ArticlePDF AvailableLiterature Review

Abstract

No matter how mild, dehydration is not a desirable condition because there is an imbalance in the homeostatic function of the internal environment. This can adversely affect cognitive performance, not only in groups more vulnerable to dehydration, such as children and the elderly, but also in young adults. However, few studies have examined the impact of mild or moderate dehydration on cognitive performance. This paper reviews the principal findings from studies published to date examining cognitive skills. Being dehydrated by just 2% impairs performance in tasks that require attention, psychomotor, and immediate memory skills, as well as assessment of the subjective state. In contrast, the performance of long-term and working memory tasks and executive functions is more preserved, especially if the cause of dehydration is moderate physical exercise. The lack of consistency in the evidence published to date is largely due to the different methodology applied, and an attempt should be made to standardize methods for future studies. These differences relate to the assessment of cognitive performance, the method used to cause dehydration, and the characteristics of the participants.
Review
Cognitive Performance and Dehydration
Ana Adan, PhD
Department of Psychiatry and Clinical Psychobiology, School of Psychology, and Institute for Brain, Cognition, and Behavior,
University of Barcelona, Barcelona, SPAIN
Key words: cognitive performance, dehydration, attention, psychomotor skills, memory, mood
No matter how mild, dehydration is not a desirable condition because there is an imbalance in the homeostatic
function of the internal environment. This can adversely affect cognitive performance, not only in groups more
vulnerable to dehydration, such as children and the elderly, but also in young adults. However, few studies have
examined the impact of mild or moderate dehydration on cognitive performance. This paper reviews the principal
findings from studies published to date examining cognitive skills. Being dehydrated by just 2%impairs
performance in tasks that require attention, psychomotor, and immediate memory skills, as well as assessment of
the subjective state. In contrast, the performance of long-term and working memory tasks and executive functions
is more preserved, especially if the cause of dehydration is moderate physical exercise. The lack of consistency in
the evidence published to date is largely due to the different methodology applied, and an attempt should be made
to standardize methods for future studies. These differences relate to the assessment of cognitive performance, the
method used to cause dehydration, and the characteristics of the participants.
Key teaching points:
This paper reviews the existing findings about the impact of dehydration in the main cognitive skills explored so far.
Children and the elderly are the populations most vulnerable to dehydration.
Healthy young adults are also at risk of a decrease in their cognitive performance when hydration is not adequate.
Attention, psychomotor, and immediate memory skills, as well as assessment of the subjective state, are the brain capabilities
most vulnerable to mild or moderate dehydration.
The relationship between hydration and cognitive performance is an emerging area of study of undoubted practical interest in
which much research still need to be carried out.
INTRODUCTION
Severe dehydration inevitably leads to marked decline in
overall functioning, including capacity to perform cognitive
tasks, and can lead to delirium, coma, and death [1–3].
Dehydration is defined as a deficit of body water when fluid
output exceeds intake and is classified as severe if the loss of
body water is more than 5%. Although this state is rare in the
general population, a state of mild or moderate dehydration can
be reached easily, and this should be an important area for
study. A state of mild dehydration is defined as a 1%–2%loss
of body water, whereas moderate dehydration is when the loss
is in the region of 2%–5%. The change of body water was
usually measured by the change of body weight, because when
an individual is in a caloric balance a body-weight loss
essentially equals water loss.
Adequate hydration is an important factor in the prevention of
accidents at work or the development of disease. This is because
it enhances performance in both physical and mental tasks and
improves the perception of well-being [4,5]. No matter how mild,
dehydration is not a desirable condition because it means there is
an imbalance in the homoeostatic function of the internal
environment [3]. This can adversely affect cognitive capacity and
interfere with adequate performance of work- or study-related
activities that require the use of specific mental skills.
The risk of suffering from dehydration is greater among
particular groups such as children, the elderly, pregnant
women, infants, and athletes who, for different reasons, are
Address reprint requests to: Ana Adan, Department of Psychiatry and Clinical Psychobiology, School of Psychology, University of Barcelona, Passeig de la Vall d’Hebron,
171, 08035 Barcelona, SPAIN. E-mail: aadan@ub.edu
The study was funded by the author. The author declares that she has no competing interests.
Journal of the American College of Nutrition, Vol. 31, No. 2, 71–78 (2012)
Published by the American College of Nutrition
71
much more vulnerable to body-water loss [6–8]. Nevertheless,
we should not ignore the fact that healthy young adults can also
become dehydrated and suffer the negative consequences, even
when not exposed to adverse environmental conditions, and we
should, therefore, be aware of how to prevent it [3]. For
example, it is estimated that the spontaneous drinking pattern
among young adults who work in high temperatures or do
strenuous exercise only replenishes two thirds of the total water
lost. In such cases, it has been found that workers do not drink
enough fluids during the working day and even arrive at work
already dehydrated [5]. Although few studies have assessed the
degree of hydration in schoolchildren or students—at all levels
of education—the data all point in the same direction [7,9].
Recent initiatives, such as those in the United States, England,
and Germany, that promote adequate hydration in schools
during the school day, have resulted in better concentration and
willingness to learn within class groups [7].
BACKGROUND
A large number of scientific studies have been conducted to
determine the extent and duration of the impact of dehydration
caused by physical exercise or sports activities. They examine
the impact of dehydration on various skills such as strength,
power, and speed [10,11] and the relationship with the factors
that induced the dehydration, including the form of rehydration
(if this was provided for in the design) and the environmental
conditions [12]. Consequently, it is estimated that a 2%loss of
body fluids causes a 20%decline in physical performance. Not
many studies, however, have looked at the impact of
dehydration on cognitive performance, and methodological
limitations do not allow us to extrapolate results or derive
robust conclusions.
