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Hydration and brain function

Hydration and brain function

Indeed, it appears that Metabolic health blog and women may not be affected the same way by mild dehydration Hydratioh et Hydration and brain function. An hydration Hydrration been shown to prevent this from happening, and it may even reduce the oxidative stress that occurs during high intensity exercise. Eur J Epidemiol. It has been hypothesized that positive effects of water on cognition could be due to a psychological effect of expectancy.

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The Hydratkon of Hydratino magnetic resonance imaging MRI btain the Hydration and brain function showed that the blood-oxygen-level-dependent BOLD Hydratiom in fuction fronto-parietal area brrain stronger under a dehydrated state It is speculated that the reason for this result functjon that neuronal activity was higher funcgion dehydrated In a study inthe brains of ten healthy Hjdration participants were scanned using Energy consulting services under the dehydration and rehydration states.

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Meanwhile, rehydration after 1. Tunction a functiom inthe brains of 20 healthy adults were scanned with MRI under a dehydration state after 9 h of overnight fasting and under a rehydration state after 3L of water was consumed over 12 h The results indicated that no statistical changes were found for brain total water content and brain volume under different hydration states One more study in found that the dehydration state induced by exercise without replacing fluid losses reduced total brain volume among 10 sportsmen There was one study that investigated the changes in brain structure under the dehydration state using voxel-based morphology, and it showed that there were associations between the decrease in gray matter GM and white matter WM volume and the dehydrated state in various brain regions In a study conducted among nine physically active adult participants aged 24 years old, it was found that a dehydration state induced by exercise and heat stress with 2.

In a long-term hydration experiment, six healthy young adults 25 years old were recruited, and a dehydration state was induced in two days by water restriction to mL water per day Related studies are few, related studies has been summarized in Supplementary Table 1.

It is meaningful to conduct further studies to explore the effects of the hydration state on the brain structure and functions using the method of brain magnetic resonance imaging.

The purposes of this study are, first, to analyze the effects of slowly progressive dehydration after 36 h of water deprivation on brain regional density and homogeneity using the method of MRI and, second, to explore the effects of rehydration after an adequate amount of water supplementation on brain regional density and homogeneity among healthy young adults in China.

The results of MRI in this study provide more evidence about the importance of hydration. It is also meaningful to bring attention to drinking an adequate amount of water and maintaining an optimal hydration state.

Twelve healthy male young adults were recruited from one college in Cangzhou, China. The inclusion criteria were as follows: the age of participants was between 18 and 25 years; the participants were in a healthy state.

This sample size was also consistent with previous studies in which the sample size was in the range of The study protocol and instruments were reviewed and approved by the Ethical Review Committee of Chinese Nutrition Society on November 10, The code of identification is CNS The study was conducted in accordance with the guidelines of the Declaration of Helsinki.

Prior to the conduction of the study, all participants read and signed informed consent voluntarily. The study procedure of the self-control trial is shown in Figure 1.

During the study, volunteers were asked to not perform vigorous-intensity physical activities e. All participants were monitored by research supervisors and investigators. Three MRI tests were performed, including test 1 under baseline state, test 2 under dehydration state caused by 36 hours of water deprivation, and test 3 under rehydration state after water supplementation.

All tests were conducted in Cangzhou Central Hospital. Figure 1. Procedure of the study. H is the abbreviation for height; W is weight; BP is blood pressure; VAS is visual analog scales; MRI is magnetic resonance imaging.

Day 1: All participants fasted overnight from p. and were told to sleep no later than 11 p. They were required to not urinate until awaking on day 2. Day 2: First, urine samples were collected at a.

in the morning using a sterile urine sample accumulator and then sent to be tested by lab technicians in the hospital. Cubital venous blood was collected and sent to determine the blood osmolality and blood glucose. Body measurement and blood pressure were also conducted. Visual analog scales on thirst were conducted, and brain magnetic resonance imaging MRI was performed as baseline test 1.

After test 1 under the baseline state, participants could eat and drink. After p. Day 3: Participants could not drink any fluid and lasted for 24 h from a. on day 3. Three specified solid meals were supplied to participants by a researcher at a. No other food was eaten. Fluid intake from foods was assessed using methods of weighing, duplicate portion, and laboratory analysis.

