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13. Sauna effects on longevity and ageing >>

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11. Sauna effects on cardiovascular health

Does using a sauna show the Tomato Effect symptoms? How else can it be explained that people with cardiovascular problems are still advised against using the sauna?

 

Does choosing to use a sauna show symptoms of the Tomato Effect? No, this issue is not related to skin colour, which can turn red like a tomato in the sauna. Tomato Effect* is a term used in medicine to describe a phenomenon in which effective, scientifically-proven therapies are ignored or rejected because, in light of general beliefs or understanding, they make no sense, or people simply ignore available evidence. (1) One such example is the story of Aspirin. It took as long as 70 years from the first research confirming its effectiveness in rheumatoid arthritis to accept its role and potential use against this devastating disease. (2) And the story of the sauna seems to be similar. How else can it be explained that people with cardiovascular problems are still advised against using the sauna?

The term Tomato Effect* was first described by Dr James Goodwin, in an article published in the Journal of the American Medical Association (JAMA) in 1984. (1) It explains how, in the 16th century, European conquerors brought new "exotic" plants such as potatoes, corn, beans, coconut, tobacco and tomatoes, from South America, which caused a kind of mini-revolution in European eating habits. Tomatoes soon became a staple ingredient of continental Europe dishes, but at the same time, were completely ignored or even actively avoided in North America. Until the early 19th century, they were neither cultivated nor consumed. They were believed to be poisonous, as they belong to the nightshade family, which also includes some genuinely poisonous plants such as (Atropa) belladonna. This perception changed only in 1820, when Robert Gibbon Johnson ate tomatoes on a court's steps in Salem, New Jersey, and "miraculously" survived. By doing so, it led people in North America to start growing and enjoying them en masse.

During a systematic scientific literature review on the effects of the sauna, it should be noted that there is a particular interest in this area. Judging by the number of studies and published articles, probably the most researched is ​the impact of the sauna on the cardiovascular system and related diseases. This is not surprising since, according to the World Health Organization (WHO), ischemic heart disease (i.e. heart problems caused by narrowed coronary arteries.) has been the leading cause of premature death in recent decades. (3)
Such an outcome is regrettable, as the cause is primarily diet (unhealthy, overly salty and fatty foods) and lifestyle (4), which we all have control over. Although advances in medicine have significantly reduced the number of cardiovascular deaths by percentage (5), the number of patients is continuously increasing, indicating that cardiovascular disease will continue to occupy leading positions on the premature mortality scale.

It is also shocking that if you are over twenty-two years old and eat the so-called "typical" Western diet, you almost certainly have the first signs of cardiovascular disease. Namely, even though you do not know or feel it, atherosclerotic changes occur in the arteries decades before coronary heart disease becomes a clinically recognised problem. (6,7)
In most cases, the first symptom of this disease is also the last, i.e. death. (8) Doctors call this "sudden cardiac death", but we know that such an event is all but sudden. It is the result of a prolonged atherosclerotic process. US experts are horrified to note that fatty lines in the arteries, the first degree of atherosclerosis visible to the naked eye, are present in almost all American children at the age of 10. (9) Even more frightening is Italian experts' findings suggesting that atherosclerosis can begin even before birth if the mother has elevated levels of LDL cholesterol* in her blood during pregnancy. (10)
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* Cholesterol is a crucial ingredient that your body needs to make new cells, hormones, vitamin D and substances that help you digest food. Cholesterol comes from two sources. Your liver makes all the cholesterol you need. The rest of the cholesterol in the body comes from foods derived from animals. For example, meat, poultry, and whole milk products contain cholesterol called dietary cholesterol. The same foods are high in saturated and trans fats. These fats cause more cholesterol to form in the liver than they would otherwise. For some people, this added production means they go from ordinary (normal) to unhealthy cholesterol levels. There are two main types of cholesterol. LDL - a low-density lipoprotein, sometimes called "bad" cholesterol, because it can accumulate in the arteries, causing them to narrow, leading to heart disease and stroke. Therefore, in general, it is healthy to have low LDL levels. On the other hand, HDL or high-density lipoprotein is a suitable ("good") type of cholesterol. It carries LDL, a so-called bad substance, away from the arteries back to the liver, where it is broken down and processed by the body. So you want your HDL to be higher.
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Does this mean that somewhere during evolution, nature made a mistake, and we are destined with cardiovascular disease? By no means! It has long been known that there are parts of the world where people are unaware of such conditions or are a few hundred times rarer than where they eat the standard American diet, also aptly called the "sad diet".

