Hydration and cognitive performance

Effects of heat strain on cognitive function among a sample of miners

Heat stress is associated with workplace injuries, likely through a combination of fatigue, reduced cognitive function, and thermal discomfort. The purpose of this study was to evaluate four cognitive tasks for sensitivity to heat stress. Eight participants performed treadmill exercise followed by assessments of serial reaction time (RT), Stroop effect, verbal delayed memory, and continuous performance working memory in an environmental chamber. A control (21.1 °C) trial, and "Hot 1" and "Hot 2" (both 37.8 °C) trials were run sequentially on two separate days to evaluate the four cognitive tasks. Heat strain (comparing Hot 1 and Hot 2 with the control trial) resulted in impairments in the serial RT test response and Stroop accuracy. Delayed memory was impacted only in the Hot 2 trial compared with the control trial. Given the demonstrated impact of heat on cognitive processes relevant to workers' real-world functioning in the workplace, understanding how to assess and monitor vigilant attention in the workplace is essential.

Relation between occupants' health problems, demographic and indoor environment subjective evaluations: A cross-sectional questionnaire survey study in Java Island, Indonesia

This study aimed to evaluate the link between health problems, demographic factors, and the indoor environment quality of residents in Indonesia. We conducted a cross-sectional design study through a questionnaire survey with 443 respondents aged between 12 and 81 years. The questionnaire was concerned with previous health problem occurrences associated with thermal discomfort experiences, indoor environments, economic conditions, and basic anthropometric factors. Logistic regression with the odds ratio (OR) was applied to evaluate the tendency of different respondent groups to suffer from certain health problems, when compared to reference groups. Furthermore, structural equation modelling (SEM) was used to incorporate certain factors (economic conditions, thermal discomfort experiences, and perceived indoor environments) into a single model to understand their direct and indirect effects on health conditions. The results indicate that economic conditions are the most significantly associated with health problems. Furthermore, we found that the low-income group was the most vulnerable to health problems, including coughing, puking, diarrhoea, odynophagia, headaches, fatigue, rheumatism, fidgeting, skin rashes, muscle cramps, and insomnia (OR: 1.94-6.04, p <0.05). Additionally, the SEM suggested that the respondents' economic conditions and thermal discomfort experiences had significant direct effects on their health problems with standardized estimates of -0.29 and 0.55, respectively. Additionally, perceived indoor environment quality, which is possible to cause thermal discomfort experience, indirectly affect health problems. These findings contribute an insightful and intuitive knowledge base which can aid health assessments associated with demographic and physical environments in developing sustainable and healthy environment strategies for the future.

Sustainable solutions to mitigate occupational heat strain - an umbrella review of physiological effects and global health perspectives

BACKGROUND

Climate change is set to exacerbate occupational heat strain, the combined effect of environmental and internal heat stress on the body, threatening human health and wellbeing. Therefore, identifying effective, affordable, feasible and sustainable solutions to mitigate the negative effects on worker health and productivity, is an increasingly urgent need.

OBJECTIVES

To systematically identify and evaluate methods that mitigate occupational heat strain in order to provide scientific-based guidance for practitioners.

METHODS

An umbrella review was conducted in biomedical databases employing the following eligibility criteria: 1) ambient temperatures > 28 °C or hypohydrated participants, 2) healthy adults, 3) reported psychophysiological (thermal comfort, heart rate or core temperature) and/or performance (physical or cognitive) outcomes, 4) written in English, and 5) published before November 6, 2019. A second search for original research articles was performed to identify interventions of relevance but lacking systematic reviews. All identified interventions were independently evaluated by all co-authors on four point scales for effectiveness, cost, feasibility and environmental impact.

RESULTS

Following screening, 36 systematic reviews fulfilled the inclusion criteria. The most effective solutions at mitigating occupational heat strain were wearing specialized cooling garments, (physiological) heat acclimation, improving aerobic fitness, cold water immersion, and applying ventilation. Although air-conditioning and cooling garments in ideal settings provide best scores for effectiveness, the limited applicability in certain industrial settings, high economic cost and high environmental impact are drawbacks for these solutions. However, (physiological) acclimatization, planned breaks, shading and optimized clothing properties are attractive alternative solutions when economic and ecological sustainability aspects are included in the overall evaluation.

