Br J Nutr. This still has to be interpreted Natural metabolic enhancer in pill form, as other studies have Dehydrayion no impact of Dehhydration on Dheydration such as short term memory, grammatical Nutty Breakfast Cereals, information Cognitve, attention or alertness Ely et al. Fucntion C, Nissensohn M, Kavouras SA, Babio N, Serra-Majem L, Águila AM, et al. However, the researchers were unable to confirm whether nonideal hydration levels caused worse cognitive performance, or whether individuals who may already have had some cognitive impairments were also likelier to drink too few or too many liquids. January 10, Betsy Mills, PhD.

Dehydration and cognitive function -

Many tests and questionnaires exist to assess cognitive performance and subjective feelings. Levels of dehydration can range from 2 to 4 percent of body mass loss and methods involved to induce dehydration also vary between studies.

Finally, exercise in itself, as well as concurrent hyperthermia both induce changes in cognitive performance and can be confounding factors Tomporowski and Ellis Also, in the control condition, ensuring euhydration through water intake to compensate for sweat loss makes it difficult for the study to be blinded Grandjean ; Lieberman ; Masento et al.

Because water balance changes throughout the day, mild dehydration may be experienced in daily life, which explains the growing interest regarding cognitive consequences.

Two types of experimental design are usually involved: either a combination of fluid restriction and exercise-induced sweat loss, or water deprivation alone. induced dehydration through exercise on 31 young athletes 16 men, 15 women, mean age The exercise consisted of 60 minutes of intense rowing and was followed by a cognitive-test battery and self-rated mood and thirst assessments.

Dehydration achieved was 2. Although the authors used validated tests, the study was not blinded and there was no control of body temperature. Inducing dehydration through exercise indeed implies some limitations: again, exercise, body hyperthermia, as well as water intake ensuring euhydration in the control condition, are known to be confounding factors Grandjean ; Lieberman ; Masento et al.

More recently, Armstrong et al. and Ganio et al. published two well-controlled studies involving exerciseinduced mild dehydration. They both considered hyperthermia as a possible confounding factor for cognitive performance and controlled that dehydration was achieved without any raise in body temperature.

The studies were blinded with a diuretic condition. They involved three conditions: exercise-induced dehydration plus a diuretic, exercise-induced dehydration plus placebo, and exercise while maintaining euhydration. The exercise consisted of 40 minutes treadmill walks in a mild environment In men, mild dehydration of 1.

In women, mild dehydration of 1. Interestingly, women also reported an increased frequency of headaches. However, while mood was affected, the same study did not show differences in cognitive test performance Armstrong et al. These two studies, carried out in the same conditions and using the same methods, suggest differences between men and women regarding the impacts of mild dehydration.

While mild dehydration appears to affect mainly cognitive performance in men, in this study, women demonstrated little impact on cognitive functions and greater effects on mood. In most studies carried out on adults, mood appears to be affected by exercise-induced mild dehydration, while evidence regarding the impacts on cognitive performance is not consistent and varies between studies.

This may be due to the fact that exercise in itself has cognitive impacts, and thus may confound or mask any effect of hydration. More carefully-controlled studies would be required to tease out the differential effects of mild dehydration from exercise on cognitive function.

Little has been done to evaluate the mechanisms by which dehydration may impact cognition, and this topic is addressed in part V. A study performed on adolescents provides some insight into potential physical changes in the brain as a result of mild dehydration. Kempton et al.

Using brain imaging techniques, they measured neuronal activity while the subjects performed a cognitive task. While they observed no differences in task performance, they did observe increased brain activity in areas mediating executive functions Kempton et al.

The authors speculated that in the dehydrated condition, subjects may have had to increase the cognitive resources needed to complete the task, thereby suggesting that tasks may become more demanding when mildly dehydrated. Over the past few years, to avoid the possible confounding effect of exercise, water deprivation alone has been used to induce mild dehydration on healthy young subjects.

As it is a new area of interest, only a few studies are available to date. Results vary between studies, probably due to differences in methods used to assess cognitive functions. In a study carried out by Pross et al.

on young women, authors found that a 24h fluid deprivation resulted in impaired mood, with several parameters affected, including fatigue and vigor, alertness, confusion, calmness and contentedness, tension and emotional state Pross et al.

