Frequent Saunas Linked to Reduced Stroke Risk

May 07, 2018

Taking a sauna may have greater health benefits than just relaxation and pleasure, with a new study linking frequent use of saunas to a substantial reduced risk for future stroke.

"The present study adds to emerging evidence that passive heat therapy such as sauna bathing could improve cardiovascular health and decrease the risk of vascular events," the authors conclude.

The study, published online May 2 in Neurology, was conducted by an international group of researchers led by Setor K. Kunutsor, PhD, University Hospitals Bristol NHS Foundation Trust, United Kingdom.

They note that sauna bathing has been shown to be associated with positive effects on blood pressure, lipid profiles, arterial stiffness, carotid intima-media thickness, and peripheral vascular resistance. Emerging evidence also suggests that it is linked to a reduced risk for hypertension, dementia, and cardiovascular and all-cause mortality.

Noting that an association between sauna bathing and risk for stroke has not yet been investigated, they conducted the current study in a cohort of middle-aged to elderly men and women from Eastern Finland.

For the study, the baseline habits of sauna bathing were assessed in 1628 men and women aged 53 to 74 years without a known history of stroke in the Finnish Kuopio Ischemic Heart Disease prospective cohort study.

Habits of sauna bathing were assessed by questionnaires that asked about frequency and duration of sauna sessions and temperature in the sauna room. Three groups were defined: one session per week, two to three sessions per week, or four to seven sessions per week.

All baseline characteristics, including cardiovascular risk markers, were evaluated on the same day at study entry.

Information on stroke outcomes was ascertained by computerized data linkage to the Finnish national hospital discharge registry and death certificate registers.

Results showed that the median frequency of sauna bathing was twice a week and the mean temperature of the sauna was 75.8°C.

Participants with the highest frequency of sauna bathing (four to seven times per week) were younger, were more likely to be male, had higher body mass index, and consumed more alcohol compared with the participants in the other groups.

During a median follow-up of 14.9 years, a total of 155 stroke events occurred. Stroke rates per 1000 person-years of follow-up were 8.1 in the individuals taking one sauna per week, 7.4 in those taking  two to three saunas per week ,and 2.8 in those taking four to seven saunas per week.

In analyses adjusted for age and sex, when compared to participants who had one sauna session per week, individuals who took four to seven saunas per week had a 61% reduced risk for stroke, with a hazard ratio of 0.39 (95% confidence interval, 0.18 - 0.83).

After further adjustment for several established risk factors and other potential confounders (body mass index; smoking; systolic blood pressure; low-density lipoprotein cholesterol; alcohol consumption; type 2 diabetes; use of hypertensive medication, aspirin, and lipid-lowering therapy; physical activity levels; and socioeconomic status), the hazard ratio remained the same.

The association was similar for ischemic stroke but modest for hemorrhagic stroke, which could be attributed to the low event rate (n = 34).

The researchers speculate that mechanistic pathways behind these observations — and the previous findings of a reduction in cardiovascular outcomes — may include reduction in systemic blood pressure; stimulation of the immune system; positive alteration of the autonomic nervous system; positive effects on circulating lipid profiles; and reduction in oxidative stress, arterial stiffness, carotid intima-media thickness, and peripheral vascular resistance.

"There is an established body of evidence that shows that the majority of the stroke burden can be attributable to suboptimal blood pressure and that the risk of stroke is considerably lowered with blood pressure lowering," the authors write. "With the accumulating evidence of a blood pressure lowering effect of passive heat therapy or sauna bathing, this pathway may potentially underlie the beneficial effect of sauna bathing on stroke risk."

They also suggest that the protective effect of sauna bathing on stroke risk may underpin previous observations that it is associated with lowered risks for dementia and Alzheimer's disease.

They say these results suggest a causal relationship, but this cannot be confirmed without randomized controlled trials.

"In the absence of such trials, regular sauna bathing is a recommendable habit as it is a well-tolerated and safe activity for most healthy people, as well as patients with stable cardiac disease."

But they warn that sauna bathing is contraindicated in patients with recent myocardial infarction, unstable angina pectoris, or severe aortic stenosis; elderly people prone to low blood pressure are also advised to exercise caution.

The authors add that sauna bathing also improves the pain and symptoms associated with rheumatic diseases; ameliorates skin diseases, such as psoriasis and urticaria; and reduces the risk for lung disease.

However, the current findings should not be extrapolated to other forms of passive heat therapy, such as infrared heat exposure, steam rooms, Waon therapy, and hot tubs that are used in other settings, they add, because these may operate at lower temperatures and do not mimic the traditional Finnish sauna conditions

Begin With Caution

In an accompanying editorial, Josef G. Heckmann, MD, Municipal Hospital Landshut, Germany, and Katriina Kukkonen-Harjula, MD, South Karelia Social and Health Care District, Lappeenranta, Finland, warn that during sauna bathing, hypotension, dehydration, arrhythmia, and hemoconcentration can occur, especially after the intake of alcohol, but that the purported benefits appear to far outweigh the risks.

"It is advised to begin with caution, test individual heat tolerance, slowly increase the frequency and intensity of bathing, and ideally combine sauna bathing with leisure physical activity," they write.

They conclude that further studies in other populations are needed to investigate a potential protective role of sauna bathing in the prevention of cerebrovascular events and to evaluate the mechanistic pathways underlying the relationship between sauna exposure and stroke risk.

Neurology. Published online May 2, 2018. Abstract, Editorial 

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