Daily saunas may reduce stroke risk

"A daily sauna could cut your risk of stroke by as much as 61%," the Mail Online reports. However, this headline is based on findings from a small subgroup of 197 people who were taking saunas 4 to 7 times a week amongst a study population of 1,628 Finnish people. Few people in the study had less than one Finnish-style sauna a week. This frequency and type of sauna bathing would be unusual in the UK.

Only 155 (6%) of the total sample had a stroke within 14 years of follow up and this small number of events makes the results less reliable. The media failed to report there were insufficient people in the study who did not have saunas at all to make a valid comparison with the UK population.

Saunas are an inherent part of Finnish culture, in the same way that pubs or fish and chips tap into the heart of UK culture. And obviously, most people in the UK won't have daily access to sauna facilities.

The researchers did speculate that saunas may be of benefit as they help lower blood pressure, reduce stress and boost the immune system. In the UK, it may be easier for you to take up regular exercise, which has similar benefits, than to add a sauna to your house.

Read more about the benefits of exercise and how to reduce your risk of stroke.

Where did the story come from?

The study was carried out by researchers from various international institutions including from the UK, the US, Finland and Austria. It was published in the peer-reviewed journal the American Academy of Neurology. The study was funded by the Finnish Foundation for Cardiovascular Research.

Both the UK and international media arguably overstated the significance of the study's results seeing that it involved a relatively small group of participants.

What kind of research was this?

This research took a sample of people from the Finnish Kuopio Ischemic Heart Disease risk factor study, which is a prospective cohort study of men and women living in rural communities in the east of Finland.

Prospective cohort studies are the best type of cohort, as they set out to examine the influence of a specific exposure or risk factor. This means they are more likely to have gathered the right information and assessed possible confounders.

Cohorts are good for suggesting associations, but have the downside of not being able to prove cause and effect or rule out confounding from other factors.

What did the research involve?

This cohort was initially based on men aged 42-61 living in rural east Finland recruited between March 1998 and December 2001. These men were followed up after 4, 11 and 20 years. At the 11 year follow up, women were added to the study. In total, the cohort consisted of 2,358 people – 1,007 men and 1,351 women from 53 to 74 years old.

Participants with a history of stroke, or missing information on their sauna activity were excluded from the analysis, which left 1,628 participants (840 women and 788 men) who had complete information on sauna bathing habits. Participants were followed up for an average of 14.9 years.

The primary outcome was a first-time stroke, which the researchers measured by linking the information of participants to hospital data and death certificates. The researchers wanted to investigate whether the frequency of bathing in saunas, adjusted for health and lifestyle factors, influenced the likelihood of stroke.

To do this, sauna bathing habits were assessed using self-administered questionnaires and included an assessment of:

frequency of sauna sessions (1, 2 to 3, or 4 to 7 times a week)
duration of sauna sessions
temperature in the sauna room measured by a thermometer

The questionnaire assessment represented average sauna bathing habits during one week and an experienced nurse cross-checked the questionnaires during initial examinations. The following known risk factors for stroke were measured using physical tests:

cardiovascular risk factors, such as levels of atherosclerosis (hardening of the arteries)
total cholesterol
the level of fat in the blood
the level of glucose in the blood following fasting
resting blood pressure

The following health and lifestyle factors were assessed using self-administered questionnaires:

medical conditions (cross-checked by a doctor)
medication use (cross-checked by a doctor)
physical activity levels
alcohol consumption
body mass index

What were the basic results?

155 strokes were recorded, 60 in women and 95 in men, which is equivalent to 6% of the total participants included in this study.
Compared to people having 1 sauna bathing session per week, the risk of stroke was reduced by 61% (hazard ratio (HR) 0.39, 95% confidence interval (CI) 0.18 to 0.83) for participants who had 4 to 7 sauna sessions per week.
This reduction in risk for stroke stayed at 61% following adjustment for heart conditions and other risk factors the researchers thought might make people more at risk of having a stroke (HR 0.39, 95% CI 0.18 to 0.84).
The reduction in risk for stroke increased to 62% when the amount of physical activity and the socioeconomic status of the participants were taken into consideration (0.38 95%, CI 0.18 to 0.81).
The researchers found that the participants' age or gender did not affect their risk of stroke when sauna bathing.
The risk of stroke was not affected for people who were having 2 to 3 saunas per week.

How did the researchers interpret the results?

The researchers conclude that this study shows middle-aged to elderly men and women who take frequent sauna baths have a substantially reduced risk of having a first stroke compared to those taking fewer saunas. They go on to state that this study adds to emerging evidence that passive heat therapy such as sauna bathing could improve cardiovascular health and reduce the risk of vascular events.

Conclusion

The results of this study look appealing, presenting evidence that a relaxing recreational activity involving very little effort could reduce the risk of stroke. But while it does show a link between taking regular saunas and a reduction in stroke, it is not possible to tell from this study whether the reduction in the risk of stroke is purely due to taking saunas, or other factors. There are also other limitations to consider.

Sauna activity was based on a one off, self-administered questionnaire. This may not be representative of life time sauna habits.

The sample size of people who were having Finnish-style saunas 4 to 7 times per week thus reducing their risk of stroke by 61% was small (12% of participants in the study). It is unlikely that this high-temperature sauna is as commonly used in other parts of the world. Most of the lifestyle characteristics were self-reported, which are likely to be biased as people are not often honest, or do not remember exactly what they do or have done in the past in relation to health behaviours.

The risk of stroke for people who were having one less sauna a week was not affected, which suggests there might be other factors positively influencing the health of people in the 4 to 7 saunas a week group other than saunas.

And finally, the results are not applicable to all age groups. The average age of people in this study was 63, therefore they are likely to be approaching (or in) retirement, with more time to take saunas and a less stressful lifestyle.

You don't need to build yourself a sauna to reduce your stoke risk. Regular exercise, a healthy diet and achieving or maintaining a healthy weight can all help.

Read more about reducing your stroke risk