Efficacy and safety of protein supplements for U.S. Armed Forces personnel: consensus statement.

To provide evidence-based guidance regarding the efficacy and safety of dietary protein supplement (PS) use by members of the U.S. Armed Forces, a panel of internationally recognized experts in the fields of protein metabolism and dietary supplement research was convened by the Department of Defense Center Alliance for Dietary Supplement Research and the U.S. Army Medical Research and Material Command. To develop a consensus statement, potential benefits, risks, and strategies to optimize military performance through PS use were considered in the context of specific warfighter populations and occupational demands. To maintain muscle mass, strength, and performance during periods of substantial metabolic demand and concomitant negative energy balance the panel recommended that warfighters consume 1.5-2.0 g · kg(-1) · d(-1) of protein. However, if metabolic demand is low, such as in garrison, protein intake should equal the current Military Dietary Reference Intake (0.8-1.5 g · kg(-1) · d(-1)). Although PS use generally appears to be safe for healthy adults, warfighters should be educated on PS quality, given quality-control and contamination concerns with commercial dietary supplements. To achieve recommended protein intakes, the panel strongly urges consumption of high-quality protein-containing whole foods. However, when impractical, the use of PSs (20-25 g per serving or 0.25-0.3 g · kg(-1) per meal), particularly after periods of strenuous physical activity (e.g., military training, combat patrols, and exercise), is acceptable. The committee acknowledges the need for further study of protein requirements for extreme, military-specific environmental conditions and whether unique metabolic stressors associated with military service alter protein requirements for aging warfighters.

A comparison of subjective and objective measures of physical exertion.

Better methods are needed to improve validity and reliability of physical activity (PA) assessment instruments. The purpose of this study was to compare individual's Borg's Rate of Perceived Exertion (RPE) scores to GT1M ActiGraph accelerometer output, with the aim to better understand estimates of perceived exertion for exercise prescription. Adults were recruited (n = 117) from Utah, with 43.1% males (n = 50), and most (53.1%) self-reporting regular exercise. Participants performed three indoor laps of increasing intensity, ranging from walking to running, and immediately completed a RPE form. A subsample was mailed the same RPE survey 6-8 weeks later to compare differences from their initial responses. Individual accelerometer data was compared to RPE levels from validated metabolic equivalents (METs). There were significant differences between the RPE ratings and the accelerometer output overall for gender (χ(2) = 10.9, P = 0.004), and exercise status (χ(2) = 15.5, P < 0.001). The odds of underestimating RPE for an exerciser were 3.67 times greater than a non-exerciser (95% CI = 1.48, 9.11). The subsample also underestimated RPE after the time lapse (Z = -2.324, P = 0.020). Overall, the RPE proved to be a useful tool for most individuals and could be used in individualised exercise prescription, although women may overestimate, and regular exercisers may underestimate exertion.

Adipose tissue cellularity and lipolysis. Response to exercise and cortisol treatment.

Male rats a 5 wk of age were subjected to 13 wk of intensive treadmill running to study the effect of exercise on adipose tissue cellularity and lipolysis. Untrained controls of the same age remained sedentary in their cages for the duration of the experiment. Adipocyte numbers were similar in eqidiymal fat pads from trained and untrained rats (12.7 plus or minus 1.3 X 10(6) vs. 15.3 plus or minus 1.3 X 10(6) cells/pad), however trained rats had smaller fat pads containing smaller cells (0.09 plus of minus 0.01 vs. 0.20 plus or minus 0.04 mug triglyceride/cell). Adipocytes from trained rats possessed greater epinephrine-sensitive lipase activity than sedentary rats on a per cell, per milligram protein, per gram adipose tissue, or per fat pad basis. Although the smaller cells of the trained rats had greater epinephrine-sensitive lipase activity than the larger cells of the untrained rats, lipolysis was positively correlated with cell size within both treatment groups. Cortisol treatment of intact animals did not significantly affect in vitro adipose tissue lipolysis. The results of this study indicate that exercise training increased the potential of adipose tissue cells to release free fatty acids in response to epinephrine stimulation. Exercise training initiated at 5 wk of age had only a small effect on adipose tissue cell numbers but significantly decreased cell size.

Association of adipose and red blood cell lipids with severity of dominant Stargardt macular dystrophy (STGD3) secondary to an ELOVL4 mutation.

