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C
Predictions of Daily Water and Sodium Requirements

To generate estimates of water and sodium losses at different energy expenditure levels and thus work rates, the U.S. Army Research Institute of Environmental Medicine (USARIEM) model was adapted for the four levels of energy expenditure identified in the Dietary Reference Intakes report on energy expenditure (IOM, 2002/2005). The USARIEM Heat Strain model is an empirical model that includes an equation to predict sweating rate during work (Moran et al., 1995, Shapiro et al., 1995). This algorithm has been used in the past to prepare military guidance for water needs during training and deployment.

The following is a description of the application of the model:

  • Variables

    • Water requirements (L/d)

    • Sodium requirements (g/d)

  • Prediction ranges

  • Four energy expenditure levels (1,900; 2,400; 2,900; and 3,600 kcal/d)

  • Temperature ranges (15°–40°C)

ANALYSIS

As shown in the example, the environmental, physiological, and individual information was inputted into the model. For any given individual, physiological, or environmental condition, the model predicted expected water losses. These data were then put into an



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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate C Predictions of Daily Water and Sodium Requirements To generate estimates of water and sodium losses at different energy expenditure levels and thus work rates, the U.S. Army Research Institute of Environmental Medicine (USARIEM) model was adapted for the four levels of energy expenditure identified in the Dietary Reference Intakes report on energy expenditure (IOM, 2002/2005). The USARIEM Heat Strain model is an empirical model that includes an equation to predict sweating rate during work (Moran et al., 1995, Shapiro et al., 1995). This algorithm has been used in the past to prepare military guidance for water needs during training and deployment. The following is a description of the application of the model: Variables Water requirements (L/d) Sodium requirements (g/d) Prediction ranges Four energy expenditure levels (1,900; 2,400; 2,900; and 3,600 kcal/d) Temperature ranges (15°–40°C) ANALYSIS As shown in the example, the environmental, physiological, and individual information was inputted into the model. For any given individual, physiological, or environmental condition, the model predicted expected water losses. These data were then put into an

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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate Excel 4.0 spreadsheet and used to generate the dataset of estimated water and sodium requirements at varying energy expenditure levels and temperatures. Environmental and individual assumptions are listed below. These data were then plotted using Sigma Plot 9.0 to generate a graphical display. ASSUMPTIONS Individual 70-kg person Height = 170 cm Walking velocity = 5 km/h 0% grade Clothing = 1.0 (cotton) Environmental Partly cloudy day Wind speed = 1 m/sec Relative humidity = 50% Outdoor Water vapor pressure = 19.094 mm Hg Load = 0 kg Dry bulb temperature = 30°C Black globe temperature = 45°C Physiological Skin body temperature = 35.0°C Rectal body temperature = 36.5°C Initial heart rate = 60 bpm Rest (N) Exposure I = 720 min (= 12 h) Exposure II = 720 min (= 12 h) Exposure III (min) = 0 Exposure IV (min) = 0 1.0 L/d minimal requirements for survival: Sodium concentration of sweat (≈ 35 mmol/L), that of a partially acclimated person

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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate Example (not used in this analysis): The version of the program used was MAT version 9/97. Figures C-1a and C-1b describe the approximate daily water (Figure C-1a) and sodium (Figure C-1b) lost due to sweating as a function of dry bulb temperature and level of physical activity derived from modeling data (Table C-1). *   The screen is an example of the input variable capabilities; however, actual data are not presented in the database.

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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate FIGURE C-1 Approximate daily water (Figure C-1a) and sodium (Figure C-1b) lost due to sweating as a function of dry bulb temperature and level of physical activity derived from modeling data (Table C-1). The hatched area indicates ≈ 1 L minimal water requirements. 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. The four lines represent the four levels of energy (in kcal/day) used in the model (1,900 kcal; 2,400 kcal; 2,900 kcal; and 3,600 kcal).

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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate REFERENCES IOM (Institute of Medicine). 2002/2005. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press. Moran D, Shapiro Y, Epstein Y, Burstein R, Stroschein L, Pandolf KB. 1995. Validation and adjustment of the mathematical prediction model for human rectal temperature responses to outdoor environmental conditions. Ergonomics 38:1011–1018. Shapiro Y, Moran D, Epstein Y, Stroschein L, Pandolf KB. 1995. Validation and adjustment of the mathematical prediction model for human sweat rate responses to outdoor environmental conditions. Ergonomics 38:981–986.

