Involuntary dehydration during exercise in cold environments is a major problem, with working in cold weather potentially leading to fluid deficits of 3 to 8 per cent of body mass, according to a research paper published in Medicine and Science in Sports and Exercise.

The paper states that in cold weather, the body’s thirst sensation is reduced by around 40 per cent and the brain does not signal the kidneys to retain water.

“It’s a trade-off – maintaining the body’s core temperature becomes more important than fluid balance,” the author’s lead, Robert Kenefick said in a media release. The research paper states that the study found similar reactions in rats and dogs.

These significant levels of dehydration are particularly concerning for those working in dangerous conditions such as working at heights or using heavy machinery and power tools because someone with 3 per cent dehydration has a delayed reaction time equivalent to a Blood Alcohol Content (BAC) of 0.08.

Cold air sucks moisture from the body:
Cold air holds less moisture than warm air, meaning that when it enters the lungs it absorbs more moisture before being exhaled and replaced with cold dry air where the process is repeated, increasing the risks of dehydration.

Furthermore, at higher altitudes we breathe more rapidly as the air holds less oxygen. For those hitting the ski slopes or working at high altitudes this and other cold weather influences combine with the physical exertion of skiing or snowboarding to exacerbate the dehydration process.

Lower temperatures suppress thirst:
Kenefick’s research paper found that cold temperatures reduce the body’s release of fluid-regulating hormones that stimulate thirst.

This occurs because during the cold, blood vessels constrict and blood moves to vital organs and the body’s core to retain heat, meaning the brain is less likely to detect the onset of dehydration and release the hormones that stimulate thirst.

The kidneys conserve less fluid:
During the onset of dehydration in warmer temperatures the brain signals the kidneys to conserve fluids, however the movement of blood to the body’s core also affects the sending of this signal, meaning cold exposure is a double-edged hydration killer.

Sweat is less noticeable:
While clothes may not become soaked with sweat in winter, the human body does not stop sweating while exercising just because it’s cold.

In fact the additional layers of clothing being worn, combined with any high vis vests and personal protective equipment (PPE) such as goggles and ear muffs all serve to increase dehydration risks.

“Our bodies also are working harder under the weight of extra clothing, and sweat evaporates quickly in cold, dry air,” Kenefick said.

Furthermore, the concentration of sodium in the sweat is around 40 per cent greater in workers exercising in winter than in summer – meaning that sodium must be replaced, either with food or with fluids containing sodium and electrolytes.

Winter Dehydration Prevention:
Kenefick encourages people to drink plenty of fluids regardless of the ambient temperature and especially when exercising or working outdoors.

“A good way to monitor proper hydration is to examine urine output – the colour should be nearly clear,” Kenefick said.

Visit THORZT’s Information Centre to access a urine colour chart and detailed guides to workplace hydration management including
hydration testing and programmed drinking information.