =5.5-L, PLC =5.1-L) and ate prescribed food supplemented with CIT or placebo in a randomized, double-blind, crossover manner. Relative changes in PV were assessed across DE and 16-h recovery. HRV was analyzed before and 16 h after DE in three conditions for altogether four 5-min periods: supine in a thermoneutral environment, supine in the heat (32°C, 46% relative humidity; 2 periods), and standing in the heat. A larger expansion of PV across 16-h recovery occurred in CIT compared to placebo trial (p < 0.0001). However, no between-trial differences appeared in HRV parameters (lnRMSSD, lnSDNN, lnLF/HF) in any 5-min period analyzed before or 16 h after DE (in all cases p > 0.05). Increases in HR (p < 0.001) and lnLF/HF (p = 0.005) and decreases in lnRMSSD (p < 0.001) and lnSDNN (p < 0.001) occurred following DE in both trials. Larger PV expansion induced by CIT supplementation after DE does not improve recovery of HRV at rest and has no influence on HRV responsiveness in endurance-trained men.

Infrared sauna as exercise-mimetic? Physiological responses to infrared sauna vs exercise in healthy women: A randomized controlled crossover trial

BACKGROUND

Passive heat therapies have been reported to have similar effects on the cardiovascular system as exercise. Studies supporting these findings in healthy populations have predominantly been done with men using warm water immersions or traditional saunas, rather than newer infrared-based saunas.

OBJECTIVE

To explore short-term thermal and cardiovascular responses in women using an infrared sauna as compared to moderate-intensity exercise.

STUDY DESIGN

Randomized controlled crossover trial with balanced allocations.

SETTING

Brisbane, Australia (August 2019 - March 2020) PARTICIPANTS: Ten healthy women (36 ± 9 years) INTERVENTIONS: 45 min of resting, infrared sauna or indoor bicycling PRIMARY OUTCOME MEASURES: tympanic/skin temperatures; respiratory rate; blood pressure; arterial stiffness; heart rate variability RESULTS: Tympanic temperatures were elevated during infrared sauna as compared to both control (mean diff = +1.05 ^oC ± SEM 0.12 ^oC, 95% C.I.: 0.73 - 1.36, p < 0.0005) and exercise (mean diff = +0.79 ^oC ± SEM 0.12 ^oC, 95% C.I.: 0.49 - 1.08, p < 0.0005). Respiratory rates were higher during exercise as compared to both control (mean diff = +7.66 ± SEM 1.37, 95% C.I.: 4.09 - 11.23, p < 0.0005) and infrared sauna (mean diff = +6.66 ± SEM 1.33, 95% C.I.: 3.20 - 10.11, p < 0.0005). No significant differences in non-invasive measures of blood pressure, arterial stiffness or heart rate variability were detected between any of the interventions.

CONCLUSIONS

These findings suggest the physiological effects of infrared sauna bathing are underpinned by thermoregulatory-induced responses, more so than exercise-mimetic cardiorespiratory or cardiovascular activations.

The Effects of Repeated Thermal Stress on the Physiological Parameters of Young Physically Active Men Who Regularly Use the Sauna: A Multifactorial Assessment

The aim of this study was to determine the effects of thermal stress (TS) on changes in blood biochemical parameters and fluid electrolyte levels in young adult men with moderate and high levels of physical activity. Thirty men (22.67 ± 2.02 years) were exposed to four 12-min sauna sessions (temperature: 90–91 °C; relative humidity: 14–16%) with four 6-min cool-down breaks. The evaluated variables were anthropometric, physiological, and hematological characteristics. The mean values of HR_avg (102.5 bpm) were within the easy effort range, whereas HR_peak (143.3 bpm) values were within the very difficult effort range. A significant increase was noted in pO2 (p < 0.001), total cholesterol (p < 0.008), HDL (p < 0.006) and LDL cholesterol (p < 0.007). Significant decreases were observed in the SBP (by 9.7 mmHg), DBP (by 6.9 mmHg) (p < 0.001), pH (p < 0.001), aHCO₃- (p < 0.005), sHCO3- (p < 0.003), BE (ecf) (p < 0.022), BE (B), ctCO₂ (for both p < 0.005), glucose (p < 0.001), and LA (p < 0.036). High 72-min TS did not induce significant changes in the physiological parameters of young and physically active men who regularly use the sauna, excluding significant loss of body mass. We can assume that relatively long sauna sessions do not disturb homeostasis and are safe for the health of properly prepared males.

