Why Dehydration Hits Harder in the Cold

Dehydration in a cold environment is a far greater risk to humans than when it occurs in a temperate environment. When you are generating sweat from work or play when the weather is warm the body’s normal mechanism is a chain reaction to the sweating. The body sweats, causing the blood volume to decrease (water leaves the blood); this triggers the hypothalamus (the brain’s thirst center), which then triggers the brain to send out a demand for an increase in fluids (water), which we normally feel as thirst sensation or a dry mouth. In cold weather our body’s react in a completely different way. People do not feel as thirsty when the weather is cold; when they don’t feel thirsty, they don’t drink as much, and this can cause dehydration. During cold exposure vasoconstriction takes place--- the body decreases blood flow to the periphery (skin surface) of the body to decrease heat loss. As a result blood flow to the body’s core increases (the blood is moving through fewer blood vessels as a result of vasoconstriction); the brain does not detect the decreased blood volume (the amount of water in the blood that has become sweat, which leaves the body). Thus a hormone AVP (argentine vasopressin) which is a fluid-regulating hormone is not secreted at the same increased rate, despite elevated blood sodium. The kidneys get a diminished signal to conserve fluid, and the thirst sensation is reduced by up to 40 percent. In November 1995 when I was lost in the Fossil Ridge Wilderness near Gunnison, Colorado during a blizzard whenever I came to a stream I gorged myself with water. I only knew I needed to consume the water to keep from dehydrating; I did not know the technical reasons until now.

The published report “Human Fluid Balance and Dehydration during Cold Weather Military Operations.” The publication date is December 1994 from the U.S. Army Research Institute of Environmental Medicine (USARAEM), Natick, MA. To quickly summarize the report; it identifies all of the basic information I had previously read in other dehydration and cold weather studies at such places as the University of New Hampshire, Mayo Clinic, and several web sites such as suite101.com. Everyone who is active during the cold weather months (when temperatures are +32 degrees F and colder) will try to dress with adequate layers of clothing so they stay warm and do not retain moisture (sweat) that they know they will be generating and which they also know will be a problem. There is no clothing system that will allow the moisture to evaporate through its layers equal to the rate it is being generated. However, as I will show later in the article you can help yourself significantly. I have spent a great deal of time in the field testing garments. When I was selling the polyester fiberfill insulation to all of the skiwear and many general outerwear manufacturers in the USA in the 1960’s and early 70’s I would take winter vacations and field test these manufacturers’ garments that were made with insulations they purchased from me. If you wanted to then or want to now stay warm you need (ed) bulk and without quilt stitching for uniform loft and expect to sweat when you are very active. However, do not expect that the sweat will leave the garment if you are wearing a first layer of clothing that is standard knit underwear made with synthetic or natural fiber. Expect that the amount of sweat generated in a cold region will be of a greater volume than if you were expending the same amount of energy when the temperature is +70 degrees or higher.

In the report done for USARAEM it states “If clothing is not carefully matched to metabolic rate, significant heat storage and sweating can occur. A person dressed in the U.S. Army Extended Cold Weather Clothing System (ECWCS) produces little sweat while resting in the cold. However, if this person performed moderate or heavy exercise in that uniform, it is estimated that nearly 2 liters per hour of sweat would be lost. Since this clothing system allows for little evaporation, the uniform might become soaked. [If the moisture does not get out then obviously it will be absorbed by the materials underneath the last layer of the system.] A wet uniform has serious implications for heat loss and subsequent cold injury susceptibility. If the cold weather clothing system is altered to reduce total insulation, sweating would be reduced five fold to about 0.4 liters per hour. Therefore, it is important that persons in cold climates dress in layers, allowing insulation to be matched to their metabolic rate. Clothing can be added when work rates decrease and removed when work rates and metabolic heat production are increased.” In my experience the best way to address the problem is to have a first layer; fishnets on to allow the sweat produced to move away from the skin surface. The last layer should be very capable of keeping one warm at a temperature 20 degrees lower than the temperature one is operating in. This would mean whatever is worn between these two layers would be limited to fewer layers. Fewer layers mean greater ease of mobility. When you start to overheat open the zipper at the neckline. The larger opening will now allow the moist warm air to easily escape. Keep in mind that your movements create a bellows action which forces the moist warm air up (heat rises) and out of the clothing you are wearing at the neckline. In this manner you are better controlling the immediate environment around your body; the environment inside your clothing. You will successfully remove the excess moisture as well which will prevent getting a chill. The fact that your skin surface is continuing to receive its normal supply of blood means that the brain’s thirst center the hypothalamus will know to trigger the proper response telling you it is time to get a drink of water. Also, if the clothing is made properly utilizing an insulating material that is proven to work at extremely low temperatures and is light in weight as well as completely un-affected by water in any of its forms you will be capable of doing your work for a longer period of time. Of course that insulation already exists and has proven itself time and time again; it is Lamilite. Wearing a Lamilite parka will mean you are wearing fewer layers which means less restriction of movement. It also means not carrying additional layers of clothing which would be cumbersome to say the least as well as take up space that would be necessary for needed supplies such as extra water. If you are wearing many layers a dehydration situation is likely to develop. Traditional knitted polyester underwear does not wick away the moisture, so it stays against the skin. Did you ever layer knitted fabrics over one another? They mesh together and bind, now do that with two or three more layers and see how easily you are able to move. Because movement will be restricted you will generate a significant amount of sweat. You will get a chill once your activity level is decreased to a resting state and your “periphery” will go into a vasoconstriction phase and all negative bodily actions will occur as has previously been noted; the end result will be dehydration. In order to have the best chance of thermoregulation of your body, it is necessary that you not fool it. | If you wear loose fitting clothing over the fishnets almost all of the sweat you generate will get away from your periphery (skin surface). It is also very important that one and all layers of the clothing you are wearing including the outer most layer be made from materials that are vapor permeable, you do not want any coated fabrics at any level of the clothing especially the last or outer most layer. Below is a picture of Rudy Rudibaugh and myself when we arrived back at base camp about 9 hours after he found me on Fossil Ridge. We are each wearing the first two Fossil Ridge parkas I made. Rudy had been out looking for me for several hours while I had been in the field for three days. Until he found me I was on foot in snow waist deep. I was walking and obviously generating sweat. As is visible since it was about -20 F all of the sweat that I generated migrated through the insulation and fabric only to condense and freeze on the exterior of my parka. When I was allowed off of my horse so I could go into the cooks tent and take off my parka I found that my skin surface was bone dry as was my cotton plaid shirt. With proper ventilation wearing a layer of cotton that does not come in contact with your skin surface is not problematic. I am living proof of that fact.

CONCLUSION: As I see it, it is irrelevant what the reason or circumstances are that causes you to be out when it is cold; soldier or hunter, you need to wear what will be of the greatest benefit to you. My personal experience and that of thousands of my customers bears out the performance of Lamilite insulation. If you want the best chance of not suffering dehydration look no further than Wiggy’s clothing.