Hot tub or sauna treatment: which is more beneficial?

Immersing yourself in hot water yields greater physiological changes compared to basking in a sauna.That’s according to a study that examined three forms of passive heat therapy—hot water immersion, traditional saunas and far infrared saunas—and the resulting physiological responses in young adults.Hot water immersion resulted in the greatest thermoregulatory, cardiovascular and immune responses compared with both sauna therapies, according to the study, which was published in May in the American Journal of Physiology. The far infrared sauna had the least impact on raising body core temperature and resultant cardiovascular and immune responses. The degree of physiological impact reflects how likely the therapy is to benefit a person’s health, the study suggested.“It is the thermoregulatory challenge and subsequent cardiovascular and other physiological adjustments to the increase in core body temperature elicited by passive heating that may result in beneficial adaptations to health with repeated exposures,” the authors wrote.Study designThe study recruited 20 adults, between the ages of 20 and 28 and evenly split between female and males, to complete three sessions of each type of heat therapy. The sessions were separated by at least one week. The hot water immersions ran for 45 minutes at 40.5°C. Participants were immersed up to their sternums. The traditional sauna sessions were broken up into three 10-minute bouts at 80°C with five-minute breaks at approximately 22°C in between. The infrared sessions lasted 45 minutes, starting at 46°C and increasing to 65°C by the end of the session.The sessions “were completed in a randomized and counter-balanced order,” the authors noted.They also noted that they designed these sessions based on how each of the heat therapies are typically utilized in “everyday life.”ResultsHot water immersions resulted in the greatest changes in core temperature from baseline to the end of each session (average +1.1°C), followed by traditional sauna treatments (average +0.4°C) and far infrared sauna treatments (average of +0.0°C). The changes to core temperature elicited by hot water immersions is “likely attributed to the high thermal conductivity of water,” which is about 24 times greater than air, the authors explained. This allows for efficient heat transfer to the body. The body is also less able to dissipate heat through evaporated sweat because it is submerged in water.Cardiac output increased the most with hot water immersions (average +3.7 litres of Qc per minute) compared with the traditional sauna sessions (+2.3 litres per minute) and the far infrared sauna sessions (+1.6 litres per minute).Hot water immersion was the only heat therapy to elicit inflammatory and immune responses, which was evidenced by increased production of interleukin-6, NK cells and CD8+ T cells following the sessions. “In agreement with our hypothesis, hot water immersion led to the most robust changes in core temperature, whole body sweat loss, cardiac output, heart rate, stroke volume, and [interleukin-6] production,” the authors wrote.“Hot water immersion also had the largest reduction in systemic vascular resistance and blood pressure.”

Hot tub or sauna treatment: which is more beneficial?

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