Fluid Replacement and Heat Stress, 1993

Pp. 195-214. Washington, D.C.

National Academy Press

15

Environmental Issues That Influence Intake of Replacement Beverages

John E. Greenleaf1

INTRODUCTION

Water is the major constituent by weight and volume in the human body. The volume of water in normal healthy people is regulated to within ±0.22% (±165 g) of the body weight each day (Adolph, 1943), and plasma volume varies by less than ±0.6% (±27 ml) of the blood volume (Greenleaf et al., 1979). Such precise regulation underscores the degree of integrated coordination for maintenance of the volumes of cellular water (33 liters, 41% of body weight) and extracellular water (20 liters, 25% of body weight) in an 80-kg man as well as the importance of water for life. Muscle cells contain more water than fat cells, and men have a greater percentage of their weight as muscle than women; thus, men have a greater percentage of intracellular water than women. The rate of increase of total body water volume in infants and children is essentially the same until puberty, when female total body water levels off at about 28 liters and male total body water volume increases to about 44 liters (Figure 15-1, upper half). There is a gradual decline in the percentage of body water content to body weight

1  

John E. Greenleaf, Laboratory for Human Environmental Physiology, Life Science Division (239-7), NASA, Ames Research Center, Moffett Field, CA 94035-4000



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FLUID REPLACEMENT AND HEAT STRESS Fluid Replacement and Heat Stress, 1993 Pp. 195-214. Washington, D.C. National Academy Press 15 Environmental Issues That Influence Intake of Replacement Beverages John E. Greenleaf1 INTRODUCTION Water is the major constituent by weight and volume in the human body. The volume of water in normal healthy people is regulated to within ±0.22% (±165 g) of the body weight each day (Adolph, 1943), and plasma volume varies by less than ±0.6% (±27 ml) of the blood volume (Greenleaf et al., 1979). Such precise regulation underscores the degree of integrated coordination for maintenance of the volumes of cellular water (33 liters, 41% of body weight) and extracellular water (20 liters, 25% of body weight) in an 80-kg man as well as the importance of water for life. Muscle cells contain more water than fat cells, and men have a greater percentage of their weight as muscle than women; thus, men have a greater percentage of intracellular water than women. The rate of increase of total body water volume in infants and children is essentially the same until puberty, when female total body water levels off at about 28 liters and male total body water volume increases to about 44 liters (Figure 15-1, upper half). There is a gradual decline in the percentage of body water content to body weight 1   John E. Greenleaf, Laboratory for Human Environmental Physiology, Life Science Division (239-7), NASA, Ames Research Center, Moffett Field, CA 94035-4000

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FLUID REPLACEMENT AND HEAT STRESS FIGURE 15-1 Total body water in relation to age. Source: Edelman et al. (1952), by permission of SURGERY, GYNECOLOGY & OBSTETRICS.

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FLUID REPLACEMENT AND HEAT STRESS in both males and females with increasing age (Figure 15-1, lower half) (Edelman et al., 1952; Galagan et al., 1957). Water content is the volume of liquid in the body at any given time; it is a more or less static quantity. Water balance is the difference between water intake and water outgo, which is a dynamic process. The major avenue of water intake is oral from food and liquid that are consumed. A typical water balance in a resting man would be as follows: Input equals 1,000 ml of beverage, plus 1,400 ml of food water, plus 250 ml of water of oxidation for a total of 2,650 ml; output equals 1,500 ml of urine water, plus 50 ml of fecal water, plus 1,000 ml of insensible water, plus 0 ml of sweat water for a total of 2,550 ml. The water balance then equals 2,650 ml minus 2,550 ml = + 100 ml. Water loss by sweating is increased by exposure, singly and in combination, to hot and dry environments and by increasing levels of metabolism (exercise). The osmotic and oncotic pressures of the cellular and extracellular fluids are important for the control of fluid movement within the body. The effective osmotic content is composed of the electrolytes sodium, chloride, and bicarbonate in the extracellular fluids and potassium, phosphate, and some protein in the cellular fluids (Greenleaf and Harrison, 1986). Thus, body water volume and distribution are controlled, in part, by fluid compartment osmotic concentrations. Also, body water volume, distribution, and osmotic concentration are primary mechanisms for stimulating thirst and drinking. PHYSIOLOGICAL FACTORS AFFECTING FLUID INTAKE AND SATIATION There are three major circumstances that stimulate drinking: (1) a deficit of body water (hypohydration), (2) an excess of osmoles (electrolytes) in the cellular and extracellular fluid (ECF) compartments, (hyperosmolality), and (3) consumption of dry food (prandial) (Adolph, 1967). Hypohydration In general, the greater the water deficit, the greater the amount of fluid an individual takes in when fluid levels are between normal euhydration and about 6% body weight (water) loss. The level of body hydration is changing continuously because water is being lost continuously (urine and insensible) while it is being gained intermittently in food and drink. Drinking may be stimulated not only from an increase in the osmotic concentration of body

