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Jn142000 1.7

The Journal of Nutrition. First published ahead of print December 21, 2011 as doi: 10.3945/jn.111.142000.
The Journal of Nutrition Ingestive Behavior and Neurosciences Mild Dehydration Affects Mood in HealthyYoung Women1,2 Lawrence E. Armstrong,3 Matthew S. Ganio,3,4 Douglas J. Casa,3 Elaine C. Lee,3 Brendon P. McDermott,3,7Jennifer F. Klau,3 Liliana Jimenez,5 Laurent Le Bellego,5 Emmanuel Chevillotte,5and Harris R. Lieberman6* 3University of Connecticut, Human Performance Laboratory, Storrs, CT; 4University of Arkansas, Department of Health, HumanPerformance, and Recreation, Fayetteville, AR; 5Danone Research, R&D Waters, Palaiseau France; and 6U. S. Army Research Institute ofEnvironmental Medicine, Military Nutrition Division, Natick, MA Limited information is available regarding the effects of mild dehydration on cognitive function. Therefore, mild dehydration was produced by intermittent moderate exercise without hyperthermia and its effects on cognitive function of women were investigated. Twenty-five females (age 23.0 6 0.6 y) participated in three 8-h, placebo-controlled experiments involving a different hydration state each day: exercise-induced dehydration with no diuretic (DN), exercise- induced dehydration plus diuretic (DD; furosemide, 40 mg), and euhydration (EU). Cognitive performance, mood, and symptoms of dehydration were assessed during each experiment, 3 times at rest and during each of 3 exercise sessions.
The DN and DD trials in which a volunteer attained a $1% level of dehydration were pooled and compared to that volunteer's equivalent EU trials. Mean dehydration achieved during these DN and DD trials was 21.36 6 0.16% of body mass. Significant adverse effects of dehydration were present at rest and during exercise for vigor-activity, fatigue-inertia, and total mood disturbance scores of the Profile of Mood States and for task difficulty, concentration, and headache as assessed by questionnaire. Most aspects of cognitive performance were not affected by dehydration. Serum osmolality, a marker of hydration, was greater in the mean of the dehydrated trials in which a $1% level of dehydration was achieved (P = 0.006) compared to EU. In conclusion, degraded mood, increased perception of task difficulty, lower concentration, and headache symptoms resulted from 1.36% dehydration in females. Increased emphasis on optimal hydration is warranted, especially during and after moderate exercise.
J. Nutr. doi: 10.3945/jn.111.142000.
healthy individuals during their ordinary daily activities, de- Adequate fluid intake and homeostasis of total body water is grades cognitive performance, alters mood, or produces adverse essential for human health and survival, including maintaining brain function. Severe dehydration clearly produces decrements Many studies use heat and exercise to produce dehydration.
in cognitive function (1,2). For example, clinical observations One of the most comprehensive (ambient temperature of 458C demonstrate severe dehydration results in acute confusion and with 30% RH8) assessed the effects of dehydration ranging from delirium (3). However, insufficient research has been conducted 1 to 4% in 1% increments in 11 healthy, young males aged 20– to determine if mild dehydration, at levels that may occur in 25 y (4). A serial addition test, word recognition test, and trail-making test were administered; all detected deterioration at 2–4% dehydration. A similar study (5) assessed the effects of 1 Supported by Danone Research, Palaiseau, France.
2 dehydration at ;1, 2, and 3% body mass loss in 8 young males.
Author disclosures: L. Armstrong is a Danone Research Scientific Advisory Moderate exercise in the heat induced dehydration and behav- Board member, paid consultant. H. Lieberman serves as a consultant toDanone Research but was not compensated for his contributions to this study. L.
ioral testing was conducted in three environments: thermoneu- Jimenez, L. Le Bellego, and E. Chevillotte are employed by Danone Research. M.
tral (378C, 50% RH), hot dry (458C, 30% RH), and hot humid Ganio, D. Casa, E. Lee, B. McDermott, and J. Klau, no conflicts of interest. The (398C, 60% RH). Tests included symbol substitution, concen- views, opinions and/or findings in this report are those of the authors, and should tration, and eye-hand coordination. Effects of dehydration were not be construed as an official Department of the Army position, policy ordecision, unless so designated by other official documentation. Citation of observed in two of three tests at 2 and 3% dehydration, but, in commercial organization and trade names in this report do not constitute anofficial Department of the Army endorsement or approval of the products orservices of these organizations.
