This suggests that heat stress, whether induced by infrared or Finnish-style sauna, causes significant sweating that is likely to lead to hormetic adaptation and beneficial cardiovascular and metabolic effects. Nevertheless, these findings point to the need for further study and serious consideration given to sauna bathing to address the ever-increasing individual, societal, and financial burdens of cardiovascular disease as well as dementia-related conditions in aging populations.
Several mechanisms of action have been proposed for the health effects of frequent sauna bathing. Together, these findings support complex multipathway end-organ effects on the central and autonomic nervous system, the peripheral vascular endothelium, and the hypothalamus-pituitary-adrenal axis, as well as on the kidneys and the liver that are continuing to be documented [ 1 , 11 , 28 , 81 ]. The complexity of how sauna bathing may influence cardiovascular risk factors is suggested by the report of beneficial effects on total cholesterol and LDL low density lipoprotein cholesterol and conflicting results on HDL high density lipoprotein levels in healthy young men and women [ 63 , 66 , 67 ].
These findings, which need to be confirmed in larger studies with nonsauna control groups, may point to differences between Finnish and infrared saunas as they contrast with previous similarly sized, yet better controlled studies of infrared sauna bathing in populations at increased risk of cardiovascular disease [ 37 , 47 , 49 ].
These findings may also be compared to the metabolic effects of exercise in healthy populations which include improvements in both LDL and HDL lipid levels [ 82 ].
This is supported by newer, single-cell analysis methods that suggest sauna bathing increases generation of free radicals and reactive oxygenated species along with enhanced antioxidant activities via proposed nitric oxide- NO- dependent processes in blood [ 62 ] and upregulation of specific HSPs heat shock proteins and HSFs heat shock factors in semen [ 27 ]. The two studies in athletes further support sauna's involvement in hormetic stress responses with the findings of plasma volume expansion after 4 days of daily postexercise sauna bathing, followed by a trend back to presauna levels by days 7—10 in one study [ 61 ], along with mean postsauna increases in axillary body temperature of 2.
Improved adaptation to stress with regular sauna bathing may be further enhanced by excretion of toxicants through heavy sweating. Many industrial toxicants including heavy metals, pesticides, and various petrochemicals may be excreted in sweat leading to an enhancement of metabolic pathways and processes that these toxic agents inhibit [ 83 ].
Sweat-induced excretion of toxic metals such as arsenic, cadmium, lead, and mercury has been reported with the rates of excretion matching or exceeding urinary routes [ 84 ]. There is also recent evidence that toxic chemicals and xenobiotics such as polybrominated diphenyl ether PBDE flame retardants, organochlorine pesticides, bisphenol-A BPA , and phthalates may be excreted via induced sweating at rates that exceed urinary excretion [ 85 — 88 ]. The importance of sweat in excretion pathways has been further documented by sweat-patch technology used to monitor illicit drug use and is based on dozens of studies of the pharmacodynamics and pharmacokinetics of amphetamine, cocaine, cannabis, opiates, and associated metabolites [ 89 , 90 ].
While sweat-induced detoxification certainly occurs, studies using sauna for detoxification purposes report more favourable findings with subjective rather than objective measures [ 68 , 69 ]. In addition to having profound physiological effects, sauna bathing is reported to have beneficial psychological effects that are reflected in the many reports of improved well-being, pain tolerance, and other self-assessed symptom-related scoring [ 34 , 36 , 43 , 45 , 46 , 50 — 56 , 58 , 60 , 68 , 69 ].
The psychological impact of sauna bathing may be due to a combination of factors that include release of endorphins and other opioid-like peptides such as dynorphins [ 81 , 92 ], forced mindfulness, psychological stress reduction, relaxation, improved sleep, time out from busy life schedules, placebo effects, and other aspects of individual psychological and social interactions that likely occur around frequent sauna activity. While it is difficult to distinguish between the different factors that produce positive psychological effects, such effects may enhance other physiological and metabolic benefits as they are likely to promote adherence to regular sauna activity.
The risk of death from saunas was examined in retrospective population studies of frequent sauna users in Sweden and Finland, with the annual death rate from saunas being reported as 0.