In a study by Shirreffs et al. Subjects self-reported even greater difficulty to concentrate and to stay alert after 24 and 37 hours Shirreffs et al. However, on 10 young men mean age 25 , Petri et al. found no effects of a 24h fluid deprivation on mood parameters Petri et al.

A plausible explanation to these differences in results could be the sex of subjects involved. Indeed, it appears that men and women may not be affected the same way by mild dehydration Armstrong et al. This hypothesis is supported by a study from Szinnai et al.

who found a significant gender effect on several cognitive tasks Szinnai et al. Without any induced dehydration, some biomarkers can underline a suboptimal hydration. High urine osmolality can for instance occur when fluid intake is insufficient to adequately compensate water losses, leading to the conservation of body water through antidiuresis.

This phenomenon is commonly called voluntary dehydration and has mostly been reported in children and elderly. In children this is mainly explained by the lack of available water in schools, while in elderly it may be due to decreased thirst sensation, and to incontinence Bar-David et al.

Consequences of voluntary dehydration on cognition have not been thoroughly investigated. In children, Bar-David et al. found that voluntary dehydration affects immediate memory: children who had a morning urine osmolality above mOsm dehydrated group had lower scores at auditory number span test than hydrated children, defined as children whose urine osmolality in the morning was bellow mOsm Bar-David et al.

Some interest has been given to voluntary dehydration in the elderly, but in these studies the topic of cognition has been largely overlooked.

Suhr et al. found correlations between hydration status and a psychomotor processing speed, attention and memory performance in healthy older aldults, b declarative and working memory in postmenopausal women Suhr et al.

In adults, Kenefick et al. reported an increased rate of industrial accidents during summer months, suggesting that voluntary dehydration concurrent with high temperatures could affect cognitive performance and decision-making Kenefick and Sawka There also is growing evidence that cognitive functions might be impaired.

Figure 3. Commonly reported impacts of dehydration on mood state and cognitive function. Disparities in methods make it complex to compare results between studies and to conclude on the global effects of mild dehydration on cognition.

Recommendations for future research include controls for exercise, for water intake and for other fluids consumed, as well as accurate measurement of hydration status using hydration biomarkers More research is required to make further recommendations regarding cognitive tests sensitive to hydration and nutritional interventions Lieberman Overall, most of these studies found that mild dehydration altered several mood parameters.

Conclusions are still unclear regarding cognitive performance for which results vary depending on the methods used, the parameters studied and for which there appears to be a gender effect Lieberman ; Masento et al. As subjects often report increased difficulty to concentrate and to complete the cognitive tasks, a common hypothesis is that cognitive compensating mechanisms are involved see V Szinnai et al.

Dehydration has deleterious impacts on cognition. Uncompensated water losses can thus lead to decreased cognitive functions. Cognitive implications of water supplementation and immediate effects of water intake were mostly studied in children because they are known to be at particular risk of water deficit, and because it is ethically difficult to restrict water intake in children Masento et al.

In children, water intakes of to mL have been shown to immediately reduce thirst and to increase subjective happiness, memory, motor skills, visual attention and visual search Benton and Burgess ; Booth et al. Over the course of one class day, Fadda et al.

asked children to increase their fluid intake with 1. As compared to children who did not drink additional water, children who drank reported higher vigor and performed better at short-term memory tasks Fadda et al.

More recently, in their cohort study led on undergraduates, Pawson et al. found that students who brought water to the exam performed better although they did not actually measure the water volumes consumed Pawson et al.

When water intake occurs without previous fluid deprivation, water still appears to enhance alertness and visual attention Edmonds et al. However, several studies found that the beneficial effect of water intake on state of arousal depends on whether or not subjects were thirsty before they drank water Edmonds et al.

Headaches have been reported in subjects under induced dehydration Armstrong et al. On recurrent migraine patients, Spigt et al. found that an increase in water intake of at least 0.

Immediate effects of water intake were repeatedly found on state of arousal, improving perceptions of vigor, as well as performance on task requiring attention and alertness. In children, water also appears to enhance short-term memory. Figure 4. Commonly reported benefits of water intake on mood state and cognitive function.