7 Present address: Department of Health and Human Performance, University of 8 Abbreviations used: DD, dehydration with diuretic treatment condition; DN, Tennessee at Chattanooga, Chattanooga, TN 37403.
dehydration with no diuretic treatment condition; EU, euhydrated treatment * To whom correspondence should be addressed. E-mail: harris.lieberman@us.
condition; POMS, Profile of Mood States; PVT, psychomotor vigilance task; RH, relative humidity; Tgi, gastrointestinal temperature; VAS, visual analogue scale.
ã 2012 American Society for Nutrition.
Manuscript received March 28, 2011. Initial review completed April 22, 2011. Revision accepted November 9, 2011.
Copyright (C) 2011 by the American Society for Nutrition
the symbol substitution test, effects were observed only at 3% in the placebo phase of their contraceptive schedule. Because experi- dehydration (P , 0.05). Other studies assessed information ments were separated by 28 d to control for the menstrual cycle, males processing during simulated sporting events with similar out- were not tested in this study. However, a separate study of males was comes (6–8); dehydration (from 21 to 24% body mass) conducted using a similar protocol during a different period of time.
impaired mood, choice reaction time, and vigilance. Collec- Procedures. To become familiar with study procedures, each partici- tively, these studies provide insight into the effects of mild-to- pant visited the laboratory for 3–5 preliminary sessions to practice moderate dehydration on cognitive performance but not a clear cognitive tests and behavioral testing on a desktop computer while indication of which aspects of cognitive performance are most sitting at a workstation and a laptop computer while walking on a affected by dehydration or its effects on mood, perceived effort, treadmill. When a woman's cognitive performance reached an asymp- or symptoms. Furthermore, the high levels of heat used to induce tote on 2 consecutive days, she could participate in experiments.
dehydration may have interacted with dehydration to exacer- Participants were instructed regarding adequate fluid intake and bate degradation of cognitive performance (1).
sleep prior to each experiment and refrained from consuming caffeine The present investigation used a battery of tests of cognitive and alcohol for 12 h prior to each. To ensure all participants began each performance, mood, perceived exertion, and symptoms sensitive experiment in a euhydrated state, they consumed 240 mL of supple- to various environmental and nutritional factors, including mild mental mineral water (i.e., above their usual/habitual water intake) onthe night before testing and 240 mL of mineral water upon waking on dehydration (9–11). To avoid confounding effects of high heat the morning of testing. This was supplied as Volvic Natural Mineral exposure, mild dehydration was induced by moderate exercise in Water (Danone), which contained the following dissolved substances a moderately warm environment (mean 6 SD, 27.6 6 0.88C).
(mg/L): calcium, 10; chloride, 8; bicarbonate, 65; magnesium, 6; nitrate, Physiological variables associated with hydration state were also 1; potassium, 6; silica, 30; sodium, 9; and sulfates, 7 (109 mg/L of total assessed. Volunteers were healthy, young females.
