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Sauna Hype

Frequent sauna bathers had fewer lung disease diagnoses until deaths were taken into account

This 2017 research letter in the European Journal of Epidemiology matched the sauna habits of 1,935 Kuopio men against hospital diagnoses of lung disease over 25 years.

The paper

Sauna bathing reduces the risk of respiratory diseases: a long-term prospective cohort study

Kunutsor SK, Laukkanen T, Laukkanen JA. European Journal of Epidemiology, 2017;32(12):1107-1111.

Read the paper ↗PubMed 28905164 ↗

See the study at a glance

Design
Prospective cohort study (research letter)
People
1,935 men
Who they were
The men were 42 to 61 and came from the Kuopio study. None had chronic lung disease or tuberculosis at the start.
What they did
A questionnaire at the start asked about weekly sauna sessions, and answers ranged from once or less up to four or more. The researchers counted hospital diagnoses of pneumonia and of chronic lung diseases such as COPD and asthma.
How long
Median 25.6 years

These numbers came out of it

0.59

Men who went four or more times a week had this hazard ratio for lung disease compared with men who went once or less. Below 1.00 means lower risk.

1.00

The same comparison came out even once the analysis allowed for men dying of other causes first.

0.63

For pneumonia alone, the top group had this hazard ratio, and its plausible range reached 1.00.

22

Of the 172 men in the top group, this many developed lung disease.

Hazard ratio with 95% confidence interval

The link faded once the analysis allowed for deaths from other causes

Once a week or less119 cases in 501 men
1.00 reference
Two or three a week238 cases in 1,262
0.73 (0.58–0.92)
Four or more a week22 cases in 172
0.59 (0.37–0.94)
Two or three a week with competing risk
0.87 (0.57–1.34)
Four or more a week with competing risk
1.00 (0.50–1.98)
Pneumonia alone at four or more a week
0.63 (0.39–1.00)
← lower risk than the reference grouphigher risk →

The main rows adjust for age, body mass index, smoking, diabetes, coronary heart disease, education, alcohol, energy intake, socioeconomic status, physical activity and C-reactive protein. The competing-risk rows come from the accepted manuscript, and the published abstract doesn't include them.

The researchers did this

The Kuopio team took 1,935 men without chronic lung disease at the start and followed them for hospital diagnoses of pneumonia and chronic lung disease through 2014.Source 1 · Cohort studySauna bathing reduces the risk of respiratory diseases: a long-term prospective cohort studyKunutsor SK, Laukkanen T, Laukkanen JA. European Journal of Epidemiology, 2017.Read the paper ↗PubMed ↗ Over a median of 25.6 years there were 379 cases, and 919 men died.

Once smoking, physical activity, socioeconomic status, inflammation and other factors were accounted for, men who went four or more times a week had a hazard ratio of 0.59 compared with men who went once a week or less. How long the sessions lasted made no difference. For pneumonia alone the figure was 0.63, and its plausible range ran from 0.39 to 1.00.Source 1 · Cohort studySauna bathing reduces the risk of respiratory diseases: a long-term prospective cohort studyKunutsor SK, Laukkanen T, Laukkanen JA. European Journal of Epidemiology, 2017.Read the paper ↗PubMed ↗

The accepted manuscript also reports a competing-risk analysis. It allows for men who died of something else before they could be diagnosed with lung disease. In that analysis the top group's hazard ratio was 1.00, and the authors put the change down to the high death rate among the men. The published abstract doesn't mention it, and we couldn't check whether the final version kept it.Source 1 · Cohort studySauna bathing reduces the risk of respiratory diseases: a long-term prospective cohort studyKunutsor SK, Laukkanen T, Laukkanen JA. European Journal of Epidemiology, 2017.Read the paper ↗PubMed ↗

A companion paper in Respiratory Medicine reported the same pneumonia hazard ratios (0.72 and 0.63) for 2,210 men.Source 2 · Cohort studyFrequent sauna bathing may reduce the risk of pneumonia in middle-aged Caucasian men: The KIHD prospective cohort studyKunutsor SK, Laukkanen T, Laukkanen JA. Respiratory Medicine, 2017.Read the paper ↗PubMed ↗ The match suggests the two papers analyzed the same events. Later analyses that lumped two to seven sessions a week together found pneumonia risk about 20% lower.Source 3 · Cohort studyHigh fitness levels, frequent sauna bathing and risk of pneumonia in a cohort study: Are there potential implications for COVID‐19?Kunutsor SK, Laukkanen JA. European Journal of Clinical Investigation, 2021.Read the paper ↗PubMed ↗Source 4 · Cohort studyAttenuated Risk of Pneumonia Due to Inflammation by Frequent Sauna BathsKunutsor SK, Jae SY, Laukkanen JA. Journal of Cardiopulmonary Rehabilitation and Prevention, 2022.Read the paper ↗PubMed ↗

The study can't tell you these things

  • The link disappeared once deaths from other causes were accounted for.
  • The top group had only 172 men and 22 cases.
  • It was published as a short letter, and the authors couldn't separate COPD from asthma.
  • Sauna habits were recorded once, and every participant was a man.
  • In this sample, frequent bathers were more physically active and better off than infrequent ones, and statistical adjustment may not catch all of that.

People quote it like this

Neither the title nor a later review by the same authors mentions the competing-risk result. The title says sauna bathing reduces the risk of respiratory diseases, and the review says frequent sauna bathing reduces the incidence of respiratory conditions.Source 5 · ReviewDoes the Combination of Finnish Sauna Bathing and Other Lifestyle Factors Confer Additional Health Benefits? A Review of the EvidenceKunutsor SK, Laukkanen JA. Mayo Clinic Proceedings, 2023.Read the paper ↗PubMed ↗

We cited these sources

  1. 01Kunutsor SK, Laukkanen T, Laukkanen JA. Sauna bathing reduces the risk of respiratory diseases: a long-term prospective cohort study. European Journal of Epidemiology. 2017;32(12):1107-1111. doi:10.1007/s10654-017-0311-6 PMID 28905164
  2. 02Kunutsor SK, Laukkanen T, Laukkanen JA. Frequent sauna bathing may reduce the risk of pneumonia in middle-aged Caucasian men: The KIHD prospective cohort study. Respiratory Medicine. 2017;132:161-163. doi:10.1016/j.rmed.2017.10.018 PMID 29229091
  3. 03Kunutsor SK, Laukkanen JA. High fitness levels, frequent sauna bathing and risk of pneumonia in a cohort study: Are there potential implications for COVID‐19?. European Journal of Clinical Investigation. 2021;51(3):e13490. doi:10.1111/eci.13490 PMID 33426640
  4. 04Kunutsor SK, Jae SY, Laukkanen JA. Attenuated Risk of Pneumonia Due to Inflammation by Frequent Sauna Baths. Journal of Cardiopulmonary Rehabilitation and Prevention. 2022;42(1):59-63. doi:10.1097/HCR.0000000000000598 PMID 33797457
  5. 05Kunutsor SK, Laukkanen JA. Does the Combination of Finnish Sauna Bathing and Other Lifestyle Factors Confer Additional Health Benefits? A Review of the Evidence. Mayo Clinic Proceedings. 2023;98(6):915-926. doi:10.1016/j.mayocp.2023.01.008 PMID 37270272