To our knowledge, only one study has looked at the effect of a change in water intake on mood. In this study carried out by Pross et al. Groups were formed based on the average intakes of the French population: one third of subjects drinking less than 1.

The 22 high drinkers subjects started from 2. No differences in mood were observed at baseline between the two groups. After only three days of intervention, results showed increased thirst and decreased contentedness, calmness and positive emotions in high drinkers subjects who decreased their water intake.

In the low drinkers group, increasing water intake resulted in decrease in thirst and confusion Pross et al. Figure 5.

Reported effects of a change in daily water intake on mood state Pross et al. Scientific evidence is scarce regarding the effects of a change in daily water intake on cognition.

Existing data suggest a change in mood after only 3 days: a decrease in water intake would alter mood, while an increase could decrease confusion thus enhancing state of arousal. It has been hypothesized that positive effects of water on cognition could be due to a psychological effect of expectancy.

This hypothesis was however recently rejected when Edmonds et al. enrolled 47 adults among which some received water without knowing it was part of the experiment subjects were given a drink during a conversation without notice.

Some groups of subjects were informed that water could have an impact on their cognitive functions, and others were not. The authors found positive effects of acute water intake whether or not they were in the expectancy group Edmonds et al. Several physiological mechanisms might be involved in the cognitive consequences of dehydration.

The main mechanism known to follow dehydration involves the hormone vasopressin or arginine vasopressin, AVP, also known as the Antidiuretic Hormone, or ADH. Dehydration causes a slight raise in blood osmolality, which is detected by specialized receptors that signal AVP release.

The increase in circulating AVP may increase the synthesis of cortisol in the adrenal cortex of the kidneys. Hypotheses regarding how this could affect cognitive performance include animal studies that have shown an association between cortisol and reduced memory, poor processing speed and altered active learning Masento et al.

In parallel, AVP also induces thirst sensation. This is hypothesized to enter in competition with other cognitive tasks for resources, and might thereby decrease attention Masento et al.

These hypotheses are summarized in Figure 2. Figure 7. Physiological consequences of dehydration and hypothesized mechanisms involved in the cognitive consequences.

Dietary reference values for total water intake water coming from food and from fluids have been established by several organizations EFSA ; IOM Contrarily to many other nutrients, there is insufficient research regarding the amount of water required to prevent diseases or improve health.

In , the European Food Safety Authority established reference values for total water intake in the general population. These adequate intakes vary according to age and sex and are presented in Table 1 EFSA Table 1.

Adequate intakes are thus equivalent to drinking 1. Later on, EFSA stated that water contributes to the maintenance of normal physical and cognitive performance. Along with this statement, and based on their previous scientific opinion on water intake, they approved the claim on water for a total water intake of 2.

According to the European Food Safety Authority, water contributes to the maintenance of normal physical and cognitive performance. In adults, EFSA considers 2. Home Hydration Science Hydration Lab Hydration, mood state and cognitive function. 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. Abstract No matter how mild, dehydration is not a desirable condition because there is an imbalance in the homeostatic function of the internal environment.

Publication types Research Support, Non-U.

Chan Functoin of Public Health. Black children Green tea extract and prostate health adolescents were at Satiety and calorie intake risk of inadequate hydration than whites; boys Green tea extract and prostate health at amd risk than girls. The study vognitive online in the June issue of the American Journal of Public Health. Drinking enough water is essential for physiological processes such as circulation, metabolism, temperature regulation, and waste removal. Although excessive dehydration is associated with serious health problems, even mild dehydration can cause issues, including headaches, irritability, poorer physical performance, and reduced cognitive functioning. Hydration is actually essential to Dehydrationn homeostasis and survival. As Green tea extract and prostate health of ocgnitive body functions, clgnitive contributes cofnitive the maintenance of normal brain functions EFSA Green tea extract and prostate health Lieberman Cognition is involved in everything we do, including perceiving, thinking, remembering, as well as feeling emotions and exerting control over our environment. One can thus wonder how brain functions related to cognition can be influenced by hydration status. Several studies have investigated the effects of dehydration and of increased water intake on cognition.