dissolved solids). The mineral water also was consumed with a A problem with previous work in this area is the difficulty standardized breakfast and during the experiments (see below). Further, designing a double-blind study of dehydration (1). Therefore, participants consumed the same meals for 24 h prior to each experiment this study disguised the treatment conditions from volunteers to reduce the effects of variation in nutritional intake on outcome and investigators responsible for testing by using several variables. The foods and beverages consumed prior to the first procedures. Inclusion of a positive control condition, dehydra- experiment (i.e., self-selected by each participant) were duplicated forthe second and third experiments. Compliance was verified with dietary tion induced by combination of a diuretic and exercise, disguised records of all food and beverages consumed during the 24 h before each the experimental conditions, because in one of two dehydration experiments, volunteers lost substantial fluid in urine. To further On the morning of each experiment, participants reported to the blind the experimental conditions, a pill (either diuretic or laboratory at 0800 or 0900 h and, after a blood sample was collected, placebo) was administered prior to every experiment and some consumed one capsule under the supervision of an investigator. Capsules fluid, with the volume disguised, was consumed. We hypothe- were prepared by a licensed pharmacist (Compounded Solutions in sized mild dehydration would primarily affect mood and Pharmacy), were identical in appearance, and contained either a diuretic symptoms of dehydration and have modest effects on cognitive (40 mg furosemide; Lasix) or placebo. Volunteers reported at two different times so testing could be staggered (times provided in the textare for women starting at 0800 h). Participants rested quietly in ananteroom adjacent to the testing rooms and consumed no food until1000 h when a standardized breakfast was provided; it contained ;700 kcal (2929 kJ9) + 174 mL mineral water. They also consumed two smallfood bars as snacks [210 kcal (879 kJ)/feeding] immediately after the first Participants. Twenty-five females (age, 23.0 6 0.6 y; body mass, 63.0 610.3 kg) attended an informational briefing and gave informed voluntary (1350 h) and second (1550 h) cognitive test batteries. A blood sample consent to participate in this study, which was approved by the was also collected at 1750 h.
University of Connecticut Institutional Review Board for Human At 1200, 1400, and 1600 h, participants entered the environmental Studies. The women were selected from 30 volunteers. Any woman chamber and began 40 min of dehydrating exercise (described below) who consumed an extreme diet, had evidence of disordered eating, was then rested for 20 min. Participants began identical cognitive test taking medications that altered fluid-electrolyte balance, was restricting batteries at 1300, 1500, and 1700 h. In the DN and DD experiments, the caloric intake, or had a chronic disease (e.g., renal dysfunction) was women consumed no water to replace water loss in urine or sweat, excluded from participation. Use of oral contraceptives for at least three except for 50 mL after completing the first and second cognitive test consecutive months prior to this investigation was an inclusion criterion.
batteries, to wet their palates and disguise the experimental condition.
Test participants were physically fit (i.e., could complete three walking Procedures in the EU experiment were identical to the DN and DD exercise sessions/d) but were neither highly trained nor totally sedentary.
experiments except fluid lost in urine and sweat was replaced by Prior to this investigation, most participated in 30–60 min of exercise on consuming an equal volume of mineral water during and after each 2–4 d/wk. All participants spoke English as their primary language.
exercise bout based on the individual's loss during that session. Ambientlaboratory environmental conditions were controlled and monitored. Inthe anteroom outside the environmental chamber and in the cognitive Experimental design. In this crossover study, women participated in 3-day-long laboratory experiments: 1) exercise-induced dehydration plus testing room, air temperature was maintained at 23.08C. Fluid lost in placebo capsule containing no diuretic (DN); 2) exercise-induced urine during the experiment was assessed by collecting each woman's dehydration plus a diuretic capsule (DD); and 3) euhydration plus total urine output. Sweat loss was calculated as the difference in body placebo capsule (EU). The order of assignment to each of the experi- mass, corrected for urine production and fluid intake.
ments was randomized. All experiments involved an identical exerciseregimen, described below. A third party, not involved in data collection, Exercise dehydration protocol. Participants performed 40 min of randomized and counterbalanced the order of experiments. Test partic- treadmill walking (5.6 km/h, 5% grade) in a moderate-warm environ- ipants as well as investigators in the environmental chamber were ment to produce body mass loss without inducing hyperthermia. Inside unaware of the treatments, but an investigator who monitored water the environmental chamber, where dehydrating exercise sessions were administration was not. The 3 experiments were conducted ;28 d apart conducted, the air temperature was 27.6 6 0.88C, the RH was 49.4 6 during the 7-d placebo phase of each woman's oral contraceptiveschedule. Prior to each experiment, participants presented their emptyoral contraceptive pill packs to a female investigator to verify they were 9 1 kcal = 4.184 kJ.