OBJECTIVE: To determine whether adipose and red blood cell membrane lipids, particularly long-chain polyunsaturated fatty acids such as docosahexaenoic acid and eicosapentaenoic acid, are significantly correlated with phenotype in a family with autosomal dominant Stargardt macular dystrophy (gene locus STGD3). A mutation in the ELOVL4 gene is responsible for the macular dystrophy in this family, and its disease-causing mechanism may be its possible involvement in fatty acid elongation in the retina. METHODS: The subjects in this study included 18 adult family members known to have a 2-base pair deletion in the ELOVL4 gene. Control subjects included 26 family members without the mutation. Each subject received a complete eye examination including fundus photographs, the results of which were used to grade the severity of macular dystrophy on a 3-tier scale. Red blood cell membrane and adipose tissue lipids were analyzed as an indication of short-term and long-term dietary fatty acid intake. RESULTS: When adipose lipids were analyzed, there was a significant inverse relationship between phenotypic severity and the level of eicosapentaenoic acid (r = -0.54; P = .04). When red blood cell lipids were analyzed, there were significant inverse relationships between phenotypic severity and levels of eicosapentaenoic acid (r = -0.55; P = .02) and docosahexaenoic acid (r = -0.48; P = .04). CONCLUSIONS: These results indicate that the phenotypic diversity in this family may be related to differences in dietary fat intake as reflected by adipose and red blood cell lipids. CLINICAL RELEVANCE: This study demonstrates that dietary factors can influence the severity of an inherited human macular dystrophy.

Salicylic acid stimulation of palmitic acid oxidation by rat skeletal muscle mitochondria.

The effects of salicylic acid on palmitic acid oxidation were studied using rat skeletal muscle mitochondria. Salicylic acid, in concentrations that exerted no effect on mitochondrial coupling (0.1 mM), significantly stimulated mitochondrial palmitic acid oxidation, with maximal stimulation occurring at subsaturating concentrations of substrate. In the same preparation, salicylate had no effect on the oxidation of palmitoylcarnitine or palmitoyl-CoA. Salicylate appears to augment the initial step of palmitic acid oxidation by lowering the apparent Michaelis constant (Km) of long chain fatty acid: CoASH ligase (AMP) (EC 6.2.1.3) for palmitic acid.

Calcium accumulation by chick intestinal mitochondria. Regulation by vitamin D-3 and 1,25-dihydroxyvitamin D-3.

We have the evaluated the effect of vitamin D-3 and its metabolite 1,25-dihydroxyvitamin D-3 on Ca2+ accumulation by chick intestinal mitochondria. Ca2+ accumulation appears to occur in two phases: an early, transient accumulation into an Na+-labile pool followed by an ATP-dependent accumulation into an Na+-resistant pool. Ca2+ accumulation is extensive at free Ca2+ concentrations greater than 3 . 10(-6) M in the presence of ATP. Ruthenium red and dinitrophenol block Ca2+ accumulation, but atractyloside does not. Oligomycin blocks ATP-supported accumulation completely with a partial inhibition of ATP and malate-supported accumulation. Little difference could be found in mitochondrial preparations from vitamin D-deficient chicks compared to those from vitamin D-3 (or 1,25(OH)2D-3)-supplemented chicks with respect to respiratory control, oxygen consumption, efficiency of oxidative phosphorylation, affinity for Ca2+, or the rate and extent of ATP-supported Ca2+ accumulation. Intestinal cytosol stimulated Ca2+ accumulation, but this was not specific with respect to vitamin D status or tissue of origin, nor was it duplicated by chick intestinal Ca2+-binding protein. 30 ng/ml 1,25(OH)2D-3 stimulated Ca2+ accumulation directly, regardless of the presence of intestinal cytosol. Other vitamin D metabolites were less potent: 25-hydroxyvitamin D-3 greater than 24,25-dihydroxyvitamin D-3 = vitamin D-3. Since increasing the free Ca2+ concentration from 3 . 10(-6) to 1 . 10(-5) M increased Ca2+ accumulation approx. 50-fold, whereas direct stimulation by 1,25(OH)2D-3 in vitro increased Ca2+ accumulation less than 2-fold, we conclude that 1,25(OH)2D-3 influences mitochondrial accumulation of Ca2+ in vivo primarily by altering cytosol concentrations of free Ca2+.

