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Rogers et al., 1964). These dehydration levels are similar in magnitude to those reported for persons in hot climates. Importantly, marked body water loss, if not replaced, will have a significant impact on the health and performance of soldiers.

Although the importance of hydration on work performance in hot climates has been recognized for years, considerably less is known with regard to hydration effects of cold climates. Few studies have specifically assessed the effects of cold-induced dehydration on physical work, thermoregulation, or susceptibility to cold injuries. In fact, neither of two major review articles that address fluid balance in the cold specifically discuss the military aspects, implications, or concerns (Bass and Henschel, 1956; Fregly, 1991).

Forty-five years ago, a U.S. Army physician described what he felt were the nutritional problems and concerns associated with conducting military operations in arctic climates. He concluded that ''the most important problem yet to be solved is that of man's water balance" (Orth, 1949, p. 205). One might argue that the statement is as true today as it was then.

Military Situation Regarding Fluid Balance in the Cold

Sixty percent of the earth's land mass has January temperature lows below 32°F (0°C), and over 25 percent of the earth's land mass experiences January temperature lows below 0°F (-18°C) (Bates and Bilello, 1966). Furthermore, many national borders of military significance are located in mountainous regions that are not only at considerable altitude but also extreme cold. Thus, it is critical that the understanding of the effects of cold on body fluid balance be improved if the health and performance of soldiers deployed to these harsh environments is to be optimized.

This chapter reviews three areas: (1) factors that increase fluid loss and reduce fluid intake in cold climates, (2) the military impact or significance of dehydration in the cold, and (3) possible countermeasures to minimize dehydration in the cold.

Body Fluid States

Figure 9-1 clarifies the terminology used in this chapter (Greenleaf, 1992). The terms euhydration, hypohydration, and hyperhydration refer to a total body water that is normal, below normal, and greater than normal, respectively. The terms dehydration, rehydration, and overhydration refer to processes by which total body water is either decreased relative to normal, increased toward normal, or increased above normal, respectively.

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