Armstrong et al.
6.9%, and the wind speed was 3.5 m/s as provided by a floor fan. Body preliminary practice sessions, each volunteer's performance was adjusted mass was measured (650 g) every 13 min during exercise when to a criterion of 60% correct detections.
participants briefly stepped off the treadmill onto a floor scale (Health-ometer model 349KLX). Heart rate was measured every 10 min with a PVT. This is a test of simple visual reaction time (16). A series of stimuli chest cardiotachometer (model S150, Polar Instruments). The T are presented at random intervals on a screen and the participant measured every 10 min of exercise by using an ingestible temperature responds as rapidly as possible when a stimulus appears. Reaction time, sensor (CorTemp, HQ). On the morning of each experiment, each false alarms, and number of lapses (long duration responses) are participant swallowed the sensor upon arrival to the laboratory. After recorded. The test requires sustained attention and responses, performed every exercise session, participants left the environmental chamber, by pressing a button in a timely manner, in response to a randomly moved to a comfortable room (23.08C, dimly lit, quiet), dried their skin appearing stimulus on the computer screen. This is the only portion of and hair with a towel, and rested on a chair for 20 min.
the cognitive test battery that was administered during treadmill The rating of perceived exertion scale [6–20 point scale (12)] was administered at 40 min of exercise; the extreme options on this scalewere "very, very light" and "very, very hard." At the same time, a Four-choice visual reaction time test. Choice reaction time tasks are perceived leg muscle pain intensity rating was obtained from each sensitive to the effects of nutritional factors on cognitive performance woman (13). This scale ranged from 0 ("no pain at all") to 10 (10,17–19). Volunteers are presented with a series of visual stimuli at one ("extremely intense pain, almost unbearable") and offered one unnum- of four different spatial locations on a computer screen. They indicate bered rating option beyond 10 ("unbearable pain").
the correct spatial location of each stimulus by pressing one of four To disguise the experimental condition, participants were unaware of adjacent keys on the computer keyboard. Correct responses, incorrect their body mass, urine volume, and ingested fluid volume during responses, response latency, premature errors, and time-out errors (i.e., experiments. This was accomplished by obscuring the body mass scale response latency . 1 s) are recorded for each test administration.
dial, collecting urine in individual aliquots and removing these samplesfrom the room before placement in the urine collection container, and by Matching to sample test. This test assesses short-term spatial memory providing mineral water in opaque, covered containers. In spite of these (working memory) and pattern recognition skills (17,20). The volunteer efforts, differences in urine flow between conditions may have been is presented with a matrix of a red and green checkerboard on a color detectable by the women. However, upon completion of all testing, screen. The matrix appears on the screen for 4 s, then is removed during a volunteers were not able to distinguish between the hydrated and variable delay involving a blank screen. After the delay, two matrices are presented on the screen: the original sample matrix and a second matrixthat differs slightly (i.e., the color sequence of two of the squares is Physiological variables at rest. A urine sample was collected shortly reversed). The volunteer selects the comparison matrix by touching keys after participants arrived at the laboratory (0800 h) for evaluation of that match the original sample matrix. The task lasts 5 min. If a urine specific gravity via a hand-held refractometer. Immediately response is not made within 15 s, a time-out error is recorded. Correct preceding the final cognitive test battery, the T responses and the response time to choose a matrix also are recorded.
gi was recorded at rest (see previous section). A blood sample was collected when participantsarrived at the laboratory (0800 h) and after the third cognitive test Repeated acquisition test. This test assesses learning and short-termmemory (17). The volunteer is required to learn a sequence of 12 key battery (1700 h). Osmolality was measured in both samples; lactate, presses on the four arrow keys of a computer; this task requires 10 min.
