This study included 2,315 healthy men between the age of 42 and 60 years (Laukkanen T, et. al., 2017).
The researchers investigated whether frequency of sauna bathing is associated with the risk of dementia and Alzheimer's disease. The sauna they used was a traditional Finish sauna.
The results showed that the men who used the sauna four to seven times per week had a 66 percent lower risk of developing dementia and a 65 percent lower risk of developing Alzheimer's disease, compared to men who used the sauna only one time per week.
This was a dry sauna, and the temperature was at least 174 degrees Fahrenheit, and the time spent in the sauna was 20 minutes per session.
Tanjaniina Laukkanen, Setor Kunutsor, Jussi Kauhanen, Jari Antero Laukkanen. Sauna bathing is inversely associated with dementia and Alzheimer's disease in middle-aged Finnish men. Age Ageing. 2017 Mar 1;46(2):245-249.