This paper reviews the currently available findings on the
effects of dehydration on cognitive performance with a brief
reference to the possible underlying neurofunctional bases of
the data gathered to date. Attention, psychomotor, and memory
skills, the executive functions, and the subjective state of
activation and mood are considered individually because these
aspects have been the most widely studied. In addition, certain
methodological aspects are discussed that need to be
considered in future research with regard to the assessment of
cognitive performance, the method of inducing dehydration,
and the participants’ characteristics, which would help to
achieve greater understanding in this field.
DESCRIPTION OF SUBJECT
Neurofunctional Bases of Dehydration
Changes in the amount of electrolytes in the body that occur
when dehydrated can alter brain activity and the functioning of
some of the neurotransmitter systems involved in cognitive
processing [1,13]. It has also been found that dehydration is
associated with changes in blood-brain barrier permeability and
decreases in the blood flow in some areas of the brain [2]. Most
previous studies addressing this issue are reviews, and it is
necessary to specify that the original data on aspects of brain
function are circumstantial and were obtained indirectly.
Using positron emission tomography, Farrell et al. [14]
found that a state of osmotic thirst induced with hypertonic
infusions is related to changes in the blood flow in specific
brain areas such as the primary somatosensory cortex, the
motor cortex (motor control), the prefrontal cortex (executive
functions, including planning and inhibitory control), the
anterior cingulate cortex (emotions and decision making), and
the superior temporal gyrus (auditory processing). These
changes are more pronounced in the elderly than in young
people. Younger subjects may exhibit cognitive compensating
mechanisms for increased tiredness and reduced alertness
during slowly progressive moderate dehydration through
increasing subjective task-related effort [15].
The brain-stem monoaminergic systems are the neurotrans-
mitter systems primarily involved [2]. Both the dopaminergic
and noradrenergic systems are important in controlling
attention, motivation, and fatigue, and there may be a decrease
in transmission in these systems when the body is dehydrated.
The serotonergic system has also been linked to a possible
impact on performance, particularly on the subjective percep-
tion of dehydration, although findings have been contradictory.
Dehydration impairs cholinergic neuromuscular transmission,
with a negative influence on performance in psychomotor tasks
[7,16].
A state of dehydration leads to the activation of the
hypothalamic-pituitary-adrenocortical axis and to the subse-
quent production of stress hormones such as cortisol.
Rehydration, however, is associated with significant decreases
in cortisol levels. An increase in the cortisol level may be an
underlying factor in the negative effects on various cognitive
functions such as perception, spatial ability, and memory
[7,17,18].
In response to dehydration, vasopressin (antidiuretic
hormone) is also secreted. Elevated plasma levels of vasopres-
sin can prove beneficial for learning and memory tasks
[7,19,20]. Furthermore, proper hydration affects the levels of
glycerol in the body and the adequate availability of glucose in
the central nervous system [21–23], which is known to enhance
learning and memory [24,25]. The production of neuronal
nitric oxide as a result of glutamatergic hyperexcitation has also
been dose-dependently associated with dehydration [13], which
may explain the mixed evidence on the impact of dehydration
on the performance of memory tasks.
Future studies need to include endocrine and biochemical
measurements, functional neuroimaging data, the quantification
of the state of dehydration, and assessments of cognitive
72 VOL. 31, NO. 2
Cognitive Performance and Dehydration
performance. This will be key for clarifying the underlying
biological aspects and to provide evidence to back previous
findings by assessing performance in similar tasks.
Attention and Psychomotor Skills
The performance of simple attention tasks was not usually
significantly impaired in states of dehydration of 1%–2%in
cold environmental conditions when assessing both the
processing rate or reaction time and accuracy or adequate
performance [12,23,26,27]. In contrast, states of dehydration
that exceeded 2%often negatively affected the attention and,
consequently, the proper performance of these tasks by young
subjects, even when evaluated at rest, when heat exposure or
exercise are the methods of dehydration [12,21,22,28–30].
Speed is the most sensitive performance parameter, although
the number of correct answers may not be affected. A recent
study by D’Anci et al. [30] also found dehydration to have a
greater negative effect on women’s performance than that of
men.
In tasks assessing reaction time to visual stimuli, no effect
was observed on the response rate for dehydration states of 2%
or higher, whether caused by fluid deprivation [15,27–30],
exposure to physical activity [30,31], or both [20]. Moreover,
dehydration increased the response rate to peripheral stimuli—
a pattern that was more emotional than performance related—
without affecting the rate of the central stimuli [26,32]. This
effect has not been found in other studies, but it seems to
disappear in motivated and trained participants [32]. The
gender factor in the performance of these tasks is essential
because in young dehydrated women, a significant decrease
was observed in both the response rate [15] and the number of
errors [30], whereas men were unaffected.
Studies with schoolchildren (6–12 years) in a state of
voluntary dehydration caused by not drinking enough fluids
despite having water available, whether environmental condi-
tions were adverse or not, showed that those who did not drink
water performed worse in tasks of visual attention and
perceptual speed midmorning than those who drank water
[8,9,33]. It is remarkable that only Bar-David et al. [9] formally
assessed the hydration status of the children, whereas all the
other studies assumed it without doing objective measure-
ments.
Other findings that require further investigation come from
the study by Rogers et al., [34], in which drinking a glass of
water improved the performance of young healthy subjects
who were thirsty in a task of simple reaction time to visual
stimuli, whereas drinking a glass of water worsened the
performance of those who were not thirsty but drank it anyway.
The decrease in reaction time in the former and the increase in
the latter is dose-dependent (they consumed 120 ml or 330 ml
of water) and is maintained for 50 minutes postconsumption
(measured at 2, 25, and 50 minutes). This suggests that
overhydration is also not beneficial to the processing rate for
visual information.