glucose, and cortisol were measured in the 1700-h sample. Osmolalitywas measured in duplicate using a freezing-point depression osmometer The outline of a rectangle is presented on the screen at the beginning of a (model 3250, Advanced Instruments). Lactate and glucose were test. Each correct response fills in a portion of the rectangle with a solidyellow color, from left to right. Each incorrect response blanks the screen analyzed (YSI 2300 Stat Plus) in duplicate using an automated enzymatictechnique. Cortisol was analyzed using a competitive cortisol enzyme for 0.5 s. When the screen returns, the volunteer is at the same point in immunoassay technique (ELISA, DSL-10–2000; Diagnostic Systems the sequence as before the incorrect response. The volunteer has to learn the correct sequence by trial and error. When a sequence is correctlycompleted, the rectangle fills, the screen blanks, and another emptyrectangle reappears for the next test. A test ends when the volunteer Cognitive test battery. Behavioral tasks were selected that assessed abroad spectrum of cognitive functions, from simple abilities to complex completes 15 correct sequences. Each test consists of a new sequence that skills, including vigilance, reaction time, learning, working memory, and is randomly selected from a list of 32 different sequences. Incorrectresponses and time to complete each test are recorded.
logical reasoning. Mood states and symptoms were also assessed. Testingwas conducted 20 min after completing each exercise session in a quiet, Grammatical reasoning. This 5-min test assesses language-based dimly lit room (23.08C) and took 45–50 min to complete. Computerized logical reasoning and has been used to assess the effects of various tasks (NTT Systems; Cognitive Test Software, version 1.2.4) were treatments on cognitive function (21). On each test, a logical statement, administered in the same order during each experiment.
such as "A is preceded by B," is followed by the letters AB or BA. Thevolunteer decides whether each statement correctly describes the order of Cognitive testing at rest. Testing at rest was conducted using desktop the two letters. The "T" key on the keyboard is pressed to indicate that a computer systems running the Windows operating system. Visual stimuli statement is true and the "F" key is pressed to indicate that a statement is were presented on 49-cm (diagonal) LCD monitors (Acer model A1716F). Participant responses were input using keyboards (RazerTarantul, model RZ03–00070100-R2U1) that recorded responses with a POMS questionnaire. The POMS is a widely used, brief, standardized 1-ms response latency.
inventory of mood states (22). It is sensitive to a wide variety ofnutritional manipulations, environmental factors, sleep loss, and sub- Scanning visual vigilance task. This test is sensitive to a wide variety clinical drug doses (14,17–20,23). The volunteers rate a series of 65 of environmental conditions, nutritional factors, sleep loss, and very low mood-related adjectives on a five-point scale, in response to the question, doses of hypnotic drugs and stimulants (14,15). The participant "How are you feeling right now?" The adjectives factor into six mood continuously scans a computer screen to detect the occurrence of stimuli subscales (tension-anxiety, depression-dejection, anger-hostility, vigor- that are infrequent and difficult to detect. The volunteer detects a faint activity, fatigue-inertia, and confusion-bewilderment). A computerized stimulus that appears randomly on a computer screen, approximately version of the POMS was administered during treadmill exercise and once per minute, then presses the space bar on the keyboard as rapidly as during seated rest.
possible. The computer records whether or not a stimulus is detected andthe response time (in milliseconds). Responses made .2 s after a VAS. To complete these scales, the participant placed a mark on a 100- stimulus was presented were recorded as false alarms. During the mm line between extreme answers at opposite ends of the line. The Mild dehydration, mood, and cognitive performance extreme answers were "very strong(ly)" and "not at all strong(ly)." The Morning body mass, urine specific gravity, and sleep questions were, "How hard was the effort required to complete these status of female volunteers prior to testing in the tests?," and "How hard did you have to concentrate to accomplish the dehydration ($1%) or the EU condition1,2 tasks successfully?" Headache symptoms also were evaluated at the endof each cognitive test trial by rating the statement, "I have a headache." Cognitive testing during exercise. In addition to cognitive testing atrest, during each treadmill walking session, three tests, the POMS, VAS, and PVT, were administered on a laptop computer (Sony, Vaio, model Urine specific gravity PCG-5G3L) placed on a stationary platform suspended in front of the Previous night's sleep, h participant while she walked at the required pace. Participants responded using a Razer DeathAdder mouse (model RZ01–00150100- Values are mean 6 SD, n = 25 or 24 (sleep, due to a missing value in the EU R3M1) with a 1-ms response time.
condition). Data were analyzed using paired t tests that compared the dehydratedbaseline values of each volunteer to that volunteer's EU values. DD, dehydration with diuretic treatment condition; DN, dehydration with no diuretic treatment condition; EU, Statistical methods. Statistical analyses were performed using IBM euhydrated treatment condition.
