Not getting enough water is enough to make you feel sluggish and give you a headache, but a new Penn State study suggests it may also relate to cognitive performance.
The researchers investigated whether hydration levels and water intake among older adults was related with their scores on several tests designed to measure cognitive function.
They found that among women, lower hydration levels were associated with lower scores on a task designed to measure motor speed, sustained attention, and working memory. They did not find the same result for men.
The findings were recently published in the European Journal of Nutrition.
“The study gives us clues about how hydration and related drinking habits relate to cognition in older adults,” said Hilary Bethancourt, a postdoctoral scholar in biobehavioral health and first author on the study.
“This is important because older adults already face an increased risk of cognitive decline with advancing age and are often less likely than younger adults to meet daily recommendations on water intake.”
Asher Rosinger, Ann Atherton Hertzler Early Career Professor in Global Health, said the researchers found similar results when the participants were overhydrated.
“We found a trend suggesting overhydration may be just as detrimental to cognitive performance as dehydration for older adults,” said Rosinger, who also directs the Water, Health, and Nutrition Laboratory and was senior author on the study.
“Because of this, being in the ‘sweet spot’ of hydration seems to be best for cognitive function, especially for tasks requiring sustained attention.”
According to the researchers, scientists have long suspected that dehydration may have an effect on cognitive performance.
However, previous studies have largely focused on young, healthy people who are dehydrated after exercise and/or being in the heat.
Bethancourt said that because exercise and elevated ambient and body temperatures can have their own, independent effects on cognition, she and the other researchers were interested in the effects of day-to-day hydration status in the absence of exercise or heat stress, especially among older adults.
“As we age, our water reserves decline due to reductions in muscle mass, our kidneys become less effective at retaining water, and hormonal signals that trigger thirst and motivate water intake become blunted,” Bethancourt said.
“Therefore, we felt like it was particularly important to look at cognitive performance in relation to hydration status and water intake among older adults, who may be underhydrated on a regular basis.”
For the study, the researchers used data from a nationally representative sample of 1271 women and 1235 men who were 60 years of age or older.
Data were collected by the Nutrition and Health Examination Survey. Participants gave blood samples and were asked about all foods and drinks consumed the previous day.
The researchers calculated hydration status based on concentrations of sodium, potassium, glucose, and urea nitrogen in participants’ blood. Total water intake was measured as the combined liquid and moisture from all beverages and foods.
Participants also completed three tasks designed to measure different aspects of cognition, with the first two measuring verbal recall and verbal fluency, respectively.
A final task measured processing speed, sustained attention, and working memory. Participants were given a list of symbols, each matched with a number between one and nine.
They were then given a list of numbers one through nine in random order and asked to draw the corresponding symbol for as many numbers as possible within two minutes.
Bethancourt said that when they first plotted the average test scores across different levels of hydration status and water intake, there appeared to be a distinct trend toward higher test scores in relation to adequate hydration and/or meeting recommended water intake. However, much of that was explained by other factors.
“Once we accounted for age, education, hours of sleep, physical activity level, and diabetes status and analyzed the data separately for men and women, the associations with hydration status and water intake were diminished,” Bethancourt said.
“A trend toward lower scores on the number-symbol test among women who were categorized as either underhydrated or overhydrated was the most prominent finding that remained after we accounted for other influential factors.”
Bethancourt said that because the data was cross-sectional, they can’t be sure whether suboptimal hydration levels are causing cognitive impairment or if people with impaired cognition are just more likely to be under- or overhydrated.
The researchers were also unsure why they failed to see the same associations among men. Still, she said the results raise interesting questions.
According to the researchers, scientists have long suspected that dehydration may have an effect on cognitive performance.
However, previous studies have largely focused on young, healthy people who are dehydrated after exercise and/or being in the heat.
“It was interesting that even though the test of attention, processing speed, and working memory took only a few minutes, it was the one most strongly associated with lower hydration levels,” Bethancourt said.
“Other research has similarly suggested that attention may be one of the cognitive domains most affected by hydration status.
This left us wondering what the effects of inadequate hydration might be on more difficult tasks requiring longer periods of concentration and focus.”
Rosinger said the findings suggest older adults may want to pay close attention to their hydration status, by both consuming enough liquids to avoid dehydration as well as ensuring adequate electrolyte balance to avoid overhydration.
