Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2005) / Chapter Skim
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From page 73... ...
Because normal hydration can be maintained over a wide range of water intakes, the AI for total water (from a combination of drinking water, beverages, and food) is set based on the median total water intake from U.S.
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. Daily water intake must be balanced with losses in order to maintain total body water.
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. Figures 4-2 and 4-3 provide the percentage of FIGURE 4-1 Total body water as a fraction of body mass (FW)
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76 DIETARY REFERENCE INTAKES MEN 90 Hydration of fat-free mass (%)
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Gender TABLE 4-1 Total Body Water (TBW) as a Percentage of Total Body Weight in Various Age and Gender Groups TBW as a Percentage of Lifestage Body Weight, Mean (range)
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The ECF is further divided into the interstitial and plasma spaces. An average 70-kg man has approximately 42 L of total body water, 28 L of ICF, and 14 L of ECF, with the ECF comprising approximately 3 L of plasma and 11 L of interstitial fluid.
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Therefore, water intake can be estimated from measured liquid volumes and tables of food composition. Water losses can be estimated from a variety of physiological and biophysical measurements and calculations (Adolph, 1933; Consolazio et al., 1963; Johnson, 1964)
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Physical activity generally has a greater effect on respiratory water loss than do environmental factors. Daily respiratory water loss averages about 250 to 350 mL/day for sedentary persons, but can increase to 500 to 600 mL/day for active persons living in temperate2 climates at sea level (Hoyt and Honig, 1996)
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From page 81... ...
. On typical Western diets, an average of 650 mOsmol of electrolytes and other TABLE 4-3 Influence of Breathing Cold Air and of Metabolic Rate on Respiratory Water Losses Temperature Relative Water Vapor Respiratory Humidity Pressure Metabolic Rate Water Loss °F °C (%)
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From page 82... ...
Figure 4-4 depicts the hyperbolic relationship between urine output and 300 275 250 Urine Volume CC/HR 225 200 X 175 150 125 100 X XX 75 X XX 50 X XX 25 XX X X X XX 94 96 98 100 102 104 Body Water as % Initial Value FIGURE 4-4 Relation of urine output to body hydration status. Reprinted with permission, from Lee (1964)
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From page 83... ...
. Urine output can vary widely to maintain total body water; however, there are clearly limits to the amount of conservation and excretion.
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From page 84... ...
Because secreted sweat drips from the body and is not evaporated, higher sweat secretions are often needed to achieve these cooling demands. If a person is physically active and exposed to environmental heat stress, sweat losses to avoid heat storage can be substantial over a 24-hour period.
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The lower daily sweat losses in the tropics were probably due to lower ambient temperatures and lower solar load (both acting to lower the required evaporative cooling) , as the precise activity levels of both groups were unknown.
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population (1977–1978 Nationwide Food Consumption Survey) , total water intake was approximately 28 percent from foods, 28 percent from drinking water, and 44 percent from other beverages (Ershow and Cantor, 1989)
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concluded that for most adult men, TABLE 4-4 Estimation of Daily Water Requirements of Infants and Children from Water Balance Studies Total Volume Total Water Intake, L/d Intake, L/d Reference Subjects (age) Conditions (mL/kg/d)
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. If modest physical activity is performed, the TABLE 4-5 Estimation of Daily Water Requirements of Adults from Water Balance Studies Reference Subjects Conditions Total Water Intake (L/d)
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. Cold exposure did not alter intake, but heat stress increased total daily water intake (Welch et al., 1958)
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The lower values in women were not accounted for by differences in body size. METHODS FOR ESTIMATING HYDRATION STATUS Total Body Water Changes Total body water (TBW)
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has recently gained attention because it is simple to use and allows rapid, inexpensive, and noninvasive estimates of TBW. Absolute values derived from this technique correlate well with TBW values obtained by isotope dilution (Kushner and Schoeller, 1986; Kushner et al., 1992; Van Loan et al., 1995)
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From page 92... ...
