Embracing sauna culture can lower dementia risk and boost brain health

I’m already a devoted cold-water swimmer, and last year I wrote about its benefits for the brain. But I’ve started seeing more and more written about heat therapy and its neurological perks. And while the evidence is only just emerging, it’s starting to look quite persuasive, so I decided to investigate further.

For science, I made the most of Scandinavian sauna culture while I was visiting Finland and Sweden last month. I also learned that “sauna” is pronounced “sow-na” (with the “ow” rhyming with “how”), rather than my south-east London pronunciation of “sorna”.

Finnish saunas, which are typically heated to between 70°C and 110°C (158°F to 230°F) and have low humidity, are the most well-studied. Regular use has been linked with many physical benefits – a lower risk of hypertension, muscular problems and respiratory conditions, for instance. But now researchers are starting to unveil cognitive benefits, too. These improvements include fewer headaches, increased mental well-being, better sleep and a lower risk of dementia.

In one of the biggest studies I came across, nearly 14,000 people between the age of 30 and 69 were asked about their sauna use as part of a bigger study on health, and were followed up 39 years later. After adjusting for other lifestyle factors, people who were more frequent sauna-goers – visiting a sauna nine to 12 times a month compared with less than four times a month – had a 19 per cent reduced risk of dementia by the end of the study.

We have seen that, beyond dementia, sauna bathing has also been linked to several other cognitive benefits. In one small trial, 37 adults with chronic headaches either received advice on headache management or regularly attended saunas and received the same advice for eight weeks. Those in the sauna-plus-education group showed significant improvement in headache intensity. Regular saunas have also been associated with a reduced risk of psychosis, as well as an increase in vitality, your ability to live life in a way that you personally value, and social functioning in older adults.

Not all heat therapies are the same, however. While traditional saunas are the most common, other types of heat therapy exist, with their own benefits. For instance, in a small trial, 26 people with major depressive disorder received either a single session of whole-body infrared warming or a sham treatment. Unlike traditional saunas that use hot air to warm the body, infrared warming uses electromagnetic waves. The sham treatment looks and sounds the same, but the waves aren’t switched on. Those who received the real treatment reported fewer symptoms over six weeks and showed changes in interleukin-6 signalling, a pathway involved in inflammation, which is strongly linked with depression.

Why does heat therapy help the brain?

Heat therapy’s anti-inflammatory effects seem to be key to its many benefits. In 2018, Setor Kunutsor, then at the University of Bristol, UK, and his colleagues analysed the sauna habits and blood markers of inflammation in 2269 middle-aged Finnish men, following them over 11 years. After controlling for factors like alcohol consumption and physical activity, the researchers found that frequent sauna sessions were associated with lower levels of several different inflammatory markers. The team concluded that sauna’s health benefits may partly stem from reduced inflammation, since chronic inflammation is strongly linked with depression, cognitive decline and other neurological conditions.

Another possible mechanism is heat shock. When your body temperature rises, due to exercise or passive heating, it triggers the production of heat shock proteins – molecules that act as chaperones for other proteins, ensuring they don’t misfold or go astray. These are critical, as misfolded proteins are a hallmark of many neurological conditions. Last year, scientists discovered more than 200 types of misfolded proteins in rat brains associated with dementia and age-related decline, beyond the familiar amyloid and tau of Alzheimer’s. This suggests the protective effect of heat shock proteins may be a key part of the story.

Improved blood circulation may also play a role. Heat causes blood vessels to dilate, improving cardiovascular function, blood pressure and arterial stiffness. Given reduced blood flow contributes to vascular dementia and Alzheimer’s disease, maintaining good cardiovascular health may indirectly benefit the brain.

Saunas may boost the amount of brain-derived neurotrophic factor (BDNF) circulating in the blood, too. These molecules act like a fertiliser, helping neurons grow, and low levels are associated with depression and anxiety. In one trial, 34 men were given either 12 or 24 sessions of infrared heating, over 10 weeks, or a low intensity exercise regime. Those who underwent repeated hyperthermia showed significantly higher BDNF levels and reported better quality of life and lower anxiety than those assigned to gentle exercise.

Can saunas help you think better?

The potential long-term neurological benefits weren’t all I was interested in. One small study of 16 men who had their brain activity recorded using EEG before and after a sauna suggests it’s not only a relaxing practice in the short term, but could help us think more efficiently, too. The participants’ brainwave activity more closely resembled a relaxed state after the sauna, and although they didn’t do any better on two tasks given to them a short while after leaving the sauna, their brain activity showed signs of greater efficiency in the tasks, suggesting less effort for the same results. The researchers regard heat therapy as a potential way to increase our ability to “maintain mental working capacity for a longer duration”.

Of course, it isn’t all good news. Most of us know the sluggish, foggy feeling that comes with spending too much time in the sun, and studies of people exposed to 50˚C (122˚F) heat for an hour back this up – exposure to that high level of heat changed the way regions of the brain communicated with each other, which was linked directly with slower reaction times. There’s also some evidence that heat exposure can impair memory consolidation, so perhaps avoid saunas if you’re cramming for an exam.

If you’re new to heat therapy, the British Sauna Society provides safety guidelines, including limiting your time in a sauna to acclimatise to the heat, moving slowly and hydrating regularly, plus other tips to keep you safe.

Can a hot bath have the same effect?

What if you don’t live in a sauna-loving society or in a trendy neighbourhood blessed with pop-up sweat boxes? Can a hot bath do the job instead? Sadly, the jury is out. Hot baths can only partially replicate the benefits of saunas, says Ali Cadili at West Virginia University Medicine. They do raise your core temperature, and repeated warm baths – 30 minutes, five days a week for four weeks – have been shown to decrease resting heart rate and promote feelings of relaxation, which can benefit mood. However, he says that there are no head-to-head comparisons between saunas and hot baths. Cadili considers baths a viable alternative to saunas if they are all that’s available, but cautions that we must keep in mind that there is a greater amount of robust, long-term data on saunas’ association with dementia and stroke prevention.

With cold water swimming and heat therapy both on offer at my nearby lake – I did wonder whether combining the two might amplify the effects of each. Research is sparse, but I came across a study on what, in Japan, is known as the totonou state – the intense feelings of happiness that people report after alternating a hot sauna with cold water.

In the study, participants alternated three times between a hot sauna, cold-water exposure and rest. Researchers measured brain activity before and after the three cycles and found increases in brainwave patterns associated with relaxation and reduced attentional demand.

It’s not clear yet whether this is a better brain state than achieved by cold or hot therapy alone, but altogether, it’s far more than I thought I would achieve by sitting in a hot wooden box. So no, I don’t need another excuse to visit the lake, or a spa, but it’s reassuring to know that, alongside the immediate pleasure I get from such visits, more regular saunas might just be giving my brain a cognitive boost too, now and for the long term.