One such example is in the rural areas of southern China and Uganda, where people eat mostly plant foods and therefore, cholesterol intake is minimal. (11-13) Or, as the renowned American physician Caldwell B Esselstyn vividly explains, "If you, as a cardiologist or a cardiac surgeon, decided to hang your shingle in Okinawa, the Papua Highlands of New Guinea, rural China, Central Africa, or with the Tarahumara Indians of Northern Mexico, you better plan on a different profession because these countries do not have cardiovascular disease." (16) And if you think that people from those areas have superior genes or a body that protects them from cardiovascular disease, you are wrong. Immigration studies prove that this is not the case. (14) When people from these areas move to countries with a high proportion of such diseases and adopt their way of life and diet, their morbidity increases sharply.

So, it is not true, as is often thought, that age is necessarily associated with cardiovascular problems. To a large extent, the development of events depends on each individual. Like diabetes, we also have to "work hard" to develop cardiovascular disease and, ultimately, heart failure down the line. But once that happens, the options are limited. Regular physical activity and a healthy diet are undoubtedly beneficial. For both, science has confirmed a positive impact and a strong reduction in risk, not only for the development of cardiovascular disease but also for cardiovascular mortality. (15,16) What about the sauna?

Similar to tomatoes and Aspirin, opinions and recommendations regarding the sauna have changed over time. From the highly sceptical thoughts from the beginnings of research, later on, a significant amount of them, especially over the last few decades, have shown very positive results. Initial sceptical opinions were based mainly on reports from an individual, albeit sporadic, cases. Initial doubtful statements were based primarily on reports from individual, sporadic cases. Moreover, they were mainly supported by theories based on "common sense".
On the other hand, epidemiological studies of all kinds, cohorts and controlled studies, systematic reviews and meta-analyses of research have provided evidence of significant positive effects of sauna usage on the cardiovascular system. Studies even suggest that "the frequency and duration of sauna bathing are strongly, conversely, and independently associated with cardiovascular deaths in middle-aged and elderly men and women. The frequency of sauna bathing improves the prognosis of long-term cardiovascular mortality risk." (17).
Simply put, More saunas less cardiovascular disease. So far, so good, but of course, we wonder why? What is it that makes a sauna so beneficial for our heart and blood vessels? Before we look at the reasons, let's take a step back and first look at how coronary heart disease (CHD) and, consequently, heart failure occurs at all.

Coronary heart disease (CHD), what, why, how?

Coronary heart disease (CHD), also called ischemic heart disease or coronary artery disease, is essentially a term that describes what happens when blood flow to the heart is disrupted due to fat accumulation in the coronary arteries. A disorder most often caused by arteriosclerosis*, a condition where the inside of the blood vessels (arteries) that carry oxygen and nutrients from the heart to the rest of the body become lined with fatty, calcified coatings called plaques. These plaques make the vessels less flexible and the lumen (through which blood flows) smaller in diameter. (Figure 1) 

*The term arteriosclerosis, a condition of the arteries, is sometimes confused with the term atherosclerosis, a process used to describe the deposition of fatty deposits on the artery walls that occurs over the years, even decades. (Figure 2) The word arteriosclerosis comes from "artery", i.e. a type of vessel, and "sclerosis", which comes from the Greek word for coagulation or clotting. The word atherosclerosis comes from the Greek words "athera" - porridge and "sclerosis" - clotting.

Atherosclerosis can affect medium to large arteries (1mm-25mm in diameter). For example, arteries of the brain, heart, kidneys and other vital organs and legs. As already mentioned, the process can begin even before birth or at a very young age due to recurrent damage to the arteries' inner walls. The reasons for the injuries are different and range from physical stress due to chronic high blood pressure to inflammatory processes and chemical abnormalities in the bloodstream resulting from an unhealthy diet and lifestyle. In addition to the aforementioned unhealthy diet, the main risk factors are insufficient exercise, excessive alcohol consumption, smoking, and some diseases such as diabetes and high blood pressure. To a lesser extent, the cause can also be hereditary.