Loss of body water of 2%or more leads to a decrease in the
performance of psychomotor tasks that require visuomotor or
hand-to-eye coordination, regardless of the method used to
induce dehydration. This has been found in both young healthy
individuals [21,22,28,35] and in elderly people [6], with
performance worsening as dehydration increased. The study by
Devlin et al. [36] with cricketers with highly trained hand-to-
eye coordination skills found that a 2.8%state of dehydration
did not influence the velocity of bowling but did greatly affect
its accuracy. Through the fluid deprivation method, the effect
on psychomotor performance was noted as early as 9 AM in
young, healthy subjects [35].
Studies evaluating different levels of dehydration have also
shown a dose-response relationship with the deterioration in
psychomotor task performance. In young subjects, there was a
decrease in both speed and efficiency at 2%water loss, which
increased if the level of dehydration was 3%[37] and 4%[38],
regardless of environmental conditions. Furthermore, the effect
was already apparent at 1%dehydration if the measurements
were taken in a hot, dry environment (458C and 30%humidity)
[37]. Although there are still relatively few works in this area,
motor pathways may be more sensitive to functional
impairment in these environmental conditions than those
involved in other attentional tasks.
Memory and Executive Functions
A level of dehydration greater than 2%decreased the ability
of short-term memory for the presentation of verbal and
numerical material in both young adults [20–22,28,37] and
elderly people [6]. This was observed regardless of the method
used to induce dehydration and of the environmental conditions
in which the measurements were taken. Gopinathan et al. [38]
found a significant detrimental effect on the short-term memory
of verbal material (remembering words), with a higher number
of incorrect answers at 1%water loss, which increased dose-
dependently in dehydration states of 2%,3%,and4%.
Schoolchildren in a state of voluntary dehydration also
performed worse on a short-term memory task—number
sequences—carried out at midday than did those who were
hydrated [9]. The impairment of short-term memory due to
fluid deprivation was evident from 9 AM in young, healthy
subjects [35].
Data on the impact of dehydration on the working memory
are more heterogeneous and appear to be mediated by the
method used to induce dehydration. Using an arithmetic
addition task of 5 digits presented orally, and with exposure
to heat and fluid deprivation, Gopinathan et al. [38] observed a
lower percentage of correct answers at 2%dehydration that
increased at 3%and 4%. On the other hand, Sharma et al. [37],
using moderate exercise and exposure to heat, found no
significant differences in the performance of a very similar task
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 73
Cognitive Performance and Dehydration
with dehydration levels between 1%and 3%. Moreover, Patel
et al. [20] did not find any negative effects in the Sternberg
working memory test, using exposure to moderate exercise and
fluid deprivation. Finally, Edmonds and Burford [8] found that
a group of children who consumed water performed better on
working memory tests compared with those who did not
consume water.
In long-term memory tasks that assess learning at the same
time, no negative effects were observed in mild or moderate
dehydration caused by moderate physical exercise in young
adults [21,22,30,39]. In elderly subjects, impaired mnemonic
ability was observed after fluid deprivation during the night [6]
using a battery of neuropsychological tests that included
estimators of learning and spatial, verbal, and numeric
memory. In contrast, the same method and the administration
of a bowel preparation for diagnostic tests did not yield
significant results in elderly subjects with a dehydration level of
approximately 2%[40].
Moderate physical exercise in cold environments can have
activating effects on cognitive performance in working and
long-term (consolidation) memory tasks, thus compensating for
performance deficits caused by mild to moderate states of
dehydration [31,39,41]. This is particularly evident in the first
20 minutes following exercise and depends on the type of
activity [42]. The increase in core body temperature produced
by exercise and the increased activity of the dopaminergic,
noradrenergic, and glutamatergic systems of the central
nervous system (CNS) have been identified as factors that
explain these benefits that temporarily compensate for the
effects of dehydration [2,13,41]. However, with prolonged
exercise at high temperatures, adverse cognitive effects can
occur as a result of alterations in thermoregulation (reaching
the level of hyperthermia), blood-brain barrier permeability,
and cerebral blood flow [43].
The assessment of executive functions involves the
implementation of various higher processes to accommodate
new or complex situations in which the individual has to
activate a process such as inhibition, planning, and problem
solving [44]. In mild to moderately dehydrated young subjects,
no decrease in performance was observed in a mental
concentration test following physical exercise [45] or with
fluid deprivation in the Stroop task, which measures response
inhibition ability [15], or a planning task [30]. In contrast, Cian
et al. [22] found that young subjects dehydrated following
physical exercise performed worse on a decision-making task,
although this was temporary with a duration of about 3.5 hours.
Schoolchildren in a state of voluntary dehydration also
performed worse on a verbal analogies task compared with
those who were adequately hydrated [9]. A study of elderly
subjects dehydrated by fluid deprivation found no negative
effects on performance of the Trail Making Tests task, which
measures inhibition ability and cognitive flexibility [40]. The
few studies that have evaluated the impact of dehydration on
executive functions tasks do not allow conclusions, although
significant data obtained encourage the development of new
studies.
Subjective Assessments
When fluid deprivation was used as a method to induce
dehydration, young, healthy subjects showed a significant
decline in subjectively assessed concentration ability and
alertness with a 1%loss of body water at 13 hours, which
increased after a 24-hour restriction (1.8%loss of body water)
and at 37 hours (2.7%loss of body water). Moreover, marked
subjective tiredness and headaches were evident from 24 hours
onward [6,15,27,35,46].