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FLUID REPLACEMENT AND HEAT STRESS fluids but also from reduced body fluid volume. In stressful laboratory situations, total voluntary water intake is related directly to the severity of the total stress (Figure 15-2). When the stress factors (heat, exercise, and dehydration) were separated statistically, it was concluded that voluntary drinking in a hot (49°C) environment was 146% greater than that in a cool (24°C) environment; when a person was previously hypohydrated, drinking was 109% greater than that when the person was fully hydrated; and drinking during exercise was only 41% greater than that when at rest (Greenleaf and Sargent, 1965). Thus, heat exposure resulted in the greatest drinking, while exercise stimulated the least drinking. In a normally active subject, drinking begins when body weight (water) is reduced by about 0.8% (600 g). In previously hydrated subjects in stressful environments, there was a threshold for sweating of about 75 g/h, below which fluid loss was replaced promptly by drinking; in a hot environment, the sweating threshold for drinking was about 275 g/h (Greenleaf and Sargent, 1965). Thus, the more stressful the total environment, the greater the water deficit before drinking begins. This delay in drinking during dehydration has been called voluntary FIGURE 15-2 Average voluntary water consumption for the control periods (days 1-4) and the eight experimental (4 h) and recovery (3 h) periods. Combinations of conditions of heat (H), exercise (E), and dehydration (D) and of cool (C), resting (R), and hydration (Hy). Source: Greenleaf (1966), with permission.

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FLUID REPLACEMENT AND HEAT STRESS dehydration (Adolph and Associates, 1947; Greenleaf and Sargent, 1965), but a more appropriate term would be involuntary dehydration or involuntary hypohydration, because the delay in drinking is not cognitive; the stimulus is just insufficient (Greenleaf, 1966). FIGURE 15-3 Mean (± standard error) water intake, sweat rate, and involuntary dehydration (fluid deficit) during the daily 2-h exercise (75 W) acclimation exposure in the control (ambient temperature, 28.8°C) and hot (ambient temperature, 39.8°C) environments. Dashed and solid lines are mean levels for the eight control and acclimation datum points, respectively. *Significantly different (P < 0.05) from control data; Significantly different (P < 0.05) from the day-1 data point. Source: Greenleaf et al. (1983), with permission.

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FLUID REPLACEMENT AND HEAT STRESS If environmentally induced body strain is reduced by exposure to intermittent bouts of exercise (acclimation) in a hot environment (Figure 15-3), the increase in the rate of voluntary water intake during the 2-h stress periods exceeds the rate of increase of water loss (sweating), so the level of involuntary dehydration (fluid deficit) is reduced significantly (Greenleaf et al., 1983). The maximal reduction in involuntary dehydration occurs after 4 days (8 h) of acclimation. Accompanying this reduction is a significant decrease in time to the first drink, a significant increase in the number of drinks, and a significantly greater average volume per drink that is unchanged during the eight acclimation exposures (Figure 15-4). The latter was probably due to the greater thirst-stimulating effect of heat exposure compared with that of exercise. Osmotic Factors Ingestion of hyperosmotic solutions (those greater than 290 mosmol/kg) of salt (NaCl) induces drinking in volumes directly proportional to the salt concentration. If the salt solutions are given through a stomach tube so that the swallowing mechanism is bypassed, a smaller volume of fluid is consumed more slowly, and the volume of water consumed is usually less than the volume required to dilute the hyperosmotic solutions to isosmoticity. An intake of fluid less than that required to achieve isosmoticity (involuntary dehydration) may be a compromise between full restitution of isosmoticity and full restoration of extracellular (plasma) volume. That is, if the extra water required to reduce the hyperosmotic solution to isosmoticity was consumed, a hypoosmotic hypervolemia would result, which may be more difficult to correct than would a slight hyperosmotic hypovolemia, which the body seems to prefer. The former would require increased sweating and urinary fluid losses with their accompanying electrolyte losses (osmoles), while the latter requires only consumption of pure water. The fewest number of osmoles (NaCl) that is necessary to induce drinking in satiated humans is that which increases the extracellular fluid volume by about 1.2% (Wolf, 1950). In an 80-kg man, the ECF volume averages 20 liters; thus, 1.2% of 20,000 ml equals 240 ml. A satiated ECF osmolality of 285 mosmol/kg would require ingestion and assimilation of 0.285 x 240 ml = 68.4 mosmol to induce drinking. This is equivalent to (6.245 g of NaCl/liter x 68.4 mosmol)/285 mosmol/kg = 1.5 g of NaCl. Consumption of fluids containing osmotic substances that do not penetrate cells easily (e.g., NaCl and KCl) provoke greater drinking than does consumption of equivalent fluids containing substances that do penetrate cells (e.g., sucrose

