Revisited: Saunas and cold plunges, where does the evidence stand?
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What is the main topic discussed in this episode?
This is The Guardian.
Hi, it's Madeline here. The Science Weekly team is taking a summer break, but we'll be back with a new episode for you on Tuesday. But for now, we're revisiting an episode from earlier this year. Saunas and cold water baths are popping up all over the place, and users say they make them feel incredible. But is there any science behind it? I spoke with my co-host Ian and Dr Heather Massey of the University of Portsmouth to find out. Enjoy. The Finns do it best, taking off their clothes and getting hot and sweaty together. In saunas, of course. And when the warmth gets overwhelming, time to plunge into a freezing lake.
What evidence question does this episode set out to answer about saunas and cold plunges?
Or an outdoor bath. Or maybe even a bucket of cold water splashed over you.
And these days, it's not just the Finns hitting the saunas and cold plunge. In the UK and plenty of other countries, people are increasingly taking up the habit and getting a shot of relaxation and adrenaline. If you talk to any of those people, you'll no doubt be told why it's unbelievably good for the body and the mind. So we just had to ask, is it? What's the scientific evidence that hot and cold immersion can improve your health and wellbeing? From The Guardian, I'm Madeleine Finlay, and this is Science Weekly.
Ian, we wouldn't be a Guardian podcast if we didn't talk about saunas and getting into cold water, plunging, swimming at some point. And to be honest, I'm shocked and surprised that it's taken us this long. Before we talk about what these things can do for us, what kind of temperatures are we actually talking about?
The temperatures can vary a lot for both, but let's start with saunas. I mean, for your traditional Finnish sauna, you know, those classic wood-lined room with a burner in the corner or a heater, you're looking at 70 to 100 degrees Celsius. So it's obviously pretty toasty. As for cold water immersion, again, huge variability as to what people class as cold water here. But we're going to focus on temperatures between 10 and 15 Celsius. I mean, ice baths, plunge pools can be as cold as a few degrees, as can rivers or lidos in the winter. And of course, some people will swim in polar waters, and those can actually go sub-zero thanks to the salt content. But that's obviously pretty risky.
Starting with the sauna, which I'm far more partial to, what happens to the body when you're sat in those nice warm temperatures?
Well, the first thing you'll notice is that obviously your skin and your hair start to heat up. And then depending on how long you stay in, your core body temperature will start to rise gradually from 37 degrees C as normal up to around 39 C. Now, your body has to respond to that rise in temperature to ensure it doesn't overheat. People will probably be aware that your blood vessels expand or dilate.
What temperature ranges define traditional saunas and typical cold plunges?
This is called vasodilation. And that improves blood flow to the skin and your heart rate also increases. So you get this boost to your circulation. At the same time, you start sweating. And when that water evaporates off your skin, it helps you to cool down. So if you think about your blood vessels opening up a bit more and allowing blood to get to the surface of your skin, it's improving how well it can do heat exchange. So it's helping you to cool down. Even though your heart is pumping faster, the dilation of your blood vessels usually leads to an overall drop in your blood pressure. But after a while, and it's going to depend on things like how often you have a sauna and how hot it is, you are going to start feeling uncomfortably hot and you'll need to get out to cool down.
That's really interesting. So that drop in blood pressure, even though your heart's beating faster, is probably why when sometimes I come out the sauna, I feel a little bit dizzy. Let's go on to cold water immersion now. I know this is more your bag, Ian.
Yeah, I mean, I may be one of the few people who does it without talking about it very much. At least I try not to talk about it very much anyway. Look, I love both of these, especially having a sauna after a
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Chapters
4 chapters
1
What is the main topic discussed in this episode?
0:00–1:00
2
What evidence question does this episode set out to answer about saunas and cold plunges?
1:00–3:43
3
What temperature ranges define traditional saunas and typical cold plunges?
3:43–4:53
4
How does the body physiologically respond to sitting in a sauna?
4:53–16:07
Speakers
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