Arginine vasopressin release is proportional to increased plasma osmolality and decreased plasma volume. While body water loss will induce plasma volume reduction and increased plasma osmolality, the influence of body water loss on each depends upon the method of dehydration, physical fitness level, and heat acclimatization status (Sawka, 1988; Sawka and Coyle, 1999)
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where plasma osmolality was measured at several hydration levels. TBW was either directly measured or calculated based upon body composition information.
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. Table 4-8 provides the serum osmolality for selected deciles of total water intake by gender in the Third National Health and Nutrition Examination Survey (NHANES III)
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were slightly lower for all age groups than the plasma osmolality levels from the balance studies previously described (Table 4-7)
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Analysis of the data on plasma osmolality and sodium concentrations measured in nine heat acclimated subjects when euhydrated and after thermal dehydration by 3 and 5 percent of their weight indicated strong negative relationships between a decrease in total body water and (1) an increase in osmolality (r = –0.92)
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If an individual dehydrates from diuretic medication, a much greater ratio of plasma loss to total body water loss occurs compared with exercise-heat induced dehydration (O'Brien et al., 1998)
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A strong relationship (r = 0.70) between plasma volume reduction and TBW reduction was seen in individual data on heat acclimatized subjects (Sawka et al., 2001)
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Urine Indicators Volume and Color Urine volume is often used as an indicator of hydration status. If healthy individuals have urine outputs of approximately 100 mL/ hour, they are probably well hydrated (see Figure 4-4)
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, urine osmolality is not considered a good indicator of hydration status. Saliva Specific Gravity Saliva specific gravity is slightly higher than water (Shannon and Segreto, 1968)
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. Body Weight Changes Body weight changes are frequently used to estimate sweating rates and therefore changes in total body water (e.g., Gosselin, 1947)
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. Potential confounding effects of urine loss, fluid intake, respiratory water loss, metabolic mass loss, water trapped perspiration in clothing on sweat loss, and therefore total body water change estimates for individuals performing exercise in hot and cool conditions have been examined (Cheuvront et al., 2002)
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and 45 to 50 percent relative humidity, their ad libitum consumption of flavored water was 45 percent greater than with unflavored water (Figure 4-13)
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Stimulation of the osmoreceptors activates drinking behavior and the release of arginine vasopressin hormone. The latter increases water permeability of the collecting tubules and thereby reduces free water loss and urine volume.
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. For example, a degradation in mental alertness, associative learning, visual perception, and reasoning ability were noted when healthy men exercised while exposed to a high climatic heat stress (Sharma et al., 1983)
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106 DIETARY REFERENCE INTAKES TABLE 4-9 Cognitive and Motor Control Functions Reported to Be Affected by Dehydration Function Reference Subjects Conditions Results Perception of Cian et al., 8 men 2.8% dehydration Increased fatigue 2000 by exercise or rating of climatic heat fatigue Rating of mood Cian et al., 8 men 2.8% dehydration No effect on 2000 by exercise or mood climatic heat Target shooting Epstein 9 men 2.5% dehydration Reduced speed et al., by climatic heat and accuracy 1980 and increase in physiologic strain Perceived Cian et al., 8 men 2.8% dehydration Discrimination discrimination 2000 by exercise or impaired climatic heat Choice reaction Leibowitz 4 men, 6-h exercise in Faster response time et al., 4 women the heat, time to 1972 causing 2.5% or peripheral 5% dehydration visual stimuli, no effect on response time to central visual stimuli Cian et al., 8 men 2.8% dehydration No effect on 2000 by exercise or response time climatic heat Visual-motor Gopinathan 11 men 1, 2, 3, or 4% Tracking tracking et al., dehydration, impaired at 1988 induced by 2% or more exercise in the dehydration heat Short-term Cian et al., 8 men 2.8% dehydration Short-term memory 2000 by exercise or memory climatic heat impaired Gopinathan 11 men 1, 2, 3, or 4% Short-term et al., dehydration, memory 1988 induced by impaired at exercise in the 2% or more heat dehydration
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From page 107... ...