Pharmacokinetics of radiolabeled polyclonal antiferritin in patients with Hodgkin's disease.

The objective was to identify pharmacokinetic parameters predictive for tumor response and normal tissue side effects after i.v. administered radiolabeled rabbit antihuman ferritin IgG. Twenty-eight patients with recurrent Hodgkin's disease received 2 mg of rabbit antihuman ferritin i.v., labeled with 4-7 mCi of In-111 followed by two doses of 0.25, one dose of 0.3, or one dose of 0.4 mCi of Y-90-labeled antiferritin per kg of body weight 1 week later. Radioactivity and HPLC measurements of blood and urine samples and liver and tumor volumes identified on sequential whole-body scans provided the data for a pharmacokinetic analysis covering the first 6 days after the administration of the radioimmunoconjugate. Side effects and tumor response were recorded. Temporary hematological toxicity was noted in all patients. Sixteen patients showed a tumor response. The Y-90 blood level at 1 h after administration correlated with the severity of subsequent hematological toxicity. The rapid blood elimination half-life of radioactivity was 4.4 h. Less than 5% of the administered radioactivity was eliminated in the first 24 h urine. The slow blood elimination half-life was 44 and 37 h for In-111 and Y-90, respectively. One of 12 retreated patients produced anti-rabbit IgG antibodies. The volume of distribution was larger for Y-90 than for In-111-labeled antiferritin (160 versus 110% of estimated blood volume). Accidentally extravasated rabbit IgG was rapidly catabolized in perivascular tissues with an effective half-life of less than 35 h. Slower catabolism was noted for rabbit IgG in blood (t(1/2) = 40 h), liver (t(1/2) = 62 h) or tumor (t(1/2) = 40-80 h). Twelve of 13 patients with an effective tumor half-life > 57 h showed a tumor response. I.v. administered polyclonal rabbit antihuman ferritin, labeled with In-111 or Y-90 is stable in vivo and targets Hodgkin's disease. Intravascular Y-90 causes a vascular leak and a larger volume of distribution for antiferritin. Elevated Y-90 blood levels at 1 h and a tumor half-life of >57 h predict for hematological toxicity and tumor response, respectively.

Fractionated radiolabeled antiferritin therapy for patients with recurrent Hodgkin's disease.

The objective of this study was to determine the therapeutic ratio of fractionated radiolabeled immunoglobulin therapy (RIT) for patients with recurrent Hodgkin's disease. Ninety patients with recurrent Hodgkin's disease received 2 mg of yttrium-90-labeled polyclonal rabbit antihuman ferritin IgG i.v. Fifty-seven patients received a single (unfractionated) administration per treatment cycle; 11 of them were treated with 0.3 mCi/kg body weight, 39 were treated with 0.4 mCi/kg body weight, and 7 received 0.5 mCi/kg body weight per treatment cycle. Thirty-three patients had their radiolabeled immunoglobulin administration separated (fractionated) in 2 x 0.25 mCi/kg body weight (total activity, 0.5 mCi/kg). The interval between fractions was 1 week. Radioimmunoconjugates did not cause serious acute side effects. In vivo radioimmunoconjugates were stable. Human antirabbit IgG antibodies were found in 2 of 50 retreated patients (<5%). Hematological toxicity was the only side effect noted in all patients, and it was usually temporary. Response rates (RRs) were 20%, 61%, and 86% after 0.3, 0.4, or 0.5 mCi/kg unfractionated yttrium-90-labeled antiferritin. The RR for patients treated with fractionated RIT was 42%. In the fractionated RIT group, complete responses were decreased, and progressive disease increased (P < 0.05). Complete responses had a medium duration of 6 months. Median survival times were 390 days for 1 x 0.4 mCi/kg and 300 days for the 2 x 0.25 mCi/kg patient group. Fractionation did not provide the expected decrease in hematological toxicity or the expected increase in tumor RRs.

Environmental and physical stress and nutrient requirements.