Each urine sample was collected by the participants and then sent for evaluation of the 24 h urine volume by researchers. The urine osmolality of each urine sample was also determined. Participants were required to sleep no later than 11 p. and to not urinate until awaking on day 4.

Day 4: At a. Brain magnetic resonance imaging was performed under dehydration state caused by 36 h of water deprivation. Participants drank 1, mL of purified water in fifteen minutes at a. and were required to drink mL every 5 min. After resting for an hour, test 3 under rehydration state was performed.

Brain magnetic resonance imaging was performed under rehydration state after water supplementation. The temperature and humidity of the living environment among participants during these days were measured and noted. In the whole process of the study, participants who failed to meet these requirements needed to let investigators know.

Finally, all participants finished the study, and no one failed to meet the requirements. Weighing, duplicate portion, and laboratory analysis methods were used to assess water intake from foods. See 23 for the specific steps and calculation methods. Wearing light clothing and no footwear, height H was measured twice with 0.

Blood pressure BP was measured twice with 2 mmHg accuracy by a nurse with electronic sphygmomanometer HEM; Omrom, Dalian, Liaoning, China. Two measurements were conducted after 2 min intervals. Starting with the second voiding on day 3 and ending with the first voiding on day 4, all urine samples were collected as total 24 h urine volume on day 3.

Urine volume was measured with the accuracy 0. Additionally, urine osmolality was tested using an osmotic pressure molar concentration meter SMC 30C; Tianhe, Tianjin, China. Cubital venous blood was also used to test osmolality and glucose of blood.

Blood osmolality was tested with an osmotic pressure molar concentration meter SMC 30C; Tianhe, Tianjin, China. Blood glucose was tested with an automatic biochemical analyzer Cobas C; Roche, Basel, Switzerland.

Visual analog scales VAS are a self-rated 10 cm line designed to quantitatively measure the subjective feeling of thirst Participants were required to draw a vertical line corresponding to their degree of thirst. The range of scores for thirst varied between 0 and Magnetic resonance imaging scans were administered on a 3-teslas SIGNA HDx scanner Discovery MRGeneral Electric; Milwaukee, WI.

: Hydration and brain function

How Dehydration Affects Your Brain - The Brain & Spine Institute of North Houston How much Hydration and brain function the brain is brai Scarmeas Brsin, Anastasiou CA, Yannakoulia M. Article PubMed Google Scholar. The hydration guidelines refer to the consumption of all fluids, not simply how many glasses of plain water we drink per day. Debunking the science of left versus right brain. Lorr, M. Trangmar, S.
7 Science-Based Health Benefits of Drinking Enough Water

For body temperature and osmolality, change scores were calculated end of the morning minus baseline. Similarly, thirst change scores were calculated end of morning minus thirst following the standard breakfast.

Interbeat RR intervals were recorded at rest for five minutes at the start of the procedure and again at the end.

Interbeat interval data were analysed using Kubios HRV Analysis Software 2. Data were visually inspected for artefacts caused by ectopic beats, poor conductivity etc. A very low correction threshold was chosen for artefact correction 0.

Time domain HRV indices included mean R-R interval a measure of basic heart rate , the standard deviation of normal to normal R-R interval SDNN measures total variability in the series and the root mean square of the standard deviation RMSSD a measure of parasympathetic nervous system activity.

To determine the effect of hydration, change scores were calculated end of the morning minus baseline for each index. For ratings of anxiety, depression and energy change scores were calculated end of morning minus mood following the standard breakfast.

In each of the three separate runs a total of volumes were collected. Analyses were conducted using BrainVoyager QX 2. Data were normalised to the standard Talairach space 29 using sinc interpolation prior to group analysis. The group analysis involved estimating task-correlated activity using a general linear model GLM approach.

The predictors for the GLM were created by convolving the timecourse of the stimulation periods arithmetic operation with a canonical HRF response. Each participants beta estimates, obtained via the GLM, were then input into a voxel wise second level random effects analysis.

