"People just don't feel as thirsty when the weather is cold,” says Robert Kenefick, associate professor of kinesiology at the University of New Hampshire. "When they don't feel thirsty, they don't drink as much, and this can cause dehydration.”
According to Kenefick, a great deal of water is lost from our bodies in the winter due to respiratory fluid loss through breathing. Our bodies also are working harder under the weight of extra clothing, and sweat evaporates quickly in cold, dry air, he says.
"Fluid balance in our bodies often relies on the stimulation of thirst, resulting in voluntary fluid intake, as well as the kidneys conserving or excreting water,” Kenefick says. "This process is mediated by fluid-regulating hormones such as plasma argentine vasopressin (AVP).”
To find out why the body reacts differently in the cold, Kenefick subjected individuals to the cold chambers at UNH, where they both exercised on a treadmill and rested. During cold exposure, he explains, vasoconstriction takes place - the body decreases blood flow to the periphery of the body to decrease heat loss.
What he also discovered was that, because blood volume at the body's core increases, the brain does not detect blood volume decrease. Thus, the hormone AVP is not secreted at the same increased rate, despite elevated blood sodium. The kidneys get a diminished signal to conserve fluid, and thirst sensation is reduced by up to 40 percent.
"It's a trade off - maintaining the body's core temperature becomes more important than fluid balance,” Kenefick says. "Humans don't naturally hydrate themselves properly, and they can become very dehydrated in cold weather because there is little physiological stimulus to drink.”
MEDICA.de; Source: University of New Hampshire