When faced with hot, cold, or high-altitude environments, humans can either modify the microenvironment to fit human physiology, adapt their physiology to fit the environment, or use a combination of these two tactics. Metabolic adaptations to heat, cold, and high-altitude exposure may, in some instances, be accompanied by changes in nutrient requirements. Energy expenditure is increased in all three environments. B-vitamin cofactor requirements increase in proportion to energy expenditure (oxidation of fat and carbohydrate). Increased B-vitamin nutrient requirements are usually adequately met by an increased consumption of the diet to meet energy requirements. Other nutrients such as iron may be required in greater amounts to meet the altitude-induced hematopoietic response in females. Additional quantities of vitamins and minerals with antioxidant properties may be beneficial to reduce the increased oxidative stress associated with work in heat, cold, or high-altitude outdoor environments.

Maintenance of iron status in healthy men during an extended period of stress and physical activity.

Body weight loss and iron status of 55 male soldiers were measured during 62 d of intense physical activity and sustained stress and sleep deprivation. Body weight declined from (mean +/- SD) 75.9 +/- 9.0 to 63.8 +/- 6.7 kg (P < 0.05). Serum iron fell from 13.7 +/- 5.6 to 8.3 +/- 3.6 mumol/L by 14 d (P < 0.05), but returned to baseline values by 8 wk. Total iron-binding capacity declined from 53.4 +/- 6.8 at baseline to 47.5 +/- 6.3 mumol/L at 8 wk (P < 0.05). During the study, hematocrit, serum hemoglobin, and erythrocyte count did not change, whereas ferritin increased from 116 +/- 84 to 202 +/- 106 micrograms/L (P > 0.05). Adequate dietary iron, initiation of training with adequate body iron stores, and physical activity not in excess of pretraining workloads contributed to the maintenance of iron status during prolonged physical activity and stress. Our results suggest that some acute phase-like disturbances in iron metabolism may be a normal component of adaptation to stress and physical activity in healthy men.

Influence of dietary iron deficiency on hemoglobin, myoglobin, their respective reductases, and skeletal muscle mitochondrial respiration.

Male weanling rats were fed a control diet (46 ppm iron) or an iron-deficient diet (11 ppm iron) for 7 wk to determine the influence of iron deficiency on heme proteins and skeletal muscle mitochondrial respiration. At the end of 7 wk, the hemoglobin in the blood of the iron deficient rats was 35% less and skeletal muscle myoglobin was 20 to 37% less than in the control animals. The concentration of myoglobin in the heart was not appreciably diminished by iron deficiency. Cytochrome c concentration was 20% less in the heart and 35% less in the mixed-fiber gastrocnemius in the iron-deficient animals. Iron deficiency did not influence the activity of metmyoglobin reductase in either heart or skeletal muscle. There was about 30% more methemoglobin reductase activity in the red blood cells of the iron-deficient animals, which resulted in methemoglobin levels that were so low as to be virtually unmeasurable. In the iron-deficient rats, skeletal muscle mitochondrial respiration with either pyruvate-malate or palmitylcarnitine as substrate was 17 to 20% less than in the control animals. This study demonstrates that dietary iron deficiency of sufficient severity to reduce blood Hb and skeletal muscle myoglobin or cytochrome c also results in an impaired skeletal muscle oxidative capacity. The study also illustrates the preferential utilization of iron, not only between tissues, but within tissues, and tissue specific adaptive responses to iron deficiency.

The development and evolution of U.S. Army field rations.

Armed conflicts create large masses of personnel that need to be fed nutritious foods in less than favorable conditions. The United States military, private industry, and academia continue to work together to develop rations that meet the needs of military personnel who find themselves in varying climates, conditions, and geography.

Field use of D2 18O to measure energy expenditure of soldiers at different energy intakes.

To test the application of doubly labeled water under adverse field conditions, energy expenditures of 16 special operations soldiers were measured during a 28-day field training exercise. Subjects were matched by fat-free mass and divided equally between an ad libitum ready-to-eat meal diet and a 2,000 kcal/day lightweight ration. Subjects recorded intakes daily, and body composition was measured before and after the exercise. At the beginning of the study, subjects moved to a new northerly location and, therefore, a new water supply. To compensate for this, a group of soldiers who did not receive heavy water was followed to measure isotopic base-line changes. Energy expenditure by doubly labeled water was in agreement with intake/balance (3,400 +/- 260 vs. 3,230 +/- 520 kcal/day). The overall coefficient of variation of energy expenditure by doubly labeled water was half that of intake/balance (7.6 vs. 16.1%). The coefficient of variation of repeat measures with doubly labeled water was 7.3%. Energy expenditure of the ready-to-eat meal group, 3,540 +/- 180 kcal/day, was not significantly different from the lightweight ration group, 3,330 +/- 301 kcal/day. Doubly labeled water was valid under field conditions.