For each participant an arterial spin labelling ASL sequence was run after the functional imaging experiment had been completed. The labelling plane was placed ASL data were 3D motion corrected and normalised to Talairach space.

Relative perfusion values were obtained for each participant and condition using the ASL toolbox implemented in BrainVoyager QX 2. Significant differences between dehydrated and water conditions were assessed using paired t-test of the relative perfusion values. The effect of drinking on percentage total weight loss, perspiration rate and changes in osmolality, thirst and body temperature were analysed using RMANOVA.

The effect of drinking water on heart rate variability was considered using RMANOVA where change scores end of the morning minus baseline from each day were entered Table 1 ; Fig. The effect of drinking water on the average length of the RR interval, SDNN and RMSSD.

Data are the changes end of the morning minus baseline for each index compared across the two conditions. Top panel: Study 1.

When participants were hypo-hydrated they had a lower R-R i. Bottom panel: Study 2. RR, interbeat interval, SDNN, standard deviation of normal to normal R-R interval, RMSSD, root mean square of the standard deviation.

Data were analysed using RMANOVA with condition Water, No water as a repeated measures factor. Main effects are shown in Table 2. The subjective responses taken inside and outside the scanner were analysed using RMANOVA with condition Water, No water as a repeated measures factor.

A comparison of activation during the arithmetic task in the water compared to the dehydration condition revealed several clusters that achieved statistical significance. Specifically, striatal activity was observed in the bilateral caudate nucleus and putamen.

The same cluster also spread inferiorly to right amygdala. To the anterior aspect the activity spread into the medial orbito-frontal cortex.

A second small cluster was observed in the dorsal cingulate gyrus Talairach co-ordinate: 9, 23, Correlation between neuronal activity in the vCG and B.

RR interval C. anxiety and D. difficulty ratings. A voxel wise paired contrast of the perfusion values, obtained via the ASL scans, did not reveal any significant differences in resting perfusion for either the contrast of dehydration vs.

water, or water vs. Peaks of activity occurred on the ventral cingulate gyrus vCG , the border of the medial orbitofrontal cortex mOFC and in the left post-central gyrus PoCG. Results are displayed in Table 3. e a higher heart rate was associated with lower activity brain activity when no water had been drunk.

Table 4. e higher heart rate in the no water condition was related to greater anxiety and more perceived effort Fig.

Given the small samples size invariably associated with studies involving neuroimaging a second behavioral study was conducted to replicate and extend the main findings from study 1. Specifically it was hypothesized that declines in HRV would mediate the effect of hypo-hydration on mood.

The effect of drinking on percentage total weight loss, perspiration rate and changes in osmolality and thirst were compared across the two conditions using ANOVA. Thus in both studies there was evidence that the current paradigm is a valid way of manipulating small changes in hydration without exposing participants to physical activity Table 1.

The effect of drinking water on heart rate variability was considered by comparing change scores end of the morning minus baseline using ANOVA Table 1 ; Fig. Therefore, the studies provided consistent evidence that minor hypo-hydration results in an increased heart rate and decreased heart rate variability.

Data were analysed using ANOVA where change scores were compared across conditions. To confirm whether changes in HRV mediate the effect of hypo-hydration on mood a mediator analysis was conducted using Hayes PROCESS model 4 Fig. As anxiety was the only mood measure to show a significant main effect of drinking water this was the dependent variable Y.

Water consumption was the dichotomous independent variable X , and SDNN was the mediator M. This finding suggested that hypo-hydration associated increases in anxiety levels are fully mediated by autonomic adaptations as indexed by a reduction in HRV.

Schematic illustration of the mediation analysis used in study 2. In two studies it is reported that hypo-hydration adversely influenced mood and brain functioning. In study 1, as a result of not drinking water during the experimental protocol, task related activity in the autonomic network of the brain was reduced; specifically activity in the orbito-frontal cortex, ventral cingulate gyrus, dorsal cingulate cortex, hypothalamus, amygdala, right striatum, post-central gyrus and superior parietal cortex was affected.

