When summer loses its grip on the northern hemisphere, long days at the beach, eating ice cream or splashing in the sea are long gone for most. But for some swimmers, the fun is just beginning.
“The best thing is going to Brighton Beach in the fall. Every week the water is a bit colder than the last. Before you know it, it’s 48 degrees!” Bonnie Schwartz Nolan, management, operational and financial consultant, swimming coach and successful English Channel swimmer from New York, tells us popular science. She’s been bobbing in the frigid waters off Brooklyn for over two decades.
In order to train for most marathon swims (a 6.2 mile or 10 km swim), swimmers must adjust to spending time in the cold, as swimmers often cannot wear a wetsuit or technical suit to stay warm, and have to rely on their own bodies instead.
“Their core temperature is 98 degrees, so even something like 80 feels cold after a while,” Nolan explained. To even qualify to swim in the English Channel, swimmers must complete a documented six-hour under-60 dive or continuous swim in water below 60 degrees Fahrenheit (about 15 degrees Celsius).
[Related: Swimming is the ultimate brain exercise. Here’s why.]
Open water swimming has even evolved into ice swimming or swimming in waters below 41 degrees Fahrenheit (5 degrees Celsius). “For me, it’s all about the challenge,” says Elaine K. Howley, a journalist and accomplished swimmer, in an interview with PopSci. “It’s that ‘can I do it’ uncertainty, just like a marathon swim.” Howley is an accomplished marathon and ice swimmer, having completed an ice mile in 2012 and is currently training for her second.
Some anecdotal “wellness” claims, including weight loss, better mental health, and increased libido, have been made by supporters of regular cold water immersion, but what about concrete evidence?
A scientific review published today in peer-reviewed International Journal of Circumpolar Health notes that jumping in cold water can reduce white adipose tissue (WAT) in men and reduce the risk of diseases like diabetes, but other benefits of ice swimming are inconclusive.
The authors analyzed 104 scientific studies and found an additional effect on brown adipose tissue (BAT). The difference between the two is that WAT stores energy instead of burning it like BAT does. Repeated exposure to cold water or air increases the production of BAT, which is also found in the blubber of marine mammals like whales and seals to keep them warm.
BAT helps the body burn calories, maintains body heat when exposed to cold temperatures, and also helps the body control blood sugar and insulin levels. It produces heat in the blood when it’s cold outside and is mainly found around the neck, kidneys, adrenal glands, heart and chest in adults. According to the Cleveland Clinic, it’s brown because the fat cells are full of mitochondria, which contain a lot of iron. The iron gives BAT the brown tint.
Exposure to cold water or air also appears to increase the production of a protein called adiponectin by adipose tissue. This is a protein that plays a key role in protecting against insulin resistance, diabetes, and other diseases. According to the data reviewed in these studies, repeated winter immersion in cold water significantly increased insulin sensitivity and decreased insulin concentrations. This occurred in both inexperienced and experienced swimmers.
Swimming in cold water also has a major impact on the body, triggering shock reactions such as increased heart rate. Some of the studies reviewed showed evidence that cardiovascular risk factors are actually improved in swimmers who have adapted to the cold. However, other studies suggest that the heart’s workload is still elevated. Overall, the authors disagreed on the overall health benefits of “the fastest growing extreme water sport.”
“It is clear from this review that there is increasing scientific support that voluntary exposure to cold water can have some beneficial health effects,” said lead author James Mercer of UiT The Arctic University of Norway in a press release.
According to the authors, many of the available studies on the health benefits of ice swimming included small numbers of participants, often of one gender, and did not account for differences in water temperature or whether the water was sweet or salty. It’s also unclear whether winter swimmers are inherently healthier than the general population.
[Related: How to avoid (and treat) hypothermia.]
“Many of the studies showed significant effects of cold water immersion on various physiological and biochemical parameters. But whether these are beneficial to health or not is difficult to judge. Based on the findings of this review, many of the health benefits claimed from regular exposure to cold may not be causal. Instead, they can be explained by other factors, including an active lifestyle, stress management skills, social interactions, and a positive attitude,” Mercer added.
The authors note that swimmers participating in these studies ranged from elite swimmers or established winter swimmers to those with no prior ice swimming experience. Some were pure ice bathers but used cold water immersion as a post-treatment exercise.
The review also identified a need for better education about the health risks that can come with a dip in icy water. These include hypothermia if a swimmer stays in the water too long or jumps into the water without acclimatization, as well as heart and lung problems associated with cold shock. Simply jumping into cold water is very dangerous, and it’s best to start ice swimming slowly over a period of time.
If swimming in icy waters sounds like fun to you, Howley and Nolan recommend doing progressively longer dives in colder waters to acclimate. Nolan also took cold showers, slept with the window open and a lighter blanket, and wore a vest instead of a coat outside to help her body adjust to the freezing temperatures.