Autonomic Nervous System Response to Far-Infrared Sauna Exposure in Firefighters

OBJECTIVES

Fire departments have employed far-infrared sauna (FIRS) use as part of post-fire call protocols to address concerns related to carcinogens. The inability of the autonomic nervous system (ANS) to fully recover following an emergency call, as demonstrated by heightened sympathetic nervous system activity and delayed parasympathetic nervous system reactivation, has been implicated as a potential factor related to sudden cardiac death. The use of a sauna post-fire call, which has been demonstrated to elevate body temperature, may interfere with the ability of the ANS to fully recover. The purpose of this study was to examine ANS responses to FIRS exposure in firefighters (FFs) with (EX) and without (NONEX) prior maximal exercise.

METHODS

Sixteen career FFs participated in this study. Body temperature (TEMP), heart rate (HR), heart rate variability (HRV), blood pressure (BP), and blood lactate (La─) were measured at the start of each testing session, following a maximal exercise test (EX only), and immediately after a 15-min FIRS exposure for NONEX and EX.

RESULTS

In NONEX, TEMP increased (P < 0.001); however, there was no change in HR, HRV, BP, or La─. In EX, BP remained unchanged while TEMP, HR, and La─ were significantly (P < 0.001) greater than baseline following FIRS exposure and HRV was significantly (P = 0.018) lower than baseline.

CONCLUSIONS

These findings indicate that FIRS following maximal exercise did support some ANS recovery, but may interfere with restoration of body temperature and parasympathetic nervous system reactivation, potentially influencing post-call cardiovascular risk in FFs.

Sauna use as a lifestyle practice to extend healthspan

Sauna use, sometimes referred to as "sauna bathing," is characterized by short-term passive exposure to high temperatures, typically ranging from 45 °C to 100 °C (113 °F to 212 °F), depending on modality. This exposure elicits mild hyperthermia, inducing a thermoregulatory response involving neuroendocrine, cardiovascular, and cytoprotective mechanisms that work in a synergistic fashion in an attempt to maintain homeostasis. Repeated sauna use acclimates the body to heat and optimizes the body's response to future exposures, likely due to the biological phenomenon known as hormesis. In recent decades, sauna bathing has emerged as a probable means to extend healthspan, based on compelling data from observational, interventional, and mechanistic studies. Of particular interest are the findings from large, prospective, population-based cohort studies of health outcomes among sauna users that identified strong dose-dependent links between sauna use and reduced morbidity and mortality. This review presents an overview of sauna practices; elucidates the body's physiological response to heat stress and the molecular mechanisms that drive the response; enumerates the myriad health benefits associated with sauna use; and describes sauna use concerns.

Effects of 12 sessions of steam bath intervention on spirometry parameters among healthy adult volunteers

OBJECTIVES

Steam bath is extensively used around the world. However, its physiological influence is not understood in detail. Objective of the current study is to examine the effects of 12 sessions of steam bath on spirometric parameters among healthy participants.

METHODS

Forty healthy adult volunteers of both sex (14 male and 26 female) aged 26.38 ± 8 years participated in the study. A steam bath session (10-15 min) was given once a week for 12 weeks. The spirometric parameters [forced expiratory volume in the 1st second (FEV1, L), forced vital capacity (FVC, L), FEV1/FVC ratio (absolute value), maximal mid-expiratory flow (MMEF, L/s) and peak expiratory flow (PEF, L/s)] were measured by Helios 401 spirometer.

RESULTS

Compared to baseline, post-intervention spirometric parameters showed significant (p<0.05) improvement in the FVC (82.40 ± 11.24 to 96.91 ± 18.76), FEV1 (86.13 ± 14.39 to 91.17 ± 12.48), FEV1/FVC ratio (86.96 ± 3.64 to 93.75 ± 4.80), MMEF 25-75% (86.96 ± 3.64 to 94.16 ± 11.57), peak expiratory flow rate (79.82 ± 14.90 to 92.18 ± 18.96).