DISCUSSION

Choosing the most effective solution or combinations of methods to mitigate occupational heat strain will be scenario-specific. However, this paper provides a framework for integrating effectiveness, cost, feasibility (indoors and outdoor) and ecologic sustainability to provide occupational health and safety professionals with evidence-based guidelines.

Gonadal hormones in female rats protect against dehydration-induced memory impairments in the novel object recognition paradigm

Dehydration impairs cognitive performance in humans and rodents, although studies in animal models are limited. Estrogens have both protective effects on fluid regulation and improve performance in certain cognitive tasks. We, therefore, tested whether sex and gonadal hormones influence object recognition memory during dehydration. Because past studies used fluid deprivation to induce dehydration, which is a mixture of intracellular and extracellular fluid loss, we tested the effects of osmotic (loss of intracellular fluid) and hypovolemic (loss of extracellular fluid) dehydration on object recognition memory. After training trials consisting of exposure to two identical objects, rats were either treated with hypertonic saline to induce osmotic dehydration, furosemide to induce hypovolemic dehydration, or received a control injection and then object recognition memory was tested by presenting the original and a novel object. After osmotic dehydration, regardless of group or treatment, all rats spent significantly more time investigating the novel object. After hypovolemic dehydration, regardless of treatment, both the males and estrous females spent significantly more time investigating the novel object. While the control-treated diestrous females also spent significantly more time investigating the novel object, the furosemide-treated diestrous females spent a similar amount of time investigating the novel and original object. Follow up studies determined that loss of ovarian hormones after ovariectomy, but not loss of testicular hormones after castration, resulted in impaired memory performance in the object recognition test after hypovolemic dehydration. This series of experiments provides evidence for a protective role of ovarian hormones on dehydration-induced memory impairments.

Effect of Dehydration on Passing Decision Making in Soccer Athletes

It seems that dehydration may impair decision-making performance in athletes.

PURPOSE

This study aimed to investigate the influence of dehydration on passing decision-making performance in soccer players.

METHOD

Participants were 40 male soccer players (M_age = 22.3 ± 2.3 years) who agreed to participate in the study and were randomly assigned to the following conditions: control (CON), dehydration (DEH), and euhydration (EUH). The players played in 2 games of 90 min in duration (2 45-min halves) followed by 2 15-min halves (overtime) with and without proper hydration. The Game Performance Assessment Instrument (GPAI) was considered for the analysis of passing decision making.

RESULTS

The GPAI analysis indicated effective reduction in the decision-making index in the DEH condition compared with the EUH and CON conditions, F(2, 38) = 31.4, p < .05, ES = 0.8.

CONCLUSIONS

In conclusion, dehydration may be considered a mediating factor in the passing decision-making performance of male soccer athletes.

Assessment of nutritional status in the elderly: a proposed function-driven model

Background

There is no accepted or standardized definition of ‘malnutrition’. Hence, there is also no definition of what constitutes an adequate nutritional status. In elderly people, assessment of nutritional status is complex and is complicated by multi-morbidity and disabilities combined with nutrition-related problems, such as dysphagia, decreased appetite, fatigue, and muscle weakness.

Objective

We propose a nutritional status model that presents nutritional status from a comprehensive functional perspective. This model visualizes the complexity of the nutritional status in elderly people.

Design and results

The presented model could be interpreted as the nutritional status is conditional to a person’s optimal function or situation. Another way of looking at it might be that a person’s nutritional status affects his or her optimal situation. The proposed model includes four domains: (1) physical function and capacity; (2) health and somatic disorders; (3) food and nutrition; and (4) cognitive, affective, and sensory function. Each domain has a major impact on nutritional status, which in turn has a major impact on the outcome of each domain.

Conclusions

Nutritional status is a multifaceted concept and there exist several knowledge gaps in the diagnosis, prevention, and optimization of treatment of inadequate nutritional status in elderly people. The nutritional status model may be useful in nutritional assessment research, as well as in the clinical setting.

Cross-sectional association of dietary water intakes and sources, and adiposity: National Adult Nutrition Survey, the Republic of Ireland

Purpose

Drinking (plain) water intake has been associated with weight loss and reducing energy intake in intervention trials. In free-living populations, replacing other beverages with drinking water is associated with reduced obesity risk. However, the association of total water intake and its sources, and body fat distribution remain unevaluated. Thus, the aim of this study was to investigate total water intake and its sources and the association with anthropometric measures.