This formation of plaques is a complex and lengthy multi-stage process. To better understand the effects of the sauna on this process, let's look at how these nasty and often fatal vascular plaques are formed.

Mechanisms of Plaque Formation and Rupture

Stage 1 - Chronic irritation of the arteries
The first stage of the plaque formation process occurs due to repeated irritation of the arteries' inner walls. It is often cholesterol or some chemical compound from cigarettes or alcoholic beverages, or chronically high blood pressure, that irritates the arteries' walls. This irritation causes inflammation on the inside of the artery walls. If such an injury occurs once or rarely, the body has mechanisms to repair it. However, constantly recurrent inflammation eventually damages the artery's inner lining, an essential and susceptible layer of cells called endothelial cells, the ones mentioned in the chapter on inflammation.

Stage 2 - Damage to endothelial cells
When endothelial cells are permanently damaged to the point that they cease to perform their functions, this results in the onset of the atherosclerosis process. (4)
Endothelial cells represent an essential single-cell barrier between the lumen (the arteries' interior) through which blood and nutrients flow and the remaining layers that make up the artery wall. However, they also have other vital functions for the proper functioning of the vascular system. (18)
One of these is the release of nitric oxide gas, a small free radical molecule with a critical signalling role in the vascular system's functioning. (19) Nitric oxide acts as a vasodilator or trigger for dilating arteries. In a way, it works like Teflon on a frying pan. It prevents the substance from sticking to blood vessel walls, allowing blood and nutrients to flow more smoothly through the arteries. Recently, however, experts have found that nitric oxide also has an important antimicrobial function. (20) Endothelial cell damage, therefore, represents the second stage of plaque formation and causes inflammation.

Stage 3 - The formation of fat lines
Damage to the endothelial barrier allows LDL cholesterol particles in the blood to stick to artery walls and penetrate inside between the endothelial barrier and the layer of smooth muscle cells, where they begin to accumulate and thus, slowly form thin lines of fat. These fat lines are the first consequence of atherosclerosis development visible to the naked eye and represent the beginning of the third stage of plaque formation. They look like an irregular yellow-white stain on the surface inside the artery. Thus, accumulated and attached cholesterol soon begins to oxidise, which adds fuel to the fire and further increases inflammation. (21)

Stage 4 - Activation of the immune system
Inflammation caused by damage to the endothelial lining and oxidised LDL cholesterol signals to the immune system that something is wrong. The immune system responds by sending the monitors(T-cells of the immune system called monocytes) to places where cholesterol accumulates and oxidises. These monitors are not exactly enthusiastic about what is happening. They do not like cholesterol sticking to artery walls, so they start taking action. (22)
They turn into macrophages (special immune cells) and begin to devour cholesterol molecules to remove them. Unfortunately, cholesterol also harms macrophages. Soon after they are well satiated with unwanted cholesterol, they begin to change into a foamy structure, so-called "foam cells", and die. (23) In doing so, they send cytokines (additional, pro-inflammatory signals for help) to the immune system. Of course, the immune system responds with a shipment of new immune cells that repeat the same process and the number of foam cells increases. If we eat fatty foods several times a day, we supply our body with a large amount of cholesterol and thus ensure that the described events' cycle is not interrupted. Suddenly, we have sticky fat deposits, immune cells, foam cells, a bunch of inflammatory mediators and other substances circulating in the vessels on the inner artery wall, and ever-increasing inflammation; in short, complete confusion. This isn't good—the coating increases, which represents the fourth stage of plaque formation.

Stage 5 - Activation of smooth muscle cells
All of the aforementioned events trigger help signals to many places. In addition to the immune system, smooth muscle cells that form artery walls also sense what is happening. In response to endothelial cells damage, the smooth muscle cells start to clone themselves and migrate against the emerging plaque to build a fibrous cap (24,25), a kind of protective barrier between the blood and the emerging lining in which oxidative stress occurs and with it, constant inflammation. To complicate issues further, oxidative stress also triggers a calcification process in which smooth muscle cells are actively involved. (26-28) Calcium begins to accumulate in the lining, making the arteries rigid and inflexible. So, we have two problems now. In addition to narrowing the artery, it also has a reduced ability to stretch and contract. This may cause an increase in blood pressure and potentially reduces the flow of oxygen and nutrients to the tissues. ( Over time, such a coating can cause quite a few problems, but it is rarely fatal as long as it remains stable. The problem, however, arises if the fibrous cover on the lining breaks.