A level of dehydration of more than 2%resulted in marked
decreases in subjectively assessed alertness and concentration
ability and increased fatigue, tiredness, and drowsiness, as well
as headaches, in young subjects [20–22,30,37], regardless of
whether the method to induce dehydration was exposure to
heat, physical exercise, fluid deprivation, or any combination.
Shirreffs et al. [46] found no significant gender differences in
the subjective effects of dehydration.
The study by Rogers et al. [34] showed that drinking a glass
of water improved subjective alertness and perception of
revitalization in a similar way in both thirsty and nonthirsty
subjects, contrary to what was observed with performance in
information processing. The effect was greater after consuming
330 ml of water than after 120 ml, occurring just 2 minutes
after consumption, but also dissipated quickly at 25 minutes
postconsumption. In schoolchildren, drinking water during the
school day had a positive effect on their subjective assessments
of thirst and happiness compared with those who remained in a
state of voluntary dehydration [33].
Methodological Issues
Assessment of Cognitive Performance. The complexity of
assessing cognitive performance can be a problem when
conducting studies in this research area. It encompasses many
specific functions or skills (e.g., attention, motor control,
learning, memory, and reasoning). Moreover, although there
are hundreds of standardized neuropsychological tasks, even
the simplest ones often require the use of more than one
function, and there is not always a consensus on their
sensitivity. The performance of a task can be assessed using
estimates of the response rate and/or accuracy (correct answers,
errors, and lapses). However, given that dehydration may not
affect these elements equally, they should all be recorded.
Many of the standardized neuropsychological tasks for
attention, memory, and executive functions are very useful for
detecting pathological conditions in clinical examination.
Nevertheless, this is not the case when they involve healthy
individuals because their performance is often in the normal
range of the available scales. The selection of specific tasks
74 VOL. 31, NO. 2
Cognitive Performance and Dehydration
carried out in psychopharmacological research might be more
useful and sensitive for detecting the effects associated with
mild dehydration over the whole range of cognitive functions.
In addition, individual variability is important in estima-
tions of performance and can result in a high dispersion of
scores that does not provide significant results, even when
controlling for the numerous socio-demographic and individ-
ual factors that are known to influence cognitive performance.
Individual variability is minimized when designing repeated
measurements, making this an excellent option for studies on
biological parameters. Nevertheless, the use of these designs
in the assessment of cognitive performance may lead to
fatigue and/or learning effects that are impossible to determine
a posteriori, which is a problem for obtaining reliable and
valid results [44,47]. This explains why most studies use a
small number of very simple tasks, but this makes it difficult
to extrapolate the results to the social and occupational
cognitive demands that people are subjected to in reality. In
this regard, as an example, it seems something of a paradox
that there has been no assessment of the effect of dehydration
on attention or reaction-measuring tasks using somatosensory
or auditory stimuli, even though these processing pathways
can be even more sensitive than the visual routes [48], which
in the main are those that are studied. The use of
counterbalanced designs in the future may be an option to
overcome these limitations.
It is a well-established fact that there are diurnal variations
in both physical and cognitive performance associated with
circadian rhythm expression, which also depend on the skill(s)
required for a specific task to be performed [44,47]. It is
estimated that intraindividual variation in cognitive test
performance, depending on the time of day, may be 20%
when comparing the best and worst moments of performance.
However, only a few studies mention and/or control the time of
day when the measurements are taken.
Method of Inducing Dehydration. The methodology
selected to induce dehydration is a key element in the study
of hydration and cognitive performance. The most common
methods, due to their efficiency and speed, are exposure to heat
(358C–458C, varied relative humidity) and sustained and
controlled aerobic exercise—the active method of dehydra-
tion—that may be carried out exclusively or combined. The use
of both methods requires a substantial degree of expertise in
order to achieve reliable changes in the hydration levels of the
participants, and their effects on the body may not be identical
[1,11].
Another problem is the characteristics of the study
participants when heat exposure or exercise are the methods
of dehydration, which often do not allow for the extrapolation
of the results to the general population. Athletes, people who
regularly practice sports, and active soldiers are often selected
to take part. These people are accustomed to both methods of
dehydration and may have an accelerated general metabolism
in order to meet increased energy needs. Consequently, they
may present higher levels of dehydration compared with
participants who perform more sedentary activities. Instead,
those dehydration levels might not be associated with
significant effects on cognitive performance on these people.
The passive dehydration method can also be used, which
involves the deprivation of water or liquids and solids with
high water content [46,49]. This requires a considerable period
of time—at least 9–13 hours—which does not pose a problem
for taking biological measurements but can be an issue for
cognitive performance and subjective condition measurements
because these measurements may be affected by the additional
factors of changes caused by the duration of the study period,
such as fatigue or boredom [1,32].
Moreover, if there is no control group that is also exposed to
the dehydration method (exercise, heat exposure, and/or
deprivation of fluids) but remains suitably hydrated, the
experimental design introduces confounding factors that are
impossible to identify a posteriori in the results [1,32]. As
such, the comparison of premeasurements and postmeasure-
ments does not allow us to determine whether the changes
observed are the sole result of dehydration, exposure to the
stress methods used to induce such dehydration, or a
combination of both [3]. It is also necessary to clarify the
relationship between intensity and duration of all the
dehydration methods, individually and combined, in terms of
biological parameters and, in particular, cognitive performance.
The temperature of the environment in which the experiment
recordings are made is another key element. A decrease in
cognitive performance is been observed, particularly apparent
in hot environments compared with thermoneutral or cold ones
[31,50]. When the temperature of the environment is not
specifically being studied in the field work, it is often excluded
altogether, even though the results could be influenced by an
environmental factor.
The few existing studies with dose-response designs have
already found effects of 1%dehydration on some tasks.
