How Sauna Use May Protect the Aging Brain

How robust is the current evidence for sauna in decreasing the risk of Alzheimer's disease? And he says, a couple of respected neurologists, Dean and Ayesha Sherzai, I never heard of these people, were a bit dismissive of the idea for limited evidence and confounding factors. I've been devoting a lot of time to sauna and I hope it's not wasted. So, The observational data on sauna use and Alzheimer's disease risk include— so there was a prospective cohort study. It was a population-based sample of about 2,315 middle-aged— they were men in eastern Finland who used the sauna 4 to 7 times per week. They had a 65% reduced risk of developing Alzheimer's disease compared to men who used the sauna only 1 time a week. So the data was adjusted for baseline age, for alcohol consumption, for body mass index, systolic blood pressure, smoking status, type 2 diabetes, a previous heart attack, resting heart rate, the low-density lipoprotein cholesterol, and other heart disease risk factors, meaning that that 65% reduction in Alzheimer's disease was found after all those factors were considered. So, obviously, prospective observational data, you can never actually, you know, you can never actually say causation is established, like sauna use will absolutely decrease Alzheimer's disease risk. But when you correct for a lot of other factors, and then you have interventional studies and mechanisms, then you kind of put together a bigger picture.

There was another prospective cohort study. This was a study involving almost 14,000 men and women between the ages of 30 and 69 that were free from dementia diagnosis. That study found that frequent sauna bathing— so this was about 9 to 12 times per month. So I would say a little bit less than the 4 to 7 times a week, right? So that was pretty robust and pretty frequent sauna use, right? 9 to 12 times a month was related to about a 20% reduced risk of dementia compared to people either not sauna bathing at all or sauna bathing less than 4 times a month. So that's like once, basically once a week. And again, this was after adjustment for all these different lifestyle factors I mentioned, metabolic risk factors, socioeconomic status, things like that. So we have these 2 pretty large population studies showing sauna use is associated with a pretty dramatic reduction in Alzheimer's disease and dementia, especially when it's more frequent.

But we also know from the last podcast with Dr. Axel Montagne that Alzheimer's disease and dementia are really, really intimately linked with vascular health. And we know that sauna mimics moderate-intensity aerobic exercise. Many of the same physiological responses occur. It's been head-to-head comparisons of that, okay? It's really not a question about sauna mimicking moderate-intensity aerobic exercise. We also know that aerobic exercise also protects against dementia and Alzheimer's disease. And, you know, maintaining an adequate blood supply, healthy vascular factors, it's really crucial for vascular dementia, but also Alzheimer's disease. So long-term sauna use has been shown to induce protective responses against the processes that drive cardiovascular disease. And some of these protective responses include lowering resting systolic and diastolic blood pressure. That's been shown in intervention studies, but also we've got observational data. It increases left ventricular ejection fraction. It reduces left ventricular ejection time. It enhances arterial compliance. It improves flow-mediated dilation. All of these things are measures of endothelial function and vascular health. So sauna improves vascular health. So does moderate-intensity aerobic exercise.

There was one study that found— this is out of Jari Laukkanen's group in Eastern Finland— found that sauna use 2 to 3 times per week had a 24% lower risk of developing hypertension. And that risk reduction was increased to 46% lower risk for people that use the sauna 4 to 7 times per week compared to only once per week. So again, you know, a lot of data suggesting that sauna use improves blood pressure.

There's also been intervention trials with hot tubs as well. So 20 minutes in a 104-degree Fahrenheit hot tub can lower blood pressure as well compared to baseline. So we've got, you know, intervention trials and we got observational data pointing to the same thing, both with sauna use and with hot baths. Well, I should say hot tubs. So I think that's pretty strong evidence. And we know that blood pressure is very intimately linked to dementia risk as well.