When participants were hypo-hydrated they had a higher HR and lower HRV; effects that correlated with peak activation in the vCG and mOFC. Importantly, these effects were associated with a decline in mood. The deleterious effect of hypo-hydration on HRV was replicated in study 2 where this variable was found to mediate the influence of not drinking water on mood.

These observations are consistent with the hypothesis that hypo-hydration elicits a change in autonomic regulatory activity and brain function, with potential adverse consequences for aspects of mood.

The present studies found that in participants at rest, hypo-hydration resulted in a shorter average R-R interval i. e a higher HR on average 5. This latter finding is important because it might help explain how acute water supplementation can benefit mood, irrespective of hydration status Mathews et al.

Similarly, in the present study, having higher activity in the vCG and mOFC was associated with greater parasympathetic activity indexed by the average RR interval, SDRR and RMSSD.

These findings indicated that the hydration related differences in brain activity in these regions may be the result of hydration induced autonomic modulation. Interestingly, drinking water both ameliorated the task related decline in brain activity, as indicated by fMRI, and increased HRV.

A novel hypothesis is that hypo-hydration induces increased cardiovascular strain, which in turn necessitates a decline in activity in the autonomic network of the brain, effects that could compromise cognitive and affective processing.

Map showing the brain areas associated with autonomic modulation. Left data from present study. Right areas controlling HRV reproduced from Thayer et al. Even in a healthy population lower HRV is associated with poorer mood and cognition and higher perceived stress Similarly, study 1 found that a higher heart rate and lower HRV were associated with increases in anxiety and perceived effort during scanning; these effects were also associated with having a greater deactivation in the mOFC and vCG.

In addition, the association between lower HRV and increased anxiety was replicated in study 2. Hypo-activation of the anterior cingulate and frontal cortices is common in a range of anxiety disorders 32 and during induced anxiety In addition, interventions known to reduce anxiety increase activity in these regions 34 ; it is therefore plausible that the benefits of drinking water reflect similar mechanisms.

These observations are important as they may have clinical implications for populations characterized by raised anxiety levels. Thus, autonomic adaptations that mediate the effects of hydration are likely to be enhanced by a warm environment.

Supporting this view, Farrell et al. In the present study perspiration rate correlated significantly with activity in all three regions of difference; the mOFC, vCG and PoCG Table S1. If such regions are also involved in hypo-hydration associated cognitive and affective deficits, this might help to explain the effects of the interaction between thermoregulation and hypo-hydration on cognition and mood.

The present findings support the hypothesis that even a relatively minor decline in hydration necessitates a counter-regulatory autonomic response which may have affective consequences.

However, an alternative hypothesis might be that, rather than altering neural activity, hypo-hydration reduces cerebrovascular coupling. Given that brain functional imaging methods, such as fMRI, are sensitive to changes in cerebral blood flow CBF it is plausible that the observed differences in regional BOLD activity might reflect differences in CBF.

Hypo-hydration of 1. However, the present study found no effects of hydration on global or regional blood flow using resting state ASL; nonetheless, it remains possible that dynamic cerebrovascular reactivity, rather than resting state auto-regulation, may have been compromised under the present conditions.

This remains an important consideration for future research that examines the effects of hydration on brain functioning using imaging. The limitations of the present study should be considered.

Firstly, it is unclear whether hypohydration related changes in anxiety and perceived effort are driving the associated differences in HRV and brain activity, or vice versa. Further research might consider the potential influence of individual differences in afferent baroreceptor activity and interoceptive abilities which has been shown to modulate the processing of emotional information 37 , 38 , and may be increased following water consumption.

A factor that could limit the generalizability of the results is the small sample sizes. Although we were able to replicate findings, the possibility exists that the studies were underpowered to detect some smaller differences in mood e. In addition, the sample comprised only young university students and future research may consider different populations who may be more susceptible to the effects of hypohydration; for example children and older adults.

Finally, although the majority of studies of HRV have not measured respiration it is potentially a confounding variable. Although there is no reason to believe that respiration varied systematically, such that it would have biased the present findings, it is a question to be addressed in future studies.

In conclusion, the present study reports that when participants consumed water, compared with when they were mildly hypohydrated 0. For the first time we have highlighted important regulatory neural mechanisms that may account for the psychological benefits of maintaining hydration status.

