Japanese adults who took a hot bath almost daily had less heart disease and stroke
This 2020 study in Heart followed 30,076 Japanese adults from 1990 to 2009 and matched their tub bathing habits against heart attacks and strokes.
The paper
Habitual tub bathing and risks of incident coronary heart disease and stroke
Ukai T, Iso H, Yamagishi K, Saito I, et al.. Heart, 2020;106(10):732-737.
See the study at a glance
- Design
- Prospective cohort study
- People
- 30,076 men and women
- Who they were
- The participants were 40 to 59 in 1990 and came from three regions of Japan. None had cardiovascular disease or cancer at the start.
- What they did
- People answered one question on how often they bathed in a tub each week and rated their bath water on a scale from lukewarm to hot. Japanese baths typically run at 40–42°C.
- How long
- 1990 to 2009
These numbers came out of it
0.72
People who bathed almost daily had this hazard ratio for cardiovascular disease compared with people who bathed twice a week or less. That's a 28% lower risk.
0.65
Daily bathers had this hazard ratio for coronary heart disease.
0.57
The hazard ratio for sudden cardiac death in daily bathers came from 28 deaths, and its plausible range included no effect.
0.74
Daily bathers had this hazard ratio for stroke. It rose to 0.82 when events from the first ten years were left out.
Hazard ratio with 95% confidence interval, almost daily against twice a week or less
Almost daily tub bathing went with lower rates of most heart and stroke outcomes
The model adjusted for age, sex, body mass index, medical history, smoking, exercise, alcohol, job, education, sleep, stress, diet and area.
The researchers did this
The Japan Public Health Center-based Prospective Study asked 30,076 adults in 1990 how often they bathed in a tub each week. For 21,618 people (71.9%), a bath almost every day was normal. Only 1,911 bathed twice a week or less, and they became the comparison group.Source 1 · Cohort studyHabitual tub bathing and risks of incident coronary heart disease and strokeUkai T, Iso H, Yamagishi K, et al.. Heart, 2020.Read the paper ↗PubMed ↗
Added together, the participants' follow-up came to 538,373 person-years. Over that time there were 2,097 cardiovascular events, and 1,769 of them were strokes. Once a long list of health and lifestyle factors was taken into account, daily bathers had a 28% lower risk of cardiovascular disease. The hazard ratios were 0.65 for coronary heart disease and 0.74 for stroke.Source 1 · Cohort studyHabitual tub bathing and risks of incident coronary heart disease and strokeUkai T, Iso H, Yamagishi K, et al.. Heart, 2020.Read the paper ↗PubMed ↗
Results were similar whether people called their water lukewarm or hot, and the test for a difference wasn't significant. Sudden cardiac death was too rare to judge. Daily bathers had 28 of those deaths, and the plausible range ran from 0.24 to 1.37.Source 1 · Cohort studyHabitual tub bathing and risks of incident coronary heart disease and strokeUkai T, Iso H, Yamagishi K, et al.. Heart, 2020.Read the paper ↗PubMed ↗
When the researchers dropped events from the first ten years, the hazard ratio for cardiovascular disease still came out at 0.79. The trends across bathing groups were no longer significant, and the stroke estimate rose to 0.82. Over a five-year window, people who bathed three or more times a week had 20% lower odds of developing high blood pressure.Source 1 · Cohort studyHabitual tub bathing and risks of incident coronary heart disease and strokeUkai T, Iso H, Yamagishi K, et al.. Heart, 2020.Read the paper ↗PubMed ↗
The study can't tell you these things
- Japanese tub bathing means sitting in water at around 40°C, so the results say little directly about saunas.
- Daily bathers had more schooling, worked in manual jobs less often, played sport more and ate more vegetables than infrequent bathers, and statistical adjustment can't remove all of that.
- Only 1,911 people (6.4% of everyone in the study) formed the comparison group.
- People were asked about bathing once. The authors point out that some may have bathed less because they were already ill.
- The discussion describes the Finnish sauna study as a six-year study, although its median follow-up was 20.7 years.Source 2 · Cohort studyAssociation Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality EventsLaukkanen T, Khan H, Zaccardi F, et al.. JAMA Internal Medicine, 2015.Read the paper ↗PubMed ↗
People quote it like this
The paper's “Key questions” box says clinicians could recommend tub bathing to prevent cardiovascular disease without taking risks of sudden death. A study that records habits can't carry a claim that far. A 2024 review by the Kuopio group describes the result as a 23–46% reduction in risk.Source 3 · 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 ↗
We cited these sources
- 01Ukai T, Iso H, Yamagishi K, Saito I, Kokubo Y, Yatsuya H, et al.. Habitual tub bathing and risks of incident coronary heart disease and stroke. Heart. 2020;106(10):732-737. doi:10.1136/heartjnl-2019-315752 PMID 32209614
- 02Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. Association Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality Events. JAMA Internal Medicine. 2015;175(4):542-548. doi:10.1001/jamainternmed.2014.8187 PMID 25705824
- 03Laukkanen 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