SPSS Statistics v19.0. Due to variability in rate and extent of dehydration 2 For the dehydrated conditions, DN and DD data were averaged if $1% dehydration over the course of the DN and DD experiments, statistical comparisons was achieved at any time point during data collection.
for all dependent variables were conducted only when a volunteer attained a level of dehydration $ 1% body mass loss. A criterion of 1%was established, because this is the lowest level of dehydration that has hostility (P = 0.04) and fatigue-inertia (P = 0.003) as well as a been suggested as capable of altering cognitive function (1,4,5).
decrease in vigor-activity (P = 0.03) (Table 2) when dehydrated.
Variability was expected, because dehydration was induced by The aggregate measure of POMS ratings, the total mood moderate exercise in a temperate environment in the absence of disturbance score also deteriorated when women were dehy- hyperthermia. To determine whether levels of dehydration induced drated (P = 0.01). The 3 VAS administered also detected adverse during DD trials compared to DN trials of $1% body mass loss were effects of dehydration [perceived task difficulty (P = 0.004); different, a paired t test was conducted comparing the change of plasma concentration (P = 0.01); headache (P = 0.05)]. During exercise, osmolality, a standard measure of hydration status, of these conditions atthe completion of testing. The increase in osmolality from the beginning adverse effects of dehydration on the POMS subscales and VAS to end of the test day was nearly identical in the DN (11 6 9 mOsm/kg) also were observed (P # 0.05) (Table 3).
and DD (10 6 6 mOsm/kg; P = 0.58) trials. In addition, a CI-based Physiological measurements revealed that post-exercise Tgi equivalence test demonstrated that the small difference in percent body and heart rate were greater (P , 0.001) following mild mass changes in DN (21.38 6 0.20%) compared to DD (21.37 6 dehydration ($1%) (Table 4). Resting Tgi, immediately before 0.17%) were equivalent (,0.2%; P = 0.93). Therefore, data from the cognitive test administration was greater (P = 0.004) when DN and DD conditions were pooled for analysis.
participants were mildly dehydrated. The change of plasma Results from cognitive tests in which participants had $1.0% body osmolality throughout the experimental day (0800 to 1750 h) mass loss were combined, regardless of whether the dehydration also was greater during $1% than during EU (P = 0.006); occurred in the DN or DD trial, and were compared using a paired however, plasma concentrations of lactate, glucose, and cortisol samples t test to the mean of the corresponding EU tests. This procedureresulted in #25 data pairs. A P value of #0.05 (2-tailed) was the were similar across these experimental conditions (Table 4).
criterion for significance. Values in the text are means 6 SD.
When female volunteers, at rest or during exercise, were dehydrated (mean loss of 1.36% body mass), vigor, fatigue, and When participants reported for testing at 0800 h each day, aggregate mood, assessed by total mood disturbance score, were there were no differences between treatment conditions in body adversely affected. Perception of task difficulty and headache mass, urine specific gravity, or self-reported sleep duration severity increased and ability to concentrate decreased when volunteers were dehydrated compared to their own EU (control) For the DN and DD trials that resulted in a $1% weight loss, trials, at rest, and during exercise. Performance on most aspects mean body mass decreased (21.36 6 0.16%). For the EU of cognitive function assessed, including psychomotor vigilance, experiments, the fluid replacement regimen was deemed suc- reaction time, working memory, and reasoning, was not affected cessful, because body mass declined very little (20.12 6 during mild dehydration with the exception of a small increase 0.05%); for our test participants, this difference was equivalent in visual vigilance false alarm errors.
to 48 mL of water in a total body water of 39.69 L (24).