“Because older adults may not necessarily feel thirsty when their body is reaching a state of underhydration and may be taking diuretics that can increase salt excretion, it is important for older adults and their physicians to better understand the symptoms of being both under- and overhydrated,” said Rosinger.
W. Larry Kenney, Marie Underhill Noll Chair in Human Performance, and David M. Almeida, professor of human development and family studies, also participated in this work.
Water is essential for the survival and development of life. The functions of water include its participation in metabolism, modulation of normal osmotic pressure, maintenance of electrolyte balance, and regulation of body temperature.
Both excessive and insufficient water intake have negative effects on health [1,2]. Dehydration, which refers to a deficiency in total body water, can impair a person’s ability to engage in physical activities and increases the risk of urinary system and cardiovascular system diseases [3,4,5].
The brain regulates cognitive performance and mood, and water accounts for approximately 75% of brain mass [6]. Associations may exist between hydration states and cognitive performance and mood.
A few studies have explored the effects of hydration on cognitive performance and mood. Some results have supported the hypothesis that cognitive performance and mood could be impaired by dehydration and improved by rehydration.
Fadda et al. investigated the effects of water supplementation on the cognitive performance and subjective mood states of school children in a hot climate, revealing negative effects of dehydration on short-term memory and beneficial effects of water supplementation [7].
Armstrong et al. reported that dehydration elicited by intermittent moderate exercise without hyperthermia increased the perception of task difficulty and resulted in mood deterioration among 25 female participants [8]. Ganio et al. showed that mild dehydration without hyperthermia impaired vigilance and working memory and increased anxiety and fatigue among 26 men [9].
The studies of Cian, Lieberman, and D’anci et al. have also supported the view that hydration state could influence cognitive performance [10,11,12,13]. However, studies have obtained inconsistent conclusions. Wittbrodt et al. showed that rehydration after water supplementation effectively mitigated physiological strain induced by mild dehydration following exercise-heat stress, but mild dehydration had no adverse effects on cognitive performance among 12 recreational athletes [14].
A randomized trial conducted by Trinies et al. of primary school pupils in Zambia also demonstrated that provision of water or hydration level did not affect cognitive performance [15]. Some other studies have demonstrated that dehydration induced by heat stress and exercise did not impair cognitive performance [16,17,18,19].
In these studies, heat stress, physical activities, diuretics, or a combination of these, were used instead of water deprivation. In response to physical activities, brain-derived neurotrophic factor increases, brain glucose is elevated, and oxygen uptake and lactate uptake increase in the temporoparietal cortex, occipital cortex, premotor cortex, and cerebellar vermis. These responses may also affect cognitive performance and mood as confounding factors [20,21,22].
Heat stress may impair cognitive performance and mood due to the associated unpleasant sensation and increase in stress hormones [23]. Thus, it is necessary to conduct hydration-related studies using water deprivation and water supplementation under free-living conditions to explore the effects of progressive moderate dehydration and acute rehydration on cognitive performance and mood.
In China, few hydration-related studies have been conducted. In one survey of 1483 adults aged 18–60 years from four provincial capital cities in 2009, approximately 32% of the participants reported that they drank less water than the amount recommended by the Chinese Nutrition Society in 2006 (1200 mL/day). Furthermore, 71.6% of participants had no knowledge of these recommendations [24].
Based on data from that water intakes survey, adequate water intake guidelines were reproposed by the Chinese Nutrition Society in 2013. The recommended adequate water intake levels for male and female adults were 1700 and 1500 mL, respectively. Another survey among young men in 2015 concluded that almost three-quarters of participants did not achieve the recommended amount of fluid intake (1700 mL) and a quarter were dehydrated [25].
Thus, conducting hydration-related studies is urgently required to emphasize the importance of hydration based on scientific evidence. However, few hydration-related health studies have been conducted, especially from the perspective of cognitive performance.
The objectives of this study involving young adults in China were first, to examine the effects of slow, progressive dehydration after 36 h of water deprivation on cognitive performance and mood, and second, to evaluate the effects of rehydration with water supplementation.
Discussion
In the study, dehydration induced by water deprivation for 36 h had negative effects on vigor and esteem-related affect. It impaired the cognitive performance, such as that related to short-term memory and attention. Another study with 16 participants in this field showed that tiredness was increased and alertness was reduced after 24 h of water deprivation; in addition, reaction times were prolonged in women but shortened in men [37].