Because dehydration can occur in a range of many different
levels and varies among subjects, the dose-response assessment
of cognitive effects constitutes an appropriate strategy for
internal control [1] if the selected cognitive tests allow for
repeated measurements.
In addition, determining the level of dehydration by
estimating the loss of body water is one of the most widely
used in studies because it is the most universal, valid,
inexpensive, feasible, and the quickest indicator. However,
this causes bias in the real state of hydration of individuals due
to the variability in body fat, and, moreover, there are no
reference values for the general population [4]. Other biologic
methods for a more precise dehydration diagnosis are available,
for example, tracer techniques and plasma or urine osmolarity
rates [51,52], that should be used in research on cognitive
effects.
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 75
Cognitive Performance and Dehydration
The type of drink used to rehydrate, if this is included in the
study, is also a variable to take into account. The benefit of
using only water to determine the effects of dehydration on
cognitive performance has already been indicated [23] because
it is the most widespread beverage. Nevertheless, the use of
other beverages that are known to result in greater physiolog-
ical and cognitive benefits for the participants should also be
considered. The composition of commercial sports drinks
allows for the rapid absorption of water and electrolytes.
Moreover, their carbohydrate content (between 6%and 8%)
increases glucose levels in the body, which is essential for
correct physical and cognitive performance [24,29]. The
consumption of low doses of caffeine with glucose, as
contained in soft drinks, could also be a better strategy than
drinking more water in order to boost performance in sustained
attention, learning and memory tasks [25,53]. Last, energy
drinks that contain both glucose and caffeine together with
other psychoactive substances (e.g., taurine or ginseng) that
improve cognitive performance [54,55], should also be
assessed. However, regular consumption of these in large
quantities is not recommended.
Participant Characteristics and Habits. Gender has been
found to be a determining factor in relation to differences in
levels of dehydration and their correlates with cognitive
performance. On average, women have lower body-water
content, and the use of the change in body-weight method that
is based on water loss represents a higher percentage compared
with men [46]. The impact of mild to moderate states of
dehydration on cognitive performance is greater on women than
on men, even when using body-weight estimates as detailed in
the preceding sections. However, most studies include either
only men in their samples or participants of both genders,
without studying them separately [42]. In the future, more
research is required on gender differences, and suitable control
for menstrual cycle should also be included because this may be
a modulating factor in the results. Hormonal changes have been
associated with fluid retention in the luteal phase of the cycle
and, consequently, with increases in body weight and effects on
the state of hydration [28,56]. There is also evidence that the
menstrual cycle affects cognitive task performance [57], which
is better in the luteal phase in terms of attention tasks and in the
ovulatory phase for visuospatial memory [58].
Over the last 20–30 years, circadian typology has been
found to be the most important individual difference in the way
people function, with 3 groups being considered: morning type,
intermediate (or neither type), and evening type. This typology
determines the differences in the optimum moments for
biological and behavioral parameters that, for the performance
of attention tasks, can be as much as 12 hours [59,60].
Circadian typology may be a decisive factor when analyzing
the effects of hydration on cognitive performance, and the
failure of previous studies to take this aspect into account may
explain the contradictory results. Likewise, the normal sleep
pattern—duration and quality—of the participants is another
variable related to the quality of the waking period, although
the studies that do consider it only analyze the night(s)
immediately prior to the experimental measurements.
Although most studies check for the consumption of
psychoactive substances (e.g., alcohol, nicotine, caffeine) for
a few hours before and during the experiments, the partici-
pants’ usual consumption is rarely taken into account and that
could affect the results of performance and subjective state.
Caffeine, owing to its widespread use in the population, is an
example. Although caffeine does not adversely affect hydra-
tion, if the participants regularly consume large quantities, they
could suffer from withdrawal during the measurements [60,61],
especially in prolonged procedures such as fluid deprivation
[1]. The use of medicines for a large number of different
conditions could also influence the hydration state and have
both positive and negative effects on cognitive performance.
For example, the use of diuretics in hypertensive subjects or of
laxatives causes dehydration [51], and antihistamines can
impair performance. This, therefore, needs to be properly
assessed and controlled when selecting participants. Moreover,
it is very useful to include objective analytical measurements
(urine, blood, and saliva) to confirm adherence to the dietary
and/or pharmacological precautions requested in the studies.
Last, there are other participant-related variables that are
known to influence the performance of cognitive tasks, such as
the level of education, personality traits related to stress levels
and the response to stress (i.e., anxiety), and the effects on
motivation of receiving payment for taking part in the study.
All of these should be specified in the relevant methodology
sections of the research because they could be factors that
explain the differences observed in the impact of dehydration
on the performance of very similar tasks.
CONCLUSION
The relationship between hydration and cognitive perfor-
mance is an emerging area of study, in which much research
still needs to be conducted. Existing data show that, in the
multivariate explanatory health model, good hydration is a
factor of specific importance [3,4] that needs to be taken into
account. Looking after hydration status, even when failing to
perceive the warning signs of thirst, is important. This factor
may affect physical and intellectual performance, even if
people are sedentary or in optimal climate conditions. Children
and the elderly are the population groups most vulnerable to
dehydration; however, healthy young adults are also at risk of a
reduction in their cognitive performance. Evidence suggests the
tasks that require attention, immediate memory, and psycho-
motor skills, as well as assessment of the subjective state, are
the most negatively affected. In contrast, working memory,
long-term memory, and executive-function skills seem to be
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Cognitive Performance and Dehydration
more preserved, especially if the method used to induce
dehydration is moderate physical exercise. Campaigns are
required to educate and promote awareness among the general
population about the importance of looking after their
hydration levels on a daily basis. Such campaigns require a
solid base of new evidence, both scientific and clinical, from
the study of large samples of participants of both genders, with
suitable control of factors that are known to lead to biased
results. This would enable a more in-depth understanding of the
effects of dehydration on cognitive performance and allow a
more reliable extrapolation of the results to the general
population.