Limited data are available on mood, cognitive performance, Cognitive performance was for the most part not affected by ability to concentrate, headache, and perception of task mild dehydration. There were no significant changes in the difficulty when volunteers are at rest or actively exercising in a scanning visual vigilance task with one exception (false alarms), mildly dehydrated state. This study demonstrates that, not only PVT, four-choice reaction time test, matching to sample, at rest but also during moderate exercise, a wide variety of repeated acquisition, and grammatical reasoning task (Table 2) adverse changes occur in slightly dehydrated, young, healthy at rest. The single aspect altered on the scanning visual vigilance females. These may, in theory, interfere with motivation to task was false alarm errors (P = 0.02), which slightly increased in continue exercise or other activities. Our findings are consistent the dehydrated condition (Table 2). During exercise on the with a study conducted by Szinnai et al. (11) in which treadmill, performance on the PVT was not affected by dehydration was induced by fluid restriction for 28 h, resulting dehydration (Table 3).
in a mean dehydration level of 2.6% body mass loss. In that When testing was conducted on a desktop computer at rest (i.
study, aspects of mood similar or identical to those we assessed e., quiet room that was adjacent to the environmental chamber, were degraded, with tiredness increasing and alertness and 23.08C, dimly lit), 3 of the 6 POMS subscales were adversely perceived ability to concentrate declining. As in our study, the affected by dehydration. Participants reported increased anger- perceived effort necessary for task accomplishment increased Armstrong et al.
Cognitive performance, mood, and VAS ratings of Vigilance, mood, perceptions of performance and female volunteers at rest in a quiet, dimly lit room symptoms reported during treadmill walking in during EU and dehydrated conditions1 female volunteers during EU and dehydratedconditions1,2 Cognitive tests and Cognitive tests and Scanning visual vigilance Correct responses, n Psychomotor vigilance test Premature errors, n Psychomotor vigilance test Premature errors, n Four-choice reaction time Incorrect responses, n Time-out errors, n Matching to sample Total mood disturbance Correct responses, n Time-out errors, n Repeated acquisition Incorrect responses, n Time to complete, s Grammatical reasoning 1 Values are means 6 SD, n = 25 comparisons. The number of women dehydrated Correct responses, n $1% in DN after exercise bout 1 was n = 2, after exercise bout 2 was n = 14, and after Incorrect responses, n exercise bout 3 was n = 24. In DD, no women were $1% dehydrated after exercise bout 1; 8 women were dehydrated $1% after exercise bout 2, and 23 women weredehydrated $1% after exercise bout 3. DD, dehydration with diuretic treatment condition; DN, dehydration with no diuretic treatment condition; EU, euhydrated treatment condition; POMS, Profile of Mood States; PVT, psychomotor vigilance task; RPE, rating of perceived exertion; VAS, visual analogue scale.
2 PVT and POMS data were recorded on a notebook computer mounted on a stationary platform that was suspended in front of the participant during treadmill 3 P values resulted from paired t tests comparing EU trials to the corresponding mean of DN and DD trials achieving dehydration of $1%.
Total mood disturbance Information-processing when dehydrated during simulated sporting events has also been investigated with similar findings (6–8). During such events, dehydration (21 to 24% body mass) impairs mood, choice reaction time, and vigilance. Although 1 Values are means 6 SD, n = 25 comparisons. The number of women dehydrated these studies assessed effects of mild-to-moderate dehydration $1% in DN after exercise bout 1 was n = 2, after exercise bout 2 was n = 14, and after on cognitive performance during simulated sporting events, they exercise bout 3 was n = 24. In DD, no women were $1% dehydrated after exercise did not determine which aspects of cognitive performance are bout 1; 8 women were dehydrated $1% after exercise bout 2, and 23 women weredehydrated $1% after exercise bout 3. DD, dehydration with diuretic treatment most affected, nor did they assess perceived effort or symptoms condition; DN, dehydration with no diuretic treatment condition; EU, euhydrated of dehydration.
treatment condition; POMS, Profile of Mood States; VAS, visual analogue scale.