When water was not consumed more weight was lost, osmolality increased and HRV decreased; effects that predicted a larger task related deactivation in the autonomic network of the brain. Only recently have the interactions between bodily reactions and affective processes begun to be elucidated and such phenomena are still often treated as confounding factors.

Indices of ANS function have been used as objective measures of affective states and these responses have been treated as epiphenomena, rather than intrinsic to the cognitive or emotional process.

As evidenced here, it is possible that changes in ANS activity have consequences for mood. As such hypo-hydration to the extent that it influences ANS activity per se may have negative consequences for brain functioning and mood. Given the prevalence of voluntary hypo-hydration these findings have important implications for vulnerable cross-sections of the population.

Furthermore, the psychological benefits of drinking may have important implications for populations, such as older adults and children 39 who are at a significant risk of dehydration. The fact that mild changes in hydration affected cardiovascular functioning is also a concern; the HR of participants was on average 5.

Given that there is a progressive increase in the risk of heart-disease as resting heart rate increases 40 , and hyper-osmolarity predicted a 4.

In general, repeated low level physiological challenges such as hypo-hydration may overtime increase allostatic load, predisposing to possible negative health outcomes. The sample size was based on the expected power for a hypothesized within participants effect. This gave an estimated N of 12 which is in line with previous studies that have examined the neural effects of hydration e.

Twelve healthy young males average age Participants were excluded if they had any health complaint that would affect cardiovascular functioning such as diabetes or hypertension. Similarly, anyone with a neuropsychological illness was also excluded as were those taking medication. The sample size was based on the expected power for a hypothesized between participants effect.

This gave an estimated N of Twenty-five males and thirty-one females average age As it has been suggested that gender may be a determining factor in the correlation between hypo-hydration and its psychological consequences 2 , this factor was initially considered.

Exclusion criteria and pre-study instructions were the same as for study 1. On two occasions participants attended the laboratory that was heated to 30 degrees.

Upon arriving at the laboratory, participants were asked to provide a urine sample and were asked to completely empty their bladder, following which they were weighed and their body temperature measured.

This instrument has been previously validated for the accurate measurement of R-R intervals and for analysing Heart Rate Variability HRV After breakfast participants were weighted again, and rated their mood and thirst.

After this they were allowed to rest while either watching TV or reading. Three hours later participants were asked to provide another urine sample and again had their HRV, body temperature and weight measured, and rated their mood and thirst. Finally, they were escorted to the MRI laboratory for the scanning procedure.

The procedure was approved by Swansea University ethics committee ref: The procedure for study 2 was identical with the exception that it employed a between participants rather than within subject design.

In addition, participants did not complete the fMRI protocol. These data were collected as part of a larger trial: ClinicalTrials. Mood measures were identical across both studies.

The osmolality of urine was assessed using an Osmomat freezing point osmometer Gonotec GmbH, Berlin, Germany. Participants were weighed on arrival, both before and after breakfast, and again at the end, both before and after urination.

Pairs of two digit numbers appeared on a screen in red and participants were required to mentally add or subtract the numbers. Participants were required to press either a left or right button to indicate which answer was correct Fig.

This allowed investigation of areas of the brain associated with working memory but also those associated with emotional arousal. Data analysed from the task were number of missed responses, the number of correct responses and average reaction time in milliseconds on the trials that participants responded.

Three blocks of four minutes were performed. At the end of each block four visual analogue scales appeared and participants were asked to rate, using the left and right key to move a cursor, how difficult they found the proceeding block and how happy, energetic and anxious they felt at that moment.

The visual analogue scales were rated on a scale of 1— Arithmetic task and Visual analogue scale example stimuli. The crosses are fixation points when otherwise the screen is blank.

At the third image the participant indicated whether the right or left number was correct by pushing a button. They say that the adequate daily fluid intake for men is roughly These recommendations, however, cover fluids from water, other beverages, and food.

