Cold Water Swimming: Benefits and Risks

Cold-water swimming has a long tradition in northern countries and regions where people have adapted to the cold. In this excerpted academic article, there can be profound benefits, and it can also be deadly. With the popularity of the frigid extreme sport on the rise, understanding the possible effects has become a subject receiving greater scientific attention.

By Eric Herman

Cold water swimming — also known as winter swimming or ice swimming — describes swimming outdoors (lake, river, sea, swimming pool, etc.) mainly during the winter or in the colder and polar regions. This special form of endurance sport is becoming increasingly popular.

Winter swimming specifically implies that it must be winter. In colder countries, it can be synonymous with ice swimming when the water is frozen over because ice swimming explicitly requires the ice to break. In recent years, ice swimming has evolved into an all-year-round sport, with many swimmers participating and competing regularly in both local and international events.

Several studies have suggested that cold-water swimming has a wide variety of health benefits, including changes in hematological and endocrine function, fewer upper respiratory tract infections, amelioration of mood disorders and general well-being. Although chronic exposure to colder water temperatures has been shown to be beneficial to one’s health, several studies have outlined the potential risks.

LONG COLD HISTORY

Since antiquity, immersion in cold water has been regarded with both reverence and fear. As far back as 450 BC, the ancient Greek historian Herodotus described the unfortunate expedition of the Persian General Mardonius, noting that “Those who could not swim perished from that cause, others from the cold.”

Centuries later, in December 1790, Dr. James Currie became interested in the physiological effects of hypothermia after helplessly observing three crew members of a stranded American sailing ship who fell and drowned in the 5° C cold sea. This experience prompted Currie to carry out the first recorded experiments on the effects of cold-water immersion and hypothermia on humans.

In certain northern countries, such as Finland, Poland, Russia, Norway, Sweden, Denmark, Estonia, Lithuania, the Czech Republic and Latvia, cold-water swimming is practiced regularly in the sense of winter swimming. In Eastern Europe and Russia, winter swimming is part of the celebration of Epiphany Naturally, many field studies investigating the influence of cold-water swimming on the body come from these northern countries on various topics such as adaptation to the cold.

As mentioned above, ice swimming is a unique form of cold-water or winter swimming. As a rule, ice swimming is carried out in an environment where freezing temperatures prevail regardless of the season, such as at the north or south pole. Ice swimming is specifically practiced by extreme athletes, where the American Lynne Cox and the Briton Lewis Gordon Pugh are considered among the best known and most extreme ice swimmers in the world.

Since 2009, there have been official ice swimming competitions. The International Ice Swimming Association (IISA) was founded on in July 2009 by South African ice swimmer Ram Barkai in Cape Town, South Africa. Barkai previously swam 1.43 miles (2.3 km) in 43 minutes at 4 °C water temperature in Zurich accompanied by a boat on 31 January 2009. This event is considered as the beginning of the so-called ice miles movement.

Since ice swimming is of increasing popularity as sports discipline, we need to consider both the risks and benefits of cold-water swimming. We need, however, to consider that swimming in cold water as an athlete is different to immersion in cold water for non-athletes. Athletes compete at rather high intensity for several minutes while non-athletes remain for a few minutes without the same level of physical activity.

SHIVERING IMPACT

Cold-water swimming is a very stressful physiological condition where the entire body is exposed to cold water. Chilled water swimmers, however, through chronic exposure to the cold-water environment, are able to reach different degrees of adaptation to the cold. The question arises whether this type of sport has health benefits or may have more harmful effects. As a form of endurance exercise, cold-water swimming, even if swimming in cold water is more strenuous, can increase tolerance to stress factors and cause hardening.

The first claims for the health benefits of cold-water swimming date back to 400 BC. According to Hippocrates, water therapy relieved fatigue, and later, Thomas Jefferson reportedly used a cold foot bath every morning for six decades to keep him healthy.

It is believed that these health benefits are a result of the physiological reactions and biochemical milieu caused by exposure to cold water. Physiological changes occur acutely during cold water swimming, with repeated cold-water swimming developing adaptations that can also affect health.

In the Middle Ages, swimming was not a skill people possessed as it was believed that if they were doomed to hell, they would not be able to cross the Styx River. However, in 1538, the first book introducing swimming and “the human stroke” was written by Wynmann in an attempt to reduce the number of drowning people.

Later in 1750, published work began to emerge that recommended swimming and drinking sea water to treat a range of diseases, with winter being the best time to do this activity. Bathing by the sea peaked in popularity in by the late 18th century when the bathing suit and the purported “bathing machine” were developed. This led to the explosive growth of whole communities and seaside resorts who touted the assumed health benefits of swimming in the sea. 

Several studies have described a positive effect on the cardiovascular system and cardiovascular risk factors. Cold-water swimming appears to have a positive impact on cardiovascular risk factors such as lipid profile or blood pressure.