There was also a randomized controlled trial with about 149 patients who had advanced congestive heart failure. 2 weeks of what's called Waon therapy. So this is an infrared far-infrared sauna, about 140-degree Fahrenheit sauna. And it improved a variety of biomarkers. So cardiovascular biomarkers, it improved— I mean, just, I don't want to go through all the medical terminology, but many different ones it improved. This was a randomized controlled trial, by the way, where people were getting a sham treatment and compared— basically, people were getting standard medical care. And the people that got the infrared sauna had much more improvements in all these different cardiovascular-related biomarkers. Another trial involving 30 congestive heart failure patients with a variety of premature ventricular contractions found that 2 weeks of infrared dry sauna significantly reduced those— the number of premature ventricular contractions. Within a 24-hour period. Lastly, there was a randomized controlled trial with 24 people who had ischemic heart disease and chronic total coronary artery occlusion that were unresponsive to non-surgical procedures. And they basically did 15 sessions of the far-infrared sauna over a 3-week period, and it improved their vascular endothelial function And it improved— so that improved their flow-mediated dilation of the brachial artery. So these are intervention trials in people with heart conditions, and sauna use is improving their vascular health. I don't think it's really arguable at this point that sauna improves vascular health. I think it's pretty conclusive that it does. So knowing that mechanism, along with the observational data on the effect of, you know, sauna use and Alzheimer's disease is pretty strong in my opinion.

But there's more. We have heat shock proteins. So heat shock proteins, as you guys know, I mean, I'll save you going into too much of it, but like they play a critical role in protein folding and misfolding. There's growing evidence that heat shock proteins are involved in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. There's animal studies that have shown that if you overexpress heat shock proteins, they can protect— they can have protective effects on the brain and help prevent and also ameliorate Alzheimer's disease and Parkinson's disease. Certain heat shock proteins, especially heat shock protein 70 and heat shock protein 90, have been shown to directly interact with amyloid beta. This is the protein that causes plaques outside of neurons where the synapses form in the brain and also interacts with tau proteins, which tangle inside of neurons, and they disrupt mitochondrial function. So HSP70 is basically helping, you know, get rid of those proteins and making them not aggregate, essentially. So I would say a lot of animal evidence suggesting that heat shock proteins are very beneficial in the context of neurodegenerative disease. We also know that There's data showing that in humans that sit in a hot 163-degree Fahrenheit sauna for 30 minutes, it elevates their heat shock protein 70 by 50% over baseline levels. Hot baths have also been shown to elevate heat shock proteins as well. So it's a conserved mechanism. It's a stress— heat shock proteins are increased with many types of stress, but heat stress is a big one. Thermal stress. And so I think that's another, you know, sort of just mechanism by which you could imagine sauna, hot tubs helping reduce the risk of Alzheimer's disease.

Inflammation is another one. Inflammation is thought to play a really big role in neurodegenerative diseases. And when I say inflammation, I mean chronic inflammation, not acute inflammation from, you know, sickness. And, you know, there's studies showing, many studies showing that sauna use, you know, is inversely associated with C-reactive protein, a biomarker of inflammation. So basically, the more frequent people use the sauna, the lower their C-reactive protein levels are. There's also intervention studies showing that sauna use can, while it does something very similar as exercise, it causes an acute inflammatory response as measured by IL-6, that cytokine. But that induces an even more potent anti-inflammatory response. IL-10, which is an anti-inflammatory cytokine, has been shown to be elevated after sauna use. And this anti-inflammatory cytokine, you know, basically has a net effect of anti-inflammatory. So similar thing, exercise does a similar thing.

There's also brain-derived neurotrophic factor, similar to aerobic exercise. You know, heat stress has been shown to increase brain-derived neurotrophic factor, which helps stave off neurodegenerative disease. So, you know, hot water baths have been shown to do this. So head-out immersion, it was a hot, very hot bath, it was 108°F water for 20 minutes, elevated brain-derived neurotrophic factor. Exercise does the same thing. In fact, exercise combined with heat even does... Even elevates brain-derived neurotrophic factor more than exercise alone. So I think there's a lot of supportive evidence that we're not just looking at confounding factors here or healthy user bias with respect to sauna use and reduced dementia risk.