Methods

Cross-sectional study of 1500 adults aged 18–90 years (Irish National Adult Nutrition Survey, 2008–2010). Total water intake and its sources were estimated using food records. Associations of total water, drinking water, beverage moisture and food moisture intakes split by tertile, and BMI (kg/m²), waist circumference (cm), and bio-impedance derived body fat (%) were evaluated using covariate-adjusted linear regression analyses including adjustment for energy intake and energy expenditure.

Results

Higher consumption of total water was associated with lower waist circumference [β-coefficient (95% CI), p trend, tertile 3 versus tertile 1: − 2.19 (− 4.06, − 0.32), 0.036], but not BMI [− 0.44 (− 1.16, 0.28), 0.336] or body fat [− 0.87 (− 1.91, 0.17), 0.146]. Higher consumption of drinking water and food moisture were associated with lower BMI [− 0.65 (− 1.30, − 0.01), 0.027; − 0.64 (− 1.41, − 0.13), 0.014, respectively], body fat [− 1.51 (− 2.43, − 0.59), 0.001; − 1.00 (− 2.12, − 0.12), 0.001], and waist circumference [− 2.83 (− 4.51, − 1.16), < 0.001; − 1.84 (− 3.86, − 0.19), 0.082]. Beverage moisture was not associated with any of the anthropometric measurements.

Conclusions

Consumption of drinking water and food moisture and not total water or beverage moisture were inversely associated with adiposity, independent of energy intake and expenditure. Advice encouraging drinking water and food moisture intake may be beneficial in addition to energy balance advice, in combating obesity.

Electronic supplementary material

The online version of this article (10.1007/s00394-018-1635-z) contains supplementary material, which is available to authorized users.

Estimated work ability in warm outdoor environments depends on the chosen heat stress assessment metric

With a view to occupational effects of climate change, we performed a simulation study on the influence of different heat stress assessment metrics on estimated workability (WA) of labour in warm outdoor environments. Whole-day shifts with varying workloads were simulated using as input meteorological records for the hottest month from four cities with prevailing hot (Dallas, New Delhi) or warm-humid conditions (Managua, Osaka), respectively. In addition, we considered the effects of adaptive strategies like shielding against solar radiation and different work-rest schedules assuming an acclimated person wearing light work clothes (0.6 clo). We assessed WA according to Wet Bulb Globe Temperature (WBGT) by means of an empirical relation of worker performance from field studies (Hothaps), and as allowed work hours using safety threshold limits proposed by the corresponding standards. Using the physiological models Predicted Heat Strain (PHS) and Universal Thermal Climate Index (UTCI)-Fiala, we calculated WA as the percentage of working hours with body core temperature and cumulated sweat loss below standard limits (38 °C and 7.5% of body weight, respectively) recommended by ISO 7933 and below conservative (38 °C; 3%) and liberal (38.2 °C; 7.5%) limits in comparison. ANOVA results showed that the different metrics, workload, time of day and climate type determined the largest part of WA variance. WBGT-based metrics were highly correlated and indicated slightly more constrained WA for moderate workload, but were less restrictive with high workload and for afternoon work hours compared to PHS and UTCI-Fiala. Though PHS showed unrealistic dynamic responses to rest from work compared to UTCI-Fiala, differences in WA assessed by the physiological models largely depended on the applied limit criteria. In conclusion, our study showed that the choice of the heat stress assessment metric impacts notably on the estimated WA. Whereas PHS and UTCI-Fiala can account for cumulative physiological strain imposed by extended work hours when working heavily under high heat stress, the current WBGT standards do not include this. Advanced thermophysiological models might help developing alternatives, where not only modelling details but also the choice of physiological limit criteria will require attention. There is also an urgent need for suitable empirical data relating workplace heat exposure to workability.