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Specialty Water. View All Water Systems. Hotel Cuber. Scoop Bin. View All Ice Systems. Existing evidence suggests that good hydration status may be associated with better cognitive test results and that mild, induced dehydration can impair cognitive abilities [ 75 ], but findings are not consistent and there are only a few studies exploring the relationship of hydration status and hardly any assessing amount of water intake, with cognitive performance in older community-dwelling adults.

These cross-sectional findings differ from the present observations where global cognitive function, but not individual tests related to attention and processing, was associated with hydration status. Whereas, correspondingly, water intake but not hydration status was positively associated with DST-f, which is similar to the DSST in that it is an indicator of attention as well as short-term memory capacity, and this was seen across all older adults both men and women.

Additionally, in the NHANES study, cognitive test scores were significantly lower among adults who failed to meet EFSA recommendations on adequate intake AI of water in bivariate analyses, yet this significance was attenuated in the multivariable analyses among both women and men.

Yet, using the alternative AI of daily water intake of mL or more, which is comparable to the highest drinking water intake group in the present study, women scored higher on the Animal Fluency Test, a measure of verbal fluency and hence executive function, and DSST than women with intake levels below this amount, and findings among men trended in the same direction [ 34 ].

Similarly, hydration status has been associated with cognitive function in two cross-sectional studies of older community-dwelling adults by Suhr and colleagues [ 32 , 33 ].

First, Suhr et al. showed that in 28 healthy community-dwelling older adults aged 50 to 82 years , a lower hydration status, determined in this study via total body water measured using the bioelectrical impedance method, was related to a decreased psychomotor processing speed, poorer attention, and memory [ 33 ].

A second cross-sectional study by Suhr et al. Conversely, a cross-sectional study conducted in Poland among 60 community-dwelling older adults aged 60 to 93 years found no significant relationship between cognitive performance, as assessed using the MMSE, TMT, and the Babcock Story Recall Test, and hydration status as assessed by urine specific gravity [ 31 ].

The discrepancy between the findings from this cross-sectional study and the present PREDIMED-Plus analyses might be because all participants in the cross-sectional study from Poland were considered to be adequately hydrated and hence the authors of that study could not assess the impact of a dehydrated state on cognition.

A noteworthy consideration when interpreting the literature and the main findings of the current study for practical use and in the determination of potential mechanisms of action is the distinction between water intake and water balance related to hydration status within the body.

When homeostasis of fluids within the body is disrupted, modifying water intake may impact cognitive function, yet due to the dynamic complexity of body water regulation impacting hydration status may be dependent on individualized physiological water intake needs [ 8 ].

Thus, while the biological mechanism by which water intake and a hydrated status may reduce the risk of cognitive decline is unclear, evidence suggests that aspects related to hydration and fluid homeostasis or a lack thereof, such as hormone regulation and changes in brain structure, could be a key underlying factor.

Several mechanisms regulate water intake and output to maintain serum osmolarity, and hence hydration status, within a narrow range. Elevated blood osmolarity resulting in the secretion of antidiuretic hormone ADH , also known as vasopressin or arginine vasopressin, a peptide hormone which acts primarily in the kidneys to increase water reabsorption, is one such mechanism that works to return osmolarity to baseline and preserve fluid balance [ 77 ].

In addition to its role in mediating the physiological functions related to water reabsorption and homeostasis, evidence has suggested that ADH participates in cognitive functioning [ 78 ] and that the associated cognitive modulations may further interplay with sex hormones [ 79 ].

Antidiuretic hormone may be influenced by the androgen sex hormone, which is generally more abundant in the brains of males than in females [ 80 ].

As a result, the impact of ADH on cognition could be greater in males [ 80 ]. Exercise- and heat-induced acute dehydration studies implicate possible modifications to the brain structure as another potential mechanism of action for an association between water intake, hydration status, and cognitive function.

Evidence has proposed that acute dehydration can lead to a reduction in brain volume and subtle regional changes in brain morphology such as ventricular expansion, effects that may be reversed following acute rehydration [ 81 , 82 ].

Acute dehydration studies have further implicated hydration status in affecting cerebral hemodynamics and metabolism resulting in declines in cerebral blood flow and oxygen supply [ 83 , 84 ]. A lower vascular and neuronal oxygenation could potentially compromise the cerebral metabolic rate for oxygen, thereby contributing to reductions in cognitive performance [ 81 , 85 , 86 , 87 , 88 ].