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FLUID REPLACEMENT AND HEAT STRESS and urea). In general, dissolved solutes increase fluid consumption if they are present in hyperosmotic concentrations and decrease drinking if they are present in hypoosmotic concentrations. Hyperosmotic concentrations require a greater volume of water to excrete the additional solute. FIGURE 15-4 Mean drinking parameters during the daily 2-h exercise (75 W) acclimation exposures in the control (ambient temperature, 23.8°C) and hot (ambient temperature, 39.8°C) environments. Dashed and solid lines are mean levels for the eight control and acclimation days, respectively. *Significantly different (P < 0.05) from control data; Significantly different (P < 0.05) from the day-1 data point. Source: Greenleaf et al. (1983), with permission.

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FLUID REPLACEMENT AND HEAT STRESS Prandial Factors The intake of food may induce drinking under three circumstances. First, when dry food is eaten, drinking is promoted to dilute the food; when moist food is eaten, a smaller drinking response is provoked. Second, removal of the salivary glands of rats induces prandial drinking related perhaps to mouth dryness in humans. The absence of salivary glands in humans induces frequent drinking of small volumes of water, but has no significant effect on average daily fluid intake or normal water and salt metabolism (Steggerda, 1941). Third, damage to the lateral thalamic area of the brain in rats can stop all drinking except that which accompanies the eating of dry food. Prandial drinking appears to respond to the call for lubrication of the mouth and throat, and it may disturb rather than preserve the body water balance. Satiation Water that is swallowed satiates with a smaller volume than does water placed in the stomach through a tube; drinking is dramatically reduced following artificial placement of water in the stomach. If the volume of water placed in the stomach equals half the water deficit, the intake is reduced by half in most species. Inflation of a balloon in the stomach has the same immediate effect on fluid consumption as does the artificial placement of water. The act of swallowing produces some satiation for a limited period, as does stomach distension, and both together act to terminate drinking. However, only the distribution of water into and through the circulation of blood produces satiation. Water intake involves participation of the nervous system. An increase in the temperature of the hypothalamus stimulates drinking, while a decrease in the temperature inhibits drinking (Andersson et al., 1964). Cholinergic stimulation (which tends to calm the body) facilitates drinking, while adrenergic stimulation (which tends to excite the body and call it into action) inhibits drinking (Grossman, 1967). In short, people drink more when they are calm than when they are excited. Taste and smell are obviously important for the replenishment of water deficit. Sweet substances are almost universally preferred by both vertebrates and invertebrates; when food is abundant and the choice is wide, man eats primarily for palatability and secondarily for nutritional benefit (Epstein, 1967). The control of drinking shares equally with the control of water output via sweating and the kidneys for maintenance of water balance and body weight. The kidneys can correct only for an excess of fluid in the body. If the body is hypohydrated, the kidneys will concentrate the urine to about 1,400

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FLUID REPLACEMENT AND HEAT STRESS mosmol/kg of H2O and continue to do so until they fail or until water is ingested. Thus, drinking is the only practical way of alleviating hypohydration. Water intake is primarily a response to a deficiency of water inside the body and not directly to stimuli from outside the body. However, external factors can influence the internal physiological state, which in turn can modify drinking. FACTORS AFFECTING MINIMAL, MAXIMAL, AND AVERAGE BEVERAGE AND TOTAL FLUID INTAKES Minimal Fluid Intakes The lowest volume of fluid required to prevent physical deterioration is that which will provide 300 ml of urine/day. Under low-stress conditions (sedentary work in a cool environment), this volume (beverage plus food) is about 1,000 ml/day (Johnson, 1964b). The longest documented period any person has survived without any water is 18 days (Wolf, 1958). Maximal Fluid Intakes In persons with diabetes insipidus (damage to the brain that results in the inability of the kidneys to retain water), water intakes of 35 to 41 liters/day have been reported (Richter, 1938). Habener et al. (1964) have studied the responses of normal men to prolonged high fluid intakes. Four men measured their daily fluid intakes without dietary restrictions for a 2-week control period, and the intakes ranged from 1,310 to 2,550 ml/day. Then, the daily water consumption for each subject was increased by 2 liters/week until 8 liters was added; the maximum intake was 7.43 to 9.57 liters/day. Body weight remained constant at these high intake levels. The important conclusion is that these levels of water consumption did not change the serum osmotic concentration, which suggests that they were not harmful. The only untoward symptoms were mild nausea, diarrhea, lassitude, and light-headedness; these symptoms passed after cessation of drinking for a few hours. The men mentioned a slight increase in thirst upon arising in the morning.