Effects of Fluid Ingestion on Brain-Derived Neurotrophic Factor and Cognition During Exercise in the Heat

We investigated the effects of fluid ingestion during exercise in different environments on the serum brain-derived neurotrophic factor and cognition among athletes. Ten collegiate male athletes (soccer, n = 5; rugby, n = 5) were enrolled, and they completed running tests in the following four conditions (60 min each): 1) thermoneutral temperature at 18°C (group 18); 2) high ambient temperature at 32°C without fluid ingestion (group 32); 3) high ambient temperature at 32°C with water ingestion (group 32+W); and 4) high ambient temperature at 32°C with sports drink ingestion (group 32+S). Serum brain-derived neurotrophic factor levels significantly increased in group 18 immediately after exercise when compared with those at rest and were significantly higher than those in group 32 immediately and 60 min after exercise (p < 0.05). In the Stroop Color and Word Test, significantly increased Word, Color, and Color-Word scores were observed in group 18 immediately after exercise compared to those at rest (p < 0.05). However, the Color-Word score appeared to be significantly lower in group 32 immediately after exercise compared to the other groups (p < 0.05) and at 60 min post-exercise compared to group 18 (p < 0.05). We found that the exercise performed in a thermoneutral environment improved cognitive function, but the exercise performed in a hot environment did not. The differences according to the exercise environment would be largely affected by brain-derived neurotrophic factor, and fluid ingestion regardless of the type of drink (water or sports beverage) was assumed to have contributed to the improvement in cognitive function caused by exercising in a hot environment.

The degree of processing of foods which are most widely consumed by the French elderly population is associated with satiety and glycemic potentials and nutrient profiles

Food processing impacts both food structure and nutritional density. The effect of food structure on satiety and glycemic potentials is well recognized. However, the association between processing, satiety and glycemic potentials and nutrient profiles has not been much studied, especially in the diets of the elderly. Therefore, this study aimed at exploring relations between the level of food processing, consumption and nutrient profiles and satiety and glycemic potentials among 6686 French elderly people (≥65 years). Dietary assessment was realized through a web-based 24 h dietary record tool. Among a total of 2688 foods, 280 generic foods were aggregated based on a consumption threshold of at least 5% by the population. The satiety potential was calculated using the Fullness Factor equation, and the glycemic potential using the glycemic index and the glucose glycemic equivalent. Foods and dishes were ranked according to an adapted international NOVA classification as raw/minimally-processed (G1), processed (G2) and ultra-processed (G3). ANOVA and correlation analyses showed that the more food is processed, the lower its satiety potential and nutrient density and the higher its glycemic impact, especially when comparing G1 and G3. Besides, the foods consumed in the greatest quantity daily tend to be the most satiating, and ultra-processed foods were among the less frequently consumed both in terms of percentage and daily quantity (around two-fold difference between minimally- and ultra-processed foods). In conclusion, because it is partly related to health food potential, the degree of processing, especially for ultra-processed products, should be taken into consideration more when evaluating consumption profiles of different populations.

Rivalry of homeostatic and sensory-evoked emotions: Dehydration attenuates olfactory disgust and its neural correlates

Neural correlates have been described for emotions evoked by states of homeostatic imbalance (e.g. thirst, hunger, and breathlessness) and for emotions induced by external sensory stimulation (such as fear and disgust). However, the neurobiological mechanisms of their interaction, when they are experienced simultaneously, are still unknown. We investigated the interaction on the neurobiological and the perceptional level using subjective ratings, serum parameters, and functional magnetic resonance imaging (fMRI) in a situation of emotional rivalry, when both a homeostatic and a sensory-evoked emotion were experienced at the same time. Twenty highly dehydrated male subjects rated a disgusting odor as significantly less repulsive when they were thirsty. On the neurobiological level, we found that this reduction in subjective disgust during thirst was accompanied by a significantly reduced neural activity in the insular cortex, a brain area known to be considerably involved in processing of disgust. Furthermore, during the experience of disgust in the satiated condition, we observed a significant functional connectivity between brain areas responding to the disgusting odor, which was absent during the stimulation in the thirsty condition. These results suggest interference of conflicting emotions: an acute homeostatic imbalance can attenuate the experience of another emotion evoked by the sensory perception of a potentially harmful external agent. This finding offers novel insights with regard to the behavioral relevance of biologically different types of emotions, indicating that some types of emotions are more imperative for behavior than others. As a general principle, this modulatory effect during the conflict of homeostatic and sensory-evoked emotions may function to safeguard survival.