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Received July 30, 2011; revision accepted February 6, 2012.
78 VOL. 31, NO. 2
Cognitive Performance and Dehydration
... Insufficient water intake is negatively associated with cognitive performance, attention, psychomotor, and immediate memory skills among young adults [96]. With no official guideline for water intake, the national DGE recommendation for young adults (2.7 L/day) falls in between the USA recommendations (Institute of Medicine) and European guidelines (Food Safety Authority) [64]. ...
... Given the above findings, multipronged strategies need an overarching focus highlighting the health-academic achievement links, e.g., insomnia, excessive alcohol and dehydration that are associated with poorer academic performance and cognition [96,99,[121][122][123]. Efforts should consider student participation in all student health promotion processes, target the student body, and particularly the identified risk groups e.g., males (lower FVC), females (eating more during stress), and BSc students (poorer nutrition/sleep quality, more ATOD use). ...
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University students frequently engage in unhealthy behaviors. However, there is a lack of studies examining a wide range of their lifestyle characteristics by sex and academic level of study. This cross-sectional survey of students enrolled in BSc, MSc, or PhD programs at one university in Germany (N = 3389) assessed physical activity (PA), sedentary behavior (SB), nutrition, sleep quality, and alcohol, tobacco, and other drug (ATOD) use by sex and academic level and was conducted with EvaSys version 8.0. Chi-squared tests compared categorical variables by sex, and binary logistic regression analyses adjusted for sex with Bonferroni adjustments evaluated differences across academic level. Although 91% of students achieved the aerobic PA guidelines, only 30% achieved the muscle strengthening exercises (MSE) guidelines, and 44% had high SB. Likewise, <10% met the fruit and vegetable consumption (FVC) recommendations, >40% of students experienced impaired sleep, and >30% had hazardous alcohol consumption. Less than 20% of the sample achieved the guideline/recommendation of all three PA, MSE and SB. Some behaviors exhibited significant sex and academic level differences. The identified at-risk groups included males (lower FVC), females (eating more during stress), and BSc students (poorer nutrition/sleep quality, more ATOD use). Given the above findings, multipronged strategies are needed with an overarching focus highlighting the health-academic achievement links. Behavioral interventions and environmental policies are required to raise awareness and promote student health.
... The RAF Air Ambulance for severely injured patients cost circa £300k/hour. 20 Efforts to reduce this cost and, where possible, retain key enabling personnel in location will benefit the individual and wider organisation-and therefore should be further explored. ...
... Environmental factors, hydration, sleep deficit and suboptimal nutrition might separately or in combination increase injury occurence. [20][21][22][23] Military training exercises can involve interrupted sleep, limited food choice and periods where dehydration occurs due to exertional sweat and respiratory water losses. Anecdotally, it was recognised in this study that environmental factors might also have played a role in the development of musculoskeletal injury, but further work is needed in this area. ...
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Introduction The Royal Marines provide the lead Service for UK Defence Mountain and Cold Weather Warfare capability. This is the first prospective study addressing musculoskeletal injury rates sustained during Cold Weather Warfare training, with the aim of informing injury mitigation interventions and assist military medical planning with respect to delivering primary care rehabilitation in theatre. Methods All musculoskeletal injuries were surveyed by the Forward Rehabilitation Team (Nov 2019–Mar 2020) during a Cold Weather Deployment to Norway (Ex CETUS 2019/20). The frequency, nature of injury (new or recurrent), onset (sudden or gradual), cause, location and exercise/treatment outcome were recorded. Results Eleven per cent (n=136 cases) of the deployed population (n=1179) reported a musculoskeletal injury, which were mainly ‘new’ (62%), and with a ‘sudden’ onset (64%). Injury rate was 17.8 injuries per 10 000 personnel days. The majority of injuries occurred due to military training (88%), specifically during ski-related (61%) and load carriage (10%) activities. The average Service Person treated by the Forward Rehabilitation Team improved from ‘injured with restricted duties’ to ‘fully fit’, and with an improvement in their self-reported Musculoskeletal Health Questionnaire from 33 to 45 over an average of two rehabilitation sessions. One hundred and seventeen Service Personnel were able to continue on Ex CETUS with rehabilitation in theatre, thus negating the requirement for aeromedical evacuation for continuation of rehabilitation in the UK. Nineteen patients were unable to continue their Cold Weather Deployment due to the nature of their musculoskeletal injury and returned to the UK for continued care in firm base rehabilitation centres. Conclusion This study identifies the nature, causation and injury location. It demonstrates the effectiveness of in-theatre rehabilitation and the ability to treat patients when deployed. Recommendations are presented to support strategies to mitigate musculoskeletal injury risk during future Cold Weather Warfare deployments to Norway.
... If poorly managed, water content of the fluid compartments can lead to a deficit (hypohydration) (Greenleaf 1992). Whilst research continues to explore the effects of hypohydration on exercise performance and physiological responses (Cheuvront and Kenefick 2014;Deshayes et al. 2020), the potential that changes in water content might have on cognition remains equivocal (Adan 2012;. Despite this, Position Statements often indicate that moderate hypohydration (≥ 2% in body mass) is detrimental to cognitive performance (Sawka et al. 2007; Thomas et al. 2016). ...