In a well-designed study, the arithmetic ability, short-term memory, and visual-motor tracking of 11 men who, on separate days, had water deficits of either 1, 2, 3, or 4 percent of body weight via thermal dehydration were assessed (Gopinathan et al., 1988)
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Physical Work Body water deficits can adversely influence aerobic exercise tasks (Sawka, 1992; Sawka and Coyle, 1999)
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. Table 4-10 presents a summary of investigations concerning the influence of dehydration on maximal aerobic power and physical work capacity (e.g., how much aerobic-type exercise could be completed under a given set of conditions)
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The influence of factors such as a person's initial maximal aerobic power, training status, and heat acclimatization status on the magnitude of aerobic performance decrements from body water deficits has not been delineated. In a study of dehydration in children at 1 and 2 percent of body weight loss, a greater increase in core body temperature than would have been expected to be observed in adults exercising in hot weather was noted (Bar-Or et al., 1980)
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From page 111... ...
As the magnitude of water deficit increased, there was a concomitant graded elevation of core temperature. The magnitude of core temperature elevation ranged from 0.1°C to 0.23°C for every percent body weight lost (Brown, 1947a; Gisolfi and Copping, 1974; Greenleaf and Castle, 1971; Montain et al., 1998a; Sawka et al., 1985; Strydom and Holdsworth, 1968)
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, F = fluid ≥ sweat losses. b CE = cycle ergometer, PR = performance ride or run, TM = treadmill, VO2max = maximal oxygen uptake.
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113 WATER Dehydration Drink (% body Environmentc Performance Resultsd Conditions weight)
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. Women and men who are of comparable physical fitness and heat acclimatization status appear to respond similarly to dehydration and exercise-heat stress (Sawka et al., 1983b)
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During the 7 percent dehydration experiments, six subjects discontinued after completing an average of 64 minutes. To address whether dehydration alters physiologic tolerance to heat strain, subjects walked to voluntary exhaustion when either euhydrated or dehydrated (8 percent of total body water)
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, control conditions not adequately described (Grucza et al., 1987; Nielsen, 1974; Nielsen et al., 1971) , and cool fluid ingestion that might have caused reduced core temperature (Gisolfi and Copping, 1974; Moroff and Bass, 1965)
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Blyth and Burt (1961) were the first to report the effects of hyperhydration on performance during exercise-heat stress.
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In another study, subjects exercised to exhaustion during uncompensable exercise-heat stress when initially euhydrated (control) or hyperhydrated (increased total body water by approximately 1.5 L)
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when an individual is dehydrated (≈ 1.6 percent of body weight)
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reported on experiments in which dogs were slowly dehydrated by water deprivation in temperate conditions and were then exposed to heat stress. When the dogs were dehydrated by 10 to 14 percent of body weight and exposed to heat, their core temperature "explosively increased," and they would only survive if
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. Cats showed similar responses, but with water deficits of up to 20 percent body weight loss and core temperatures of up to 43°C (110°F)
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Dehydration and Chronic Diseases Kidney Stones Increased fluid intake has been found to be inversely associated with an increased risk of developing kidney stones (Curhan et al., 1997, 1998) , and increased fluid consumption has long been suggested as means to prevent recurrence of kidney stones (nephrolithiasis)
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. One randomized controlled trial with 5 years of follow-up tested the effects of increased water intake as a means of preventing recurrent kidney stones in 199 individuals (134 men and 65 women)
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with low fluid consumption was suggested in a small group of patients (n = 30) with gallstones whose typical daily drinking water intake was estimated to be 0.4 to 0.7 L/day (Math et al., 1986)
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It was also noted that the risk of bladder cancer was reduced by 7 percent for every addition of 240 mL (~1 cup) in daily fluid intake.
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were given approximately 1.3 L of either an electrolyte-carbohydrate beverage or water in five servings during the long flight. Compared with the water group, the men given the electrolyte-carbohydrate beverage gained more body weight, had lower urine output, and had improved net fluid balance.
