Winter-Swimming Scandinavian Men Can Teach Us How the Body Adapts to Extreme Heat and Cold

Summary: A study of Scandinavian Winter swimmers reveals alternating between cold water swimming and hot sauna sessions may affect the way in which brown adipose fat burns energy and produces heat.

Source: Cell Press

The Scandinavian winter swimming culture combines brief dips in cold water with hot sauna sessions—and now, a study of young men who participate regularly in these polar plunges finds that winter swimming may allow the body to adapt to extreme temperatures.

The findings, publishing October 11 in the journal Cell Reports Medicine, suggest that routinely alternating swims or dips in chilly water with sauna sessions might affect how brown fat, also known as brown adipose tissue (BAT), burns energy and produces heat.

“Our data underscore that BAT in adult humans is part of the collective body temperature regulation system in collaboration with skeletal muscle and blood flow,” says senior study author Camilla Scheele of the University of Copenhagen.

“Regular winter swimming combining cold dips with hot sauna might be a strategy to increase energy expenditure, which could result in weight loss if compensatory increase in food intake can be avoided.”

In the Denmark-based study, Scheele and her collaborators examined whether the Scandinavian practice of winter swimming is associated with changes in body temperature, resulting in acclimation to both cold and hot challenges. They also looked for differences in brown fat tissue, given its role in producing heat in response to exposure to cold environments.

To explore these ideas, first author Susanna Søberg of the University of Copenhagen recruited eight young male winter swimmers who had alternated several swims or dips in cold water with hot sauna sessions every week for at least two years.

For the purposes of this study, winter swimming was loosely defined as swimming or sitting in open water and wearing only swim trunks or nothing. By contrast, the eight control participants did not use any cold or heat therapies during the study and had no history of winter swimming.

“We expected winter swimmers to have more brown fat than the control subjects, but it turned out that they instead had better thermoregulation,” Søberg says. I

n preliminary tests, the participants submerged one hand in cold water for three minutes. While both groups responded to the cold exposure, the swimmers displayed signs of cold tolerance, with a lower increase in pulse and blood pressure.

They also had higher skin temperature, pointing to greater heat loss as a potential adaptation to frequent sauna exposure. In another preliminary test, the researchers used an adjustable system consisting of two water-perfused blankets to control and lower the participants’ body temperature. Here, the swimmers also showed a higher increase in skin temperature in response to cooling.

Using positron emission tomography, the researchers next measured activation of brown fat tissue in the participants as they were exposed to a comfortable temperature. Unlike the swimmers, the control subjects showed signs of activated brown fat tissue, as indicated by an uptake of glucose.

“The findings support the notion that brown fat tissue fine tunes body temperature to a comfortable state in young adults,” Scheele says. “It was, however, a surprising finding that the winter swimmers had no activity at all when exposed to comfortable temperatures.”

Upon cold exposure, the activity of brown fat tissue increased in both groups. But the swimmers showed much higher heat production, or energy expenditure, in response to cool temperatures.

“Winter swimmers burned more calories than control subjects during cooling, possibly in part due to higher heat production,” Scheele says.

The researchers also looked at thermoregulation for both groups over the course of a full day at a comfortable temperature. They found that swimmers reached a lower core body temperature—potentially a sign of heat acclimation due to regular sauna visits. Their skin temperature in areas close to BAT showed a distinct peak between 4:30 am and 5:30 am and revealed signs of a 24-hour rhythm in brown fat tissue activity and heat production, at least during rest at a comfortable temperature.

This shows a man swimming
Upon cold exposure, the activity of brown fat tissue increased in both groups. Image is in the public domain

“The difference between groups is possibly explained by increased maturation and cold adaptation of BAT in the winter swimmer group,” Scheele says.

The study’s small sample size, the absence of female participants, and the inability to draw causal conclusions about the direct effect of winter swimming on temperature regulation or brown fat tissue are all potential limitations to the findings. “We compared experienced winter swimmers with control subjects, which allows for the possibility that other lifestyle factors or genetic factors not measured in the current study also could impact the differences between the groups,” Søberg adds.

Nevertheless, the findings may have important health implications, given that brown fat tissue activity is associated with a lower risk of metabolic diseases. In future studies, the researchers plan to assess the potential effects of winter swimming on metabolic health in overweight participants. They would also like to examine the molecular mechanisms underlying brown fat activation, and how brown fat communicates with the brain to regulate feeding behavior.

“Our results point to winter swimming as an activity that could increase energy expenditure, thus proposing a new lifestyle activity that might contribute to weight loss or weight control,” Scheele says.

Funding: This work was supported by TrygFonden, the Novo Nordisk Foundation, the European Research Council, and Rigshospitalet, the University Hospital of Copenhagen.

About this neuroscience research news 

Author: Carly Britton
Source: Cell Press
Contact: Carly Britton – Cell Press
Image: The image is in the public domain

Original Research: Open access.
Altered brown fat thermoregulation and enhanced cold-induced thermogenesis in young healthy winter swimming men” by Søberg et al. Cell Reports Medicine


Altered brown fat thermoregulation and enhanced cold-induced thermogenesis in young healthy winter swimming men


  • Winter swimmers have a lower core temperature at a thermal comfort state than controls
  • Winter swimmers had no BAT glucose uptake at a thermal comfort state
  • Winter swimmers have higher cold-induced thermogenesis than control subjects
  • Human supraclavicular skin temperature varies with a diurnal rhythm


The Scandinavian winter-swimming culture combines brief dips in cold water with hot sauna sessions, with conceivable effects on body temperature. We study thermogenic brown adipose tissue (BAT) in experienced winter-swimming men performing this activity 2–3 times per week. Our data suggest a lower thermal comfort state in the winter swimmers compared with controls, with a lower core temperature and absence of BAT activity. In response to cold, we observe greater increases in cold-induced thermogenesis and supraclavicular skin temperature in the winter swimmers, whereas BAT glucose uptake and muscle activity increase similarly to those of the controls. All subjects demonstrate nocturnal reduction in supraclavicular skin temperature, whereas a distinct peak occurs at 4:30–5:30 a.m. in the winter swimmers. Our data leverage understanding of BAT in adult human thermoregulation, suggest both heat and cold acclimation in winter swimmers, and propose winter swimming as a potential strategy for increasing energy expenditure.

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