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FLUID REPLACEMENT AND HEAT STRESS Factors Affecting Average Beverage and Total Fluid Intakes Some of the factors affecting beverage and total fluid intake in man are presented in Table 15-1. Most of the environmental and some of the nutritional-chemical factors have been discussed previously. Table 15-1 Factors Affecting Average Beverage and Total Fluid Intake Nutritional-Chemical Socioeconomic-Psychological Environmental Protein content Carbohydrate Fat content Osmotic concentration Electrolyte concentrations Drugs Acidity (pH) Carbonic acid concentration Temperature Color of drink Cost of drink Taste Smell Color Sound (fizz, etc.) Appearance (packaging) Religious preference Customs and mores Masculine/feminine ratioa Viscosity Temperature Pressure Humidity Wind speed Gravitation a Some drinks may appeal more to men, others to women. ENVIRONMENTAL AND OTHER EXTERNAL FACTORS AFFECTING FLUID INTAKE It was stated above that fluid intake is related to the level of water deficiency in the body. It should be reiterated that water lost insensibly (from the respiratory tract and skin) is pure water and contains no osmoles (salt). Sweat and urinary fluids contain salts and contribute to both water and salt loss. Various environmental factors such as temperature, humidity, radiation, and atmospheric pressure affect mainly sweating and urinary water loss, while physical exercise affects, in addition, increased respiratory water loss from the increased expiratory volume and frequency of breathing. Temperature The relationship between environmental temperature and fluid intake is presented in Figure 15-5 (lower curve). Water intake increases at an ambient temperature of about 27°C, the temperature at which sweating begins. Thus,

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FLUID REPLACEMENT AND HEAT STRESS the increased water intake when temperatures are above 27°C tends to compensate for sweat loss. There is also a cold diuresis (increased urinary output), but its effect seems to be well regulated by fluid intake because the curve is nearly level from -30°C to 16°C (Figure 15-5, lower curve). The upper half of Figure 15-5 shows the water intake requirements of young men in the heat (between 35°C and 50°C) at four levels of energy expenditure: resting (2,000 kcal/day), light work (2,800 kcal/day), moderate work (3,500 FIGURE 15-5 Beverage requirements of men in relation to environmental temperature and work intensity. Sources: Top panel, Nelson et al. (1943); bottom panel, Nelson et al. (1943) and Welch et al. (1958), with permission.

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FLUID REPLACEMENT AND HEAT STRESS kcal/day), and heavy work (4,500 kcal/day). The range of daily drinking water requirements is 2 liters at rest at 35°C to 15 liters during heavy work at 50°C. Greenleaf et al. (1966) have performed a statistical analysis of the relationships among 22 selected metabolic variables for their value in predicting voluntary water consumption in 87 young male military recruits in basic training living in a hot, moist environment. The equation for estimating water consumption is as follows: Predicted water intake (ml/day) = -11,502.40 + 1.15 [mean daily urinary volume, (ml/day)] + 45.81 [serum osmolality (mosmol/kg of H2O)] - 18.72 [resting pulse rate (beats/min)] + 4.39 [mean daily urinary Cl (meq/day)] - 18.86 [mean daily urinary K (meq/day)] + 1.77 [rate of sweating (ml/hr)] The predicted water intake had a multiple correlation coefficient of 0.79 with the measured water intake. The subjects were allowed unrestricted consumption of water; other beverages such as cocoa, tea, and coffee were allowed only at meal times, and their volumes were added to the water intake. The average liquid intake over the 6-day period was 3,256 ± 900 ml/day, and the range was 1,950 to 5,850 ml/day. Humidity The effects of humidity on water intake have not been studied intensively, but lower humidities would allow greater evaporation of sweat under high temperatures and a greater insensible water loss at lower temperatures. Presumably, the faster the water is lost, the greater the drinking, except for the problem of involuntary dehydration when, under stressful conditions, water intake lags far behind water loss. In some circumstances it takes 2 days to recover the lost fluid (Greenleaf et al., 1967). Barometric Pressure Gee at al. (1968) measured fluid consumption in 12 men exposed for 16 days to a simulated space cabin pressure of 258 Torr (8,230 m). Water intake varied from 1.2 to 5.6 liters/man/day despite the relatively equal food