Lower limit of body fat in healthy active men.

We examined body composition changes in 55 normal young men during an 8-wk Army combat leadership training course involving strenuous exercise and low energy intake, with an estimated energy deficit of 5.0 +/- 2.0 MJ/day and a resultant 15.7 +/- 3.1% weight loss. Percent body fat (BF) measured by dual-energy X-ray absorptiometry (DEXA) averaged 14.3% (range 6-26%) and 5.8 +/- 1.8% (range 4-11%) at the beginning and end of the course, respectively. Men who achieved a minimum percent BF (4-6%) by 6 wk demonstrated only small additional total and subcutaneous fat losses in the final 2 wk and sacrificed increasingly larger proportions of fat-free mass. Percent BF estimated from skinfold thicknesses reflected relative changes in fat mass, although actual percent BF was overestimated. Instead of reaching a plateau after fat stores were substantially depleted, abdominal, hip, and thigh girths continued to decline with body weight loss. Final percent BF for the leanest men was similar to that observed after a 25% body weight reduction in the 1950 Minnesota study (5.2% by underwater weighting), and height-corrected final fat mass was the same (1.0 +/- 0.2 vs. 0.9 +/- 0.7 kg fat/m2), suggesting that these values represent a minimal body fat content in healthy men and that weight loss subsequent to achieving this level is contributed from the fat-free mass. Our results suggest that 4-6% BF or approximately 2.5 kg fat represents the lower limit for healthy men, as assessed by DEXA or by underwater weighing.

Doubly labeled water measurement of human energy expenditure during strenuous exercise.

The energy expenditures (EE) of 23 adult male Marines were measured during a strenuous 11-day cold-weather field exercise at 2,200- to 2,550-m elevation by both doubly labeled water (2H2 18O, DLW) and intake balance methods. The DLW EE calculations were corrected for changes in baseline isotopic abundances in a control group that did not receive 2H2 18O. Intake balance EE was estimated from the change in body energy stores and food intake. Body energy-store changes were calculated from anthropometric [-1,574 +/- 144 (SE) kcal/day] and isotope dilution (-1,872 +/- 293 kcal/day) measurements made before and after the field exercise. The subjects kept daily logbook records of ration consumption (3,132 +/- 165 kcal/day). Mean DLW EE (4,919 +/- 190 kcal/day) did not differ significantly from intake balance EE estimated from food intake and either anthropometric (4,705 +/- 181 kcal/day) or isotope dilution (5,004 +/- 240 kcal/day) estimates of the change in body energy stores. The DLW method can be used with at least the same degree of confidence as the intake balance method to measure the EE of active free-living humans.

Endocrine markers of semistarvation in healthy lean men in a multistressor environment.

We tested the hypothesis that key endocrine responses to semistarvation would be attenuated by changing only the food intake in a multistressor environment that also included sustained workload, inadequate sleep, and thermal strain. Serum hormones were compared within and between two groups of healthy young male volunteers participating in the 8-wk US Army Ranger course, with four repeated cycles of restricted energy intakes and refeeding: group 1 (n = 49) and group 2 (n = 48); energy deficits averaged 1,200 and 1,000 kcal/day, respectively. After 8 wk, most of group 1 achieved a minimum body fat, serum 3,5,3'-triiodothyronine (T(3)) was below normal (78 +/- 20 ng/dl), testosterone (T) approached castrate levels (4.5 +/- 3.9 nmol/l), insulin-like growth factor I (IGF-I) declined by one-half (75 +/- 25 microg/l), and cholesterol rose from 158 +/- 31 to 217 +/- 39 mg/dl. Bioavailable T(3) and T were further reduced by increases in their specific binding proteins in response to declining insulin. Refeeding, even with continuation of the other stressors, produced prompt recovery of T(3), T, and IGF-I. Higher energy intakes in group 2 attenuated the subclinical hypothyroidism and hypercholesterolemia, whereas consistent luteinizing hormone suppression indicated centrally mediated threshold effects on gonadal hormone suppression. We conclude that low T, T(3), and IGF-I remained reliable markers of acute energy deficits in the presence of other stressors; elevated cholesterol and cortisol provided information about chronic status, corresponding to diminishing body fat stores.