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It is unknown how hypohydration influences fine motor performance training and motor learning. Here, 30 participants (aged 19–46 years) were randomly assigned to a hypohydration (HYPO) or control (CON) group (both n = 15). Moderate hypohydration (~ 2.4% loss in body mass) was produced in HYPO via active dehydration before a 46 min fluid restricted rest period was undertaken. The conclusion of rest coincided with when CON attended the facilities. Both groups undertook a discrete sequence production task consisting of 6 training blocks, and returned ~ 300 min later to complete a delayed retention and transfer test while euhydrated. Bilateral pre-frontal cortex (PFC) haemodynamics were assessed using functional near-infrared spectroscopy throughout training and delayed learning assessments. Response time improved across training ( P < 0.01) and was similar between the groups (both P = 0.22). Analysis of training PFC haemodynamics revealed a significant group by block interaction for oxygenated (O 2 Hb; P < 0.01), but not deoxygenated haemoglobin ( P = 0.77). In training block 1, bilateral O 2 Hb was higher in HYPO ( P = 0.02), while bilateral O 2 Hb increased in CON between blocks 2–3 and 5–6 (both P ≤ 0.03). During the delayed retention and transfer test, no group differences or interactions were found in response time, response error, or PFC haemodynamics (all P ≥ 0.27). Moderate hypohydration does increase PFC activation during motor skill learning, however, this appears to be transient and of little consequence to training or delayed retention or transfer performance.
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The global COVID-19 pandemic has revealed the extent to which schools are struggling with the provision of safe drinking water, sanitation and hygiene (WASH). To describe the WASH conditions in schools and discuss the implications for the safe reopening of schools during the ongoing COVID-19 pandemic, a systematic review of peer-reviewed literature on WASH in schools in low- and middle-income countries was performed. In April 2021, five databases, including MEDLINE (via PubMed), Web of Science, Scopus, AJOL, and LILACS, were used to identify studies. Sixty-five papers met the inclusion criteria. We extracted and analyzed data considering the Joint Monitoring Programme (JMP) definitions and the normative contents of Human Rights to safe drinking water and sanitation. Publications included in this systematic review considered 18,465 schools, across 30 different countries. Results indicate a lack of adequate WASH conditions and menstrual hygiene management requirements in all countries. The largely insufficient and inadequate school infrastructure hampers students to practice healthy hygiene habits and handwashing in particular. In the context of the COVID-19 pandemic, being hindered to implement such a key strategy to contain the spread of SARS-CoV-2 in the school environment is of major concern.
... A loss of 10% of body water may be fatal. Reduction in body weight of 2 to 3% are considered to impair cognitive performances [21], although the literature is inconsistent with some studies indicating that a dehydration level of 1% may already affect cognitive performances [22], impair exercise performance and increase the risk of kidney stones [23]. Fluid intake following dehydration was found to improve exercise performance, whereas evidence for improved cognitive performance was limited [24]. ...
Technical Report
Given the limited amount of current evidence linking total water intake to health outcomes, further data would be needed to guide evidence-based recommendations on water intake. In particular, scientific evidence on the levels of long-term water intake needed to reduce the risk of common chronic diseases is currently limited.
... However, so far, it was unclear whether positive effects can only be accomplished by medication or routinely used products may also lead to improved well-being and an improved health status. Previous studies have shown that dehydration can lead to decreased cognitive performance (Grandjean and Grandjean, 2007;Adan, 2012) and physical functioning (Baker et al., 2007). Our study aimed to analyze the effects of OLPs when subjects used a commonly used product. ...
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In recent years, the postulation that deception is necessary for placebos to have an effect on pain relief or increased well-being has come into question. Latest studies have shown that an openly administered mock drug works just as well as a deceptively administered placebo on certain complaints. This open-label placebo effect has primarily been used in the area of pain treatment so far. This study is the first to examine the effect of such placebos on healthy individuals with the use of drinking water. In two experiments, participants were required to use certain specified water bottles for their daily drinking water consumption. At the beginning of Experiment 1, all participants (N = 68) received one bottle of water, which they were asked to refill themselves each day during a 2-week intervention period. In Experiment 2, participants (N = 75) received a new sealed water bottle every day. In both experiments, participants were randomly assigned to one of four groups: no treatment (control group CG), open-label placebo without rationale (OPR–), open-label placebo with rationale (OPR+), and open-label placebo with additional rationale in a suggested relaxed state (group OPR++). We conducted baseline and post-treatment measurements of the subjective perceived physical and mental well-being of the participants. In Experiment 1, only the OPR++ group reported enhanced vitality at the post-treatment level compared to the other groups. In Experiment 2, post-treatment measurements showed improvements for the OPR++ group in the Physical Performance Capability, Mental Performance Capability, Emotional Balance, Overall Recovery, Negative Emotional State, and Overall Stress categories compared to the other groups. Our results support the idea that placebos with an additional rationale in a suggestive relaxed state are more effective than with just a rationale in a normal state. Furthermore, our study shows the tendency that OLP++ in the form of water with health claims may be more effective when the water is given in several sealed bottles separately than in one sealed but refillable bottle.
... However, there appears to also be a somewhat equal number who did quite a bit worse on the second testing stage. Reasons for either the increase or decrease could be, for example, differing levels of motivation (Deci et al., 1999;Van Lange et al., 2011) or effects on cognition due to aspects such as testing on a different time of day (Wesensten et al., 1990), varying levels of fatigue (Kronholm et al., 2009) or even potentially prior levels of food/liquid intake (Adan, 2012). We also propose that possible different speeds of stimuli at test and re-test due to chance could have contributed. ...