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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate TABLE C-1 Generated Database from the USARIEM Prediction Model Given: kcal/h watts per 12 h (kcal) Rest 76 88 912 Light 234 273 2,808 Mod 382 444 4,582 Hard 531 618 6,372 Assumption: 1.0 liter water essential (daily resp water loss and kidney loss) Predicted Sweating Rates (mL/h) Air Tdb Rh Rest Light Mod Hard 10 50 32 100 355 628 15 50 65 204 456 722 20 50 108 339 618 911 25 50 151 473 763 1,069 30 50 201 629 938 1,263 35 50 265 829 1,168 1,524 40 50 361 1,129 1,524 1,934 12 h Air Scenario Rest Light Mod Hard Kcal Water Loss 10 0.95 0.05 0 0 1,006.8 425 15 0.95 0.05 0 0 1,006.8 867 20 0.95 0.05 0 0 1,006.8 1,440 25 0.95 0.05 0 0 1,006.8 2,009 30 0.95 0.05 0 0 1,006.8 2,672 35 0.95 0.05 0 0 1,006.8 3,522 40 0.95 0.05 0 0 1,006.8 4,796 WBGT Rest Light Mod Hard Kcal Water Loss 9.9 0.7 0.25 0.05 0 1,570 782 14.2 0.7 0.25 0.05 0 1,570 1,434 18.8 0.7 0.25 0.05 0 1,570 2,299 23.1 0.7 0.25 0.05 0 1,570 3,148 27.4 0.7 0.25 0.05 0 1,570 4,141 31.7 0.7 0.25 0.05 0 1,570 5,416 36.2 0.7 0.25 0.05 0 1,570 7,336

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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate Hard A:J13 khard A:E7 klight A:E5 kmod A:E6 krest A:E4 light A:H13 mod A:I13 Rest A:G13 sr A:E13.I20 WBGT A:F13 ttl kcal ttl water loss   1,918.8 1.4 35 23 1,147 1,918.8 2.4 35 23 1,905 1,918.8 2.9 35 23 2,367 1,918.8 3.5 35 23 2,825 1,918.8 4.2 35 23 3,358 1,918.8 5.0 35 23 4,042 1,918.8 6.3 35 23 5,068 ttl kcal ttl water loss   2,481.5 2.3 35 23 1,837 2,481.5 2.9 35 23 2,362 2,481.5 3.8 35 23 3,058 2,481.5 4.6 35 23 3,742 2,481.5 5.6 35 23 4,541 2,481.5 6.9 35 23 5,568 2,481.5 8.8 35 23 7,113

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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate WBGT Rest Light Mod Hard Kcal Water Loss 9.9 0.65 0.15 0.15 0.05 2,020 1,445 14.2 0.65 0.15 0.15 0.05 2,020 2,130 18.8 0.65 0.15 0.15 0.05 2,020 3,115 23.1 0.65 0.15 0.15 0.05 2,020 4,047 27.4 0.65 0.15 0.15 0.05 2,020 5,148 31.7 0.65 0.15 0.15 0.05 2,020 6,578 36.2 0.65 0.15 0.15 0.05 2,020 8,754 WBGT Rest Light Mod Hard Kcal Water Loss 9.9 0.45 0.25 0.2 0.1 2,666 2,078 14.2 0.45 0.25 0.2 0.1 2,666 2,925 18.8 0.45 0.25 0.2 0.1 2,666 4,179 23.1 0.45 0.25 0.2 0.1 2,666 5,350 27.4 0.45 0.25 0.2 0.1 2,666 6,741 31.7 0.45 0.25 0.2 0.1 2,666 8,552 36.2 0.45 0.25 0.2 0.1 2,666 11,316

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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate ttl kcal ttl water loss   2,931.9 2.9 35 23 2,371 2,931.9 3.6 35 23 2,922 2,931.9 4.6 35 23 3,715 2,931.9 5.5 35 23 4,465 2,931.9 6.6 35 23 5,352 2,931.9 8.1 35 23 6,503 2,931.9 10.3 35 23 8,254 ttl kcal ttl water loss   3,578 3.6 35 23 2,881 3,578 4.4 35 23 3,562 3,578 5.7 35 23 4,572 3,578 6.9 35 23 5,515 3,578 8.2 35 23 6,634 3,578 10.1 35 23 8,091 3,578 12.8 35 23 10,317