CONCLUSIONS

Taking steam bath improves the spirometric parameters of healthy adult participants. However, future randomized controlled trials with on a large scale have to done to validate our findings.

Endocrine Effects of Repeated Hot Thermal Stress and Cold Water Immersion in Young Adult Men

The aim of the study was to determine the effect of repeated hot thermal stress and cold water immersion on the endocrine system of young adult men with moderate and high levels of physical activity (PA). The research was conducted on 30 men aged 19–26 years (mean: 22.67 ± 2.02) who attended four sauna sessions of 12 min each (temperature: 90−91°C; relative humidity: 14–16 %). Each sauna session was followed by a 6-min cool-down break during which the participants were immersed in cold water (10−11°C) for 1 min. Testosterone (TES), cortisol (COR), dehydroepiandrosterone sulfate (DHEA-S), and prolactin (PRL) levels were measured before and after the sauna bath. The participants’ PA levels were evaluated using the International Physical Activity Questionnaire. Serum COR levels decreased significantly (p < .001) from 13.61 to 9.67 µg/ml during 72 min of sauna treatment. No significant changes (p >.05) were noted in the concentrations of the remaining hormones: TES increased from 4.04 to 4.24 ng/ml, DHEA-S decreased from 357.5 to 356.82 µg/ml, and PRL decreased from 14.50 to 13.71 ng/ml. After sauna, a greater decrease in COR concentrations was observed in males with higher baseline COR levels, whereas only a minor decrease was noted in participants with very low baseline COR values (r =−0.673, p <.001). Repeated use of Finnish sauna induces a significant decrease in COR concentrations, but does not cause significant changes in TES, DHEA-S, or PRL levels. Testosterone concentrations were higher in men characterized by higher levels of PA, both before and after the sauna bath.

Sauna bathing frequency in Finland and the impact of COVID-19

OBJECTIVES

Recent research has revealed multiple potential health benefits of frequent sauna bathing. Finland is a country with extraordinary sauna culture and bathing opportunities. However, coronavirus disease 2019 (COVID-19) pandemic introduced regulations and unprecedented closures to shared sauna facilities. In this study we aimed to examine the previously unknown baseline bathing frequency and its possible change during the epidemic.

DESIGN

We investigated several aspects of sauna bathing with self-reports: the frequency, its possible changes, reasons for change, and beliefs about its health effects among a representative sample of thousand Finns aged 18-75 years. This online survey was administered in May 2020.

RESULTS

Before the pandemic, 59 % of our respondents had enjoyed sauna at least once a week. Since the pandemic began, up to 23 % had reduced or stopped their bathing. This was often due to restricted sauna access. However, 11 % of respondents bathed more frequently and attributed this change to seeking relaxation and passing time. These findings demonstrate a surprising flexibility in this health-promoting national pastime. Men were more active bathers than women overall and women under 35 enjoy sauna more seldom than older women. Only 7.9 % of all respondents bathed at least four times a week, exceeding a suggested threshold for maximum health benefits.

CONCLUSIONS

Finnish people are active sauna bathers. The COVID-19 pandemic demonstrated that the frequency of bathing is dependent on good access to sauna facilities. This flexibility and wide access could be exploited to improve public health in the long term if more frequent bathing became a standard.

