Does sauna bathing protect against dementia?

Repeated heat exposure like sauna bathing is suggested to beneficially affect against dementia development. The epidemiological evidence is, however, scarce. Therefore, we studied the association between heat exposure during sauna bathing (i.e., the frequency of sauna bathing, frequency of heat sessions, length of stay in heat, sauna temperature) and the subsequent risk of dementia. A prospective cohort study was conducted based on 13,994 men and women aged 30-69 and free from dementia diagnosis from the Finnish Mobile Clinic Follow-up Survey. During a follow-up of 39 years, a total of 1805 dementia patients were diagnosed. The sauna bathing data was gathered from a questionnaire. Analyses based on the Cox model included the sauna bathing variables and the potential confounding factors. Sauna bathing frequency was related to a reduced risk of dementia after adjustment for the potential sociodemographic, lifestyle, and metabolic risk factors of dementia considered. The hazard ratio of dementia between individuals sauna bathing 9-12 times per month in comparison with those not sauna bathing or sauna bathing less than four times per month was 0.47 (95% CI = 0.25-0.88) during the first 20 years of follow-up and 0.81 (95% CI = 0.69-0.97) during the whole follow-up. The results are in line with the hypothesis that sauna bathing provides protection against dementia. Further studies are required to verify the suggested benefits of sauna bathing.