Detailed comparative analysis of adverse effects between studies was limited by small sample sizes, heterogeneity of sauna types and study design many without control groups , and inconsistent reporting of adverse side effects within outcome measures. The highest intensity of adverse effects moderate levels of heat intolerance occurred in populations afflicted with chronic fatigue syndrome, chronic pain, rheumatoid arthritis, and ankylosing spondylitis.
The direct adverse effects of heat may also be responsible for the impairment of sperm counts, concentration, and motility and upregulation of heat-stress-related genes reported in the sperm of 10 healthy men after a 3-month course of Finnish-style sauna [ 27 ]. While these findings are based upon one identified study of only 10 men, the findings are consistent with some earlier research on the effects of genital heat stress on semen quality [ — ].
While this supports current recommendations for men seeking to optimize fertility to avoid sauna-type activities [ ], further research is required to determine if similar effects on sperm occur with lower temperature infrared sauna bathing or if sauna bathing has any effect on male fertility.
To the best of our knowledge, this is the first systematic review to include both Finnish-style and infrared sauna studies. However, we did not include studies of steam sauna interventions and therefore may have overlooked some evidence of the effects of heat on health. Another limitation of this study is the inclusion of only English language, especially since sauna activity is frequent in non-English speaking countries.
Furthermore, the quality of the reviewed studies was variable with many studies having small sample sizes, poorly described methodology, variable use of controls, differing types of sauna and sauna protocols, variable duration and frequency of sauna interventions, and inconsistent mention of cooling therapies or rehydration protocols along with heterogeneous outcome measures.
The great heterogeneity of studies makes meaningful comparisons across studies difficult and provides insufficient evidence to recommend specific temperature, frequency, or duration of sauna bathing for any specific health outcome. In the months since this systematic review was conducted, a number of new research findings have been published, analyzing various subsets of the same Finnish prospective cohort of over men who regularly sauna-bathed, initially aged 42—60 years, followed over 20 years as part of the KIHD Kuopio Ischemic Heart Disease study, as detailed in two of the studies included in Table 1 : cardiovascular disease- CVD- related sauna studies.
These newer findings cite reduced risk of acute and chronic respiratory conditions [ ], reduced risk of pneumonia [ ], reduced serum levels of C-reactive protein marker of systemic inflammation [ ] with more frequent sauna bathing, and reduced risk of hypertension [ ] and additional improved all-cause mortality when jointly associated with cardiorespiratory fitness [ ].
These findings add further support to the conclusions of this review. Further study of these metabolic pathways might also help to elucidate the stress-related pathways of immune and inflammatory activity that may be involved in conditions such as chronic fatigue syndrome, chronic pain, rheumatoid arthritis, and ankylosing spondylitis. Studies examining heart rate variability HRV as an outcome assessment are increasing and further results may better inform the physiological models of what is thought to be happening with repeated sauna of either Finnish or infrared types.
Conducting more studies of repeated sauna in healthy but nonathletic participants may further help to elucidate the similarities and differences in metabolic pathways between repeated sauna activity and regular exercise.
Further studies are also needed to distinguish between the health effects of Finnish saunas, which often involve brief periods of increased humidity and dramatic cooling interventions, compared to the lower temperature infrared saunas that typically do not have such variations.
The mechanisms for these effects may include increased bioavailability of NO nitric oxide to vascular endothelium, heat shock protein-mediated metabolic activation, immune and hormonal pathway alterations, enhanced excretions of toxicants through increased sweating, and other hormetic stress responses.
Currently there is insufficient evidence to recommend specific types of sauna bathing for specific clinical conditions. While regular sauna bathing appears to be well-tolerated in the clinical setting with only minor and infrequent adverse effects reported, further data on the frequency and extent of adverse effects is required. Further studies are also required to explore the mechanisms by which sauna bathing exerts physiological, psychological, and metabolic effects, as well as to better define the benefits and risks of distinct types of saunas and the optimal frequency and duration of sauna bathing for beneficial health effects.
This manuscript was developed as part of study conducted by Dr. Joy Hussain during her Ph. Joy Hussain is supported by a Ph. National Center for Biotechnology Information , U. Evid Based Complement Alternat Med. Published online Apr Joy Hussain and Marc Cohen. Author information Article notes Copyright and License information Disclaimer.
