Hormesis (exposure to stress to create a benefit) is proving to be an incredibly valuable tool in our health arsenal. From fasting to cold exposure and much more in between, the field has plenty of potential. Part 5 in our 7 part series addresses one of the most common forms of hormesis, heat exposure (thermotherapy), which many of us do this unwittingly. Some of the benefits most accept as fact are lacking in data, while the most profound roles in this activity are discussed by only a few.
For a full introduction to Hormesis read the first part of our Hormesis series.
Heat Exposure (Thermotherapy)
Thermotherapy or heat therapy is one of the most widely used techniques to battle chronic pain as well as muscle and joint stiffness. There are many easy and safe methods to use, such as heat pads, hot baths or hot tubs, infrared radiation, saunas, and steam rooms.
Other activities incorporate heat into the overall activity, such as hot yoga. We are beginning to learn that heat therapy comes with numerous benefits and is not limited to aching muscles and joints.
My Experiences with Heat Therapy
To the same extent that I am incredibly tolerant of cold exposure, I am vulnerable to heat exposure. I’ve considered that since cold affects me very slightly compared to others, it may mean that it comes with less therapeutic impact for myself personally, and how easily my world is rocked by a bit of heat exposure, may mean that I can utilize the benefits greatly as long as I control my exposure.
My most frightening health experiences have been from severe heatstroke, after only hours in hot temperatures, culminating in days of illness. Heat therapy has also greatly helped me at other times in my life.
In my mid-20s, I was living in Toronto and training martial arts upwards of 8 hours a day. When I started this hobby and lifestyle my mobility and flexibility were not where I would have liked them to be. It wasn’t terrible, I was flexible in many of the ways typically tested, such as touching my fingers to the ground, but my hip mobility was lacking. For martial arts, specifically muay thai and Brazilian jiu jitsu which I was practicing, hips were critical.
The condo I was living in had both a steam room and a dry sauna. I quickly realized I was not cut out for the steam room. I would become dizzy and disoriented almost immediately.
The dry sauna was a different beast. I had some frightening experiences early on. While stretching in the sauna, all of a sudden, my vision would start going dark after five minutes. The first time this happened I got out immediately. After that, I always set timers, and the one time I couldn’t muster any strength to leave the sauna, the timer was set for around 10 minutes. It took me quite a while to get up and leave when the room started cooling, and I had to sit under a cold shower in the spa for a long time. I was dehydrated, dizzy, and nauseous.
That first scare where I couldn’t get up happened maybe a few weeks into my daily sauna regimen. Before that, I had been setting the timer for five minutes, and falsely believed I was becoming more accustomed to the heat, as by the end of the five minutes I was still feeling fine. Perhaps I was, but the change to 10 minutes on the timer was too drastic.
I continued on as I was noticing a tangible improvement in flexibility and accompanying strength in movements requiring flexibility. I started bringing 4 L jugs of ice water in with me, extending sauna sessions to 15 and eventually 30 minutes. Drinking the ice water as I was stretching allowed me to get through 30 minutes in the sauna, and a quick cold shower immediately after left me feeling fantastic. My flexibility and mobility had also skyrocketed in short order.
Fast forward a few years later, I tried hot yoga. The first time trying I was only two months returned to Vancouver and had used the sauna many times since returning, although no longer daily. I cannot exaggerate how poorly my first experience went.
I brought 4 L of ice water and falsely believed I would be OK. As I went through the movements of stretches I was not accustomed to and strains I had not accounted for, I quickly blew through my 4 L of ice water, which had been melting at an alarming pace. I started getting dizzy and wobbly and the instructor suggested I lay down and take a break.
The instructor didn’t realize how poorly I was doing and as I lay there until the class was finishing, my vision started going black. I am not sure if it was pride, inability to muster any strength or a combination of both, but I did not alert anyone to my condition. I just lay there.
When the class ended and someone opened the door, I continued to lay in my spot. I think I missed thanking the instructor which others may have viewed as rude because I was incapable of standing and my vision wasn’t properly working. When I finally made it up and out of the room, I went and ran my head under cold water for as long as I could. It was the last class of the day and they were closing up.
I got in my car and went to drive home, made it three blocks, and had to pull over. It was late fall/early winter, so the air was cool. I pulled onto the side of the road, opened my windows, and closed my eyes. I woke up three hours later, cold and wet.
About six months later, a friend of mine joined another hot yoga location. It wasn’t part of the “major chain,” and they let me know they kept it a few degrees cooler than the “chain,” as they had noticed many could not tolerate that level of heat. I tried again and went about 10x. I kept making it through the classes, but they took their toll. I want to say classes were an hour, give or take, and while 30 minutes in the sauna lightly stretching left me feeling fantastic, an hour of more arduous movements left me floored.
I was attending these classes at the peak of my fitness and found that I had to take the following day off to recover after each and every hot yoga session. My muscles would ache, I’d feel run down, and what was alarming was my decreasing flexibility and joints feeling stiffer than before!
This level of heat therapy is likely needed for many people. Just as I can hold a conversation during a cryosauna session with no discomfort, many others can barely or cannot make it through two to three minutes, and most people at the hot yoga classes seemed largely unaffected by the heat. Heat therapy is a stress, it is hormesis. Just as a certain level of exercise will have different impacts on different people’s bodies, different levels and durations of heat will as well. What may be therapeutic to someone may be harmful to another. This is the problem with “one size fits all” advice, especially concerning forms of hormetic therapies.
