Review
Benefits and risks of sauna bathing

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Abstract

Although sauna bathing causes various acute, transient cardiovascular and hormonal changes, it is well tolerated by most healthy adults and children. Sauna bathing does not influence fertility and is safe during the uncomplicated pregnancies of healthy women. Some studies have suggested that long-term sauna bathing may help lower blood pressure in patients with hypertension and improve the left ventricular ejection fraction in patients with chronic congestive heart failure, but additional data are needed to confirm these findings. The transient improvements in pulmonary function that occur in the sauna may provide some relief to patients with asthma and chronic bronchitis. Sauna bathing may also alleviate pain and improve joint mobility in patients with rheumatic disease. Although sauna bathing does not cause drying of the skin—and may even benefit patients with psoriasis—sweating may increase itching in patients with atopic dermatitis. Contraindications to sauna bathing include unstable angina pectoris, recent myocardial infarction, and severe aortic stenosis. Sauna bathing is safe, however, for most people with coronary heart disease with stable angina pectoris or old myocardial infarction. Very few acute myocardial infarctions and sudden deaths occur in saunas, but alcohol consumption during sauna bathing increases the risk of hypotension, arrhythmia, and sudden death, and should be avoided.

Section snippets

Methods

We searched four databases using search words “sauna,” “Finnish bath,” and MeSH term “Baths, Finnish.” The databases were Medline (1966 to 2000, n = 336 documents in English or German), Embase (1974 to 2000, n = 61), Biosis Previews (1970 to 2000, n = 135), and Medic (1978 to 2000, n = 6). We supplemented our search by examining citations in the articles. Of the 271 documents that provided information on the chosen topics (sauna and the cardiovascular system, lungs, rheumatic diseases, skin,

The sauna (finnish bath)

Unlike the Turkish bath, the sauna (or Finnish bath) has dry air and a high temperature (4). The basic modern sauna is an unpainted, wood-paneled room with wooden platforms and a rock-filled electric heater. The walls are made of spruce or pine, and the benches are made of obeche, spruce, or aspen because these types of wood are less hot to sit on. The size of a sauna is at least 3 m2 to encourage the correct balance between heat, humidity, and ventilation. The recommended temperature is 80°C

Cardiovascular effects

The cardiovascular effects of sauna bathing have been reviewed earlier 7, 9, 10, 11, 12 and are summarized in Table 1. Skin temperature increases rapidly to about 40°C 5, 9, 13, 14, whereas the increase in rectal temperature depends on heat exposure 15, 16, 17. Sweating begins quickly and reaches its maximum at about 15 minutes, with an average total secretion of 0.5 kg 6, 9, 18. Skin blood flow is increased from 5% to 10% so it becomes 50% to 70% of the cardiac output, while blood flow to

Sauna and drugs

Vanakoski et al 52, 53 have reviewed the effects of heat exposure on the pharmacokinetics of drugs. The effects of hyperthermia on the absorption, distribution, and elimination (54) of orally administered drugs were shown to be minor in studies with propranolol (47), captopril (47), midazolam 55, 56, ephedrine (55), and tetracycline (57). Increased skin blood flow during sauna did, however, enhance the systemic absorption of transdermally administered nitroglycerin (58) and nicotine (59). The

Sauna and the lungs

Sauna bathing decreases pulmonary congestion and increases the vital capacity, tidal volume, minute ventilation, and forced expiratory volume of the lungs 9, 62. Patients with asthma or chronic bronchitis report that sauna bathing improves their breathing (62). Twelve patients with obstructive pulmonary disease who took sauna as a part of their rehabilitation program also demonstrated improved lung function (63). Other data, however, reveal no such changes 64, 65. Studies by Ernst et al (66)

Sauna and rheumatic disease

Sauna bathing has been used as thermal therapy to treat pain and other symptoms of rheumatic disease, although clinical studies are limited. In studies based on interviews of 70 patients (73) and 119 patients (74) with rheumatoid disease, 40% to 70% of participants reported that sauna bathing alleviated pain and improved joint mobility. Approximately half of the patients experienced exacerbated pain on the day after sauna bathing but reported that this pain could often be prevented by a cool

Sauna and the skin

In general, sauna bathing is harmless for the skin. Repeated stays in the sauna (30 minutes 4 times per day for 7 days) cause no withering of the skin and no change in transepidermal water loss 76, 77. Although sauna bathing is seldom used as a therapy for skin disease, it may benefit patients with psoriasis by helping to keep skin lesions free of thick scales (77). In some atopic subjects and patients with cholinergic urticaria, sauna bathing may cause intense itching of the skin (77). Contact

Sauna and hormonal changes

Sauna bathing activates the sympathetic nervous system, the renin-angiotensin-aldosterone system, and the hypothalamus-pituitary-adrenal hormonal axis. The hormonal changes related to sauna use are summarized in Table 2. Changes in the endocrine system are brief and reversible, with no permanent effects (81).

Fertility

Sauna bathing does not influence fertility. In men, serum concentrations of testosterone and gonadotropins do not change even after repeated sauna use 82, 83, 84, 85. Prolactin concentration increases temporarily in both men and women during sauna bathing 82, 83, 84, 85, 86, 87. A few studies have reported decreased sperm count or decreased sperm movement after sauna bathing 88, 89, 90. Finnish men, however, have high sperm counts 91, 92, and the time to pregnancy (a sensitive indicator of

Sauna and children

Healthy children who are accustomed to sauna bathing tolerate it well when their parents supervise bathing time and temperature. In Finland, children typically take sauna once per week with their parents, who adjust the conditions according to each child’s reaction (109). Children usually have shorter sauna baths (5 to 10 minutes) than their parents and sit on the lower bench where the temperature is not as hot (110).

Jokinen et al 111, 112, 113, 114 studied the effects of sauna bathing in 81

Summary

For most healthy people, as well as for most patients with stable coronary heart disease, sauna bathing is well tolerated and safe. The physiological (Table 1) and hormonal (Table 2) changes that occur during sauna bathing are transient. Sauna bathing does not cause drying of the skin 76, 77. The effects of hyperthermia on the pharmacokinetics of several orally administered drugs are minor 47, 54, 55, 56, 57. Sauna bathing does not lower fertility in men or women 91, 92, 93 nor is it harmful in

Acknowledgements

The excellent help of Marja Snyder in the literature search is greatly appreciated. We also thank Ellen K. Shair, MA, for editing the manuscript.

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      Hypertension is associated with a higher risk of developing AD (Edwards Iii, et al., 2019; Glodzik, et al., 2014), and hypertension in AD mouse models was shown to increase tau phosphorylation (Shih, et al., 2018). As sauna bathing can decrease blood pressure (Hannuksela and Ellahham, 2001; Winterfeld, et al., 1993), it could therefore indirectly lower tau phosphorylation by modulating blood pressure. However, we observed that tau was dephosphorylated in neuronal cells exposed to mild hyperthermia, suggesting that this treatment can lead to neuronal tau dephosphorylation per se, independently of potential blood pressure effects.

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