A few months ago, I explored the benefits and applications of cold therapy . Today, I’m going to talk about the benefits and applications of heat therapy—one of the most ubiquitous and ancestral therapies in the history of humankind. You name a culture and—as long as they didn’t live in perpetual tropical heat—they probably had some form of heat therapy. Native Americans had the sweat lodge, those of Central America the temazcal. The Romans had the thermae, which they picked up and refined from the Greeks. Other famous traditions include Finnish saunas, Russian banyas, Turkish hammams, Japanese sentó (or the natural spring-fed onsen), and the Korean jjimjilbang. People really like the heat.
Right off the bat, that’s one major benefit to heat therapy compared to cold: It’s an easy sell. “You can luxuriate in a sauna for half an hour or lower your naked body, genitals first, into a bathtub filled with ice water. Your choice.” People are far more likely to sit in the hot room for 20 minutes than they are to sit in an ice bath for 3 minutes or even take a cold shower. Short-term heat exposure is generally regarded as pleasant. Cold exposure is generally regarded as torture. If heat therapy offers legit health benefits, this is a major point in its favor. So, does it?
In a recent review  of the available observational studies, controlled trials, and interventions, researchers found evidence that sauna usage has an impressive array of beneficial effects on health and wellness:
- Increased lifespan and decreased early mortality.
- Reduced cardiovascular disease.
- Lowered blood pressure.
- Improved cognitive function and reduced the risk of neurodegenerative disease.
- Improved arthritis symptoms.
What’s going on here? How could sitting in a hot room do so many good things?
Stress, in a word. One of the coolest things about us is that encountering, facing down, and then growing resistance to one type of stress tends to make us better at dealing with stress from other sources. A 30-minute sauna session at 174 ºF/80 ºC raises body temperature by almost 1 degree C, spikes your flight-or-flight hormones, raises cortisol, and triggers a powerful hormetic response  by the rest of your body. That’s a stressor. After such a session, subjects report  feeling “calm” and “pleasant.” This isn’t a surprise. Intense exercise also raises cortisol  in the short term. And like regular exercise, longer term sauna usage (daily for four weeks in one study ) actually reduces stress hormones. It’s a classic hormetic response , where acute doses of the stressor increase oxidative stress enough to provoke a compensatory adaptation by the organism.
What does this sauna-induced hormetic stress do for us?
Benefits of Heat Therapy
It reduces oxidative stress. Short term, it increases stress (that’s why we see the transient spike in cortisol and other stress hormones). Long term, it reduces oxidative stress. Long-term sauna use has an inverse association  with levels of C-reactive protein (CRP), a “catch-all” biomarker for oxidative stress and inflammation. The more often you use the sauna, the lower your CRP.
It may reduce mortality. The more frequently a person visits the sauna, the lower his risk  of premature death from heart attack and all causes. There is a dose-response relationship happening here, which has me leaning toward “causal.” Those using the sauna two to three times a week had a 23% lower risk of fatal heart attack compared to men who used it just once a week. Men who used the sauna four to seven times a week had a 48% reduced risk of fatal heart attack compared to once-a-weekers. The more frequently men used the sauna, the greater the protection (for other causes of mortality, too).
It improves vascular function. A single bout of sauna (or exercise, for that matter) reduces  vascular resistance—the amount your blood vessels “resist” blood flow—in hypertensive patients for up to two hours.
It’s good against type 2 diabetes. Sauna use has been shown  to improve almost every marker related to type 2 diabetes, including insulin sensitivity, fasting blood sugar, glycated hemoglobin, and body fat levels.
It can improve depression scores. Patients with depression who underwent heat therapy saw improvements  in their Hamilton Depression Rating.
If you’re an athlete, or exercise at all, you should try the sauna. Training magnifies the benefits of the sauna.
Finally, pairing exercise and heat therapy together is a boon for cardiovascular health. For instance, people who frequent the sauna and the gym have a drastically lower risk  of heart attack death than people who do either alone. That combo also reduces  24-hour blood pressure in hypertensive patients and confers  special protection against all-cause mortality above and beyond either variable alone.
Post-workout sauna sessions improve endurance performance in runners : For three weeks, endurance runners sat in 89° C (+/- 2° C) humid saunas for 31 minutes following training sessions. This amounted to an average of 12.7 sauna sessions per runner. Relative to control (no sauna), sauna use increased time to exhaustion by 32%, plasma cell volume by 7.1%, and red cell volume by 3.2% (both plasma cell and red cell volume are markers of increased endurance performance).
Post-workout sauna use increases plasma volume in male cyclists : Following training sessions, cyclists sat in 87° C, 11% humidity saunas for 30 minutes. Just four sessions were sufficient to expand plasma volume. This is important because increasing plasma volume improves  heat dissipation, thermoregulation, heart rate, and cardiac stroke volume during exercise.
Post-workout sauna—either dry or steam—can also alleviate muscle fatigue.
How About Pre-Workout?
The effects are more mixed. In one study , pre-workout sauna reduced strength endurance and 1 rep max leg press, had no effect on 1 rep max bench press, and improved maximum power (vertical leap). Another study  found that in female athletes but not in males, maximum power decreases after sauna use. It’s possible that these performance disturbances are caused by dehydration  rather than the heat itself, so make sure you rehydrate  if you’re planning on training after a sauna session.
If you want to apply heat pre-workout without overdoing it, I’ve always liked a nice hot bath to help limber up, mobilize my joints, and clear out any stiffness for the coming workout session.
Oh, and It Can Help You Detox
I was going to write the full word “detoxification,” but I figured I’d write “detox” just to trigger the hardcore skeptics reading this…. Heat exposure can augment your natural detoxification capacities by at least two mechanisms.
First, exposure to extreme heat increases something called heat shock proteins, or HSPs. HSPs are responsible for many of the benefits of heat therapy, including enacting beneficial hormetic  effects on our detoxification capacity. They trigger compensatory adaptations and activate antioxidant defenses  in the blood of healthy volunteers. They even increase regeneration of the body’s main detoxifying organ —the liver—after it’s been damaged.
Second, contrary to popular belief, sweating can aid detoxification. Sweat itself contains bioaccumulated toxins,  including BPA —even when it doesn’t show up in the blood or urine. Sweat also contains certain phthalate compounds and their metabolites , none of which we want. Sweat also contains arsenic and lead in people exposed to high levels of the metals . Sweating may even improve the function of another important detoxification organ—the kidney—by restoring nitrogen excretion in people with kidney disease . In one study , police officers with chronic illnesses caused by exposure to high levels of meth lab chemicals experienced major improvements after sauna therapy.
What If You Don’t Have Access To a Sauna?
There are other options.
Steam rooms work. Only problem with them is it’s difficult to remain in one long enough to trigger the necessary stress response. Saunas, with their dry heat, are easier to stick with. Steam rooms feel different enough that I wonder if there’s something unique about them. Not enough evidence to go on, unfortunately. Perhaps I can revisit this later.
Jacuzzis and hot baths work. A recent paper  found that taking regular hot baths at home improved insulin sensitivity and increased nitric oxide synthase activity about as much as working out. Another found  that, compared to showering, bathing improved mood, perceived stress, blood flow, and accumulation of metabolic waste products.
You could probably sit in a black car on a hot day with the windows rolled up and get an effect.
Just get hot, as hot as you can stand. Then stay a little longer. (As always, be sure to talk to your doctor. Certain conditions and scenarios, like pregnancy, require extra caution with saunas or other forms of heat therapy.)
Have you used the sauna? Are you a regular attendee? Or do you use other means of heat therapy? I’m curious to hear your experiences, tips, and stories below.
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