One 2006 study looked at the incidence of hypothermia in 109 participants in the Rot nest Channel Swim, an annual 19.2km mass participation event off the coast of Western Australia, near Perth. Hypothermia (defi ned here as an oral or rectal temperature of 35° C or below) was identifi ed in 26 individuals, despite reasonable water temperatures in the range of 17-22°C. The key fi ndings were that for every point increase in Body Mass Index (BNI) the risk of hypothermia decreased by 43%, while every hour in the water increased the chance of hypothermia by 77 %. Because of its slow onset, hypothermia can be diffi cult to spot,
for both swimmers and observers and so extra vigilance is needed. Swimmers should also be aware that the likelihood of drowning in cold water is increased not only because muscles become fatigued when cold, but because nerve impulses slow, and co-ordinated movement falters.
Despite the dangers cold water swimming is becoming increasingly popular, so it’s worth reviewing quickly some of the growing evidence in support of its health benefi ts. The ability of cold-water swimming to bolster the human body’s immune system is one area of debate, but a fi rm link between cold-water exposure and the body’s immune defences is only just starting to be unravelled. One study looked at male athletes immersed in 14°C water for one hour at a time, and compared before and aſt er blood samples. Upon repeating the experiment three times a week for six weeks they found small but statistically signifi cant changes in the activity and composition of certain immune cells. However, the study lacks a control group, and so is inconclusive, because other sources of immune system stimulation can’t be ruled out. Other evidence of the health benefi ts of cold-water swimming is out there. Among the claimed benefi ts of winter swimming are:
○ Increased immune cell numbers, a claim reinforced by one study that showed a 40% reduction in respiratory tract infections in a group of winter swimmers, compared to non-participant control group
○ The improved ability of the body to negate cancer-causing oxidants. A study of 36 winter swimmers found that, relative to controls, the body’s defences against oxidants were elevated.
The temptation to swim in cold water will always be there – whether for thrills, bragging rights or in search of health benefi ts – but so will the dangers. If you do go looking for cold water chills, we recommend you get a health check fi rst, swim in good company and keep it short, sweet and close to the shore. ○
British Royal Marines take part in cold-water shock
training during Cold Response, an annual cold-climate training exercise run by the Norwegian Armed Forces
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Photo © Royal Navy. Crown Copyright
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