Meditation and Cardiovascular Health in the US

The 2017 American Heart Association Scientific Statement on meditation and cardiovascular risk suggested that meditation may be considered as an adjunct to guideline-directed cardiovascular risk-reduction interventions. Meditation could potentially increase physical and mental relaxation, leading to improved outcomes after a major cardiovascular event. We hypothesized that meditation is associated with lower cardiovascular risk in the US general population. Using data from the 2012 and 2017 National Health Interview Survey, we identified all patients with hypercholesterolemia, systemic hypertension (SH), diabetes mellitus (DM), stroke, and coronary artery disease (CAD), as well as those who reported that they meditate. Multivariable logistic regression analyses were performed to evaluate the association between meditation and risk of hypercholesterolemia, SH, DM, stroke, and CAD, adjusting for potential confounders. Of 61,267 the National Health Interview Survey participants, 5,851 (9.6%) participated in some form of meditation. After adjusting for age, gender, body mass index, race, marital status, cigarette smoking, sleeping duration, and depression, meditation was independently associated with a lower prevalence of hypercholesterolemia (odds ratio [OR] 0.65; 95% confidence interval [CI] 0.54 to 0.79; p = 0.001), SH (OR 0.86; 95% CI 0.75 to 0.99; p = 0.04), diabetes (OR 0.70; 95% CI 0.59 to 0.84; p = 0.0001), stroke (OR 0.76; 95% CI 0.58 to 0.99; p = 0.04), or CAD (OR 0.51; 95% CI 0.39 to 0.66; p <0.001), compared with those who did not meditate. In conclusion, using a large national database, we found that meditation is associated with a lower prevalence of cardiovascular risks factors and disease.

Impact of Finnish sauna bathing on circulating markers of inflammation in healthy middle-aged and older adults: A crossover study

OBJECTIVES

Finnish sauna bathing is associated with a reduced risk of adverse health outcomes. The acute physiological responses elicited by Finnish sauna bathing that could explain this association remain understudied. This study characterized the acute effect of Finnish sauna bathing on circulating markers of inflammation in healthy middle-aged and older adults.

DESIGN

With the use of a crossover study design, 20 healthy middle-aged and older adults (9 men/11 women, 66 ± 6 years old) performed 3 interventions in random order: 1) 1 x 10 min of Finnish sauna bathing (80 °C, 20 % humidity); 2) 2 x 10 min of Finnish sauna bathing; 3) a time-control period during which participants sat outside of the sauna for 10 min.

MAIN OUTCOMES

Venous blood samples were obtained before (≤15 min) and after (∼65 min) each intervention to determine circulating concentrations of interleukin 6 (IL-6), interleukin 1 receptor antagonist (IL-1RA), and C-reactive protein (CRP).

RESULTS

IL-6 increased in response to 2 x 10 min of sauna bathing (+0.92 pg/mL [+0.16, +1.68], P = 0.02), but not following the 1 x 10 min session (+0.17 pg/mL [-0.13, +0.47], P = 0.26). IL1-RA increased during the 1 x 10 min (+51.27 pg/mL [+20.89, +81.65], P < 0.01) and 2 x 10 min (+30.78 pg/mL [+3.44, +58.12], P = 0.03) sessions. CRP did not change in response to either sauna session (P = 0.34).

CONCLUSION

These results demonstrate that typical Finnish sauna bathing sessions acutely increase IL-6 and IL1-RA in healthy middle-aged and older adults.

Hand heating lowers postprandial blood glucose concentrations: A double-blind randomized controlled crossover trial

OBJECTIVES

Examine effect of single hand heating with and without negative pressure on fasting blood glucose (FBG) and postprandial blood glucose (PBG).

DESIGN

Double-blind randomized controlled trial with crossover design.

SUBJECTS

FBG experiment: 17 healthy subjects (4 males). PBG experiment: 13 healthy subjects (1 males).

INTERVENTIONS

Devices included one providing heat only, one heat and negative pressure, and one acting as a sham. For the FBG experiment the devices were used for 30 min. For the PBG experiment the devices were used for one hour during an oral glucose tolerance test (OGTT).

OUTCOME MEASURES

Blood glucose measurements were used to determine change in FBG, peak PBG, area under the curve (AUC), and incremental AUC (iAUC).

RESULTS

Temperature: Change in tympanic temperature was ≤ 0.15 °C for all trials. FBG: There was no effect on FBG. PBG: Compared to the sham device the heat plus vacuum and heat only device lowered peak blood glucose by 16(31)mg/dL, p = 0.092 and 18(28)mg/dL, p = 0.039, respectively. AUC and iAUC: Compared to the sham device, the heat plus vacuum device and heat only device lowered the AUC by 5.1(15.0)%, p = 0.234 and 7.9(11.1)%, p = 0.024 respectively and iAUC by 17.2(43.4)%, p = 0.178 and 20.5(34.5)%, p = 0.054, respectively.

CONCLUSIONS

Heating a single hand lowers postprandial blood glucose in healthy subjects.