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It is assumed, unless otherwise noted, that a more constant component of the daily total water intake is derived from food (as metabolic and compositional water provided by food and beverages)
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The effect of sustaining these high sweating rates can markedly increase daily total water requirements. For example, the daily fluid intake of soldiers performing either "normal" work (~ 3,350 kcal/day)
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Figure 4-16 suggests that in extreme heat stress and activity conditions, the daily fluid requirements could be greater than 16 qt (15.2 L)
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if resting in the shade. The figure suggests that in extreme heat stress and activity conditions, the daily water requirements could be greater than 20 qt (19 L)
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. Generally, physical activity is curtailed in hot weather, so high levels of water intake, such as 14 qt/day (13.3 L/day)
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. The net effect is a total body water deficit reduction during altitude exposure (Anand and Chandrashekhar, 1996; Hoyt and Honig, 1996)
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. It has long been thought that consumption of caffeinated beverages, because of the diuretic effect of caffeine on reabsorption of water in the kidney, can lead to a total body water deficit.
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. Hence, unless additional evidence becomes available indicating cumulative total water deficits in individuals with habitual intakes of significant amounts of caffeine, caffeinated beverages appear to contribute to the daily total water intake similar to that contributed by noncaffeinated beverages.
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Although changes in solute and urea nitrogen excretion were reported, these changes were appropriate for the changes in protein intake. Thus increased protein intake did not affect water intake or urine volume in the setting of ad libitum water consumption.
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. Sodium Intake The effects of increased sodium intake on urine volume, a proxy of water intake, have been assessed in two experimental studies (He et al., 2001; Luft et al., 1983)
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In these individuals, weakness and confusion further reduce fluid intake and lead to greater dehydration. Cystic Fibrosis The concentration of sodium chloride in the sweat of patients with cystic fibrosis (CF)
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FIGURE 4-19 Cumulative voluntary water intake (top graph) and involuntary dehydration (bottom)
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. Diuretics and Medication Use There are no medications that directly stimulate water intake.
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Compared with children and adults, infants have a higher total body water content per kg of body mass (Altman, 1961) , a higher surface area-to-body mass ratio, a higher rate of water turnover (Fusch et al., 1993)
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Total water intake reflects the sum of plain drinking water and the water content of all foods and beverages consumed. Data on plain drinking water intake were provided by a proxy in response to the question, "How many fluid ounces of plain drinking water, that is, tap water or any bottled water that is not carbonated, with nothing added to it, did you drink yesterday?
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From page 142... ...
. Based on water balance studies, daily water intake increases twofold between the first month of life and months 6 to 12 (Goellner et al., 1981)
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. Therefore, the AI for total water is set based on the median total water intake using data from NHANES III (Appendix Table D-1)
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From page 144... ...
. Data from NHANES III demonstrate that normal hydration status for all adults, as measured by serum osmolality, can be achieved with a wide range of water intakes (e.g., first through 99th percentile of total water intake)
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provided about 3.0 and 2.2 L/day for 19- to 30-year-old men and women, respectively, representing approximately 81 percent of total water intake (Appendix Table D-3)
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146 DIETARY REFERENCE INTAKES TABLE 4-14 Daily Water Intake from a Diet Providing 2,200 kcal Meal Food/Beverage Consumed Energy (kcal) Water (mL)
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This includes approxi mately 2.2 L (≈ 9 cups) as total beverages, includ ing drinking water.
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concentrations with age, since ANP has been demonstrated to suppress arginine vasopressin release in response to hyperosmolality in young and old individuals (Clark et al., 1991)
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. In studies of water ingestion after intravenously induced hyperosmolality, elderly individuals demonstrated marked reductions in their water intake and rate of return of plasma osmolality to baseline when compared with the younger group (Murphy et al., 1988)
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Summary. While there are differences in renal physiology that occur with aging, Appendix Table G-1 (which provides serum osmolality values by percentile of water intake)
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Total body water has been measured during gestation with deuterium, the stable isotope of oxygen, or by bioelectric impedance (Catalano et al., 1995; Chesley, 1978; Forsum et al., 1988; Hytten, 1980; Hytten and Leitch, 1971; Lindheimer and Katz, 1985)
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. In the NHANES, water from food provided 22 percent of the estimated total water intake, slightly more than the 19 percent of the estimated total water consumption seen in nonpregnant women (Appendix Table D-4)
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is set based on median total water intakes during lactation estimated in the NHANES III (Appendix Table D-1)
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indicate that individuals reporting leisure time activity five or more times per week had higher median daily water intakes by ≈ 0.5 L/day (e.g., 19 to 30 years: men 3.16 to 3.78 L/day, women 2.60 to 2.93 L/day)
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From page 155... ...