Level 6 - Plaque rupture
Plaque rupture - unstable arteriosclerotic plaque breaking down quickly is the last and potentially fatal stage of atherosclerosis. When the plaque breaks down (meaning that its fibrous covering or cap is torn), the substance inside the layer, a mix of fat molecules, calcium, foam cells, and other coating substances, is suddenly exposed to the bloodstream. This material, accumulated over the years, triggers the formation of blood clots. These blood clots can suddenly block all blood flow through an artery, which presents a major cause of a heart attack or stroke. Sometimes these blood clots or parts of blood clots break off, travel through the bloodstream and block an artery elsewhere in the body.
The reasons for the disintegration and the tearing of the lining cover can vary, both mechanically and biologically. An obvious one is repetitive mechanical deformations caused by the cardiac cycle, which plays an essential role in the stability of plaques or lesions. Each time the heart pushes blood into the system, the arteries dilate. When blood pours into the veins, however, the arteries constrict. In this way, the arteries actively participate in the circulation and reduce the load on the heart. The constant contraction and dilation of the vascular system with each heartbeat causes constant mechanical stress on the lining. At one point, some of them may fall apart. Therefore, the fibrous cover's structure and thickness that maintains the stability of the lining is critical. (29) Over time, they may begin to thin due to inflammation within the lining, which accelerates smooth muscle cell ageing inside the lining and, thus, their ability to regenerate the covering. (30)
Besides that, inflammatory processes accelerate the production and function of specific enzymes (Matrix metallopeptidases - MMPs), which play an essential role in tissue decomposition and transformation in the body and further contribute to the breakdown and thinning of fibrous coatings. (31-33) This seriously increases the risk of injury, as in the advanced stages of lining, fibrous caps are the only protection against a fatal event. And what can you do to avoid such a scenario?

Diagnosis and treatment

Because atherosclerosis is an asymptomatic process detected only at a late stage or at autopsy, prevention is the most effective treatment method. Unfortunately, most people ignore preventive recommendations, so the medical profession has developed various diagnostic methods, drugs and advanced surgical procedures that contribute to faster diagnosis and more effective treatment. Timely diagnosis is undoubtedly important, but given the findings of the early onset of disease processes, the question of whether you have heart disease does not seem to be the right one. The real question is, do you want to get rid of the heart disease you probably already have? Of course, what follows is the question: how?  

Even the famed Mayo Clinic, one of the largest, oldest and most respected health research institutions in the US, has an article that states, "Lifestyle changes such as healthy eating and exercise are often the most appropriate treatment for atherosclerosis. Sometimes medication or surgery may also be recommended." (34) 

At first glance, it seems as if this institution, which makes its money selling drugs and advanced surgical procedures, "spits in its bowl" or acts against its self-interest. However, fear not, as they know, a majority of people prefer to swallow pills or go under a surgical knife than change their lifestyle. Therefore, with the statement above, they do not endanger their business model but increase their credibility. Anyhow, such a public recommendation from an institution as the Mayo Clinic certainly has significant weight and clearly shows that cardiovascular disease treatments have only limited power compared to diet and lifestyle changes.

The article also presents drugs and surgical procedures to treat and lifestyle changes to prevent cardiovascular diseases. Of course, they all have special meaning. Surgical interventions in acute emergency cases save lives. Regarding drugs, sometimes they are the only acceptable option for the patient. They mainly work in four directions (worth remembering, at least in the later part of this chapter, which discusses the vascular system's sauna effects). The most popular and also best-selling drugs are called Statins, used for lowering LDL cholesterol. They also use anticoagulants to help prevent blood clots, substances for blood pressure lowering and painkillers to reduce pain.

