An Instagram video with over 92,000 likes includes claims about the health benefits of saunas, that overstate the evidence and are based on poor understanding of the science.
The person in the video says: “If you use sauna one day a week, your risk of dying of all things goes down like 30 to 40%, maybe even more. But interestingly, if you use sauna three times a week, your risk goes down another 30 or 40%.”
There is no good evidence to support these claims.
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What does the evidence say?
A systematic review (wherein researchers try to find and bring together all the evidence on a topic) from 2018 found that while studies on saunas and health have generally shown positive results, most of those conducted have been on very small groups of people, and “there is insufficient evidence to recommend specific types of sauna bathing for specific clinical conditions”.
The post doesn’t provide any sources. The figures may originate from a Finnish study that was widely reported in 2015.
This study did indeed find an association between time spent in a sauna and lower all cause mortality (death from any cause). The study compared men who went to saunas once a week, two to three times a week, and four to seven times a week, and followed them up for around 20 years.
The second group had a 31% reduction in risk compared to the group who had only one sauna session per week. It's unclear what total effect the video is claiming, but it seems to be claiming a reduction in risk of death by using a sauna three times a week somewhere between 50 and 80%—clearly an inaccurate portrayal of this finding.
The final group that went most frequently had a 39% reduction. This may be where the 40% figure originally comes from. The video makes no mention of this high use group.
The study had no comparison group who did not use saunas. So it provides no data to suggest that using a sauna once a week reduces all cause mortality by 30 to 40% compared to never using them at all. Full Fact was unable to find any other source for this figure.
Correlation doesn’t mean causation
Furthermore, there are a number of issues with making the claims in the video based on this study, even if the numbers were more accurate.
Most importantly, to take this study which shows an association with lower risk and state that using saunas reduces your risk is confusing correlation with causation, something we have covered many times before. From this study alone, we can’t say that the saunas were what caused these lower death risks.
There may have been other factors affecting this. For example, there may be other lifestyle factors involved, such as people who go to saunas very regularly may also do things like eat healthier diets. We also don’t know if people who are sicker or have heart problems already are less likely to use saunas—for example if they find them uncomfortable due to their illness.
The study tried to account for some of these issues, like obesity and smoking, but it is hard if not impossible to account for all possible other factors in these kinds of studies. The study also only looked at quite a specific group of people—Finnish men. This means we have to exercise caution in applying the findings to the global population at large. The study authors also say further studies would be needed to look at other groups.
Other similar studies by some of the same research team, one of which did include female participants, found similar results, with one showing even larger decreases seen in the most frequent users. But they both had the same limiting issues as the earlier research.
More research would be needed to make any definitive conclusions about the health effects of saunas. Saunas can be dangerous for certain groups—the NHS is cautious about use during pregnancy.
Featured image courtesy of Estoniansaunas
