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Exposure to high heat while sauna bathing causes mild hyperthermia – an increase in the body’s core temperature – that induces a thermoregulatory response to restore homeostasis and condition the body for future heat stressors. These adaptations to high temperatures involve increased production of brain derived neurotrophic factor (BDNF), a promoter of neuroplasticity, and irisin, a biomarker of exercise. Findings of a new report demonstrate that whole-body hyperthermia increases BDNF and irisin in healthy young adults.
Whole-body hyperthermia is a therapeutic strategy used to treat various diseases, including cancer and depression. Previous research has shown that use of a hyperthermia chamber increases BDNF to a greater extent than light intensity exercise. Some research has suggested that BDNF production is stimulated by irisin, a hormone secreted from muscle in response to exercise. Irisin may mediate some of the beneficial effects of exercise and sauna use in humans, but additional research is needed.
The authors recruited 20 male participants (average age, 22 years) and assessed their baseline heat tolerance using a hyperthermia protocol. Participants reclined in a hyperthermia chamber while the researchers increased the temperature of the chamber by 50 degrees F every ten minutes until the participant reached their personal heat threshold. Next, participants completed ten hyperthermia sessions tailored to their baseline conditioning, during which the hyperthermia chamber was set to a temperature of 150 to 175 degrees F. Following a three-week wash-out period, they completed ten sham treatments over two weeks, during which the hyperthermia chamber was set to a temperature of 75 to 77 degrees F.
Participants had an average core body temperature of 102 degrees F at the end of each whole-body hyperthermia treatment. Following ten whole-body hyperthermia treatments, participants had a significant increase in circulating irisin levels (6.3 micrograms per milliliter) compared to their baseline levels (5.0 micrograms per milliliter) and compared to their irisin levels following the sham treatment (5.4 micrograms per milliliter). Whole-body hyperthermia treatment also significantly increased BDNF levels (28.3 picograms per liter) compared to baseline (25.9 picograms per liter).
In healthy young adults, ten whole-body hyperthermia significantly increased irisin and BDNF levels. The authors noted that future studies should explore the effects of whole-body hyperthermia on adipose tissue, which also produces irisin.
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