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Swimming in Cold Water & the Increased Frequency of Urination

By Michelle Matte

Whether you're taking a swim class, lounging at the beach or training for a triathlon, when you submerge your body in cold water, it responds by going into survival mode to prevent hypothermia. One inconvenient symptom of cold water immersion is increased urine production according to an article in "Cool Antarctica." While skipping fluids before your swim might seem like a solution, all evidence points to the contrary.

Physical Responses to Cold

When immersed in cold water, the body loses heat quickly and is vulnerable to hypothermia. A healthy human body maintains a core temperature of about 98.2 Fahrenheit. When exposed to cold conditions, your body takes measures to preserve heat, but prolonged exposure will cause your core temperature to drop. A drop of 10 degrees Fahrenheit can predispose individuals to unconsciousness and heart arrhythmia. Symptoms of decreased core temperature include impaired neuromuscular function, goose bumps, shivering, the shunting of blood away from the skin's surface and increased urine production.


Dehydration is as significant a threat in cold environments as in hot. University of New Hampshire associate professor Robert Kennefick set out in 2005 to discover why people don't feel thirsty when exposed to a cold environment, even though they are dehydrated. Kennefick found that the shunting of blood away from the surface of the skin to preserve heat causes an abundance of fluid in the body's core, so the brain does not perceive the threat of dehydration. Increased blood volume in the core also triggers an elimination response in the kidneys, stimulating urine production in order to maintain fluid balance and exacerbating dehydration. This response can have important implications for triathletes and swimmers whose performance might be affected during competition by dehydration.


A companion to dehydration, hyponatremia, is the excessive loss of sodium in the body. Sodium is an electrolyte that regulates fluid balance, facilitates nerve and muscle function and controls blood pressure. Excess urine production brought on by exposure to cold can deplete sodium, putting athletes at risk for weakness, muscle cramps, confusion, seizures and loss of consciousness.

Restoring Balance

While increased urine production is an uncomfortable and inconvenient side effect of swimming in cold water, adequate hydration is crucial to maintain optimal performance, particularly when participating in athletic competition. However, water alone might not be enough, and might even cause further depletion of sodium. To replenish sodium and fluids, the website Peak Performance recommends beverages containing a combination of water, glucose and electrolytes.

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