Cardiovascular disease (CVD) includes all diseases of the heart and circulatory system, and is the leading cause of death in all countries with a moderate to high standard of living. Accordingly, CVD researchers and other health care professionals are continuously seeking lifestyle strategies by which CVD risk can be decreased in the population. In recent years, passive heat therapy has emerged as one such strategy. Passive heat therapy simply means elevating core body temperature by use of sauna, hot whirlpool, and other modalities that do not include physical activity.
Sauna use has been extremely popular in Finland for generations. A traditional Finnish sauna has dry air (10-20% humidity), with a temperature of approximately 180 degrees F. A 2015 study published in JAMA Internal Medicine examined the relationship of frequency (how often) and duration (how long) of sauna use on the risk of sudden cardiac death, fatal coronary heart disease, and fatal cardiovascular disease (CVD). At baseline, a total of 2315 middle-aged Finnish men underwent a comprehensive examination which included questions regarding the frequency and duration of sauna use. Participants were then placed into three frequency groups (1 time per week, 2-3 times per week, or 4-7 times per week), and three duration groups (less than 11 minutes per session, 11-19 minutes per session, or greater than 11 minutes per session). The group was carefully followed for an average of 19 years. After taking known CVD risk factors such as age, resting blood pressure, smoking, blood cholesterol and glucose levels, body mass index, physical activity level, and cardiorespiratory fitness into account, Figure 1 below shows the risk of fatal CVD based on frequency of sauna use.
Figure 1 shows that men who used the sauna more frequently were significantly less likely to experience fatal cardiovascular disease than the men who used the sauna less frequently. Similar results were found for sudden cardiac death and fatal coronary heart disease.
After taking known CVD risk factors into account, Figure 2 below shows the risk of fatal CVD based on duration of sauna use.
Figure 2 shows that men who used the sauna for a longer duration were significantly less likely to experience fatal cardiovascular disease than the men who used the sauna for a shorter duration. Similar results were found for sudden cardiac death and fatal coronary heart disease.
Remember, all of these results occurred after taking known CVD risk factors into account. Many similar studies using both men and women and other modalities such as hot whirlpool (approximately 104 degrees F) have been performed since that time and have also shown beneficial changes in the cardiovascular system. Therefore, you may be wondering exactly how passive heat therapy can decrease cardiovascular disease risk. In recent years, scientists have discovered substances called heat shock proteins (HSPs) which are released by several tissues when physical activity is performed or when core body temperature rises. HSPs cause the inside lining of our arteries to produce nitric oxide, which causes the arteries to become less stiff and relax. When that happens in an individual with hypertension, their resting blood pressure decreases. HSPs have been shown to improve insulin sensitivity, which in turn decreases the risk of developing Type 2 diabetes. As a bonus, HSPs decrease levels of inflammation, which is a known cause of many types of cardiovascular disease.
Does this mean that passive heat therapy can take the place of physical activity?
For individuals who are capable of performing physical activity, the answer is a resounding NO! Regular physical activity results in beneficial changes over and above what can be provided by passive heat therapy. However, for those who are unable to perform physical activity due to disability, injury, or illness, regular sessions of passive heat therapy will definitely provide some cardiovascular health benefits.
Here are a couple of safety reminders. It takes time for your body to acclimate to passive heat therapy. Start with a short duration, and gradually increase the number of minutes for each session. Use common sense and do not stay in the sauna or whirlpool for too long. Also, since heavy sweating takes place during passive heat therapy, be sure to stay hydrated by drinking plenty of cool water during and after your sessions.
Laukkanen, T., et al. (2015). Association between sauna bathing and fatal cardiovascular and all-cause mortality events. JAMA Internal Medicine. 175(4):542-548.