The risk of dehydration may increase when exercising or working in cold conditions because lower temperatures suppress thirst even when the body requires fluids.

“People just don’t feel as thirsty when the weather is cold… they don’t drink as much,” prominent research physiologist, Robert Kenefick said in a media release from the University of New Hampshire, where he conducted research on people exercising in the cold.

He found that cold temperatures reduce the body’s release of fluid-regulating hormones that stimulate thirst and conserve bodily fluids. Resultantly, even when dehydration occurs, the body’s sensation for thirst is reduced by around 40 per cent compared to warm conditions. Furthermore, the kidneys conserve less fluid – leading to increased risk of dehydration.

Kenefick said that during cold exposure, blood vessels constrict, pushing blood away from the skin and to the body’s core to decrease heat loss. This means the brain is less likely to detect the onset of dehydration and therefore less likely to release the hormones that stimulate thirst and fluid conservation.

“It’s a trade off – maintaining the body’s core temperature becomes more important than fluid balance,” Kenefick said.

“Humans don’t naturally hydrate themselves properly, and they can become very dehydrated in cold weather because there is little physiological stimulus to drink.”

Mild dehydration is classified as a loss of 1% – 4% of body mass in fluids which results in reduced performance and impaired cognitive ability causing serious safety issues for those on a worksite. Even when sedentary, the average male loses at least this amount of fluid each day through urination, breathing and the skin.

Add a physically demanding task and fluid losses can reach two or three litres an hour. Research has found sweating still occurs at significant levels in cold conditions – it simply evaporates more quickly and is therefore less noticeable. What’s more, the concentration of salt in sweat has been found to be around 40 per cent greater in workers exercising in winter than in summer – increasing the need for replacement fluids to contain sodium and electrolytes.

Adding fuel to the winter dehydration risks is research discussing how cold air – which holds less moisture than warm air – enters the body, is warmed and “saturated with moisture” before being exhaled and replaced by more cold dry air.

This combination of factors can quickly lead to potentially dangerous levels of dehydration in cold conditions. Kenefick encourages people to drink plenty of fluids regardless of the ambient temperature and especially when exercising or working outdoors.

Given thirst is such a poor indicator of hydration – especially in the cold – more advanced hydration management can be employed using a number of evaluation tools. Monitoring urine output – which usually should be pale or clear – and comparing with a urine colour chart is one such measure. Other hydration management solutions include testing the urine for specific gravity or cross referencing body mass change over a shift or workout.

To learn more about dehydration and how to manage it, contact Thorzt.