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FLUID REPLACEMENT AND HEAT STRESS intakes and activity levels. Daily urinary outputs ranged from 0.5 to 4.4 liters/man/day, insensible water loss increased by 50%, from 0.8 to 1.2 kg/man/day, and total body water decreased from 44.4 to 41.6 liters. In general, people going to increased altitudes incur negative water balances (Consolazio et al., 1968). Studies of mountain climbers are contaminated with the concomitant fluid perturbations caused by cold exposure, by physical exercise, and usually by inadequate food intake. The negative fluid balance of mountain climbers is often very great, and large body weight and fluid losses (to 9.6 kg) have been reported (Nevison et al., 1962). Most investigators have reported hypovolemia of 6% - 21% during 2-3-week exposures to 2,000-4,500 m altitudes (Alexander et al., 1967; Dill et al., 1974; Krzywicki et al., 1971; Surks et al., 1966), with a 29% decrease observed after 18 weeks at 5,790 m altitude (Pugh, 1962). On the other hand, Krzywicki et al. (1971) found in well-fed men a small increase in extracellular fluid volume of 1.3 liters after they spent 6 days at 4,300 m. Also, Greenleaf et al. (1978) observed no significant change in plasma volume or fluid balance during 8 days at 2,287 m in well-fed and well-hydrated men. Thus, hypovolemia and hypohydration observed at high altitudes appear to be related to involuntary dehydration and to food deficits (anorexia). Consumption of Food Intakes of food and water are closely related (Johnson, 1964a); food intake is reduced during water deprivation, and water intake is reduced during starvation (Andersson and Larsson, 1961). Subjects undergoing acute starvation for 10 days with water, tea, and coffee given ad libitum exhibit an immediate increased loss of water by the kidneys followed by a lessening of the diuresis (Consolazio et al., 1967). The fluid intake declined progressively as starvation continued, and water balance was achieved on day 9 when the fluid intake and output were the same. Fluid intake increased greatly when food was eaten during the recovery period. Thus, food has a water-retaining effect. FACTORS AFFECTING REHYDRATION BEVERAGE COMPOSITION AND SELECTION Beverage Composition Starkenstein (1927) conducted the first comprehensive laboratory study of the thirst-quenching properties of various concentrations of carbonic acid

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FLUID REPLACEMENT AND HEAT STRESS and salt solutions. Some of the more important observations and conclusions are as follows: Water Intake Under Normal Conditions The temporary thirst-quenching properties of such drugs as cocaine and opium are the result of elimination of the unpleasant sensation of being thirsty. The cholinergic class of drugs (pilocarpine, etc.) exert their thirst-quenching effects by causing an increased secretion from organs and glands that move water to dehydrated regions of the body. Thirst is not always quenched by drinking pure water, but depends upon the composition of the water (osmotic concentration) and the ability of the body to hold water. Retention of ingested fluids depends on the osmotic concentration of the drink and the osmotic concentration of the blood. If sugar is given with water, the osmotic effect of the sugar is lost when the sugar is metabolized. Urinary excretion is influenced by the acidity (pH) of the drink. The lower the pH (greater acidity), the greater the amount of urine excreted. The addition of carbonic acid to water lowers the pH. Therefore, fluids with high concentrations of carbonic acid are less suitable for quenching thirst than are those with a lower carbonic acid content. The ability to retain ingested water does not depend solely on the water's salt concentration (osmotic concentration) and its relation to the osmotic content of the blood, but on the combined result of its salt and carbonic acid concentration. When the carbonic acid concentration decreases (pH increases), urinary excretion decreases. However, this pH effect is operative only with hypotonic solutions (those more dilute than blood plasma). Retention of isotonic solutions cannot be counteracted by increasing the acidity. Under normal temperatures, diuretics (caffeine) merely rechannel the otherwise extrarenally excreted water into the kidneys. Caffeine can stimulate thirst, especially when a person is sweating. Water intake following resting-thermal dehydration Distilled water cannot quench thirst when the loss of water by sweating is high. Tap water has no effect on sweat excretion at low sweat rates but greatly increases sweat excretion that is already at a higher than normal rate. The increase in water content that is usually produced by the intake of a NaCl solution can be nullified by profuse sweating.