Surgical interventions and drugs are undoubtedly a top-notch demonstration of modern science and medicine. However, it is certainly the desire of each of us never to need them. Also, because they present additional risks that are not negligible. (35,36)

As previously mentioned, the article also touches on recommendations for reducing or preventing cardiovascular disease. It advises against smoking, recommends regular exercise and healthy food, emphasising whole, predominantly plant-based foods. They also recommend the loss of excess weight, stress management and certain dietary supplements that are supposed to affect the cardiovascular system positively. 

In short, a wide range of what the professional and interested public has known for a long time is presented, with one notable exception. There isn't a sauna mentioned anywhere. I admit I was a little surprised. My eyes wandered over the article and searched for the word sauna unsuccessfully. How is this possible? Aren't they aware of the sauna's potential? Of course, they are. A few weeks before this article came out, an article called "Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence" (37) was published in the Mayo Clinic Proceedings. 

Among the others, it states: "Emerging evidence suggests that beyond its use for pleasure, sauna bathing may be linked to several health benefits, which include a reduction in the risk of vascular diseases such as high blood pressure, cardiovascular disease, and neurocognitive diseases; nonvascular conditions such as pulmonary diseases; mortality; as well as amelioration of conditions such as arthritis, headache, and flu. The beneficial effects of sauna bathing on these outcomes have been linked to its impact on circulatory, cardiovascular, and immune functions. It has been postulated that regular sauna bathing may improve cardiovascular function via improved endothelium-dependent dilatation, reduced arterial stiffness, modulation of the autonomic nervous system, beneficial changes in circulating lipid profiles, and lowering of systemic blood pressure; etc." So, it is evident that there is no lack of information. Besides, the Mayo Clinic experts participated in the research, and they already established a sauna's safety for people with chronic heart failure (CHF) in a study from 2009. (38) 

So, I wondered how such a fantastic cardiovascular enhancing tool as a sauna is missing in their public recommendation? Isn't this an obvious demonstration of the Tomato Effect? Or the sauna isn't so helpful after all? Let's find out the answer by the systematic review of scientific literature from the last four decades.

What does science say about the effects of saunas on cardiovascular health and related diseases? 

It has long been known that a sauna greatly accelerates the heartbeat. Sir Charles Blagden wrote about this observation 250 years ago. 

This kind of body response could be the reason or may dictate that the sauna represents an additional effort for the heart and that people with cardiovascular problems should avoid it. Despite a lack of scientific basis, this belief still prevails among the lay public. It sounds reasonable until we know that a faster heartbeat is only the body's compensation, discussed in the previous chapter, to avoid an excessive drop in blood pressure and does not really increase the heart's effort or increases it negligibly.  

In other words, to use an analogy with a modern road bike: If you drive on flat terrain, say in the fifth of ten gears, this is a medium load on the muscles. If the landscape turns into a slight uphill slope, the burden is significantly increased. By shifting from fifth to, say, first gear, you adjust and balance or even reduce the load compared to driving flat terrain in fifth gear. Consequently, you turn the pedals faster, but as long as the slope isn't too steep, you're more likely to use less power than driving a flat in fifth gear. And, the vascular system adjustments when acclimating to high temperatures show similar results. The heart beats faster, but the loads are not very high as most of the muscular system is at rest. 

 It isn't unusual that the lay public thinks that the sauna is unsuitable for heart patients. For many, the sauna is still an exotic activity, not well understood. It is more unusual that such thinking is not uncommon among many public sauna providers, sauna manufacturers, or even medical doctors. Even though the sauna has been used to lower blood pressure, one of the main risk factors for cardiovascular disease, in some respected medical institutions for decades. (39)

The beginnings of slightly more intensive research of the sauna connected with cardiovascular diseases date back to the 1980s. Researchers first tackled fundamental safety issues, for example, on the safety of using a sauna during the rehabilitation of heart patients. Encouraged by the results, they wrote that swimming and sauna could be safely recommended during the rehabilitation of coronary patients if acute patients are excluded. (40) 

But some of the earliest sauna research findings were not exactly favourable. For example, one study found that heart patients whose disease was stable tolerated sauna use clinically well. But, as they wrote, its use is associated with reduced blood flow to the heart, which prevented the heart muscle from getting enough oxygen (in other words, it caused myocardial ischemia) (41). Another study stated that a single use of a sauna resulted in reduced blood fluidity, which, as the study found, was less pronounced in the case of regular use for at least eight weeks. Thus, they recommended that (probably in terms of "better safe than sorry") such aspects of the sauna should be considered in patients with high cardiovascular risk and markedly reduced blood flow (hypoperfusion). (42) Of course, caution, especially when it is about health, can never be disputed. Still, it makes sense to follow science development and adapt the opinions of the latest scientific findings. 

