On Wednesday, for the umpteenth time in the last year, I found myself in swimming shorts, dripping in sweat, and making small talk with strangers. Even in the UK, saunas are a great place to meet people.
“What even is the benefit of doing a sauna, anyway?”
I’ve heard that question while sweating my guts out so many times that I really wonder what brought them there in the first place. You just walked through the door, son, you tell me!
But I love showing off, so I tell them all about The Science of Saunas. Then I thought I should probably write it all down so that, instead of mumbling something vague about brain-derived neurotrophic factor, I can be more accurate with my next sauna science speech.
As Richard Feynmann said, if you really want to learn something, teach it to a toddler. You are my toddlers. And if you’ve never saunaed, I hope this changes your mind.
Sidebar: What is a sauna?
- A sauna is a room that’s super hot and super dry.
- Most of the science has been done on saunas that are at least 80°C.
- Your sauna should have a thermometer and a hygrometer, so check these when you first walk in. Ask them to turn it up if it’s too cold.
- A sauna is not a steam room.
- Also: please don’t die.
I’m not a science person, but luckily other people are and they’ve done a lot of studies on what happens when we sauna. Rhonda Patrick is a medical science PhD and she summarised these studies in a report published on her website.
UPDATE April 2022: Rhonda Patrick has updated this report, the bones of which are now available on her website and in more detail as a downloadable document when you sign up to her newsletter.
Here’s the dope, from her report with my explanations in [brackets]:
Saunas can enhance endurance by:
- Increasing nutrient delivery to muscles thereby reducing the depletion of glycogen stores. [Glycogen is one form in which body fuel is stored; stored primarily in the liver and broken down into glucose when needed – you want to hold on to as much as you can for as long as you can.]
- Reducing heart rate and reducing core temperature during workload. [Our bodies must work within the limits of our maximum heart rate and core temperature. Through training, our bodies learn to do more with less. If you run every week, gradually your heart rate will come down and you can run faster or further; if you sauna every week, you’ll train your body to better manage its core temperature – and you’ll be able to run further or faster.]
Saunas can increase muscle hypertrophy [enlargement] by preventing protein degradation through the following three means:
- Induction [stimulation] of heat shock proteins and a hormetic response [where something toxic acts like a stimulant in small doses] (which has also been shown to increase longevity in lower organisms).
- Cause a massive release of growth hormone [a hormone that promotes growth in humans].
- Improving insulin sensitivity. [As shown in an experiment on diabetic mice.]
Hyperthermic conditioning [hanging out somewhere really hot, like a sauna] also has robust positive effects on the brain:
- Increases the storage and release of norepinephrine, [a chemical] which improves attention and focus.
- Increases prolactin, [a hormone] which causes your brain to function faster by enhancing myelination [myelin sheaths insulate nerve fibres and thus “strengthen” connections in your brain] and helps to repair damaged neurons.
- Increases BDNF [brain-derived neurotrophic factor], which causes the growth of new brain cells, improves the ability for you to learn new information and retain it, and ameliorates [makes better] certain types of depression and anxiety.
- Causes a robust increase in dynorphin [a chemical that makes you feel queasy from the heat], which results in your body becoming more sensitive to the ensuing endorphins [chemicals that make you feel gooood].
I think a toddler would get that, don’t you?
In short: Controlled stress is good. Controlled heat stress is fantastically good.
The Big Question: How hot, how long, how often?
If you’re a runner:
- One ~30 minute ~89C sauna immediately after training, 4 times a week for 3 weeks.
A 2007 study in the Journal of Science and Medicine in Sport found that this protocol increased the time that it took for club runners (N=6) to run until exhaustion by 32% compared to baseline. This is the equivalent of a ~2% increase in running performance – an astonishing result after just 3 weeks of sitting in a hot room.
If you’re looking for the growth hormone improvements, then either:
- Two 20-minute 80°C saunas separated by a 30-minute cooling period to increase growth hormone levels two-fold over baseline.
- Two 15-minute 100°C saunas separated by a 30-minute cooling period for a five-fold increase.
If this is all a bit too confusing, then you could do a lot worse than following in the tiny footsteps of one group of diabetic mice who were made to take a 30-minute sauna three times a week for twelve weeks. It made them significantly less insulin-resistant, which was probably a relief given that the mean scientists probably induced diabetes in the first place.
It’s a cruel world.