Hot Box Health! Science of Saunas for the Heart, Brain & Longevity

What if I told you sitting in a 170F box a few times a week could reduce your risk of heart disease, improve brain function, and even help you live longer? Let’s break down the science of saunas.

What if I told you sitting in a 170-degree wooden box a few times a week could reduce your risk of heart disease, improve brain function, and even help you live longer?

Sounds like wellness hype—but the research says otherwise. Let’s break down the science of saunas.

Types of Saunas

Quickly, let me explain the basic types of saunas—traditional Finnish (dry) , steam, and infrared.

• A traditional Finnish sauna is a dry sauna, generally heated with a wood-burning stove or electric heater with stones placed on top. Temperature ranges from 70–100°C (158–212°F), and humidity is typically low (<20%), unless you toss water on the stones to create bursts of steam. These saunas are intense, good for cardiovascular conditioning, and probably have the strongest data overall for outcomes like reduced all-cause mortality (i.e. death).

• Then there are steam saunas. These are cooler, typically 40–50°C (104–122°F), generally in a closed, tiled room filled with high humidity. While less intense, steam saunas can feel great for clearing out congestion and soothing the airways and still impart a decent amount of heat stress.

• Finally, infrared saunas use lamps to directly heat your body with infrared radiation. They operate at lower temperatures, in the 45–60°C (113–140°F) range, and with low humidity. Since the infrared penetrates deep tissue, it’s great for muscle recovery and reducing inflammation. The lower temperatures allow longer sessions, and these saunas have the advantage of accessibility and are good for home use.

Now, let’s delve deeper into the scientific literature on the health benefits of saunas, starting with heart health and the cardiovascular system.

Heart Health

Saunas can improve heart health, in part, by mimicking cardiovascular exercise. They increase heart rate—and can increase cardiac output by up to ~70%—and improve blood flow throughout the body. They can also help reduce chronic inflammation, with more frequent sauna use being associated with lower levels of inflammatory markers like C-reactive protein (CRP). Saunas also increase levels of anti-inflammatory molecules like IL-10, and they can help improve the function of the endothelial cells lining blood vessels. But I’m getting ahead of myself. I promise we’ll get deeper into the mechanisms on the back half of this video.

Let’s first look at some human studies to convince you saunas may be worth your time.

The notable benefits for heart health were popularized by several major studies, including one published in JAMA Internal Medicine, where researchers followed a group of 2,315 Finnish men for a median of 20.7 years and compared the frequency of sudden cardiac death and cardiovascular disease between those who used the sauna frequently (4–7 times per week) vs. those who used it rarely (about once per week).

They found that those who used the sauna 4–7 times per week had a 67% reduced relative risk of sudden cardiac death compared to low sauna users.

And this was after adjusting for age, BMI, systolic blood pressure, smoking, alcohol consumption, diabetes, physical activity, and socioeconomic status. Similarly, there was a 50% reduction in fatal cardiovascular disease.

As for the specifics, the average temperature of the Finnish (dry) sauna used by the population was 174°F, with sessions lasting 14.5 minutes on average. Notably, longer sessions (those lasting >19 minutes) elicited an even more robust effect, suggesting a clear dose-response. In other words, more might be better in terms of frequency and duration, at least up to a point. But based on these data, ~15 minutes four times per week would be excellent.

Brain Health

First, saunas can increase levels of the brain-protective hormone brain-derived neurotrophic factor (BDNF). One study showed that heat challenge—in this case, 20 minutes of hot water immersion at 42°C—significantly increased BDNF levels, whereas immersion in thermoneutral water did not.

BDNF supports neuroplasticity (the brain’s ability to form new connections), improves memory and learning, and may protect against neurodegenerative diseases like Alzheimer’s and Parkinson’s.

Furthermore, saunas increase levels of heat shock proteins (HSPs). HSPs help other proteins fold properly, which is absolutely critical in preventing neurodegenerative diseases like Alzheimer’s and Parkinson’s, both of which are characterized by misfolded proteins.

The idea is that saunas can increase levels of proteins that prevent misfolding—and those HSPs stick around well after you’ve gotten out of the sauna. If you sauna routinely, you can effectively keep boosting your HSP levels to potentially keep your brain healthier as you age.

In one randomized controlled trial comparing a 30-minute session at 73°C (163°F) to no heat stress in 25 healthy young men and women, the sauna increased levels of one HSP (HSP72) by 48.7%.

Other studies have shown that bouts of heat stress can increase various HSP levels by ~35–50%, and that this adaptation has a lingering effect. In other words, routine sauna use can keep your HSP levels consistently elevated, which is thought to confer a neuroprotective effect. (Diagram below, from Patrick and Johnson, Sauna use as a lifestyle practice to extend healthspan.)

Interestingly, and as a quick aside, ketones produced by the body on ketogenic diets also appear to help with misfolded proteins in a complementary manner to potentially prevent Alzheimer’s disease. For more, see this video, which includes input from the first author of the key paper in question.

But, back to saunas…

In a prospective study on Finnish sauna users—drawing from the same population of 2,315 Finnish men discussed earlier— researchers found that routine sauna use 4–7 times per week was associated with a 65% reduced risk of Alzheimer’s disease compared to those who used saunas only once per week. Impressive, right?

And remember, this statistic includes adjustments for BMI, age, smoking, alcohol intake, diabetes status, blood pressure, among other factors. Because these human studies are associational—you can’t practically do a 20.7-year-long randomized controlled trial—they can’t prove causality. However, the consistency of the results, the size of the effect, and the biological plausibility (BDNF, HSPs) are collectively compelling.

Longevity

Now, a quick comment on longevity. Typically, better healthspan—as reflected by lower rates of chronic disease—should translate to longer life at a population level. And we do in fact see that.

There is a 40% reduced risk of all-cause mortality in those who used saunas 4–7 times per week compared to once-per-week users.