Though the general health benefits of sauna bathing have been known for a long time, the use of saunas for preventing brain diseases, like Alzheimer’s disease, is a more recent subject of research. In this blog post, I'll review a research study by Knekt and colleagues, published in the December issue of Preventive Medicine Reports, which has found Finnish sauna bathing may protect against dementia.
What is a Finnish sauna?
Saunas are an important part of Finnish culture. In fact, the Finnish sauna culture was recently added to UNESCO's list of Intangible Cultural Heritage.
There is more than one sauna for every three people in Finland. Nearly 99% of the sample in the investigation by Knekt et al. reported using saunas. According to Finland’s Ministry for Foreign Affairs, even the “president has an official sauna, as does the prime minister.”
People using Finnish saunas, which are typically made of wood and have wooden benches, are exposed to dry heat at very high temperatures (typically 80–100°C or 158-212°F). Not surprisingly, heart rates during a heat session can reach 120-150 beats per minute.
However, these heat sessions are often short (5-20 minutes) and interspersed with cooling breaks (e.g., shower, swimming).
But does sauna bathing help prevent health conditions, such as Alzheimer’s disease? To find out, let us review the investigation by Knekt and collaborators.
The sauna study: sample and methods
The data came from the Finnish Mobile Clinic Follow-up Survey (FMCF), which, in the mid-1970s, assessed thousands of participants’ height, weight, body mass index (BMI), blood pressure, cholesterol, triglycerides, fasting blood sugar, and other health-related indicators.
The present investigation used data from 13,994 FMCF participants—those aged 30 to 69 years who had not received a diagnosis of dementia.
Characteristics of the sample include: 51% males; average age of 48 years; 71% with basic education; 78% married; 27% smokers; and an average BMI of 26.
The researchers obtained information regarding participants’ sauna use, lifestyle, and health—physical activity, alcohol consumption, smoking, medications, and chronic illnesses (e.g., heart disease, hypertension, diabetes, mental illness).
Examining the sample data, from 1973 to 2011, the authors identified 1,805 dementia cases.
The relationship between sauna bathing and dementia
The results showed sauna bathing was associated with a reduced risk of dementia.
This was true even after adjusting for a variety of factors—age, sex, region, education, marital status, smoking and drinking, BMI, leisure-time physical activities, blood pressure, glucose, cholesterol, and triglycerides.
The hazard ratio for individuals who bathed 9-12 times was 0.81 (95% CI = 0.69-0.97), compared with participants who bathed 0-4 times per month. The hazard ratio for 0-4 and 13-30 monthly sauna users did not differ.
In addition, a continuous stay in the heat for 5-14 minutes, compared to less than 5 minutes, was linked with a reduced risk of developing Alzheimer’s disease. The sauna temperature range most highly linked with dementia protection was 80-99°C (176-210°F).
Frequency of sauna bathing was also associated with dementia risk:
“During the first 20 years of follow-up, the dementia risk of those reporting 9-12 sauna baths per month [roughly three times a week] was less than a half of the risk of those who had sauna baths only 0-4 times per month.”
However, extreme heat seemed to increase the risk for dementia. Specifically, based on the data from the first 20 years, the risk for dementia in people who bathed using temperatures higher than 100°C (212°F) was double compared to individuals who used temperatures below 80°C (176°F).
Why might sauna bathing prevent dementia?
At this point, no definitive answers exist as to why sauna bathing could prevent dementia.
Perhaps passive body heating, which occurs during a sauna session, leads to beneficial health changes that reduce the risk for dementia. But how?
Passive body heating may activate heat shock proteins, which assist and control protein formation. Abnormalities in protein construction, folding, and degradation (e.g., accumulation of protein aggregates) are common in neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. So, regular activation of heat shock proteins could potentially play a role in protecting against neurodegenerative changes.
Another possibility concerns the facilitation of healthy circulation. A 2016 investigation found passive heat therapy had several health benefits, including improved cardiovascular function and reduced blood pressure and arterial stiffness. Adequate blood supply and a healthy vascular system might protect against dementia and other neurological degenerative diseases.
Other potential mechanisms linking frequent sauna bathing with reduced risk of dementia include reduced inflammation, better sleep, stress reduction, and increased relaxation.
In summary, in keeping with a previous investigation that found frequent sauna bathing was associated with reduced risk for dementia and Alzheimer’s disease, the research reviewed here concluded sauna bathing, particularly three times a week, might protect against dementia.
So, is sauna bathing an effective way to help prevent Alzheimer’s disease? Perhaps. At the same time, it is possible that the reasons for the protective effects of sauna bathing are related to cultural factors that would not apply as much to sauna bathing outside of Finland. Only further research will determine if regular sauna baths should be added to the list of recommended strategies for dementia prevention—strategies like regular exercise, socializing, healthy eating, and cognitive stimulation.