In the following years, more and more research focused on clinically measurable physiological effects to understand the mechanisms of action, especially concerning blood circulation and, surprisingly, constant positive effects on reducing blood pressure. (43-46) However, the researchers were also interested in purely practical sauna use, such as the sauna's effects on patients after venous bypass heart surgery. Here, too, they found markedly positive results. (47) Thus, more and more research tips the scales of understanding the sauna's use in favour of the view that the sauna is, in fact, safe for heart patients as well. Simultaneously, one study from Finland suggests that the risk of cardiovascular complications when bathing in a sauna is minimal, no more significant than when walking. (48) But, perhaps the rapid cooling in the sauna could potentially endanger patients with cardiovascular disease as it can cause cardiac arrhythmia. (49) They also investigate questions regarding the use of blood pressure-lowering drugs and the use of a sauna at the same time. The sauna lowers the pressure so effectively that, when taking medicines simultaneously, such a combination could cause patients to have too much pressure reduction during or after the sauna, so caution is advised in such cases. (50) 

For a more in-depth understanding, let's turn to those who have the most experience, both with the sauna and cardiovascular disease. And who else could it be but Finnish doctors who undoubtedly have a lot, if not the most, experience with both? Few people know that Finland, known as a sauna-loving country to much of the world, was the world's leading country in the number of premature deaths due to cardiovascular disease after the Second World War, especially in the 1960s. (51) Obtaining this information without understanding the context could quickly shake confidence in the sauna, so here's a brief explanation.

After the Second World War, Finnish men returned home to a country that lost on many fronts. Returning to a rapidly changing nation and the economy was utterly challenging for many of them, describes Emily Willingham in an extensive article about the events of that time in Finland and the phenomenon that marked Finnish society after the Second World War. (52)
"The Finnish government rewarded its veterans with plots of land, but men of the borderlands were used to cutting down trees for a living. Turning to familiar ways and easy stock, they deforested the land allotted to them and used it to raise cows and pigs. Where fish, game, rye bread and root vegetables once ruled the day, salt pork and dairy cream took over in the 1950s and 1960s. Where some plants had once fed humans, the stock animals got the bulk of the greens instead", Willingham writes and continues. "Days were filled with the haze of cigarette smoke — a habit picked up during service — the briny smell of salted meats from the pigs, the heavy aroma of fatty cream and butter from the cows, and the eye-watering sting of alcohol numbing the psychic scars of war. It was, as one resident put it, a life burdened with the curses of the borderland."

At this crossroads of unhealthy eating and drinking and depression, men began to die, young and sudden, from cardiovascular disease. The rates in 1969 were so surprising and so high compared to the rest of the world that public health authorities could not ignore them.

Finnish mortality from coronary heart disease was twice or even three times higher than in other European countries and Japan. And nowhere was it as high as where Finland lost its border to the Soviet Union: the eastern province of North Karelia. The extremely high mortality has caused great concern to the local population, who have petitioned the Finnish government to take action. In response, a North Karelia project was launched in 1972 to implement a comprehensive community-based prevention program. (53) After the first five years, prevention activities also began at the national level. The main goal was to reduce extremely high serum cholesterol, blood pressure and smoking levels through lifestyle changes and improved drug treatment, especially against high blood pressure. With the enthusiasm of youth and an abundance of fresh ideas, a doctor called Pekko Pusk, then barely 26 years old, and his colleagues, took measures and mortality from cardiovascular disease fell by 84% among the middle-aged population from 1972 to 2014. According to experts, about 2/3 of the reduction in mortality was attributed to changes in risk factors, i.e. changes in lifestyle and eating habits, and 1/3 to improvements in new treatments developed since the 1980s. (53)

