Infrared Sauna
Infrared Sauna use can have extensive health benefits
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Infrared Sauna use, which sometimes referred to as “sauna bathing,” has been
popular in a range of cultures for hundreds of years and is characterised
by short-term exposure to high temperatures, typically ranging from
45 0C to 100 0C (113 0F to 212 0F), depending on the modality chosen. This
heat exposure elicits mild hyperthermia and stimulates a wide range of
co-ordinated bodily responses including cardiovascular, neuroendocrine,
and cytoprotective mechanisms that position sauna bathing as a viable
means to extend both lifespan and healthspan.
Sauna Basics
Heat and sauna therapy for the purposes of healing, cleansing and
purification is an ancient practice that can be found across cultures
throughout hundreds, if not thousands, of years. Variations of heat
therapy include ancient Romans baths, Native American sweat lodges,
Japanese hot soaking tubs, Russian banyas and Finnish saunas. Modern
saunas come in 3 main varieties: dry, steam and infrared, and all utilise
short-term exposure to high temperatures, typically ranging from 45 0C
to 100 0C (113 0F to 212 0F), depending on the modality chosen (1).
A dry sauna is based on the traditional Finnish sauna, with low humidity
and a high temperature, typically from 80 to 100° C (176 to 212° F) (2). A
steam sauna has higher humidity, which makes sweating and cooling
the body more challenging and therefore cannot be as hot as a dry
sauna and are reported to be more uncomfortable and stressful than dry
sauna (3). Infrared saunas use infrared radiation lamps that emit both
visible and infrared light, with the infrared light being either near- or
far-infrared spectrums. Far-infrared saunas emit longer wavelengths of
infrared light that penetrate tissue to 0.1 mm deep, whilst near-infrared
saunas emit shorter wavelengths that can penetrate the body up to 5
mm (4). Some modern saunas capable of emitting both wavelengths
and these are known as full-spectrum infrared saunas. Because of the
deep tissue penetration, infrared saunas operate at cooler temperatures
than dry saunas while still heating up the body, typically 45 0C to 60 0C
(113 0F to 140 0F) (1, 4).
The Health Benefits of Saunas
By Paul Taylor, BSc, MSc, MSc (Med Sci)
Physiological & endocrine response to heat stress
All varieties heat the body to the point where the usual means of cooling
through sweating is not enough to compensate for the extreme heat, so
the body elicits a rapid, robust response that affects primarily the skin
and cardiovascular systems. The skin heats first, rising to approximately
40 0C (104 0F), followed by changes in core body temperature, rising
slowly from 37 0C to approximately 38 0C (98.6 0F to 100.4 0F) and then
increasing rapidly to approximately 39 0C (102.2 0F) if exposure lasts long
enough (5, 6, 7). Cardiac output may increase by as much as 60–70%,
while the heart rate increases and the stroke volume remains stable (8).
Additionally, approximately 50–70% of the body’s circulation redistributes
from the core to the skin to facilitate sweating, driving fluid losses at a
rate of approximately 0.6 to 1.0 kg per hour (9).
The endocrine system responds to the heat by increasing the production
of several important hormones (2). There are increases in Betaendorphins, which are responsible for the “pleasure” and “analgesic”
effects of a sauna. Norepinephrine (sometimes called Noradrenaline),
which is associated with improved mood, focused attention and
raised heart-rate, also increases (5). Growth hormone, whose secretion
progressively declines with age and may contribute to sarcopenic
obesity and frailty, increases in a manner that is dependent on time,
temperature and frequency of exposure. For example, two 20-minute
sauna sessions separated by a 30-minute cooling period has been
shown to result in a 2 to 5-fold elevation in Growth Hormone secretion
and sauna use and exercise work synergistically to significantly elevate
growth hormone when used together (10, 11).
Immune Effects
Sauna bathing stimulates the immune system by increasing white
blood cell, lymphocyte, neutrophil, and basophil counts, which may
translate to fewer illnesses (12). For example, a six-month study reported
that participants who engaged in regular sauna baths had significantly
fewer colds than the control group over the same time period (13). The
positive impacts on the immune system are at least partly derived by the
increases in molecular proteins known as Heat Shock Proteins (HSPs),
which are activated when the body is exposed to stressors like exercise,
heat and cold. Evidence suggests that certain HSPs play roles in both
innate and adaptive immunity (14) and it has also been suggested that
HSPs may offer protection against neurodegenerative diseases (15).
