Regular winter swimming could boost health

This extreme Nordic tradition burns calories with no exercise, and potentially improves sleep
19 October 2021


A bearded man with a winter coat covered in ice.


Wild water swimming is becoming ever more popular and, according to a new study published recently in Cell Reports Medicine, combining dips in cold water with time in a hot sauna could cause enhanced calorie burning and a lower core body temperature, resulting in more weight loss and better sleep.

It is well known that the key tissue that is responsible for controlling your body’s temperature when exposed to cold is brown fat, a special type of fat located mostly around your neck. This fat burns calories when you’re exposed to the cold in order to keep your body at a constant temperature. So if you are trying to lose weight, you actually want to have more brown fat. This is in contrast to the more well known white fat that is more prominent in overweight individuals.

Previous studies into winter swimming have shown that if you repeatedly cool the body from room temperature in near-freezing water over many months, the amount of brown fat in your body tends to increase due to the effect of the cold.

In the study, they recruited young, male winter swimmers who enjoy alternating dips in cold with time spent in an 80° sauna 2-3 times a week during winter. They then compared the swimmers’ thermal responses at room temperature and in extreme cold to that of a control group.

Senior author Camilla Scheele said “We found that the winter swimmers had a higher cold-induced thermogenesis, meaning that they burn more calories when they are cooled down.” The observed increased calorie burn was not from any exercise in the water but just from being in the cold water.

They had expected the winter swimmers to have more brown fat due to increased, frequent cold water exposure. However, to their surprise, they found that the winter swimmers were simply better able to regulate the use of their brown fat: not using it unnecessarily at comfortable temperatures and activating it to a greater extent when exposed to extreme cold. They put this down to the additional effect of the swimmers’ sauna sessions, as it's known that frequent exposure to heat in a sauna lowers the body’s core temperature.

Scheele and her team found that this lowered core temperature in the winter swimmers led  to a different brown fat response  when at room temperature: “We saw that the winter swimmers had no [brown fat] activity at all, while the control subjects actually had some activity.” This lower core temperature, they suggest, is also responsible for the higher calorie burn in the cold water.

Exposing your body to these extremes means your body burns calories  without you having to do anything strenuous, so it would seem to be ideal for those who are less mobile but want to keep themselves fit. In fact, the effects could be more pronounced in the elderly, “because the brown fat activity goes down with aging, it could have been interesting to look at an older subject group...I can imagine that we would see an even bigger effect”, said Scheele.

More surprisingly, the study also showed that winter swimming could also have a beneficial effect on your sleep: “We also looked at [core] temperature over a 24 hour timespan and there we could see that the winter swimmers had a lower core temperature and that could be beneficial for your sleeping quality”.

However, these findings need to be confirmed through further study. Scheele and her team are actively working on this, including an intervention study on overweight subjects.


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