Cold water immersion has long been known to the northern Europeans as a fortifying activity, but the science behind this cultural/medicinal practice is actually way cooler.

In a recent review of more than 100 studies, scientists determined that one of the most significant changes that occurs in the body during exposure to cold air, but especially cold water, is that white fat adipose tissue is converted into brown fat adipose tissue (BFAT).

BFAT is kind of like a working fat, rather than a storage fat, because it burns calories to maintain body temperature to repel the cold, unlike ‘bad’ white fat which stores energy.

Experts say the increasing popularity of cold exposure to air or water, sometimes called cryotherapy, has an impact on fats and could prevent obesity and cardiovascular disease.

Dunking yourself in cold water during the winter months has also been found to reduce the risk of diabetes by significantly increasing insulin sensitivity and decreased insulin concentration.

Adiponectin is produced by BFAT, and plays a vital role in protecting against insulin resistance, diabetes, and other diseases. Further, the impact of old water dips on insulin worked for experienced and inexperienced swimmers alike.

Another huge benefit of cold water immersion that doesn’t relate to obesity, is that being up to your neck in water (around 40°F) increases your brain’s production of norepinephrine by 300% – in just a few minutes. A dunk at the more manageable temperature of 57°F will still convert WFAT cells to BFAT cells and increase norepinephrine by 500%.

Norepinephrine is similar to adrenaline, and leads to a feeling of positive elation. It’s also a neurotransmitter, so can also facilitate the speed of brain activity.

The study, carried out by The Arctic University of Norway and University Hospital of North Norway and lead author James Mercer from UiT, found that “it is clear there is increasing scientific support that voluntary exposure to cold water may have some beneficial health effects.”

“Many of the studies demonstrated significant effects of cold-water immersion on various physiological and biochemical parameters, but based on the results from this review, many of the health benefits claimed from regular cold exposure may not be causal,” he continues. “Instead, they may be explained by other factors including an active lifestyle, trained stress handling, social interactions, and a positive mindset.”

Mercer may be cautious in his conclusions, but other researchers are less so. Popular science communicator Rhonda Patrick Ph.D. has put together her own review of the literature, and while the obligatory “may” is placed before any conclusion, Dr. Patrick feels much more strongly that these results are causal.

“Studies in animals and humans have indicated that brown fat can improve glucose and insulin sensitivity, increase fat oxidation, and protect against diet-induced obesity,” Patrick outlines.

“Cold exposure also increases brown fat volume, drives glucose uptake, and increases oxidative metabolism in brown fat. Cold-induced glucose uptake in brown fat exceeds the rate of insulin-stimulated glucose uptake in skeletal muscle in healthy humans”.

There are tens of thousands of papers done on the physiology of people who lead an active lifestyle, but only a small percent involve cold-water immersion. The stark changes in key cardio-metabolic markers makes for a persuasive argument that taking a cold bath or going swimming in a cold pool is, in fact, all it’s cracked up to be.