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Introduction
In my last article on the topic of using the sauna for hyperthermic conditioning, I suggested that regular sauna use may:
● improve athletic endurance
● prevent muscle atrophy
● improve insulin sensitivity
● increase neurogenesis (the growth of new brain cells)
● improve learning/memory
● possible increase longevity
In this article, I’m going to pick up where we left off: Longevity. A very recent study (April 2015) was published in the Journal JAMA Internal Medicine , which showed that sauna use was in fact associated with longevity. The study recruited over 2000 middleaged men in Finland and compared frequency of sauna use with sudden cardiac death, fatal coronary heart disease, fatal cardiovascular disease, and allcause mortality including cancer over the course of 20 years. The study found that fatal cardiovascular disease was 27% lower for men who used the
sauna 2 to 3 times a week and 50% lower for men who used the sauna 4 to 7 times a week compared with men who just used the sauna once per week. Moreover, they found that using the sauna 23 times per week was associated with 24% lower allcause mortality and 47 times per week 40%. Temperature is a very important parameter to discuss since there may be a lot of variation from one sauna to the next. The average temperature of the dry sauna used in this study was 79º C or 174º F (that is hot!), often with a splash of water poured over rocks to increase the humidity and for a duration up to or exceeding 20 minutes. This means the results may not be directly applicable to steam rooms, hot tubs, and some other types of saunas, like infrared, which can operate at lower temperatures. That doesn’t mean something that steam rooms, hot tubs, and infrared saunas have no merit, but it does mean that there are some subtle differences if you’re comparing them to these types of hot finnish saunas used in the study. Some of the positive benefits of the sauna on heart health may have to do with similar
benefits seen with regular physical exercise. Heart rate may increase up to 100 beats per minute during moderate sauna bathing sessions and up to 150 beats per minute during more intense warm sauna use, which is pretty fast , and in the latter case corresponds to moderateintensity
physical exercise . It is not surprising that longterm sauna use has been shown to generally improve blood pressure, endothelial function,
and left ventricular function .
Sauna Reduces Mortality: Role of Heat Shock Proteins
I think there are a couple of good molecular explanations for how sauna use may influence longevity. First, we’ll turn to a topic we discussed previously: heat shock proteins (also known as HSPs). Heat stress like sauna use or even or even exercise (to a lesser extent) activates genes that make more HSPs. Heat shock proteins have many important functions inside the cell. One very important function is to make sure proteins, which do all of the biological work in the cell, keep their proper 3dimensional structure in the cell when under stress, whether we’re talking about stress from heat or other stressors like exposure to ultraviolet radiation from the sun, cell injury, or even the aging process , in general. Maintenance of protein structure is critical for each protein’s ability to do its specific function, and it is also important for the longevity of the protein.
Normal metabolism and normal immune function, in other words “just being alive,” create reactive byproducts (called reactive oxygen and nitration species), which damage proteins and disrupt their structure. This not only interrupts the function of those proteins, preventing them from doing their work, but also can lead to protein aggregation. The damage from these reactive byproducts accumulates with age and
contributes to the normal aging process . Protein aggregation is associated with cardiac diseases including heart failure, cardiomyopathy, and atherosclerosis as well as with neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and Huntington’s disease . Increased expression of heat shock proteins has been shown to prevent protein aggregation because HSPs help repair proteins that have been damaged ( Figure 1) . HSPs have also been shown to protect against neurodegenerative diseases . It has been shown that being acclimated to heat, such as from regular sauna use, results in more heat shock proteins under normal conditions and even more under stressful conditions such as cell and tissue injury. This is good because as we age we make less HSPs so anything to boost them is beneficial.
So since we know that HSPs are awesome because they help us resist stress of both the exceptional variety such as in injury, as well as the everyday variety that is associated with aging, perhaps you won’t be surprised that the effects of heat stress on longevity have been shown in flies and worms to increase their lifespan by up to 15% . The mechanism of lifespan extension was also teased out in these organisms and
shown to be specifically dependent on heat shock proteins . Heat shock proteins have also been linked to human longevity. Humans with a gene polymorphism associated with producing more of a certain heat shock protein is associated with being a centenarian .
Figure 1: Heat Shock Proteins Repair Damaged Proteins
The same damage that damages DNA also damages proteins. This damage disrupts their 3D structure and leads to protein aggregation, which can lead to neurodegenerative diseases. Heat Stress induces the production of more heat shock proteins, which repair damage that is inflicted on proteins inside the cells and prevent protein aggregation.
Sauna Reduces Mortality: Role of FOXO3
In addition to HSPs, FOXO3 is another molecular pathway that may explain how using the sauna could improve longevity. Foxo3 is a gene that is associated with longevity, and, indeed, heat stress (such as from using the sauna) activates FOXO3 . Humans with a polymorphism that makes more of foxo3 have up to a 2.7fold increased chance of living to be a centenarian and In mice, having more of their homologous version of this gene can extend their lifespan by up to 30% ! The mechanism by which FOXO3 increases longevity has to do with the fact that it is a master regulator of many different genes. When it is on, it increases the expression of several genes that make you more resilient various types of stress that occur with aging . Many of the genes that FOXO3 increases happen to decrease with age, so it is good to boost their expression. One particularly important type of stress that FOXO3 protects against is DNA damage. The same type of reactive byproducts (from normal metabolism and immune function) that damage proteins in the cell also damage DNA. DNA damage can lead to mutations
and a damaged cell with a mutation may then replicate to form cancer. Foxo3 increases the expression of DNA repair genes that repair that damage to DNA so that a mutation never occurs ( Figure 2 ). It also increases the expression of genes that kill cell damaged cells so that they do not become cancer cell.
FOXO3 also makes cells more resilient to damage by increasing the expression of genes that combat this damage including antioxidant genes (which are much more potent than dietary antioxidants) and prevent the damage from reaching the cell. When a cell becomes damaged or its telomeres become critically short, the cell can become senescent (which means the cell does not die but it is not alive either) and it just sits round causing more damage because a senescent cell releases proinflammatory cytokines and other factors that damage more cells. Well, foxo3 increases genes involved in autophagy , which means the cell will eat itself up so that it is not secreting inflammatory molecules that damage more cells. FOXO3 also increases the expression genes involved in immune function (which declines with age) so that your immune cells can fight off bacteria, viruses and cancer cells better. FOXO3 also regulates genes involved in metabolism and stem cell function just to name a few!
Figure 2: FOXO3 Increases DNA Repair DNA damage occurs everyday and can lead to breaks in both DNA strands (called doublestrand
breaks). This type of DNA damage is very dangerous because it is the most difficult to repair and leads to mutation that are known to cause cancer. Heat stress activates FOXO3, which increases the production of genes that produce DNA repair enzymes to repair this damage so a cancercausing mutation does not occur.
Summary
Sauna use was found to improve longevity, the more frequent the sauna use the stronger the effect of longevity. Heat stress activates heat shock proteins which have been shown to increase lifespan in worms and flies and hsps protect against a type of damage associated with aging. Heat stress also happens to activate one of the most well known genes associated with longevity, FOXO3, which makes cells resilient to a variety of types of stress that compound with aging. For these reasons, it comes as very little surprise that using the sauna regularly might come with some genuine health benefits that could encompass longer life. As for me, you can bet I’ll continue to mix a little sauna in with my workout routine every chance I get.
By Rhonda Perciavalle Patrick, Ph.D.