A second Finnish study found no dementia benefit in its most frequent sauna users
Published in Preventive Medicine Reports in 2020, this study followed 13,994 Finnish men and women for up to 39 years. It's independent of the Kuopio study that produced the 66% figure.
The paper
Does sauna bathing protect against dementia?
Knekt P, Järvinen R, Rissanen H, Heliövaara M, et al.. Preventive Medicine Reports, 2020;20:101221.
See the study at a glance
- Design
- Prospective cohort study
- People
- 13,994 men and women
- Who they were
- Adults aged 30 to 69 without a dementia diagnosis were examined in 12 Finnish municipalities between 1973 and 1976. Men made up 51.2%, and the average age was 47.9.
- What they did
- People filled in a questionnaire that a nurse then checked. It asked about sauna baths per month, heat sessions per bath, session length and sauna temperature. Frequency groups ran from 0–4 to 13–30 baths a month, and 99.0% of participants used a sauna.
- How long
- Up to 39 years (1973–2011)
These numbers came out of it
0.81
People who bathed 9 to 12 times a month had this hazard ratio for dementia compared with people who bathed four times or fewer. That's a 19% lower risk.
0.91
People who bathed 13 to 30 times a month had this hazard ratio, and its plausible range included no effect.
2.04
In the first 20 years, people whose saunas ran hotter than 100°C had about double the dementia risk of people whose saunas stayed under 80°C.
1,805
National registers recorded this many dementia cases over the follow-up.
Hazard ratio with 95% confidence interval
Only one frequency group had a clearly lower dementia risk over the full follow-up
The full model adjusted for sex, age, education, marital status, region, leisure-time physical activity, smoking, alcohol, body mass index, blood pressure, glucose, triglycerides and cholesterol.
The researchers did this
The Finnish Mobile Clinic survey examined 19,518 people in 12 municipalities between 1973 and 1976. This analysis used the 13,994 adults aged 30 to 69 who had no dementia diagnosis and followed them through national registers until 2011.Source 1 · Cohort studyDoes sauna bathing protect against dementia?Knekt P, Järvinen R, Rissanen H, et al.. Preventive Medicine Reports, 2020.Read the paper ↗PubMed ↗
Nearly everyone bathed (99.0%), and the average was about six times a month. Over the follow-up, 1,805 people developed dementia. Compared with people who bathed four times a month or less, those who bathed 9 to 12 times had a hazard ratio of 0.81. At 13 to 30 baths a month it was 0.91, and the plausible range included no effect.Source 1 · Cohort studyDoes sauna bathing protect against dementia?Knekt P, Järvinen R, Rissanen H, et al.. Preventive Medicine Reports, 2020.Read the paper ↗PubMed ↗
In the first 20 years the link was stronger, and 9 to 12 baths a month went with a hazard ratio of 0.47. Neither session length nor temperature showed a significant link over the whole follow-up, although saunas above 100°C carried a hazard ratio of 2.04 in the first 20 years.Source 1 · Cohort studyDoes sauna bathing protect against dementia?Knekt P, Järvinen R, Rissanen H, et al.. Preventive Medicine Reports, 2020.Read the paper ↗PubMed ↗
The authors wrote that the data allow no firm conclusions. Their tables show sauna habits traveling with other habits. Regular exercisers bathed 6.59 times a month and inactive people 5.80 times, and heavy drinkers bathed more often than non-drinkers.Source 1 · Cohort studyDoes sauna bathing protect against dementia?Knekt P, Järvinen R, Rissanen H, et al.. Preventive Medicine Reports, 2020.Read the paper ↗PubMed ↗
The study can't tell you these things
- Sauna habits were recorded once in the 1970s, and a lot can change in 39 years.
- Dementia diagnoses came from registers, and 784 of the 1,805 cases appeared in only one of them.
- The paper doesn't report case counts for the first 20 years, so there's no telling how big the early groups were.
- With 271 people and 29 cases, the most frequent group gives a wide plausible range.
- People chose their own sauna habits, and frequent bathers exercised and drank differently from everyone else.
People quote it like this
The Kuopio group's 2024 review cites this paper for a 53% lower dementia risk in the first 20 years and a 19% lower risk over the whole follow-up. It doesn't mention that the most frequent bathers showed no benefit or that saunas above 100°C went with higher risk.Source 2 · ReviewThe multifaceted benefits of passive heat therapies for extending the healthspan: A comprehensive review with a focus on Finnish saunaLaukkanen JA, Kunutsor SK. Temperature, 2024.Read the paper ↗PubMed ↗
From our sister magazine
Sauna Monthly picks thermometers that show whether a sauna runs past 100°C
We cited these sources
- 01Knekt P, Järvinen R, Rissanen H, Heliövaara M, Aromaa A. Does sauna bathing protect against dementia?. Preventive Medicine Reports. 2020;20:101221. doi:10.1016/j.pmedr.2020.101221 PMID 33088678
- 02Laukkanen JA, Kunutsor SK. The multifaceted benefits of passive heat therapies for extending the healthspan: A comprehensive review with a focus on Finnish sauna. Temperature. 2024;11(1):27-51. doi:10.1080/23328940.2023.2300623 PMID 38577299