Assessment of hydration status in a large population

Both acute and chronic dehydration can have important implications for human behaviour and health. Young children, non-autonomous individuals and the elderly are at a greater risk of dehydration. Mild hypertonic dehydration could be related to less efficient cognitive and physical performance and has been reported to be associated with frequently occurring pathological conditions, especially nephrolithiasis. The assessment of hydration status in a large sample appears to be of interest for conducting epidemiological and large clinical studies aimed at improving preventive and curative care. Especially in large-population studies, methods that are used have to be accurate, cheap, quick and require no technical expertise. Body weight change is widely used to determine acute hydration changes, but seems to be insufficiently accurate in longitudinal studies. Bioimpedance analysis methods enable the assessment of total body water content, but their use is still under debate. Because plasma osmolality directly reflects intracellular osmolality, it constitutes a good marker to assess acute hydration changes, but not chronic hydration status because it changes constantly. Moreover, venepuncture is considered to be invasive and is not suitable for a large-sample study, especially in children. Urinary markers appear to be good alternatives for assessing hydration status in large populations. Collection of urine samples is non-invasive and cheap. High technical expertise is not required to perform urinary marker measurements and these measurements can be carried out quickly. Thus, methods based on urinary markers are very well suited for field studies. Urine colour is probably the least sensitive marker despite its high specificity. Urine osmolality and especially urine specific gravity could be easily used for determining hydration status in large-sample studies.

Mild to moderate dehydration combined with moderate alcohol consumption has no influence on simulated driving performance

OBJECTIVE

Many people consume alcoholic beverages following a period of physical activity that results in fluid loss through sweating (e.g., after sports, work). Adequate rehydration following physical activity may not occur, consequently resulting in the consumption of alcohol in a dehydrated state. This may have serious implications for the safety of individuals operating motor vehicles. Therefore, this study investigated the impact of mild-moderate dehydration in combination with moderate alcohol consumption on simulated driving performance.

METHODS

Fourteen healthy males participated in a placebo-controlled crossover design study involving 4 experimental trials (separated by 4 days or more). In each trial, participants were dehydrated by ∼2 percent body mass through exercise. After a 30-min recovery, participants completed a 15-min computerized simulated driving task (drive 1). In 2 of the trials, participants were provided with water equivalent to either 50 or 150 percent body mass loss and also received salt capsules (NaCl, 50 mmol/L). A set volume of alcohol or placebo was then consumed in each trial, incorporating the conditions: dehydration-placebo (DP), dehydration-alcohol (DA), partial rehydration-alcohol (PA), and full rehydration-alcohol (FA). The volume of the alcoholic beverage was individually calculated and intended to raise the blood alcohol content (BAC) to ∼0.05 percent. The same driving task was then readministered (drive 2). Primary outcome measures of driving consisted of standard deviation of lateral position (SDLP), number of side and center line crossings (LC), number of failures to stop at red traffic signals (FTS), number of impacts/collisions with other vehicles or objects (IMP), and time to collision with a specified lead vehicle (TTC). In addition, reaction time (RT) and incorrect inhibition response (IIR) behavior to critical events were collected throughout each experimental drive. Subjective ratings of mood and estimates of alcohol intoxication and driving impairment were also recorded in each trial.

RESULTS

No effects of trial condition were observed on any of the driving performance measures or on subjective ratings of mood, alcohol intoxication, and driving impairment. SDLP was higher following the consumption of alcohol compared to the placebo trial. However, no differences in SDLP were recorded between the alcohol trials, indicating that hydration level had no observable interaction with alcohol to influence SDLP performance.

CONCLUSIONS

Overall, it appears that dehydration does not exacerbate impairment in driving performance caused by mild-moderate alcohol intoxication. Further research is required to clarify the effects of alcohol and dehydration at various alcohol doses.

The Hydration Equation: Update on Water Balance and Cognitive Performance

To become aware of the most practical measures of hydration status.To describe sources of water input and output and the basics of water balance.To understand how hydration status may impact daily cognitive performance.

CONDENSED VERSION AND BOTTOM LINE

Water is a crucial nutrient and euhydration is necessary for optimal daily functioning. Water balance is precisely regulated within the body and many methods exist for assessing hydration status. Cognitive performance measures an individual's attentiveness, critical thinking skills, and memory. Traditionally a 2% or more body water deficit was thought to produce cognitive performance decrements; however, recent literature suggests that even mild dehydration - a body water loss of 1-2% - can impair cognitive performance. Counseling clients about their health and wellbeing should include conveying the importance of water for normal body functioning, as well as its effects on physical and cognitive performance.