Staying Hydrated in the Winter

11/30/2015

Many years ago, I was working at a remediation site when the first cold weather that announced winter hit us. We had our tailgate meeting and, of course, because of the obvious changed weather, we discussed the importance of staying warm. Topics such as wearing appropriate clothing (wearing layers so that we could avoid sweating after work began), the susceptibility of our extremities and the difficulty to work with hand tools were discussed. And then someone brought up the importance of staying hydrated. I remember that we all just nodded, and accepted this without question. Yet I could feel that none of us really knew why hydration was important when evaporative effects were not a perceived issue. It was obvious we all wanted to an explanation as to why would there be any type of concern for dehydration in such a cold environment. 

No doubt, everyone agrees that it is important to stay hydrated during the dog days of summer. But what about during the winter months? After all, evaporative effects should be so minimal that retaining moisture within our bodies should not be a concern.  We don’t often associate performing work or even playing in the cold weather with dehydration. This is why so many of us do not prepare for this condition and thus unexpectedly, find ourselves susceptible to losing fluids very rapidly.

There are many reasons for dehydration in the winter. In cold weather, the body’s thirst response is diminished (by up to 40 percent even when dehydrated). This happens because our blood vessels constrict when we’re cold to prevent blood from flowing freely to the extremities. (If you’ve ever had cold hands in winter, you know the feeling). This enables the body to conserve heat by drawing more blood to its core.  But because of this, the body is fooled into thinking it’s properly hydrated (e.g. you don’t feel as thirsty and your body doesn’t conserve water). This is why many people, even athletes, are less likely to drink water voluntarily during the winter months. In addition, the kidneys aren’t signaled by hormones to conserve water, causing urine production to increase; a condition known as cold-induced urine diuresis.

While diminished thirst response and increased urine production are two contributing factors, there are other conditions that can lead to winter dehydration. These are:

• Wearing extra clothing. Heavy jackets, long underwear and other pieces of warm clothing help your body conserve heat. But the added weight is one factor that makes the body work between 10 and 40 percent harder. By working harder, the body produces more sweat, contributing to fluid loss.
• Increased respiratory fluid loss. In cold weather, we lose more fluids through respiratory water loss. For example, when you can see your own breath, that’s actually water vapor that your body is losing. The colder the temperature and the more intense the exercise, the more vapor you lose when you breathe.
• Sweat evaporates more quickly in cold air. We often think we aren’t sweating in cold, dry weather, because it tends to evaporate so quickly. This is another factor that can contribute to a diminished thirst response.

Your body depends on water to survive. Every cell, tissue, and organ in your body needs water to work correctly. For example, your body uses water to maintain its temperature, remove waste, and lubricate joints. Water is needed for good health.

The body is about two-thirds water, and when the total water level drops by only a few percent, we can become dehydrated. It has been reported that there are fluid deficits of 3 to 8 percent of body mass during work in cold environments and dehydration is a major problem with exercise in the cold.
     
Yet the loss of fluid from our bodies, which triggers thirst in warmer weather, does not elicit the same response when the temperatures dip. It’s not simply because we don’t feel hot.  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 (mentioned above). This process is mediated by fluid-regulating hormones such as plasma argentine vasopressin (AVP).
         
There are two factors that trigger the response of this fluid-regulating hormone. As our bodies lose water, sodium levels in the blood increase. Overall blood volume also decreases. These two responses trigger the hypothalamus to secrete AVP, which causes the kidneys to slow down their production of urine. This restores body fluid. At the same time, the hypothalamus signals the brain’s cortex to create a thirst drive to force the increased water intake needed to restore the normal salt level.
         
During cold exposure vasoconstriction takes place causing a decrease in blood flow to the periphery of the body.  And 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.
         
Thus we have a trade off! Maintaining the body’s core temperature becomes more important than fluid balance. Humans typically do not (naturally) hydrate themselves properly, and they can become very dehydrated in cold weather because there is little physiological stimulus to drink.
Symptoms of dehydration include the following:

• Little or no urine, or urine that is darker than usual
• Dry mouth
• Sleepiness or fatigue
• Extreme thirst
• Headache
• Confusion
• Dizziness or lightheaded feeling
• No tears when crying

Don’t wait until you notice symptoms of dehydration to take action. Actively prevent dehydration by drinking plenty of water.

Nobody ever understands what a pioneer is doing – Timothy Leary