A stint in a sauna is not only pleasant and relaxing but may also improve health, according to the authors of a new, comprehensive literature review. Among the benefits they identified were a reduced risk for cardiovascular, neurocognitive, and pulmonary illnesses such as asthma and influenza; amelioration of pain conditions such as rheumatic diseases and headache; decreased risk for mortality; and an improved quality of life.
Overall, "[t]he physiological responses produced by an ordinary sauna bath correspond to those produced by moderate- or high-intensity physical activity such as walking," Jari A. Laukkanen, MD, PhD, from the Faculty of Sport and Health Sciences, University of Jyväskylä; the Department of Internal Medicine, Central Finland Health Care District, Jyväskylä; and the Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, all in Finland, and colleagues write in an article published online July 31 in Mayo Clinic Proceedings. In fact, the advantages of sauna bathing plus physical activity may be additive, they write.
The findings build on earlier research by the same authors linking sauna use to a decreased risk for stroke. In that study, there was an inverse relationship between frequency of weekly sauna visits and stroke rates per 1000 person-years of follow-up. The authors listed a variety of positive effects associated with sauna baths that might account for that finding, including lower blood pressure and improvements in lipid profiles, arterial stiffness, carotid intima-media thickness, and peripheral vascular resistance, as well as a reduced risk for hypertension, dementia, and cardiovascular and all-cause mortality.
Key Findings Emerge
In the current review, the researchers examined observational studies as well as randomized and nonrandomized controlled trials on the health effects of sauna bathing available on MEDLINE and EMBASE from the inception of those search engines until February 24, 2018. They confined the analysis to traditional Finnish sauna baths, as those have been the most widely studied to date.
In a Finnish sauna, temperatures range from 80°C to 100°C (176°F - 212°F), with 10% to 20% relative humidity. A bather will usually spend 5 to 20 minutes in the sauna and follow it with a swim, a shower, or just a cooling-off period at room temperature, the authors explain. Finnish people typically have "a sauna bath at least once per week, with the average habitual frequency being 2 to 3 times/wk."
Several key studies included in the review showed a decreasing risk for certain acute and chronic conditions associated with greater sauna use. For example, in one study the risk ratio of hemorrhagic stroke among people who had four to seven sessions per week was 0.33 (95% confidence interval [CI], 0.07-1.51) compared with people who used the sauna only once per week. In another study, four to seven sauna sessions per week was associated with a relative risk for dementia and Alzheimer disease of 0.34 (95% CI, 0.16 - 0.71) and 0.35 (95% CI, 0.14 - 0.90), respectively, compared with one session per week. Similarly, sessions of 19 minutes or more were associated with a relative risk for sudden cardiac death and all-cause mortality of 0.48 (95% CI, 0.31 - 0.75) and 0.83 (95% CI, 0.87 - 1.20), respectively, compared with sessions lasting 11 minutes.
Two experimental studies on middle-aged adults have shown beneficial effects on systolic and diastolic blood pressure after single, 30-minute sessions in a sauna, whereas in one long-term prospective study, the risk of developing hypertension was reduced by 47% in white men followed for 24.7 years, leading Kunutsor and colleagues to caution that any protective effect of regular sauna bathing on the risk for hypertension will have to be confirmed in a more robust, randomized clinical trial.
Many physiologic pathways have been implicated as possible mediators of sauna benefits, including reduced blood pressure, "improvement in endothelial function; reduction in oxidative stress and inflammation; beneficial modulation of the autonomic nervous system; positive alteration in levels of circulating vascular risk factors such as natriuretic peptides and lipids; hormonal changes; improved arterial stiffness, arterial compliance, and intima media thickness; and improvement in the cardiorespiratory system as well as cardiovascular function," the authors write.
The growing body of evidence on the cardiovascular effects of sauna sessions, plus "the established role of physical activity" in maintaining good health suggests that both activities together may enhance health benefits even more, they add. "Indeed, we have recently shown that a combination of good fitness levels due to aerobic exercise and frequent sauna bathing confers more protection against the risk of cardiovascular and all-cause mortality events."
However, the authors caution that more evidence is needed before any direct links can be made between the health effects of sauna exposure and subclinical outcomes such as arterial wall changes.
Good Safety Profile
Along with its health benefits, sauna bathing has a good safety profile, the authors write. Sauna use has been associated with some cases of sudden death, but "these incidents have been shown to be at least partly due to alcohol consumption, which may have led to these accidents."
However, saunas are not without risks. The rapid shift from the heat of the sauna to a colder environment may lead to sudden hemodynamic changes or arrhythmias, making it risky for people with a recent history of myocardial infarction. Hence, saunas are contraindicated for people with conditions such as "unstable angina pectoris, recent myocardial infarction, uncontrolled hypertension, ischemic or decompensated heart failure, or severe aortic stenosis," the authors warn. The evidence suggests that it is safe for people with stable cardiovascular conditions such as recovery from a myocardial infarction or stable angina pectoris.
Other possible contraindications include infectious or inflammatory conditions, fever, and certain skin conditions such as abrasions or urticaria.
Overall, more studies are needed "to confirm whether the observed associations reflect a true causal effect of frequent sauna bathing on these health conditions, and more studies are warranted to find whether regular sauna bathing could produce longer-term changes in cardiovascular health," the authors add.
In addition, it is not known whether these benefits would extend to saunas operating at lower temperatures or to other forms of passive heat therapy, such as infrared heat exposure, steam rooms, hot tubs, or the Japanese version of sauna bathing known as Waon therapy.
However, they conclude, "based on the current knowledge and evidence, sauna bathing may have beneficial effects and has therapeutic potential to reduce the risk of adverse health outcomes in the general population," particularly among people who may find it difficult to exercise.
The authors have disclosed no relevant financial relationships.
Mayo Clin Proc. Published online July 31, 2018.
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Cite this: Saunas Linked to Numerous Health Benefits - Medscape - Jul 31, 2018.