How does the body react to extreme temperature changes? In search of answers, Danish researchers have conducted experiments with habitual users of saunas and ice bathers.
Ice Bath
People in Scandinavian countries are big sauna enthusiasts. Some of them also like dipping into ice-cold water for a few minutes after being in the sauna. Some enthusiasts practice this alternation of hot and cold several times a week each winter. How does the human body adapt to these extreme temperature changes? Researchers at the University of Copenhagen have tried to answer this question. At the center of their thinking is brown fat, the body’s heating station, along with the bloodstream and muscles.
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Brown fat, important for body temperature
Brown fat is present in large quantities in animals that hibernate or live in cold regions. It is also found in humans, especially in infants. In adulthood, brown fat consists of small deposits in the armpits and neck, and along the spine. Brown fat differs from white fat in the nature of the adipocytes it contains. Adipocytes are cells that store fat in one or more lipid vesicles. White fat adipocytes are unilocular, i.e., they have a single large vesicle that presses the nucleus against the plasma membrane. Brown adipocytes are multilocular, with several vesicles of different sizes and a nucleus in the center. White fat acts as an energy store, whereas the main function of brown fat is thermogenesis, the production of heat through the breakdown of lipids in the vesicles.
Better adaptation to cold and heat
The Danish researchers recruited eight young men who were sauna and ice bath enthusiasts and eight others who had never had this habit. All 16 men had a similar profile: the same age, weight, and BMI. The researchers looked into the differences in the participants’ brown adipose tissue levels after several tests. “We expected the winter swimmers to have more brown fat than the controls, but it turned out that their thermoregulation was much better,” explains Susanna Søberg, first author of the study. In a test in which participants immersed their hands in 4°C water for three minutes, the men who were used to icy water showed greater tolerance to cold than the controls. In another test, in which participants were covered with a cold blanket, the ice water swimmers had a higher skin temperature than the control subjects.
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In addition, the brown adipose tissues of the eight male control subjects were active at pleasant temperatures, while those of the ice water bathers were inactive. By tracking changes in body temperature under the same conditions, the Danish researchers observed that it dropped to a lower level than in the controls, indicating a possible adaptation to the sauna and ice water bath sessions.
The small size of this study does not allow conclusions to be drawn about a causal relationship between the sauna and ice bathing tradition and changes in body temperature regulation. Nevertheless, it remains interesting and may have applications in health care, especially in the treatment of obese people.
References
Søberg, S., Löfgren, J., Philipsen, F. E., Jensen, M., Hansen, A. E., Ahrens, E., Nystrup, K. B., Nielsen, R. D., Sølling, C., Wedell-Neergaard, A. S., Berntsen, M., Loft, A., Kjær, A., Gerhart-Hines, Z., Johannesen, H. H., Pedersen, B. K., Karstoft, K., & Scheele, C. (2021). Altered brown fat thermoregulation and enhanced cold-induced thermogenesis in young, healthy, winter-swimming men. Cell Reports Medicine, 2(10), 100408. https://doi.org/10.1016/j.xcrm.2021.100408