It also seems to have a positive effect on insulin metabolism. In a field study, 30 cold water swimmers were examined for six months with regard to body composition and insulin sensitivity. The chilled water swimmers were overweight compared to a control group and had a higher percentage of body fat with differences between the sexes. For female and swimmers with lower body fat percentage, there was an increased insulin sensitivity as well as a reduction in insulin secretion and resistance.

Swimming in cold water also affects other hormones, such as ACTH and catecholamines. As such, it was found that if swimmers participated in winter swimming three times a week at water temperatures of 0–3 °C for 12 weeks, there was an increase in ACTH and cortisol as well as norepinephrine. Water immersions were 20 s per week for 3 winter months in water of a temperature of 0–2 °C.

It is believed that an increase in norepinephrine may lead to reduced pain perception, such as with whole-body cold therapy or with ice swimming. In contrast, regular three-month winter swimming resulted in a decrease in the concentration of catecholamines when measured immediately after immersion. It was concluded that adaptation through habitual exposure to the cold of winter swimming weakened the physiological response and inhibited the rise of the catecholamines.

MIND & BODY

Swimming in ice-cold water has also been shown to have a positive effect on the mental side of humans and can even be anti-depressive. Regular winter swimming led to an improvement in general well-being in swimmers who suffered from rheumatism, fibromyalgia, or asthma.

Due to the increase in catecholamines, cold water swimming could be a treatment for depression as it activates the sympathetic nervous system and increases the concentration of norepinephrine and β-endorphin.

There is rising evidence that winter swimmers are more resistant to certain illnesses and infections, experiencing them less frequently and more mildly. The incidence of infectious diseases of the upper respiratory tract is 40% lower in winter swimmers compared to a control group. Furthermore, it has been shown that swimming in cold water has an impact on immune-specific hematology.

Anecdotally, cold-water swimmers state that they suffer fewer and milder infections from regular swimming in cold water. Improved immune response and function is biologically plausible primarily through the release of stress hormones in response to cold exposure. 

It is interesting to note that the ice swimmer only spends a few minutes immersed in cold water, however, the short exposure duration is still sufficient to illicit a measurable physiological response.

RISKY RECREATION

Despite repeated claims about the benefits of swimming in cold water, there is mounting evidence that it can be potentially harmful. In a study by Collier et al., the authors asked the participants to report episodes of upper respiratory tract infections each week over the course of the investigation. They noted a positive correlation between the prevalence and severity of upper respiratory tract infections and events of cold water exposure.

While short-term exposure in cold water can certainly improve the activity of the immune system, repeated exposure without sufficient recovery may actually lead to a reduced immune function.

Even if cold-water swimming can provide a benefit in certain cases, the risks, especially with ice swimming, should not be disregarded. When swimming, it is important to be aware of potential cardiac and pulmonary risks that arise due to the cold exposure. It is also important to note that the thermoneutral temperature of humans is approximately 37 °C, and that prolonged immersion in water colder than 35 °C may produce hypothermia as body heat is lost to the environment.

The origin of this belief was formulated following the sinking of Titanic disaster and supported by several observations made during the maritime conflicts of World War II. In recent years, research has been directed towards elucidating the pathophysiology of cold-water immersion.

Prolonged exposure to the cold may, indee, lead to hypothermia, but a hypothermic state usually does not arise for at least 30 minutes in healthy adults. There is a greater variability between the low body core temperature and the onset of signs and symptoms of hypothermia. Hypothermia is a physiological state that affects cellular metabolism and function, may result in hemostasis, lactic acidosis, vascular insufficiency, cognitive impairment and arrythmia.

A reduction in performance and initial cardiorespiratory responses (cold-shock response) to immersion in cold water are probably the main factors that contribute to drowning emergencies in swimmers. In controlled laboratory settings, the first reactions to immersion or “cold shock” were classified as the most dangerous period and accounted for the majority of deaths from immersion in cold water.

These deaths were most often attributed to drowning, with the physiological reactions of wheezing and uncontrollable hyperventilation being triggered by the dynamic response of the cutaneous cold receptors and the small volume of water required to trigger the drowning process.

Swimming in ice-cold water can also lead to pulmonary problems. The development of pulmonary edema is the most common. A systematic review of available data showed that there is a connection between water temperature and the occurrence of a SIPE (swimming induced pulmonary edema). The presence of the clinical symptoms cough, shortness of breath, foam and hemoptysis strongly suggests a SIPE during or immediately after swimming.

The above is an abridged version edited by Eric Herman. Read the full original text here.

Authors: Beat Knechtle, Zbigniew Waśkiewicz, Caio Victor Sousa, Lee Hill, and Pantelis T. Nikolaidis, originally published in the International Journal for Environmental Research and Public Health. 2020 Dec. 17.

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