Sauna Therapy: Healing with Heat

Heat as therapy. How it works. 13 benefits you've likely never heard of. And a full protocol to embrace your inner Finn.

We’re back this week with one of my favorite topics in the health space - sauna therapy. I consider it the most important “supplement” to my training regimen. As we’ll see, the more dialed in your foundation is, the more benefits you can draw from frequent, intense sauna sessions. And we’ll be getting into what many of those benefits are later.

First, let’s set the agenda for this week’s post.

What we’ll cover this week:

History of Sauna Therapy

How It Works Physiologically

Health Benefits

Protocol

Further Reading

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History

To explore the historical context of sauna therapy, we need to travel back more than 5,000 years ago to modern-day Pakistan where the earliest evidence of sauna-like structures were built. These rooms consisted of heated floors & channels circulating warm air throughout. Despite ancient civilizations embracing some forms of heat therapy, this wouldn't be a proper homage to the full history of sauna therapy without discussing the birthplace of the modern sauna: Finland.

More than 4,000 years ago, some of the oldest known saunas were constructed as pits dug into the ground lined with stone along the edge. These early Finnish saunas were known as savusauna or "smoke saunas". They featured a fireplace heating stones to high temperatures where water was eventually poured on these stones to create steam. A well-heated savusauna could retain warmth for up to 12 hours.

Fast forward thousands of years, the Industrial Revolution introduced wood-burning stoves with chimneys, which later evolved into electric sauna stoves in 1938. As Finns migrated around Europe, saunas gained popularity in Scandinavia & German-speaking Europe post-WWII, partially due to German soldiers experiencing Finnish saunas during the Second Soviet-Finnish War. Returning soldiers brought the custom back to their home countries in Germany, Austria, Switzerland & the Netherlands.

Though the Finns are primarily regarded as the inventors of modern sauna technology, we can't discount other cultures who embraced heat as a therapy. Native Americans built sweat lodges purposed for various ceremonies & rituals.

Islamic cultures used what are known as hammams - emerged from the idea of Roman baths centuries earlier.

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Mechanisms of Action

While the exact mechanisms are still hotly debated, we'll discuss what I believe to be the primary ones at play - where the strongest evidence points to.

Let's start here: the entire premise of sauna's mechanisms are centered around its ability to function as an exercise mimetic. Like exercise, sauna is an acute stressor on the body as we’ll see in detail. Most benefits we see through sauna therapy have been similarly studied as physiological advantages of exercise as well.

Cardiovascular Adaptations

Resting Heart Rate Reduction

The decrease of resting heart rate can be attributed to enhanced autonomic nervous system function over time. Similar to exercise, acute heat exposure acts as a form of hormetic stress on the body by increasing parasympathetic activity & decreasing sympathetic tone. Or in other words, we boost our heart rate variability. The suppression of the sympathetic nervous system’s activity helps to optimize immune system function by relaxing skeletal muscle & the nervous system throughout the body. The mechanisms implicated in this action include:

1. Inhibiting normal heat production

2. Enhancing peripheral blood flow to the skin’s surface

3. Sweating

We see this form of acute stress via the steady rise in heart rate during sauna sessions - typically from baseline to 120 - 150 beats/min is the norm. This also explains why acute heat exposure in the form of sauna therapy can be so beneficial for stress reduction in the matter of months. More on that later.

Blood Pressure Regulation

Heat stress induces endothelial nitric oxide synthase (eNOS) activity facilitating increased levels of nitric oxide (NO) production. NO serves as a strong vasodilator improving vascular relaxation, reducing systemic vascular resistance and enhancing peripheral blood flow.

One of the key indicators showcasing the efficacy of this thermal vasodilation mechanism: left ventricular function. A 1995 study showed the effects following four weeks of sauna therapy - ejection fraction (% of blood pumped with each contraction) increased from 24% to 31% and end-diastolic dimension (size of the ventricle in relaxation phase) decreased from 66 mm to 62 mm on average.

Endothelial dysfunction, commonly associated with hypertension, is typically the result of three mechanisms: 1) impaired eNOS signaling, 2) reduced eNOS expression, or 3) oxidative stress limiting nitric oxide availability. Intense sauna sessions enhance endothelial function by increasing shear stress within blood vessels helping to upregulate eNOS activity & expression, thus increasing vasodilation. We see this enhanced level of blood flow shown in research demonstrated by brachial artery blood flow increases of 68% following a 15-min sauna session and stays elevated 30 min after the conclusion of the session.

Now that our nitric oxide availability has increased, our blood vessels become dilated where wider vessels reduce vascular resistance enabling blood to flow more easily. Thus yielding lower systolic & diastolic blood pressure biomarkers. Similar to a short-term increase in RHR, think of this as an acute form of stress being imposed on the vascular system. We even see this graphically in the short-term of a single sauna session.

More on these specific effects later as we explore some of the benefits seen in hypertensive individuals over longer-term controlled trials.

Metabolic Effects

PGC-1a Upregulation & AMPK Activation

Heat exposure increases the expression of AMP-activated protein kinase (AMPK), which stimulates our master regulator of mitochondrial biogenesis & oxidative metabolism - PGC-1α.

