The risk of dehydration increases in cold temperatures.

The risk of dehydration can increase when working or exercising in cold conditions, as cold temperatures reduce thirst when the body needs fluids.

"People just don't feel as thirsty when it's cold ... they don't drink as much".

These are the words of eminent physiology researcher Robert Kenefick spoken at a press conference at the University of New Hempshire when he was conducting research into the physiology of people training in cold temperatures.

He discovered that cold temperatures reduce the body's secretion of hormones that stimulate thirst and retain body fluids. As a result, even when dehydration occurs, the body's sensation of thirst is reduced by up to 40%, compared to warm conditions. In addition, the kidneys conserve less fluid thus increasing the risk of dehydration.

Kenefick said that during cold exposure, blood vessels constrict, 'pushing' blood into the body to prevent loss of body temperature. This means that the brain perceives the signs of dehydration much less strongly which leads to a reduction in the secretion of hormones responsible for increasing thirst and fluid retention in the body.
"It's a trade-off - managing the body's internal temperature, becomes more important than maintaining fluid balance," concludes Kenefick.
"People don't naturally hydrate themselves enough, which can make them dehydrated in cold conditions because the physiological stimulus to drink is less noticeable."
The average level of dehydration is classified between a loss of 1% and 4% of body weight in fluids. It can reduce performance and impair cognitive abilities, leading to serious risks in training or in the workplace.

Combine physically demanding tasks and fluid loss, which can be as much as 2 or 3 litres per hour. Studies have shown that sweating even in cold temperatures is significant - it simply evaporates faster, making it less noticeable. What's more, the concentration of salts in sweat is around 40 per cent higher during winter than in summer - thus raising the need to replenish their deficiencies, with drinks containing salts and electrolytes.

Adding fuel to the fire of winter dehydration risk, is research discussing how cold air - which has less moisture than warm air - is inhaled, warmed, saturated with moisture from the lungs before being exhaled, then replaced again with colder and drier air. This combination of factors can quickly lead to potentially high levels of dehydration even in cold temperatures.

Feeling thirsty is such a poor indicator of hydration - especially in cold conditions - it is worth considering a methodology for determining hydration levels using a range of other tools.

Monitoring urine colour, which should normally be clear or pale, and comparing it to a urine colour chart is one such method. Other methods of measuring body hydration include testing urine for its specific gravity. Measuring weight change during increased physical activity is also a good method.