Joy Hussain: moc. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article has been cited by other articles in PMC. Abstract Introduction Many health benefits are claimed by individuals and facilities promoting sauna bathing; however the medical evidence to support these claims is not well established. Methods A systematic search was made of medical databases for studies reporting on the health effects of regular dry sauna bathing on humans from onwards.
Results Forty clinical studies involving a total of participants met the inclusion criteria. Conclusions Regular dry sauna bathing has potential health benefits. Introduction Sauna bathing is a form of whole-body thermotherapy that has been used in various forms radiant heat, sweat lodges, etc. Methods PRISMA guidelines for conducting systematic reviews were followed, including the use of validated tools to assess the risk of bias in randomized controlled trials [ 70 — 72 ].
Eligibility Criteria Studies of humans undergoing repeated dry sauna bathing that reported on health measures were included in the review. Data Extraction Abstracts of initially identified studies were screened by investigator JH and then the complete full-text articles of potentially eligible studies were carefully screened by both investigators JH and MC for research design, population descriptive data, timing and physical details of dry sauna intervention, outcome measures, key results, and adverse effects.
Assessment for Risk of Bias Included randomized controlled trials RCTs were assessed for risk of bias according to the Cochrane Collaboration's tool for assessing bias and calculated Jadad et al. Results 3. Literature Search Figure 1 summarises the screening and assessment strategies used with the search results. Open in a separate window. Figure 1. Table 1 Cardiovascular disease- CVD- related sauna studies. Table 3 Airway conditions and repeated sauna therapy.
None Pach et al. Symptom severity scoring 0—10 on four different days; intake of common cold medications daily during week of intervention. Mild , cough directly stimulated by face mask in both groups 2 in treatment group; 1 in control group. None Umehara et al. Table 4 Repeated sauna and athletes. Table 5 Sauna studies of healthy populations. None Kowatzki et al. None Pilch et al. None Gryka et al. Table 6 Repeat sauna therapy and detoxification.
Mild , heat discomfort. Table 7 Repeated sauna and male fertility. No significant changes in plasma sex hormones at any timepoints. Study Design Of the forty studies, 13 were randomized controlled trials RCTs , 6 were trials with nonrandomized control groups and 2 were prospective cohort studies.
Table 8 Risk of bias assessment in randomized controlled trials. Random sequence generation Allocation concealment Blinding of participants and personnel Blinding of outcome assessment Incomplete outcome data Selective reporting Other bias Jadad et al. Setting and Participant Characteristics The reviewed studies included a total of participants living in 12 different countries. Interventions Eleven studies investigated the use of Finnish saunas and 25 studies utilised infrared sauna interventions.
Outcome Measures Some studies focused solely on measuring subjective quality of life and symptom scoring surrounding sauna activity such as SF item short form health survey ; FASE Foundation for Advancements in Science and Education item survey of symptoms and sleep, CMI Cornell Medical Index survey of somatic complaints; VAS visual analogue scales for hunger, relaxation, and specific types of pain i. Health Outcomes 3. Chronic Pain Syndromes Two randomized controlled trials investigated the subjective effects of repeated sauna on chronic pain disorders.
Lungs and Airways Two studies focused on the effects of infrared sauna on patients diagnosed with COPD chronic obstructive pulmonary disease. Athletes Two small noncontrolled interventional trials studied the physiological effects of repeat sauna in athletes.
Healthy Populations Two small uncontrolled, single-gender studies reported reduced total cholesterol levels 4. Detoxification Populations burdened with toxicants were the subject of two studies. Spermatogenesis One longitudinal time-course study examined the effects of Finnish sauna activity on male sperm and fertility measures in 10 healthy men. Adverse Side Effects Of the 40 included studies, only eight reported any adverse symptoms from sauna bathing.
Discussion 4. Principal Findings The findings of this review suggest frequent dry sauna bathing improves a variety of subjective and objective health parameters and that frequent Finnish sauna bathing is associated with improved outcomes such as reduced overall mortality and reduced incidence of cardiovascular events and dementia, at least in men [ 38 , 39 ]. Mechanisms of Action: Sauna Bathing Several mechanisms of action have been proposed for the health effects of frequent sauna bathing.
