A study found that bathing by alternating between cold and hot water may provide important health benefits for the body.
The findings suggest that youngsters who regularly participate in Scandinavian winter swimming, which combines short dips in cold water and hot sauna sessions, can adapt to the temperature extremes.
The Danish study, published October 11 in the journal Cell Reports Medicine, explains that routinely swimming or immersing in cold water with hot sauna sessions may affect how brown fat, also known as brown adipose tissue (BAT), burns energy and produces heat.
Brown fat, or brown adipose tissue, is a special type of body fat that turns on (activates) when it cools. Brown fat produces heat to help maintain body temperature in cold weather.
“Regular Scandinavian winter swimming that combines a cold dip and a hot sauna may be a unique strategy to increase energy intake, which may lead to weight loss if the compensatory increase in food intake can be avoided,” says lead study author Camilla Schell from the University of Copenhagen.
Schell and her colleagues examined whether the Scandinavian winter swimming practice was associated with changes in body temperature, which lead to adaptation to both cold and hot challenges. They also looked for differences in brown adipose tissue, given its role in heat production in response to exposure to cold environments.
The study’s first author, Susanna Soberg of the University of Copenhagen, recruited eight experienced young swimmers in the winter, who took turns swimming or diving in cold water with hot sauna sessions every week for at least two years.
Plus another group of eight participants were only entering the sauna, considering that they had no history with winter swimming.
In the initial tests, participants immersed one hand in cold water for three minutes. While both groups responded to exposure to cold, the swimmers showed signs of cold tolerance, with fewer increases in pulse and blood pressure.
They also had a higher skin temperature, suggesting a possible adaptation to frequent sauna exposure.
In another test, the researchers used an adjustable system consisting of two water-filled blankets to control and lower the participants’ body temperature. Here, the swimmers also showed a higher increase in skin temperature in response to cooling.
The researchers then measured the activation of the participants’ brown adipose tissue, as they were exposed to a comfortable temperature.
In contrast to the swimmers, only the sauna participants showed signs of active brown adipose tissue, as indicated by glucose uptake.
“The results support the idea that brown adipose tissue adjusts body temperature to a comfortable state in young adults,” says Shell. “However, it was a surprising discovery that the swimmers had no activity whatsoever for these tissues when exposed to comfortable temperatures.”
When exposed to cold, brown adipose tissue activity increased in both groups. But the swimmers showed much higher heat production, or energy expenditure, in response to lower temperatures.
“Swimmers burn more calories than people in a sauna only while cooling down, possibly due in part to the increased heat production,” Shell explains.
The researchers noted that there are limitations to their findings, including the study’s small sample size, the absence of female participants, and the inability to draw causal conclusions about the direct effect of Scandinavian winter swimming on temperature regulation or brown adipose tissue.
However, the findings may have important health implications, given that brown adipose tissue activity is associated with a lower risk of metabolic disease.
In future studies, the researchers plan to evaluate the potential effects of winter swimming on the metabolic health of overweight participants. They also wish to examine the molecular mechanisms underlying brown fat activation, and how brown fat communicates with the brain to regulate feeding behaviour.