By now, if you’re on Health X, you’ve seen this acronym thrown around quite often. So what does it actually mean for us metabolically?

First, PGC-1α’s primary role: to promote mitochondrial growth & function. It also acts as a coactivator for transcription factors supporting the regulation of our gene expression. For example, some of those transcription factors upregulate antioxidant enzymes, promote cellular stress resilience, and of course support mitochondrial energy metabolism. As PGC-1α is upregulated, mitochondria in the cell undergo a continuous “remodeling” improving their “structural” integrity.

As a result, we get more & denser ATP-generating mitochondria providing us with an enhanced cellular capability to handle stress & maintain redox balance.

Two of the key indicators we can use to test the validity of heat’s impact on mitochondria: 1) protein content & 2) respiration. In a 2019 study, participants had one leg immobilized for a 10-day period. When heat was applied directly to the immobile leg of the subjects, both protein content & mitochondrial respiration increased significantly relative to the unheated control group. Overall, the passive heat treatment lessened overall muscle atrophy & preserved mitochondrial respiration as shown in Figures A & B, respectively.

Anti-Inflammatory Response

As we’ve seen thus far, sauna therapy induces an acute phase response across a number of different biomarkers. This time we’re focused on the acute increase in certain inflammatory markers like interleukin-6 (IL-6) & interleukin-1 receptor antagonist (IL-1RA). Sound familiar? (*coughs* exercise *coughs*)

While IL-6 is typically considered pro-inflammatory, it also has anti-inflammatory properties when released during exercise or heat stress. IL-1RA, an anti-inflammatory cytokine, acts as a natural inhibitor of the pro-inflammatory effects of IL-1β.

Sauna therapy has also been associated with a reduction in high-sensitivity C-reactive protein (hsCRP) - one of the key markers of systemic inflammation. A longitudinal study of 2,084 men found an inverse relationship between sauna session frequency & serum CRP levels. These heat stress-induced changes are driven primarily by anti-inflammatory cytokine production & hepatic acute phase protein synthesis.

Thermoregulatory Response

Now to my favorite mechanism at play due to its uniqueness to sauna therapy. And one I personally believe should be a critical component to most adjunct cancer protocols. Let’s find out why.

Heat Shock Protein

While the other mechanisms outlined are critical, thermoregulation of sauna therapy acts as the root mechanism. And one that shows tremendous promise for future chronic disease treatment & prevention.

During typical sauna sessions (time & temperature dependent), our body can increase its temperature anywhere from 1- 4° F. This rapid rise in body temperature can temporarily halt the production of regular proteins and prompt the creation of specialized proteins - heat shock proteins.

Heat shock proteins (HSP) are special proteins found in all cells that help repair and regenerate damaged cells. They’re produced in response to varying forms of stress: heat (of course), ATP depletion, or inflammation, temporarily halting normal protein production to focus on cell recovery. Once triggered, HSP production can last up to nine days and can even enhance our epigenetic makeup. In some of the latest research reviews, HSPs have been implied to inhibit cancer growth & even improve conditions like congestive heart failure.

How do these HSPs actually work?

HSPs assist in refolding and reassembling damaged proteins, a process known as renaturation. They bind to severely damaged proteins preventing them from clumping together or forming aggregate versions - crucial for maintaining cellular health & preventing the accumulation of potentially toxic protein clusters. Lastly, HSPs guide the damaged proteins where they can be recycled properly.

Why aren’t we simply injected with these as a form of therapy?

HSPs are highly idiosyncratic to each of us. Remember: what’s yours is yours, what’s mine is mine…yea well it’s true in biological processes even more so.

One of the more interesting oncology developments in the past decade has been the advancements of cancer “vaccines” where tumors are being extracting & reinjected into the patient to produce an HSP counter-response. As a side note, we’ve likely got a long road ahead of us if we continue to treat cancer as a genetic disease, rather than a metabolic one.

Think of HSPs as an emergency response force. They are incredibly energy-demanding to produce endogenously and therefore are preserved only for the most critical of physiological responses.

Lucky for us - we have this high stress demand signal attainable to us via sauna therapy.

In a 2007 study, healthy individuals were exposed to 165°F for 30 minutes and their HSP72 levels increased by 49%.

In another study in 2018, healthy subjects received deep tissue heat therapy for six days. Following the treatment, HSP70 and HSP90 increased 45% & 38%, respectively.

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Health Benefits

Now that we’ve covered the intricacies of the mechanisms of heat exposure, let’s get to what we truly care about: what outcomes can sauna therapy provide for us? By now, you can reasonably guess some of the big ones. But I've explored the depths of the research hole to find some you may have never known about.

Similar to exercise, the efficacy of usage is best determined by two main variables: frequency & duration of sessions.

Cardiovascular Health

Reduction in cardiovascular disease

Across 1,688 participants & a median follow-up time of 15 yrs, subjects who did 1 sauna session/week compared to those doing 2-3x/week had a 29% lower risk of CVD mortality. While those doing 4-7x/week had a 70% lower risk.