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FLUID REPLACEMENT AND HEAT STRESS Renal activity is inhibited neither by profuse sweating at room temperature nor with intake of a saline solution. When one drinks pure water, renal secretion is markedly reduced because of sweating. Drinking of saline solution inhibits sweat excretion in people in a steam bath, while drinking of saline solution increases renal excretion in hot as well as at normal temperatures. In conclusion The best fluid for quenching thirst is 0.7% to 0.9% saline (isotonic solution), for the body retains it to a higher degree than it does any other fluid. In addition, the ingested salt is able to inhibit excessive sweating and thus prevent additional water loss and further development of thirst. Optimal drinks for workers in hot environments are slightly hypotonic solutions. To be suitable for the quenching of thirst, a fluid must not only have the proper ingredients but it should also taste good. The taste of drinking water is determined not only by its temperature and its hardness (mineral content) but also by its acidity (carbonic acid content). Acidified isotonic salt solutions can be used effectively as tasty liquids for the quenching of thirst. The so-called soda waters (artificial seltzer waters) are not suitable for the quenching of thirst for they are rich in carbonic acid, which stimulates diuresis and sweating. Beverage Selection The only reasonably complete study of voluntary beverage selection (Sohar et al., 1962) was conducted on 19 fit young men (18-21 years old) who marched 370 miles from Eilat in the south of Israel to Metulla in the north of Israel in 24 days; this included 3 days of rest. They marched 17 miles/day, and each person carried a load of 16 kg. The various drinks investigated were warm tap water (20°-30°C), cold tap water (10°-16°C), cold sweetened lemon tea, water with sweetened citrus syrup, pasteurized bottled milk, soda water, a bottled citrus drink, carbonated lemonade, Malton (a cola), and beer. All drinks except tap water were kept between 10°C and 16°C. One 650-ml bottle of beer or citrus juice was given to each man at lunch, regardless of any other drinking. Tea and coffee were provided ad libitum at dinner. The drink preferences were taken 11 times during the 24-day march and were divided into four groups: the most preferred drinks to the least preferred drinks.

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FLUID REPLACEMENT AND HEAT STRESS Table 15-2 Beverage Preferences during Marching in the Heat   Men who Preferred the Beverages (n) Beverage Most Least Citrus juice 3 0 Citrus syrup 3 0 Cold lemon tea 2 1 Cold water 2 1 Soda water 1 1 Malton (cola) 0 0 Milk 0 0 Beer 0 1 Carbonated lemonade 0 3 Warm water 0 4 The results in Table 15-2 indicate that the most preferred drinks were cold and sweetened and tasted of citrus. That carbonated lemonade was one of the least preferred drinks suggests that the carbonation--and not the citrus taste--was the offensive agent. General observations on the drinking behavior of the men are as follows: When forced to drink carbonated beverages, the men would shake their bottles to release the gas. They maintained that the gas content made it difficult to drink the beverage in large quantities. Milk was tried only once, and it produced diarrhea in four of five men and so was discontinued. Beer was tried only once because it produced intoxication very easily in the hot environment. During 2 days when the choice of all drinks was free, citrus juice was the leader, making up one-third to one-half of the total beverage consumption. On both days, warm water was preferred to all the varieties of carbonated drinks offered. At the end of the total experiment, each man was questioned as to his beverage preference when it was necessary to drink large amounts during a short period of rest. Of 19 men, 17 preferred citrus juice or water with citrus syrup, while only 2 preferred a carbonated drink. The carbonated drink gave the men a feeling of fullness in the stomach and prevented the ingestion of large quantities. Cold water (10°-16°C) was preferred to warm water (20°-30°C) six out of seven times.

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FLUID REPLACEMENT AND HEAT STRESS Table 15-3 Beverage Chemical Composition Beverage Osmol/kga pHb Olympade (Coca Cola, can) 842 2.4 Beer (Olympia) 830 4.2 Sport cola (Canada Dry) 808 2.1 Fanta grape (Coca Cola) 800 2.7 Fanta orange (Coca Cola) 790 2.6 Bitter lemon (Schweppes) 788 2.6 Hi-C orange (Coca cola) 754 2.6 Hi-C grape (Coca Cola) 727 2.6 Hi-C citrus cooler (Coca Cola) 725 2.3 Cola (Pepsi Cola) 706 2.5 Orange juice (frozen) (Minute Maid)c 674 3.7 Mountain Dew (Pepsi Cola) 645 3.3 Sport Cola (Canada Dry) 644 2.4 Frozen orange juice (Whole Sun)c 590 4.0 Cola (Coca Cola) 586 2.5 Cola (Shasta) 585 2.5 Cola (Royal Crown) 569 2.6 Sprite (Coca Cola) 566 2.9 Rootbeer (Mug) 532 3.9 Dr. Pepper 510 3.1 Seven-up 484 3.2 Ginger ale (Canada Dry) 477 2.7 Ginger ale (Vernors) 456 3.5 Olympade (bag) (Coca Cola)c 394 2.9 Lemonade (frozen) (inute Maid)c 389 2.4 Tang (General Foods)c 366 3.0 Gatorade (lime) (Stokley) 336 2.8 Olympade (Coca Cola) 335 2.2 Gatorade (orange) (Stokley) 320 2.8 Normal human serum or plasma 290 7.3 Fresca (Coca Cola) 99 2.3 Tab (Coca Cola) 84 2.4 Wink (Canada Dry) 72 2.8 Coffee (perked for 6 min) (Maxwell House)c 72 4.9 Fresca (Coca Cola) 58 2.6 Diet cola (Pepsi Cola) 41 2.6 Diet cola (Royal Crown) 38 2.7 Club soda (fresh) (Canada Dry) 36 5.4 Coffee (instant) (Folgers)c 35 4.9 Club soda (flat) (Canada Dry) 27 8.5 Coffee (freeze dried) (Taster's Choice)c 26 5.0 Tea (bag) (Lipton)c 8 5.5 Tea (loose) (Lipton)c 7 5.6