Thermoregulation during cold water immersion is unimpaired by low muscle glycogen levels.

This investigation studied the importance of muscle glycogen levels for body temperature regulation during cold stress. Physiological responses of eight euglycemic males were measured while they rested in cold (18 degrees C, stirred) water on two separate occasions. The trials followed a 3-day program of diet and exercise manipulation designed to produce either high (HMG) or low (LMG) preimmersion glycogen levels in the muscles of the legs, arms, and upper torso. Preimmersion vastus lateralis muscle glycogen concentrations were lower during the LMG trial (144 +/- 14 mmol glucose/kg dry tissue) than the HMG trial (543 +/- 53 mmol glucose/kg dry tissue). There were no significant differences between the two trials in shivering as reflected by aerobic metabolic rate or in the amount of body cooling as reflected by changes in rectal temperature during the immersions. Postimmersion muscle glycogen levels remained unchanged from preimmersion levels in both trials. Small but significant increases in plasma glucose and lactate concentration occurred during both immersions. Plasma glycerol increased during immersion in the LMG trial but not in the HMG trial. Plasma free fatty acid concentration increased during both immersion trials, but the change was apparent sooner in the LMG immersion. It was concluded that thermoregulatory responses of moderately lean and fatter individuals exposed to cold stress were not impaired by a substantial reduction in the muscle glycogen levels of several major skeletal muscle groups. Furthermore, the data suggest that, depending on the intensity of shivering, other metabolic substrates are available to enable muscle glycogen to be spared.

Supplemental dietary carnitine and lipid metabolism in exercising rats.

Rats were physically trained by treadmill running and fed normal, high fat, or identical diets supplemented with 1.0% D,L-carnitine. Fatty acid oxidation, stimulated by exercise and/or by a high fat diet was studied to determine if it might be further augmented by supplemental dietary carnitine. Fatty acid oxidation in vitro or in vivo was unaffected by carnitine feeding. Carnitine feeding was associated with an increase in heart and muscle palmitylcarnitine acyltransferase activity and reduced serum cholesterol in trained rats fed the high fat diet. Under the conditions of this study, supplemental dietary carnitine did not greatly alter glyceride synthesis, lipolysis, or fatty acid oxidation, which indirectly indicates that the increased demands for fatty acid oxidation resulting from exercise or from fat feeding are adequately supported by endogenous levels of carnitine.

Dietary sodium and plasma volume levels with exercise.

Sodium is the major cation of the extracellular fluid and has a potent influence on fluid movement. Sodium has been likened to a sponge that draws fluids into the extracellular space, including the plasma volume, to equalize gradients in concentration. Conventional wisdom suggests limiting dietary intake of Na+ to decrease risk of hypertension. However, there are some extreme occupational or exercise-related conditions where sweat losses are great and Na+ losses may exceed normal dietary intake. This can occur acutely such as in an ultra-endurance event or chronically as in hard manual work in the hear. In such cases, additional Na+ in the form of a higher Na+ diet or adding Na+ to beverages used for fluid replacement may be warranted. A higher Na+ diet also appears to accelerate the cardiovascular and thermoregulatory adaptations that accompany heat acclimation or short term exercise training. Saline ingestion before exercise causes an expansion of plasma volume at rest and throughout the subsequent exercise bout. This expansion of plasma volume alters cardiovascular and thermoregulatory responses to exercise in ways that may lead to beneficial changes in endurance exercise performance. Plasma volume expansion also occurs with saline infusion during exercise, but exercise performance advantages have yet to be reported. The purpose of this article is to review the literature concerning dietary sodium and its influence on fluid balance, plasma volume and thermoregulation during exercise. It contains 2 major sections. First, we will discuss manipulations in daily Na+ intake initiated before or throughout an exercise regime. Second, we will examine studies where an acute Na+ load was administered immediately before or during an exercise trial. The dependent variables that we will discuss pertain to: (i) body water compartments, i.e. plasma volume; (ii) thermoregulatory variables, i.e. core temperature and sweat rate; (iii) cardiovascular variables, i.e. heart rate and stroke volume; and (iv) performance, i.e. time trial performance and time to exhaustion. Particular attention will be given to the route by which Na+ was administered, the environmental conditions, the level of acclimation of the participants and specifics relating to Na+ administration such as the osmolality of the Na(+)-containing beverage.