The physiological mechanism(s) responsible for deterioration 2 P values result from paired t tests comparing EU trials to the corresponding mean of of mood and related factors due to dehydration is not known.
DN (exercise-induced dehydration with no diuretic) and DD (exercise-induced dehydration plus diuretic) trials achieving dehydration of Hypothalamic neurons detect dehydration (27) and may signal higher-order cortical brain regions regulating mood when initialphysiological indicators of dehydration appear, resulting in with dehydration. Cognitive performance was not affected in adverse mood and symptoms. In humans, dehydration induced that study, although some sex differences in performance were by thermal stress in the same range as this study modified fronto- noted (11). In addition to Szinnai et al. (11), other studies have parietal blood oxygen level-dependent response assessed by not found substantial changes in cognitive performance at functional MRI without affecting cognitive performance (26).
dehydration levels ,2% body mass loss including one we Given the critical physiological importance of maintaining conducted in men (25,26). Our study demonstrates that a wide hydration, adverse changes in mood and related perceptions variety of mood states and symptoms are adversely affected at may serve as a signal that evolved to alert humans before more dehydration of 1.36% body mass loss, which is substantially less severe consequences occur, such as degradation in performance.
than the 2.6% induced by Szinnai et al. (11). In addition, we Once cognitive or physical performance is degraded, survival detected adverse effects in ,8 h and these effects were present may be affected, because the ability to find water or respond to when individuals were both exercising and resting.
threats is diminished.
Mild dehydration, mood, and cognitive performance Tgi, heart rate, and plasma constituents in female dehydration (Tgi change of 0.38C, heart rate change of 9 bpm) volunteers at the end of each experimental session (Table 4) were minimal, making it unlikely that these factors affected mood (37).
In conclusion, this study demonstrates that, in healthy young women, mild levels of dehydration result in adverse changes in key mood states such as vigor and fatigue as well as increasedheadaches and difficulty concentrating, without substantially Postexercise Tgi,3 8C altering key aspects of cognitive performance. Future studies Postexercise heart rate,3 bpm should determine the level of dehydration (i.e., loss) at which cognitive performance initially is degraded in Resting plasma osmolality change,5 mOsm/kg females and which aspects of cognition are most readily affected.
Resting plasma lactate,5 mmol/L We also recommend that the effects of dehydration on cognition Resting plasma glucose,5 mmol/L be examined in young men and at-risk populations such as Resting plasma cortisol,5 nmol/L 92.7 6 43.9 105.4 6 39.2 children, elderly individuals, and those with diabetes or stroke, 1 Values are means 6 SD, n = 25 (resting and postexercise Tgi), 24 (heart rate, lactate, because those medical conditions can result in dehydration (33– glucose, and cortisol, due to inability to complete a venipuncture), or 22 (osmolality, due to equipment malfunction). DD, dehydration with diuretic treatment condition; DN, dehydration with no diuretic treatment condition; EU, euhydrated treatment condition; Tgi, gastrointestinal temperature.
2 Paired t tests compared EU trials to the corresponding mean of DN and DD trials The authors thank Dr. Matthew Kramer and Christina E.
achieving dehydration of $1%.
3 Carvey for statistical assistance and Lauren A. Thompson for At the end of the third 40-min exercise bout (27.68C air temperature).
technical assistance with manuscript revision and submission.
At rest, immediately before cognitive test administration (23.08C air temperature).
5 At rest, immediately after cognitive test administration (23.08C air temperature).
L.E.A., D.J.C., L.J., L.L.B., E.C., and H.R.L. designed research;L.E.A., M.S.G., D.J.C., E.C.L., B.P.M., and J.F.K. conducted research; L.E.A., M.S.G., E.C.L., and H.R.L. analyzed data; This study has a number of practical implications. Although and L.E.A., M.S.G., and H.R.L. wrote the manuscript and had cognitive performance was not substantially impaired in healthy, primary responsibility for its final content. All authors read and young females who were mildly dehydrated, key mood states approved the final manuscript.
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Mild dehydration, mood, and cognitive performance

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