Winter-swimming Scandinavian men can teach us how the body adapts to
extreme heat and cold

Date:
October 11, 2021
Source:
Cell Press
Summary:
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 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.



FULL STORY ==========================================================================
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.


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"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 Scheel 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 So/berg 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," So/berg says.

In 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. "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," So/berg 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.

========================================================================== Story Source: Materials provided by Cell_Press. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Susanna So/berget al. Altered brown fat thermoregulation and
enhanced
cold-induced thermogenesis in young, healthy, winter-swimming
men. Cell Reports Medicine, 2021 DOI: 10.1016/j.xcrm.2021.100408 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211011110818.htm

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