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... Dehydration and/or hyperthermia-induced alterations in cerebral blood flow, 30,31 as well as, greater heat production in the brain can impair cognitive function, 31 motor-cognitive function, complex motor tasks, and promote psychological strain (e.g., increase thermal sensation, decrease thermal comfort). 17,[32][33][34] Research has suggested that brain activity under hyperthermia is altered through increases in brain catecholamines and an increase in the ratio between alpha and beta wave frequency. 31 These changes are linked to decrements in cognition, arousal, and perception of physical exertion, all of which can increase fatigue and result in reductions in working capacity. ...
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Heat stress is a growing concern in the occupational setting as it endangers worker health, safety, and productivity. Heat‐related reductions in physical work capacity and missed workdays directly and indirectly cause productivity losses and may substantially affect the economic wellbeing of the organization. This review highlights the physiological, physical, psychological, and financial harms of heat stress on worker productivity and proposes strategies to quantify heat‐related productivity losses. Heat stress produces a vicious‐cycle feedback loop that result in adverse outcomes on worker health, safety, and productivity. We propose a theoretical model for implementing an occupational heat safety plan that disrupts this loop, preventing heat‐related productivity losses while improving worker health and safety.
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Health and Self Care for Health Professionals explores the topics of Health, and of Self Care. It aims to provide information for readers to consider and debate - and if appropriate, apply to themselves or other situations Health is so often taken for granted. Furthermore, many people use Denial (I'm Fine) and Displacement (I'm too busy) to pay attention to their own needs - thus leading to the other D's of Distress, Despair, Disillusionment, Drink, Drugs or Depression. Much of this is avoidable is we remember to take care of and pay attention to our own health as Human Beings as well as Human Doings. Yet Health Professionals are taught a great deal about Illness (eg the results of car crashes) without learning about Health (how to prevent car crashes) This book aims to support those who wish to explore the topic. Good luck and Go Well!
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Significant scientific evidence documents the deleterious effects of hypohydration (reduced total body water) on endurance exercise performance; however, the influence of hypohydration on muscular strength, power and high-intensity endurance (maximal activities lasting >30 seconds but <2 minutes) is poorly understood due to the inconsistent results produced by previous investigations. Several subtle methodological choices that exacerbate or attenuate the apparent effects of hypohydration explain much of this variability. After accounting for these factors, hypohydration appears to consistently attenuate strength (by ≈2%), power (by ≈3%) and high-intensity endurance (by ∼10%), suggesting alterations in total body water affect some aspect of force generation. Unfortunately, the relationships between performance decrement and crucial variables such as mode, degree and rate of water loss remain unclear due to a lack of suitably uninfluenced data. The physiological demands of strength, power and high-intensity endurance couple with a lack of scientific support to argue against previous hypotheses that suggest alterations in cardiovascular, metabolic and/or buffering function represent the performance-reducing mechanism of hypohydration. On the other hand, hypohydration might directly affect some component of the neuromuscular system, but this possibility awaits thorough evaluation. A critical review of the available literature suggests hypohydration limits strength, power and highintensity endurance and, therefore, is an important factor to consider when attempting to maximise muscular performance in athletic, military and industrial settings.
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Submitted 8 healthy, endurance trained men (mean age 27.4 yrs), unacclimated to heat, to variations in body hydration. The Ss were kept euhydrated, dehydrated by controlled passive hyperthermia or exercise on a treadmill up to a weight loss of 2.8%, or hyperhydrated using a solution containing glycerol, with a total ingested volume equal to 21.4 ml/kg of body weight. On completion of a 90-min recovery period, the Ss were assigned a pedaling exercise and psychological tests of perceptive discrimination, psycho-motor skill, memory, fatigue and mood, were administered. Both dehydration conditions impaired cognitive abilities without any relative differences between them. Following arm crank exercise, further effects of dehydration were found for tracking performance only. Moreover, long-term memory was impaired in both control and hydration situations, whereas there was no decrement in performance in the hyperhydration condition. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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Beneficial effects for mood and cognitive performance are believed to influence food and drink choice. The purpose of the present study was to demonstrate a sensitive methodology for providing objective evidence of such effects. A mildly fatiguing repetitive task formed the context for assessing the potential restorative effects of caffeine-containing ‘energy’ drinks. The methodology used was designed to account for a range of theorised variations in the data, many of which are often overlooked in current research. Significant effects of the energy drinks on task performance and self-rated mood were found. These effects can be summarised with the terms ‘alerting’, ‘revitalising’, ‘awakening’ and providing mental energy, and appear to be mainly caffeine related.
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Studies examining the influence of the menstrual cycle on cognitive function have been highly contradictory. The maintenance of attention is key to successful information processing, however how it co-vary with other cognitive functions and mood in function of phases of the menstrual cycle is not well know. Therefore, neuropsychological performance of nine healthy women with regular menstrual cycles was assessed during ovulation (OVU), early luteal (EL), late luteal (LL) and menstrual (MEN) phases. Neuropsychological test scores of sustained attention, executive functions, manual coordination, visuo-spatial memory, verbal fluency, spatial ability, anxiety and depression were obtained and submitted to a principal components analysis (PCA). Five eigenvectors that accounted the 68.31% of the total variance were identified. Performance of the sustained attention was grouped in an independent eigenvector (component 1), and the scores on verbal fluency and visuo-spatial memory were grouped together in an eigenvector (component 5), which explained 17.69% and 12.03% of the total variance, respectively. The component 1 (p<0.034) and the component 5 (p<0.003) showed significant variations during the menstrual cycle. Sustained attention showed an increase in the EL phase, when the progesterone is high. Visuo-spatial memory was increased, while that verbal fluency was decreased during the OVU phase, when the estrogens levels are high. These results indicate that sustained attention is favored by early luteal phase progesterone and do not covaried with any other neuropsychological variables studied. The influence of the estrogens on visuo-spatial memory was corroborated, and covaried inversely with verbal fluency.