Several mechanisms of action have been proposed for the health effects of frequent sauna baths. Exposure to heat increases cardiac output and reduces peripheral vascular resistance and induces other physiological changes in cardiovascular parameters, such as decreased systolic and/or diastolic blood pressure [31, 35, 37, 46-49, 60, 65], increased HRV, improved markers of heart function and improved arteriolation mediated by the flow of small and/or large blood vessels [34, 40, 42, 45, 47–49]. With regard to hormonal and metabolic models, decreased levels of epinephrine and / or norepinephrine, increased levels of nitric oxide metabolites in blood and urine, decreased levels of total and LDL cholesterol, increased serum levels of growth hormone, adrenocorticotropic hormone and cortisol, decreased fasting blood glucose levels, increased plasma ghrelin levels and decreased urine levels of prostaglandins (8-epi-prostaglandin F2α).
Saunas can cause some side effects, such as frequent urination, discomfort with heat and low blood pressure, but such cases benefits of using a sauna are rare. However, keep in mind that you should not go to the sauna if you are taking medications that anesthetize you.
Together, these findings support the complex effects of multi-pathway end organs on the central and autonomic nervous systems, peripheral vascular endothelium, and hypothalamus-pituitary-adrenal axis, as well as on the kidneys and liver that are still documented. There is considerable evidence that sauna baths can cause profound physiological effects [4, 11-17]. Intense short-term exposure to heat increases the skin temperature and core temperature of the body and activates thermoregulatory pathways through the hypothalamus and CNS that lead to activation of the autonomic nervous system. Activation of the sympathetic nervous system, the hypothalamic-pituitary-adrenal hormonal axis and the renin-angiotensin-aldosterone system leads to well-documented cardiovascular effects with increased heart rate, skin blood flow, cardiac output and sweating.
More studies are also needed to distinguish between the health effects of Finnish saunas, which often include short periods of increased humidity and dramatic cooling interventions, compared to low-temperature infrared saunas that generally have no such variations. Other intervention studies focused on obtaining objective measurements related to sauna activity. Studies in patients with increased cardiovascular risk or studies of healthy patients with the goal of detecting changes in cardiovascular risk with sauna activity used some of the same physiological parameters listed above, as well as serum lipid profiles, fasting plasma glucose levels, serum uric acid levels, plasma ghrelin levels, serum leptin levels, plasma Hb and HCT levels, and urinary prostaglandin levels. As the heat from the blood begins to move to the surface of the skin, the body’s nervous system sends signals to the millions of sweat glands that cover the human body. Sweat production is mainly designed to cool the body and consists of 99% water. However, deep sweating in a sauna can help reduce levels of lead, copper, zinc, nickel, mercury and chemicals, which are toxins that are often absorbed by interacting with our daily environment.
Participants reported feeling that their physical health, overall health and social functioning improved and that stress and fatigue levels decreased. Saunas or thermotherapy include periodic exposure to dry air heated at temperatures between 80 and 100 degrees for 10 to 20 minutes at a time. Some of the various benefits of sauna, such as removing toxins from the body, relieving pain in people with rheumatoid arthritis, boosting immunity, etc., have been extensively studied, especially with regard to dry sauna.
Despite differences in sauna types, temperature, frequency and duration of interventions, far-infrared sauna studies in patients with cardiovascular disease and congestive heart failure suggest favorable results that reinforce previous findings from interventional studies of Finnish sauna and cardiovascular disease [75-79]. This suggests that heat stress, whether caused by infrared or Finnish sauna, causes significant sweating that is likely to lead to hormetic adaptation and beneficial cardiovascular and metabolic effects. This is supported by the two large observational studies that found surprising reductions in the risk of sudden cardiac death (63%) and all-cause mortality (40%), as well as dementia (66%) and Alzheimer’s disease (65%), in men who used a sauna 4-7 times a week compared to just once a week. While these large cohort studies are based on hazard ratios calculated with adjustments for common cardiac risk factors, it has been noted that the association between sauna activity and health outcomes may be non-causal and that sauna use is simply an indicator of “healthy lifestyle” and other socioeconomic confounding factors. However, these findings point to the need for more studies and serious attention to sauna baths to address the increasing individual, social and financial burdens of cardiovascular disease, as well as dementia-related conditions in aging populations.
The sauna pool is inexpensive and widely accessible with Finnish-style saunas most often used in family, group and public environments and infrared saunas that are usually built and marketed for individual use. Public sauna facilities may be located in exercise facilities, and the relationship between saunas and exercise, including synergistic hormeric responses, is an area of active research [3-8]. The use of private saunas, especially infrared saunas, is also increasing, and saunas are used for physical therapy in massage clinics, spas, beauty salons and home homes.
The resulting sweat evaporates from the surface of the skin and produces a cooling that facilitates temperature homeostasis. Essentially, sauna therapy plays on the thermoregulatory property of homeothermia, the physiological ability of mammals and birds to maintain a relatively constant core body temperature with minimal deviation from a set point. It is currently unclear whether steam saunas evoke the same degree of physiological responses as dry saunas, as higher humidity results in water condensation on the skin and less evaporation of sweat. Studies examining heart rate variability as an assessment of outcomes are increasing, and additional results may better inform physiological models about what is thought to happen with repeated saunas of Finnish or infrared types. The concepts of hormone stress and linking “sauna fitness” or habituation to the physiological effects of repeated sauna activity may have implications for preventive or therapeutic goals in the future. Conducting more repeated sauna studies in healthy but non-athletic participants may further help clarify the similarities and differences in metabolic pathways between repeated sauna activity and regular exercise.