Hot baths in Japan: a second country, a similar link
A study of 30,000 Japanese adults found that people who took a hot bath almost every day had fewer strokes and heart attacks. It is a link, and it is hot baths, not sauna.
The short version
Researchers followed 30,076 Japanese adults for up to 19 years and compared how often they took a hot bath with who later had a heart attack or a stroke. People who bathed almost every day had fewer of both than people who bathed twice a week or less. It matters because it comes from a different country and a different group of people than the Finnish sauna studies. But it is observational, habits were asked once, and a Japanese hot bath is not a sauna.
Keep in mind
A link between habits and illness, not proof that bathing prevents it. Hot baths, not sauna, and bathing habits were asked about only once.
What they found
Over the follow-up, 2,097 people had heart disease or a stroke.
People who bathed almost every day had a lower rate of heart disease and stroke combined than people who bathed twice a week or less: a hazard ratio of 0.72 (95% confidence interval 0.62 to 0.84).
For stroke alone the ratio was 0.74 (0.62 to 0.87), and for coronary heart disease 0.65 (0.45 to 0.94). The link was clearest for bleeding in the brain: 0.54 (0.40 to 0.73).
There was no link with sudden cardiac death, although with only 53 such deaths the study could not say much either way.
What this means for your practice
A second population pointing the same way makes the link between regular heat and heart health harder to dismiss. It does not show that bathing or sauna prevents a stroke.
This does not establish a bathing or sauna routine to follow.
Methods and limitations
What the researchers did
The Japan Public Health Center-based study enrolled 30,076 adults aged 40 to 59 who had no heart disease or cancer at the start, and followed them from 1990 to 2009.
At the start, people said how often they took a tub bath: zero to two times a week, three or four times, or almost every day. The researchers then recorded heart attacks, sudden cardiac deaths and strokes.
They took age, blood pressure, smoking, diabetes, diet and other known risk factors into account. Nobody was asked to change their bathing.
How much can this tell us?
This matters for the rest of the library. Most long-term sauna findings come from one Finnish study. Here is a separate group of people, in another country, where regular heat went with fewer strokes and heart attacks.
It is still observational. People who bathe every day may differ in ways the statistics cannot capture: more time, better housing, healthier routines. Habits were asked once, in 1990.
A Japanese tub bath is hot water up to the shoulders, usually at home. It is heat, but it is not a sauna. The water temperature and the length of the bath were not reported in the abstract.
What makes it useful
- A large group, 30,076 adults, followed for up to 19 years
- A different country and population from the Finnish studies
- Adjusted for many known heart risk factors
What limits it
- Observational: a link, not proof of cause
- Hot baths, not sauna
- Bathing habits asked about once, at the start
- Few sudden cardiac deaths to study
Where this study fits
Where this study fits
We score claims, not single studies. This one is part of the evidence for:
Regular sauna means fewer deaths from heart disease. Some support
Low certaintyLarge effectIllness and death
Regular sauna means fewer strokes. Some support
Low certaintyLarge effectIllness and death
Stroke, Japan (hot baths) 26% fewer
Likely 13% to 38%
Fewer cases than the comparison group. The bar is the best estimate, the band behind it the likely range.
Read the original
Ukai T, Iso H, Yamagishi K, Saito I, Kokubo Y, Yatsuya H, Muraki I, Eshak ES, Sawada N, Tsugane S. Habitual tub bathing and risks of incident coronary heart disease and stroke. Heart. 2020;106(10):732-737.
DOI 10.1136/heartjnl-2019-315752 · PubMed 32209614