In one study, healthy men and women who were exposed to heat for
30 min at 73 0C (163.4 0F) increased HSP72 levels by 49% (16). In another
study, healthy men and women had their HSP70 and HSP90 levels
increased by 45% and 38%, after undergoing deep tissue heat therapy for
six days (17)
Cardiovascular Effects
Heat exposure from sauna bathing induces protective mechanisms that
promote cardiovascular health, some of which are the same as those
experienced during exercise. For example, heart rate has been shown
to increase up to 100 beats per minute during moderate-temperature
sauna bathing sessions and up to 150 beats per minute during hotter
sessions, similar to the increases observed during moderate- to vigorousintensity physical exercise (18).
Heart disease was once contraindicated for saunas, but recent research
is proving that saunas can be not only safe, but beneficial for people
with cardiovascular disease. A range of findings on cardiovascular health
have been reported from the ongoing landmark Kuopio Ischemic
Heart Disease (KIHD) Risk Factor Study, which has been following 2,315
middle-aged Finnish men for more than 20 years. The study has found
that those men who frequented saunas the most (four to seven times
per week) had a significantly lower risk of sudden cardiac death, fatal
coronary heart disease, and fatal cardiovascular disease compared to
those who visited saunas two to three times per week or one time per
week (3). In addition to these findings, the study found that increased
sauna use was also associated with a 40% reduction in all-cause
mortality (19).
Brain & Mental Health
Sauna bathing is associated with reduced risk of developing agerelated neurodegenerative diseases such as dementia and Alzheimer’s
disease, in a dose-dependent manner (more frequent bathing has a
bigger effect). In the KIHD study mentioned earlier, men who reported
using the sauna 4–7 times per week had a 66% lower risk of developing
dementia and a 65% lower risk of developing Alzheimer’s disease,
compared to men who reported using the sauna only once weekly (20).
There may be multiple mechanisms by which frequent sauna use may
protect against neurodegenerative diseases, such as improved blood
flow to the brain, improved cardiovascular health and the positive health
effects of Heat Shock Proteins (1). The health benefits of sauna use also
extended to other aspects of mental health as well. Men participating in
the KIHD study who reported using the sauna 4–7 times per week had a
77% reduced risk of developing psychotic disorders (21). In a randomised
controlled trial of depressed individuals, those who received 4 weeks
of sauna sessions experienced reduced symptoms of depression and
participants in another randomised controlled trial who received a single
session of heat therapy experienced an acute antidepressant effect that
was apparent within 1 week of treatment and persisted for 6 weeks after
treatment (22).
Detoxification
Many websites promote sauna bathing as a way of increasing
detoxification, but the evidence for this is not yet as robust as the
evidence for other health impacts, such as cardiovascular benefits
mentioned above. However, several small studies have demonstrated
a benefit. In one study, Police officers were treated successfully
for methamphetamine exposure using a combination of exercise,
nutritional support, and sauna therapy (23) and women with
occupational exposure to solvents improved after therapy that included
sauna use (24). Interestingly, the high rate of sweating to assist with
cooling the body during sauna bathing has been reported to facilitate
higher excretion of some heavy metals including aluminum (3.75-
fold), cadmium (25-fold), cobalt (7-fold), and lead (17-fold), compared to
elimination via urine (10). Sauna use to aid in detoxification is a promising
additional health benefit, but further research is required to understand
the mechanisms.
Other benefits
A number of studies highlight many other benefits of regular sauna use,
including increased left ventricular ejection fraction, cardiac output,
endothelial function, lower oxidative stress markers and improved
exercise tolerance with infrared sauna use (25, 26, 27, 28, 29). Sauna use
has also been reported to reduce pain in Fibromyalgia patients (30) and
to reduced fatigue, anxiety, and depression in individuals with chronic
fatigue syndrome (31). Sauna use may also help prevent or treat diabetes
Sauna use may also help prevent or treat diabetes by improving insulin
sensitivity (32) and improvements in respiratory symptoms, including
vital capacity, minute ventilation, and forced expiratory volume of lungs
have also been reported (33,34).
Contraindications
People with hypotension (low blood pressure) should obtain medical
advice before using the sauna and those with heat sensitivities (such as
those with multiple sclerosis), a recent myocardial infarction, unstable
angina and people who are experiencing an illness accompanied by a
fever should avoid the sauna (38). A sauna should also be avoided if you
are drinking alcohol, as most sauna accidents and death involve alcohol
consumption (39).
Conclusion
Sauna bathing is clearly associated with many health benefits, from
cardiovascular and cognitive health to physical fitness and immune
system support. It is generally considered safe for healthy adults
and may be safe for special populations with appropriate medical
supervision. Heat stress via sauna use upregulates positive molecular
mechanisms that protect the body and brain from damage, similar to
the responses elicited by moderate- to vigorous-intensity exercise, and
may offer a means to slow aging and extend healthspan.