"minimal," "average," and "liberal" water requirements of 2.1, 3.4, and 5.0 L/ day, respectively, are fairly consistent with this figure, except for very active persons in hot weather. The daily water requirement increases with activity and ambient temperature are a result of increased sweating to meet evaporative cooling requirements.
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The y-axis represents the predicted water requirements that increase because of increased sweat losses to enable thermoregulation. The x-axis is the average daytime dry bulb temperature.
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. Figure 4-21 shows the sources and quantities of water consumed as Total Juice Carbonated drinks Coffee 1994-1996 CSFII 1977-1978 NFCS Milk Drinking water Other 0 5 10 15 20 25 30 35 40 g water / kg body weight / day FIGURE 4-21 Sources and quantities of beverage intake for individuals aged 20 to 64 years as provided by the 1977–1978 National Food Consumption Survey (NFCS)
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From page 158... ...
Analysis of other data (Ershow and Cantor, 1989) showed total water intake with approximately 28 percent coming from food, 28 percent from drinking water, and 44 percent from other beverages.
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The expanding range probably results from differences in body size, physical activity, and environmental exposure. Table 4-18 summarizes the median values of total water intake (food and beverages)
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. These data do not represent the water requirements for a specific metabolic rate, but rather the total water intake on a given day (whether or not the
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From page 161... ...
. The median daily intake of drinking and beverage water was estimated to be 1.8, and the intake of water from food was 0.7, providing a total water intake of approximately 2.5 L from foods, beverages, and drinking water.
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in proportion to the excess fluid intake to reestablish water balance (Freund et al., 1995; Habener et al., 1964)
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. Increased total body water, which dilutes the ECF sodium, occurs from overconsumption of water.
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. Dose-Response Assessment While hazards associated with overconsumption can thus be identified, there are no data on habitual consumption of elevated water intakes resulting in identifiable hazards in apparently healthy people.
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. • Better understanding of the relationship between body water deficits and heat stroke or cardiac arrest associated with intense physical activity.
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2000. Endocrine control of water balance.
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1997. Thermal and circulatory responses during exercise: Effects of hypohydration, dehydration, and water intake.
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1995. Estimating body composi tion in late gestation: A new hydration constant for body density and total body water.
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Med Sci Sports Exerc 23:1338–1348. Costi D, Calcaterra PG, Iori N, Vourna S, Nappi G, Passeri M
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J Appl Physiol 61:1031–1034. Durr JA, Hoggard JG, Hunt JM, Schrier RW.
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1989. Total Water and Tapwater Intake in the United States: Population-Based Estimates of Quantities and Sources.
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1994. Comparison of body fat estimates derived from underwater weight and total body water.
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1995. Validity of urine-blood hydrational measures to assess total body water changes during mountaineer ing in the Sub-Arctic.
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J Appl Physiol 57:868–873. Hytten FE.
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1986. Estimation of total body water by bioelectrical impedance analysis.
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1983. The effect of dietary sodium and protein on urine volume and water intake.
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1997. Ef fects of hypertonicity on water intake in the elderly: An age-related failure.
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Med Sci Sports Exerc 29:661–668. Montain SJ, Sawka MN, Latzka WA, Valeri CR.
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1997. Coffee con sumption and total body water homeostasis as measured by fluid balance and bioelectrical impedance analysis.
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1970. Variation in total body water with muscle glycogen changes in man.
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1999. Influence of body water and blood volume on ther moregulation and exercise performance in the heat.
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1950. The measurement of total body water in the human subject by deuterium oxide dilution.
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1999. The diuretic effects of alcohol and caffeine and total water intake misclassification.
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1998. Age-related change in body water and hydration in old age.
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1987. Water intoxication due to excessive water intake: Observation of initiation stage.
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