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FLUID REPLACEMENT AND HEAT STRESS c 5.5 Club soda (flat) (Canada Dry) 27 8.5 Coffee (freeze dried) (Taster's Choice)c 26 5.0 Tea (bag) (Lipton)c 8 5.5 Tea (loose) (Lipton)c 7 5.6 Tea (instant) (Lipton)c 6 6.7 Demineralized water (Ames) 6 Tap water (Ames) 5 8.3 a Advanced instrumentation osmometer b Research pH meter (Beckman Instruments) c Prepared following the manufacturer's directions (1 cup = 8 oz.) consumption at a time of physical effort. Milk, beer, or the various carbonated drinks may be preferred when small quantities are ingested during leisure periods, but they were not consumed in large quantities as well as the nonalcoholic, noncarbonated sweetened, cold, citrus fruit beverages were. The osmotic and hydrogen ion concentrations of some current beverages are presented in Table 15-3. They are listed in descending order of osmotic concentration. In general, beer and the colas had the highest osmolality, while club soda and the diet drinks with artificial sweeteners had lower osmolalities. With the exception of club soda, all the manufactured beverages had hydrogen ion concentrations below 4.3. The beverages became more alkaline (the pH increased) as the carbonation escaped (see club soda). REFERENCES Adolph, E.F. 1943 Physiological Regulations. Jacques Cattell Press, Lancaster, Penn. 502 pp. Adolph, E.F. 1967 Regulation of water intake in relation to body water content. Pp. 163-171 in W. Heidel, ed. Handbook of Physiology, Section 6. Alimentary Canal, Vol. I. Control of Food and Water Intake. American Physiological Society, Washington, D.C. Adolph, E.F., and Associates. 1947 Physiology of Man in the Desert. Interscience, New York. 357 pp. Alexander, J.K., L.H. Hartley, M. Modelski, and R.F. Grover. 1967 Reduction of stroke volume during exercise in man following ascent to 3,100 m altitude. J. Appl. Physiol. 23:849-858. Andersson, B., and S. Larsson. 1961 Physiological and pharmacological aspects of the control of hunger and thirst. Pharmacol. Rev. 13:1-16. Andersson, B., C.C. Gale, and J.W. Sundsten. 1964 Preoptic influences on water intake. Pp. 361-379 in Thirst, M.J. Wayner, ed. Proceedings of the First International Symposium on Thirst in the Regulation of Body Water Held at the Florida State University in Tallahassee, May 1963. Macmillan Company, New York.

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FLUID REPLACEMENT AND HEAT STRESS Consolazio, C.F., L.O. Matoush, H.L. Johnson, R.A. Nelson, and H.J. Krzywicki. 1967 Metabolic aspects of acute starvation in normal humans (10 days). Am. J. Clin. Nutr. 20:672-683. Consolazio, C.F., L.O. Matoush, H.L. Johnson, and T.A. Daws. 1968 Protein and water balances of young adults during prolonged exposure to high altitude (4,300 meters). Am. J. Clin. Nutr. 21:154-161. Dill, D.B., K. Braithwaite, W.C. Adams, and E.M. Bernauer. 1974 Blood volume of middle-distance runners: effect of 2,300-m altitude and comparison with non-athletes. Med. Sci. Sports 6:1-7. Edelman, I.S., H.B. Haley, P.R. Schloerb, D.B. Sheldon, B.J. Friis-Hansen, G. Stolland F.D. Moore. 1952 Further observations on total body water. I. Normal values throughout the life span. Surg. Gynecol. Obstet. 95:1-12. Epstein, A.N. 1967 Oropharyngeal factors in feeding and drinking. Pp. 197-218 in W. Heidel, ed. Handbook of Physiology, Section 6. Alimentary Canal, Vol. I. Control of Food and Water Intake. American Physiological Society, Washington, D.C. Galagan, D.J., J.R. Vermillion, G.A. Nevitt, Z.M. Stadt, and R.E. Dart. 1957 Climate and fluid intake. Public Health Rep. 72:484-490. Gee, G.F., R.S. Kronenberg, and R.E. Chapin. 1968 Insensible weight and water loss during simulated space flight. Aerosp. Med. 39:984-988. Greenleaf, J.E. 1966Some observations on the effects of heat, exercise and hypohydration upon involuntary hypohydration in man. Int. J. Biometeorol. 10:71-76. Greenleaf, J.E., and M.H. Harrison. 1986 Water and electrolytes. Pp. 107-124 in Nutrition and Aerobic Exercise, D.K. Layman, ed. ACS Symposium Series 294. American Chemical Society, Washington, D.C. Greenleaf, J.E., and F. Sargent II. 1965Voluntary dehydration in man. J. Appl. Physiol. 20:719-724. Greenleaf, J.E., E.G. Averkin, and F. Sargent II. 1966 Water consumption by man in a warm environment: a statistical analysis J. Appl. Physiol. 21:93-98. Greenleaf, J.E., L.G. Douglas, J.S. Bosco, M. Matter Jr., and J.R. Blackaby. 1967 Thirst and artificial heat acclimatization in man. Int. J. Biometeorol. 11:311-322. Greenleaf, J.E., E.M. Bernauer, W.C. Adams, and L. Juhos. 1978 Fluid-electrolyte shifts and VO2max in man at simulated altitude (2,287 m). J. Appl. Physiol. 44:652-658. Greenleaf, J.E., V.A. Convertino, and G.R. Mangseth. 1979 Plasma volume during stress in man: osmolality and red cell volume J. Appl. Physiol. 47:1031-1038. Greenleaf, J.E., P.J. Brock, L.C. Keil, and J.T. Morse. 1983 Drinking and water balance during exercise and heat acclimation. J. Appl. Physiol. 54:414-419. Grossman, S.P. 1967 Neuropharmacology of central mechanisms contributing to control of food and water intake. Pp. 287-302 in W. Heidel, ed. Handbook of Physiology, Section 6. Alimentary Canal, Vol. I. Control of Food and Water Intake. American Physiological Society, Washington, D.C.