The Science of Thermotherapy
Heat Shock Proteins
As we discussed in our article Hormesis - Exercise, heat shock proteins (HSPs) are released in response to many stressful conditions and hormetic stressors. As the name implies, we first attributed these proteins to heat shock, and as such are closely related and applicable to heat therapy. As is the case with many items we detail, there are pros and cons associated with HSPs.
Very rarely is a biological function “always good” or “always bad,” with most functions having a beneficial role when functioning homeostatically and a deleterious role when behaving improperly. Regarding HSPs and other functions that we do not completely understand, the best we can do is make educated predictions based on overall health outcomes.
Heat shock proteins act as “supervisors” or “chaperones” during protein folding, making sure proper folding occurs. Basically, proteins start out as a long and random “coil or string,” and to function properly, they need to fold into a specific 3D shape. Imagine taking a rope stretched out and twisted in random ways, and coiling it into a tighter and specific pattern.
Misfolded proteins may simply not function properly or in some cases, may operate in modified functions, not as intended, or even in a toxic manner. In fact, misfolded proteins have been implicated in many neurodegenerative diseases1 and also in many allergies and even cancer.2, 3 ,4, 5
As discussed in our article on exercise as a form of hormesis, we know exercise increases HSPs.6 As logic follows (but isn’t always the case in our physiology), misfolded proteins lead to neurodegenerative diseases and exercise decreases the risk of neurodegenerative diseases, such as Alzheimer’s.7
We have also observed in a longitudinal cohort study out of Finland following thousands of participants that frequent sauna use decreased the risk for Alzheimer’s and dementia.8 A follow-up study from the Finnish team examined 103 men and reported on heart rate, blood pressure, and several other factors, finding that a 30-minute sauna session had similar impacts as a mild to a moderate bout of exercise.9, 10
As we discussed in the exercise article, exercise is also linked to a decrease in cancer risk11, 12 and encouraged while undergoing cancer treatment.13 Likewise, heat therapy is used in localized, regional, and whole-body applications to treat cancer and tumours.14, 15
As a note of caution, there are limitations to the data on heat therapy for cancer, and when it is used, it is used along with other approved treatments. Do not take this as any sort of recommendation to abandon approved therapies for alternatives that are early on in research, and even if successful, would not constitute a total replacement. Heat therapy may be a secondary adjuvant therapy to improve outcomes.
While aerobic exercise has been shown to improve repair following traumatic issues, such as stroke,16 heat therapy has had mixed results. It was announced as a potential new ER therapy, alternating with cold exposure with results from one Taiwanese study,17 however, another study found no benefit for this use,18 and another that was set to finish five years ago was seemingly never published.19
There is reason to believe that heat therapy could positively impact conditions following acute stress, with one study showing that daily heat therapy maintained mitochondrial function and mitigated atrophy in 23 participants who had been immobilized.20 That said, in one study using rats, while benefits were observed in immobilized rats, elderly rats saw no benefit in heat therapy for muscle atrophy.21
As we have discussed throughout the entire hormesis series, moderation is imperative. As a reminder from our exercise article, elevated HSPs have been linked to increased risk of both Alzheimer’s and cancer,22 perhaps by increasing DNA damage and protein crosslinking.23
In fact, it is some of the very same HSPs, such as HSP90 (titled based on its molecular weight), that both heat therapy and exercise specifically increase, which are linked in the strongest matter to increased carcinogenesis.24 There are actually anti-cancer drugs and vaccines currently in development to inhibit HSPs as a form of cancer prevention and treatment.25, 26, 27 The role of HSPs in cancer and their inhibition remains a hot topic of research. 28, 29
What does this mean for heat therapy enthusiasts? Don’t worry about it, but don’t overdo it. Moderation is important and knowing what your body can handle is even more important. There can be “too much of a good thing” in this case, with the “good” becoming “bad” rather abruptly.
The Science on Muscle Recovery, Pain, and Stiff Joints
When we start diving into the typical benefits most people associate with heat therapy, the evidence starts getting a bit dicier. This doesn’t mean the benefits described above, but the research showing heat therapy and sauna use lowers cardiovascular and even cause mortality30 is bogus.
For rheumatoid arthritis, a review of three studies found that while no statistical benefits were observed in markers of inflammation, pain, or x-ray measured joint degradation, 94% of participants still preferred the therapy over no therapy at all.31
As for muscle soreness, some studies suggest that heat therapy may be superior for delayed onset of muscle soreness to cold therapy while improving blood flow and tissue flexibility.32 I know that certainly supports my personal experience using saunas to stretch post-training, however, reviews on the subject conclude there is a dearth of evidence to support this position.33 We need more evidence to know for sure if it works, but for now, what we have suggests it may.
Hormesis - Heat Exposure (Thermotherapy) Conclusion
For athletes, professional and recreational alike, it is an easy tool to improve performance and flexibility. As with all forms of hormesis, moderation is necessary. Do not let mild heat stress turn to serious stress as the damage will outweigh the benefits.