Sauna and Brain Health
Our daily lives are spent predominantly in climate-controlled environments, with furnaces and air-conditioning units regulating the temperatures of our living spaces within a relatively narrow range. The typical comfort zone for humans is within an air temperature of 64-74 degrees F, depending on humidity. Our ancestors, however, were most certainly exposed to extremes in environmental temperatures that we would now consider uncomfortable, prior to the availability of suitable clothing and shelter. A modern lifestyle lacking exposure to physiologic stresses such as variability in temperatures may be contributing to decreased resilience and fitness, particularly in regard to brain health.
Exposure to both extremes of temperature – hot and cold – appears to produce positive, invigorating effects among participants, including improvement in mood. Is there science to support the claims reported by advocates of sauna bathing and cold water immersion?
What is sauna bathing?
Sauna bathing is an activity characterized by passive exposure to high levels of heat. It has been a tradition in Finland for thousands of years, popular for being a pleasurable and relaxing activity that can be enjoyed by nearly everyone. The typical Finnish sauna provides a high-temperature environment with dry air, typically ranging from 80 – 100 degrees C. Sauna sessions typically involve brief stays in the sauna room followed by cooler periods (often swimming, showering, or resting at room temperature).
How does sauna differ from whole-body hyperthermia?
While sauna is thought of as a recreational activity, whole-body hyperthermia is a therapeutic strategy directed at achieving an increase in body temperature to drive a stress response.
Effects of sauna bathing on mental health
- Reduced anxiety and chronic fatigue syndrome
- Reduced depressive symptoms in a randomized controlled trial
- Individuals with depression who were exposed to a single session of whole-body hyperthermia raising their body temperatures to 38.5 deg C (101.3 deg F) experienced a substantial reduction in their depressive symptoms within the first week, and that beneficial effect lasted for 6 weeks.
- Decreased risk of psychotic disorders
Effects on neurologic health
Decreased risk of dementia
Sauna bathing is associated with a decreased risk of developing dementia, and the frequency of sauna bathing appears to be a significant factor. A 39-year prospective study on 13,994 adults in Finland demonstrated a 53% decreased risk of demen
tia in those who participated in sauna bathing 9-12 times per month compared to less than 4 times per month. However, exposure to levels of heat that are too high appear to negate some benefit. Bathing in sauna temperatures over 100 deg C was associated with double the risk of dementia compared to temperatures under 80 deg C in the first 20 years of follow-up.
In another prospective study, Finnish men aged 42 to 60 years at baseline who participated in 4-7 sauna sessions per week compared to those who did only 1 session per week had a 66% decreased risk of dementia and 65% decreased risk of Alzheimer’s Disease.
How does heat exposure affect brain function?
Several mechanisms are proposed to explain the hypothetical benefit of sauna bathing on the risk of developing dementia.
Sauna bathing produces a physiologic response that is similar to the body’s response to exercise, with increases in heart rate, blood pressure, norepinephrine, prolactin, and heat-shock protein. With repeated exposure, there is evidence of the body adapting to these changes – an example of hormesis. Exposure to an agent at low doses that is damaging at higher doses can induce favorable adaptive changes in an organism.
Heat shock proteins
Exposure to heat causes the activation of heat shock proteins, which regulate cell functions and play a role in controlling protein formation. Neurologic diseases are associated with impaired protein formation, and thus heat shock proteins may be relevant in this regard.
Adequate blood flow to the brain tissue is imperative for proper brain functioning and is an important factor in vascular dementia and Alzheimer’s Disease. Sauna bathing is also associated with decreased high blood pressure (hypertension), decreased arterial stiffness, and improved cardiovascular function.
Inflammation is known to be a significant factor in neurodegenerative diseases. Sauna bathing appears to decrease markers of inflammation in regular bathers, which may be another mechanism of benefit.
Sauna bathing is often described as a pleasurable experience, which might be at least partially explained by the observed increase in endorphin levels. Endorphins are part of the body’s natural painkilling system and appear to be responsible for the pleasurable feeling in response to exercise.
Are there risks to sauna bathing?
Sauna bathing appears to be a safe activity, even for those with cardiovascular disease. While there have been reports of sudden death during sauna bathing, these incidents are often associated with alcohol use, which can increase the risk of cardiovascular problems. Individuals with unstable heart disease should avoid sauna use. A common practice is to alternate periods of sauna bathing with periods of cold water immersion. There is increased risk from rapid cold water immersion, due to the constriction of blood vessels. Thus, individuals with unstable cardiovascular disease should exercise great caution at any extremes of temperature.