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FLUID REPLACEMENT AND HEAT STRESS Habener, J.F., A.M. Dashe, and D.H. Solomon. 1964 Response of normal subjects to prolonged high fluid intake. J. Appl. Physiol. 19:134-136. Johnson, R.E. 1964a Human nutritional requirements for water in long space flights. Pp. 159-169 in Conference on Nutrition in Space and Related Waste Problems. Publ. No. NASA SP-70. National Aeronautics and Space Administration, Washington, D.C. Johnson, R.E. 1964b Water and osmotic economy on survival rations. J. Am. Diet. Assoc. 45:124-129. Krzywicki, H.J., C.F. Consolazio, H.L. Johnson, W.C. Nielsen Jr., and R.A. Barnhart. 1971 Water metabolism in humans during acute high-altitude exposure (4,300 m). J. Appl. Physiol. 30:806-809. Nelson, N., L.W. Eichna, and W.B. Bean. 1943 High Temperatures in Tanks. Determination of Water and Salt Requirements for Desert Operations. Project No. 2-6, May 20. Armored Force Medical Research Laboratory, Fort Knox, Ky. Nevison, T.O., Jr., J.E. Roberts, W.W. Lackey, R.G. Scherman, and K.H. Averill. 1962 1960-61 Himalayan Scientific and Mountaineering Expedition. I. USAF High Altitude Physiological Studies. Paper Presented at the 33rd Annual Aerospace Medical Association Meeting, Atlantic City, N.J., April 10. Pugh, L.G.C.E. 1962 Physiological and medical aspects of the Himalayan scientific and mountaineering expedition, 1960-61. Br. Med. J. 2:621-627. Richter, C.P. 1938 Factors determining voluntary ingestion of water in normals and in individuals with maximum diabetes insipidus. Am. J. Physiol. 122:668-675. Sohar, E., J. Kaly, and R. Adar. 1962 The prevention of voluntary dehydration. Pp. 129-135 in Symposium on Environmental Physiology and Psychology in Arid Conditions. Proceedings of the Lucknow Symposium. United Nations Educational Scientific and Cultural Organization, Paris. Starkenstein, E. 1927 Wasserhaushalt und Durststillung. Klin. Wochenschr. 6:147-152. Steggerda, F.R. 1941 Observations on the water intake in an adult man with dysfunctioning salivary glands. Am. J. Physiol. 132:517-521. Surks, M.I., K.S.K. Chinn, and L.O. Matoush. 1966 Alterations in body composition in man after acute exposure to high altitude. J. Appl. Physiol. 21:1741-1746. Welch, B.E., E.R. Buskirk, and P.F. Iampietro. 1958 Relation of climate and temperature to food and water intake in man Metabolism 7:141-148. Wolf, A.V. 1950 Osmometric analysis of thirst in man and dog. Am. J.Physiol. 161:75-86. Wolf, A.V. 1958 Thirst. Physiology of the Urge to Drink and Problems of Water Lack. Charles C. Thomas, Springfield, Ill. 536 pp.