Similarly, during 24 h of voluntary water deprivation in one study of 10 participants, a significant deterioration was observed in cognitive performance, such as that related to solving time in psychological tests; however, self-estimated mood did not changed significantly [38].
In a study of athletes, it was revealed that mild dehydration after 12 h of water deprivation impaired cognitive-motor task performance, such as judgment of distance to a target [39]. Few cognitive performance studies related to dehydration have been conducted using water deprivation to induce dehydration. Most studies obtained similar results, revealing that dehydration impaired cognitive performance and mood; however, the mechanisms behind these effects have not been fully studied.
A study demonstrated that water deprivation influences the transcription of many genes in the brain, such as the upregulation of clathrin, serum/glucocorticoid-regulated kinase, and protein kinase anchor protein 8-like; and the downregulation of janus kinase, microtubule interacting protein 1, and neuronal PAS domain protein 4 [40].
In some studies, MRI was conducted to explore these related mechanisms among participants in the acute stage of dehydration. It was revealed that the ventricular system expanded, with the most substantial change occurring in the left lateral ventricle in one study, which may induce the short-term changes in cognitive performance [41].
In another study, using a brain MRI scan, it was demonstrated that the lateral ventricle was enlarged and fronto-parietal blood-oxygen-level-dependent response was increased after acute dehydration induced by a thermal exercise protocol. These changes may be related to the complex mechanisms behind the brain’s response to dehydration.
As stated, a key concern of this study was whether rehydration after water supplementation could improve cognitive performance and mood. The results determined that sufficient water supplementation is an effective method of ensuring optimal hydration and improving cognitive performance and mood.
A placebo-controlled crossover design study of 16 male participants showed that rehydration after dehydration induced by exercise attenuated alcohol-related impairment of cognitive functions [42]. In another study of 32 young adults and 30 older adults, the alertness and attentiveness of participants increased, their fatigue decreased, and their reaction ability improved after rehydration.
Furthermore, one study confirmed the dose-response effects of water supplementation on cognitive performance in children and that visual attention can be enhanced by even a small intake of water (25 mL) [43]. For school children, it was revealed that focusing on drinking an adequate volume of water to retain optimal hydration throughout the day may be the key to enhancing cognitive performance. However, the results of some studies have been inconsistent [44,45].
A systematic review concluded that evidence for the benefits of water supplementation on cognitive performance is insufficient, with further confirmation required [46]. Different methods of inducing dehydration, degrees of dehydration, methods of conducting cognitive performance tests, and amounts of water supplementation may have caused these inconsistent conclusions.
Thus, additional studies should be conducted to elucidate the effects of water supplementation on cognitive performance. The plausible mechanism should also be explored through the aspects of hormonal, neurochemical, and vascular functions in response to hydration status.
The study has certain strengths and limitations. Only water deprivation was used to induce dehydration. A pure method of water deprivation and water supplementation in free-living conditions may be more helpful for exploring the effects of hydration on cognitive performance. Urine osmolality during the period of water deprivation was monitored to changes in hydration status and to verify the adherence of participants.
The obtained urine osmolality trends suggested that the osmolality of most participants increased with the prolongation of water deprivation. Furthermore, nine participants (75%) were in a state of dehydration for the whole day. These reflect the favorable compliance of participants and the high quality of the study process.
In terms of limitations, the effects of long-term water interventions and the mechanisms governing hydration and cognitive performance were not studied. Only male participants were recruited, thus gender differences were not studied. The conditions at each participant’ places were not recorded. Water loss through sweating and excretion of feces were not monitored in this study.
Conclusions
Dehydration had negative effects on vigor, esteem-related affect, short-term memory, and attention. Rehydration after water supplementation improved fatigue, TMD, short-term memory, attention, and reaction. Our results confirm that drawing attention to the importance of water intake and hydration is necessary. Water-related health education should be provided effectively to advocate drinking adequate amounts of water and maintaining a state of optimal hydration.
Source:
Penn State
Media Contacts:
Katie Bohn – Penn State
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Original Research: Closed access
“Cognitive performance in relation to hydration status and water intake among older adults, NHANES 2011–2014”. Hilary J. Bethancourt, W. Larry Kenney, David M. Almeida, Asher Y. Rosinger.
European Journal of Nutrition doi:10.1007/s00394-019-02152-9.
