Scientific evidence for the benefits of saunas

Scientific proof of the benefits of sauna (News Japan)

Recently, publications have appeared in the Japanese media that demonstrate the unexpectedly increased interest of the scientific community in the sauna. It is noteworthy that until recently, claims about the possible benefits of the sauna were rarely supported by medical evidence.

As the novel coronavirus pandemic has increased our awareness of our own health and everyday life, the question arises - what medical benefits can be expected from the increasingly popular sauna?

This time we were joined by Takafumi Horie from the Association for the Promotion of Preventive Medicine and the president of the Japanese Sauna Society, as well as Yotaka Kato, an assistant professor at the Cancer Center at Keio University School of Medicine. They discussed the medical mechanisms underlying the performance and health benefits of sauna use. Evidence Pyramid Kato: Last time I talked about the perception of evidence. This time I would like to talk about the various benefits of sauna based on scientific evidence. Evidence, from an academic perspective, can be divided into a hierarchy called the evidence pyramid.

1. Systematic review: A collection of clinical trial reports from medical journals and conference presentations that are evaluated, summarized, and summarized. 2. Randomized comparison test: a clinical trial in which a group of patients receiving treatment is compared with a group that is not receiving treatment and is only observed, but the groups are divided randomly. 3. Non-random comparison test: A clinical trial in which a treatment group is compared with an observation group, but the groups are not randomly assigned. 4. Epidemiological study (cohort study): a general term for a study conducted on a large number of people to study the incidence and prevalence of diseases and the causes of their occurrence. 5. Description of disease symptoms: a study that describes and reports the progress of a patient's treatment. 6. Expert opinion not based on data. In this article, we will explain the various benefits of a sauna, considering the above levels.

The basic procedure in a sauna is a cycle of three stages: being in the steam room (about five to ten minutes), taking a cold bath (about one minute) and then being in the fresh air (about five to ten minutes). The heat in the sauna and the cold of the plunge pool are harsh conditions that we do not encounter in everyday life. When the human body finds itself in such an environment, it perceives it as a life-threatening situation and activates the sympathetic part of the autonomic nervous system.

In Sweden, the Finnish sauna is recognized as cultural heritage

A bath followed by relaxation in the fresh air causes a greater than usual activation of the parasympathetic nervous system, which turns on when the body feels that it is out of danger and feels better. This extreme oscillation of the autonomic nervous system is believed to relax the body and improve autonomic function. There is an important epidemiological study that provides evidence in favor of sauna use. It's called FMCF. FMCF (Finnish Mobile Clinic Follow-up Survey) Kato: FMCF is a large epidemiological study in Finland. When Lenin's Soviet government granted Finland independence in 1919, it was forced to struggle with chronic diseases due to poor medical facilities.

Between the 1960s and 2013, about 60 thousand people were examined. Based on this information, around 2015, a certain amount of information about saunas began to be received. Let's talk in detail about the benefits of a sauna from the point of view of real disease prevention. Reduces the risk of myocardial infarction by approximately 50% (level of evidence: 4) Kato: It has been proven that visiting a sauna reduces the risk of myocardial infarction by 50%. The level of evidence for epidemiological studies is 4, but the level of evidence for the mechanism is one lower: 5.

The specific mechanism for reducing the risk of myocardial infarction is through physical softening of the blood vessels. Softer blood vessels improve blood flow, and as the vessels harden, it decreases, which leads to increased stress on the heart, which in turn results in myocardial infarction. It is believed that the sauna softens the blood vessels and therefore reduces the risk. Reduces the risk of developing dementia by approximately 60% (Level 4 evidence) Spending more time in slow-wave sleep, or deep sleep, is thought to help prevent dementia by removing the substances that cause it from the body (level 5 evidence). As for the positive effect of the sauna on the slow-wave sleep phase, I conducted my own experiments, so the level of evidence can be attributed to the fifth. I found that the slow-wave sleep phase increases by about one and a half times. In particular, the higher the body temperature in the periphery and the greater this difference, the easier it is to fall asleep. The temperature in the sauna is almost 100 degrees Celsius, so you can warm up to the bones. After a sauna and cold bath, the temperature in the periphery decreases, while the temperature in the center of the body remains high. About an hour after the sauna, the body temperature decreases, and the temperature of the extremities increases to a greater extent than if the person did not enter the steam room. Reduces the risk of mental disorders by approximately 78% (Level of Evidence 4) When comparing people who used a sauna once a week with those who did it four to seven times, there was a 78% reduction in the risk of mental disorders such as depression and schizophrenia. It is assumed that this mechanism involves neural circuits such as the passive mode network of the brain and the central executive network. The passive mode network of the brain is a neural circuit that is activated when a person is not consciously active, that is, in prostration. The central executive network, on the other hand, is a neural circuit that is activated when a person pays attention to a specific area. In terms of energy consumption, the passive network uses 60 - 80% of the brain's energy, while the central network uses about 5%. When you concentrate on something, the central network is activated, and it may seem that more energy is consumed, but in fact, less energy is used, and accordingly the degree of brain fatigue decreases. Indeed, the passive network has been suggested to correlate with brain fatigue and depression, and although the exact cause-and-effect relationship has not yet been established, I think that activating the central network, that is, concentrating on something, improves well-being.

So, let's look at how the balance between the passive and central network of the brain changes in the sauna. There, the activity of the first decreases, and the second increases due to the need to focus on extreme conditions, because the heat reaches almost 100°C.

In a sauna, blood flow to the skin increases and blood flow to the brain decreases, resulting in decreased levels of brain activity. This balance relieves brain fatigue and helps prevent mental disorders.

By consciously shifting the balance of brain activity towards the central network, for example, concentrating on breathing while in a sauna, you can more effectively eliminate brain fatigue.