Similarly to ice baths, sauna’s have proven to be a hot topic (pardon the pun) in improving health outcomes. But how much of this is evidence based and how much is supported based on instagram-merit? This blog will unpack the findings of the 2018 study “Clinical Effects of Regular Dry Sauna Bathing: A Systematic Review”  to see if sauna’s are worth your time!

Sauna bathing has been used in varying methods (heating, humidity and structural variations) for various reasons (spiritual, social, health) for centuries. The most investigated form of sauna’s are Finnish saunas which involve 5-20 minute exposure periods at 80-100°C at low humidity (10-20%). A large body of research proposes that the increased skin and core body temperature initiates thermoregulatory processes which can provide positive physiological effects. This includes metabolic, cardiovascular and cellular changes. 

The review analysed health effects of regular dry sauna exposure from 2000 onwards in 40 studies. To differentiate from other papers, this systematic review analysed the impact of regular sauna exposure in order to simulate repeated sauna use as part of a lifestyle. 13 of these studies were randomised control trials with small sample sizes (<40 participants) and 1 study demonstrated negative health impact which was reversible once sauna exposure was ceased. Of the 40 studies, 8 reported some adverse effects from regular sauna exposure- the majority of these being mild discomfort from the high temperatures which did not impact participation.

The review analysed the impact of regular dry-sauna exposure on the following areas: 

• Cardiovascular Disease
  • 9 studies of adults with Chronic Heart Failure (CHF) found a small improvement in 6-minute walking distances & an improved classification of CHF.
  •  1 study of infants with ventricular septal defects and CHF proposed a decrease in septal defect shunt ratios (negating the need for surgical intervention in 75% of children). 
  • Another study found that the number of premature ventricular contractions in individuals with congestive heart failure reduced significantly following regular sauna exposure. 
  • 2 studies found improvements in pain scores and 6 minute walking distance with individuals with peripheral arterial disease.
  • 1 study noted improved myocardial perfusion scans on individuals with chronic total occlusion of coronary arteries.
  • The 2 largest studies included in this review investigated 2000+ Finnish men for cardiovascular disease related outcomes found a 66% risk reduction of dementia. 65% risk reduction of Alzheimer’s, 63% risk reduction of sudden cardiac death and a 40% risk reduction of all cause-mortality. 
• Immune Related Conditions
  • 1 study reported decreased pain and stiffness in individuals with Rheumatoid Arthritis or Ankylosing Spondylitis- not sustained after 4 weeks. 
  • 1 study noted subjective improvements in pain, improved quality of life and fewer pain areas in individuals with fibromyalgia and/or other rheumatological conditions.
  • 2 studies found an improvement in fatigue levels and mental health (anxiety and depression outcomes) for individuals with chronic fatigue syndrome.
• Chronic Pain
  • 2 studies reported positive impacts on individuals with chronic pain- 1 reported a 44% decrease in headache intensity and another reported an increased likelihood of return to work and lower anger scores.
• Depression
  • 1 study found subjective improvements in depression, relaxation, complaints and hunger for individuals with mild depression. 
• Respiratory
  • 2 studies investigated individuals with Chronic Obstructive Pulmonary Disease (COPD) and found an improved forced expiratory flow, exercise tolerance, oxygen saturation and decreased pulmonary arterial pressure whilst exercising. 
  • 1 study noted an improvement in nasal inspiratory flow rates and improved forced expiratory volume. 
  • 1 study investigated symptoms of common cold sufferers and found an improvement in symptoms 2 days post sauna exposure, but this improvement was not maintained 3 days post exposure. 
• Physical Performance & Athletes
  • 2 studies reported small increases in venous pH levels, venous oxygen and haemoglobin concentration and a right translation of the oxygen-haemoglobin dissociation  curve (allowing improved oxygen uptake) which was maintained 5 months post sauna exposure. 
• General Population
  • 2 studies noted a reduction in total and low-density-lipoprotein (LDL) cholesterol levels among men and women. This study also reported an increase in heart rate, systolic blood pressure, growth and adrenocorticotropic hormones and cortisol levels along with a decrease in plasma volume and diastolic blood pressure. 

Whilst the above outcomes demonstrate potential health benefits, there is insufficient evidence of regular dry-sauna exposure and the suggested benefits. Further research is required, with larger sample sizes, to determine the impact of regular sauna use on specific medical conditions and for specific purposes (improved athletic performance). 

The bottom line is: there are few adverse effects from regular sauna use so if it is enjoyable to you then feel free to do so! However if specific improvements in health outcomes and athletic performance are your focus, keep in mind that the literature at hand is limited.

References:

Hussain, J. and Cohen, M. (2018) “Clinical effects of regular dry sauna bathing: A systematic review,” Evidence-Based Complementary and Alternative Medicine, 2018, pp. 1–30. Available at: https://doi.org/10.1155/2018/1857413.