Even if this story is not directly related to the sauna, it supports the assertions about Finnish doctors' rich experience and the finding that a change in diet and lifestyle has more power than medication and surgery. Simultaneously, another important fact was pointed out: the use of a sauna cannot be an excuse for unhealthy eating and lifestyle, as there were no reports that Finnish men gave up saunas during this period. In other words, "You can't out-sweat a bad diet!" But it helps! Many years later, they realised that in a study published in 2017 in the American Journal of Hypertension. Researchers from Finland, the UK and Austria joined forces. They established a link between the frequency of sauna use and high blood pressure in a sample of 1,621 men aged 42 to 60 from eastern Finland, the area from the previous story with the highest mortality from cardiovascular disease. They found that regular sauna use is associated with a reduced risk of high blood pressure (hypertension), which may be the mechanism underlying the reduced cardiovascular risk associated with sauna use. (54)

The findings are consistent with the earlier opinion of two Finnish doctors, A. Eisalo and O.J. Luurila. They published an article in the Annals of Clinical Research in 1988. They wrote in the introduction:" It has been claimed that the thermal stress caused by sauna bathing can be harmful to persons with cardiovascular disorders. Furthermore, elderly persons, in general, who have experienced no symptoms from bathing, have also been cautioned. However, several studies conducted in Finland did not confirm the adverse effects of bathing on the elderly and cardiovascular patients. The controversial results obtained in Finnish and some foreign studies are at least partly due to the different test conditions. The typical Finnish sauna bath is safe, and even patients who have recovered from acute myocardial infarction can enjoy the sauna without incurring any harmful cardiovascular effects." (55)

There were even more such and similar opinions or appeals from experts from different countries in the following years. (56 - 60)

And while in 1988, due to a relatively small amount of scientific findings could still be doubted, this is much less understandable in 2021. Namely, despite a large body of evidence in professional literature, the sauna is still not advised for heart patients in some places.
Perhaps this is why many studies begin with: "In general, the sauna is not recommended for patients with chronic heart failure. However, research shows ..."
Although overheard, the experts continued to work and research.
In the first half of the 1990s, a group of researchers from Berlin decided to investigate the long-term effects of a sauna on cardiovascular patients. They published several articles. In the first one, they noted that the sauna's long-term use (at least twice a week) positively affected blood pressure regulation in heart patients studied after one and three years. (61) The study included patients with high blood pressure or coronary heart disease, and some recovered after heart surgery. In another article, the same team proposed mechanisms for the positive effects of a sauna. They suggested a significant improvement in the peripheral vascular system's responsiveness as a possible reason. In other words, improving the vascular system's functioning is supposed to help the heart by reducing its effort. It was also reported that all the described groups of patients practised sauna therapy regularly and tolerated it very well. (62,63)
At about the same time, on the other end of the world, Japanese experts intensively began to study the effects of saunas on the cardiovascular system. As previously believed in Japan, the sauna was a great burden on the heart. That is why it was generally not recommended for patients with severe heart failure, a condition of reduced cardiac pumping capacity, which is often the last stage in developing many cardiovascular diseases. This opinion also did not have a scientifically researched basis, so the scientists decided to verify it. Unlike the Germans, Japanese researchers used an infra-red sauna, invented in Japan in the mid-1960s. They tested the effect of an infra-red sauna in 32 patients with dilated cardiomyopathy (enlarged heart). (64) A clinical test was performed on 34 patients with chronic heart failure (CHF) and found positive effects resulting in a reduction in the heart's workload. This type of treatment has even been proposed as a new non-pharmacological therapy for this type of disease. (65,66)
If in the 80s and 90s of the last century, the professional public's interest in saunas' effects on cardiovascular diseases was still somewhat modest or timid, we can no longer say the same for the new millennium. The number of studies has increased significantly. The research results and the realisation that the sauna can be an interesting and valuable complementary method in preventing and even treating cardiovascular disease started to spread to other parts of the world, including the US and Canada, where the sauna began to gain popularity. (67,68)

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Note:In continuation, you can read about the latest research and findings on the effects of sauna on cardiovascular health. For better transparency, the findings are divided according to the type of sauna, infrared and Finnish.

Reading time: approx 24 min 

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