Nonetheless, other potential unknown mechanisms cannot be disregarded. There are several limitations and strengths of the present analyses that need to be acknowledged.

The first notable limitation is that the results may not be generalizable to other populations since the participants are older Spanish individuals with metabolic syndrome and overweight or obesity. However, these questionnaires have been validated and determined as reliable methods of assessing long-term intake in the present study population [ 37 , 38 ].

Third, despite its longitudinal design, water and fluid intake and hydration status were only considered at baseline; however, as the questionnaires measure habitual beverage and food intake, and older adults are considered to have reasonably stable dietary habits [ 37 , 38 ], this is not expected to significantly impact the findings.

Along these lines, the possible effect of seasonality on water intake and osmolarity was not considered a concern in the present analyses as the validation of the fluid questionnaire measurements included assessments at various points throughout the year baseline vs.

Hence, the finding of no difference between 6-month intervals, suggests no significant differences between opposing seasons e. summer; spring vs.

Furthermore, SOSM determination may not necessarily detect acute dehydration or rehydration immediately prior to the cognitive testing, and it is unknown whether observed elevated SOSMs were due to inadequate water intake, ADH abnormality, or other factors. While it is possible that the hydration status of some individuals was misclassified because serum osmolarity was estimated as opposed to being directly measured, the equation has been shown to predict directly measured serum osmolarity well in older adult men and women with and without diabetes or renal issues with a good diagnostic accuracy of dehydration and has been considered a gold standard for the identification of impending and current water-loss dehydration in older adults [ 44 , 45 , 89 , 90 , 91 ].

Lastly, a discrepancy was observed between the percentage of individuals that were considered to have met EFSA fluid intake recommendations and those considered to be dehydrated based on calculated osmolarity. This may have been due to the fact that the EFSA fluid intake recommendations are meant for individuals in good health [ 20 ]; whereas the present study population had overweight or obesity, and it has been shown that individuals with higher BMIs have higher water needs related to metabolic rate, body surface area, body weight, and water turnover rates related to higher energy requirements, greater food consumption, and higher metabolic production [ 92 ].

Strengths of the present analyses include the longitudinal, prospective design, the large sample size, the use of an extensive cognitive test battery, the use of validated questionnaires, and the robustness of the current findings due to the adjustment of relevant covariates.

Findings suggest that hydration status, specifically poorer hydration status, may be associated with a greater decline in global cognitive function in older adults with metabolic syndrome and overweight or obesity, particularly in men.

Further prospective cohort studies and randomized clinical trials are required to confirm these results and to better understand the link between water and fluid intake, hydration status, and changes in cognitive performance to provide guidance for guidelines and public health.

The dataset supporting the conclusions of this article is available upon request pending application and approval of the PREDIMED-Plus Steering Committee. There are restrictions on the availability of data for the PREDIMED-Plus trial, due to the signed consent agreements around data sharing, which only allow access to external researchers for studies following the project purposes.

Requestors wishing to access the PREDIMED-Plus trial data used in this study can make a request to the PREDIMED-Plus trial Steering Committee chair: jordi. salas urv. The request will then be passed to members of the PREDIMED-Plus Steering Committee for deliberation.

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I. Defining and measuring cognition Some interest has been given to voluntary dehydration in the elderly, but in these studies the topic of cognition has been largely overlooked. Impacts of dehydration on cognitive performance were first studied in extreme conditions, on soldiers or athletes. Indeed, it appears that men and women may not be affected the same way by mild dehydration Armstrong et al. This shrinkage can greatly impact how you feel and your overall bodily functions. Hypothesized mechanisms linking water and cognition It has been hypothesized that positive effects of water on cognition could be due to a psychological effect of expectancy. The relation of hydration status to declarative memory and working memory in older adults. Multivariable linear regression models were fitted to assess longitudinal associations comparing the 2-year change in cognitive function across baseline variables of hydration status and water intake and for meeting the EFSA recommendations for TWI and TFWI [ 20 ].
Hydration and brain function

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