Acknowledgments This manuscript was developed as part of study conducted by Dr. Conflicts of Interest The authors declare that they have no conflicts of interest. References 1. Hannuksela M. Benefits and risks of sauna bathing. American Journal of Medicine. Beever R. Far-infrared saunas for treatment of cardiovascular risk factors: summary of published evidence.
Canadian Family Physician. Brockow T. The role of mild systemic heat and physical activity on endothelial function in patients with increased cardiovascular risk: results from a systematic review.
Research in Complementary Medicine. Gayda M. Effects of sauna alone versus postexercise sauna baths on short-term heart rate variability in patients with untreated hypertension. Journal of Cardiopulmonary Rehabilitation and Prevention.
Littmann A. Whole body heat stress increases motor cortical excitability and skill acquisition in humans. Clinical Neurophysiology. Minett G. The Cochrane Library; Calabrese E. Defining hormesis. Human and Experimental Toxicology. Mattson M. Hormesis defined. Ageing Research Reviews. Arena R. Healthy lifestyle interventions to combat noncommunicable disease—a novel nonhierarchical connectivity model for key stakeholders: a policy statement from the American Heart Association, European Society of Cardiology, European Association for Cardiovascular Prevention and Rehabilitation, and American College of Preventive Medicine.
European Heart Journal. The heart rate rises as the body attempts to keep cool. It is not uncommon to lose about a pint of sweat while spending a short time in a sauna. Wood burning : Wood is used to heat the sauna room and sauna rocks. Wood-burning saunas are usually low in humidity and high in temperature. Electrically heated : Similar to wood-burning saunas, electrically-heated saunas have high temperatures and low humidity. An electrical heater, attached to the floor, heats the sauna room.
Infrared room : Far-infrared saunas FIRS are different to wood-burning and electrically-heated saunas. Temperatures are typically lower than other saunas, but the person sweats in a similar way. Steam room : These are different from saunas. Instead of dry heat, a steam room involves high humidity and moist heat. When a person sits in a sauna, their heart rate increases and blood vessels widen.
This increases circulation, in a similar way to low to moderate exercise depending on the duration of sauna use. Heart rate may increase to beats a minute while using a sauna. This may bring some health benefits. Increased circulation may help reduce muscle soreness, improve joint movement, and ease arthritis pain.
As the heat in a sauna improves circulation, it may also promote relaxation. This can improve feelings of well-being. The reduction in stress levels when using a sauna may be linked to a lower risk of cardiovascular events. One study, conducted in Finland, followed 2, men ages 42 to 60 over the course of 20 years. Findings suggested that people who use a sauna may have a lower risk of dying from cardiovascular disease. Of the participants in the study, a total of died from cardiovascular disease, coronary artery disease , or sudden cardiac death.
Participants were categorized by how often they used a sauna, including once a week, two to three times a week, and four to seven times a week. After adjusting for cardiovascular risk factors, increased sauna use was linked with a reduced risk of fatal cardiovascular-related diseases. Participants who used the sauna two to three times a week were 22 percent less likely to experience sudden cardiac death than those who only used it once a week.
Those who used a sauna four to seven times a week were 63 percent less likely to experience sudden cardiac death and 50 percent less likely to die from cardiovascular disease than those who only used a sauna once a week. More research is needed to find out if there is a definite link between sauna use and a decrease in deaths from heart disease. Sauna use may also be associated with lower blood pressure and enhanced heart function. Health news headlines can be deceiving.
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Menopause and memory: Know the facts. How to get your child to put away toys. In Finland and other Scandinavian countries, the sauna has a culturally significant role. But for many Americans, adopting a sauna routine may take a bit of practice. More expensive saunas tend to be ones to construct within your home or outdoors. Less expensive saunas are portable tent-like structures. Regardless of which you choose, make sure to follow any directions in setup and use. You don't have to get totally naked to enjoy a sauna session either.
You may begin with about 10 or 15 minutes at a time, and then may increase the length of your sessions based on your comfort level. Not only can using a sauna clear your mind, it could potentially help you reach your fitness goals faster, says McKinney.
One recent study found that sauna use can help preserve muscle mass, as well as help guard against inflammation. The sauna also may increase cardiovascular endurance, as it may lower your resting heart rate over time. However, used in conjunction with a workout plan, you may find yourself being able to go harder for longer and recover more quickly than if you skipped the sauna.
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