Dehydration and Cognitive Performance

Hydration and cognitive performance

A clinical link exists between severe dehydration and cognitive performance. Using rapid and severe water loss induced either by intense exercise and/or heat stress, initial studies suggested there were alterations in short-term memory and cognitive function related to vision, but more recent studies have not all confirmed these data. Some studies argue that water loss is not responsible for the observations made, and studies compensating water losses have failed to prevent the symptoms. Studies in children have suggested that drinking extra water helps cognitive performance, but these data rely on a small number of children. In older adults (mean age around 60) the data are not strong enough to support a relationship between mild dehydration and cognitive function. Data on frail elderly and demented people are lacking. Methodological heterogeneity in these studies are such that the relationship between mild dehydration and cognitive performance cannot be supported.

Alcohol pharmacokinetics and risk-taking behaviour following exercise-induced dehydration

This study investigated the influence of exercise-induced dehydration on alcohol pharmacokinetics, subjective ratings of impairment, and risk-taking behaviours. Twelve male volunteers participated in 3 experimental trials completed in a randomised cross over design separated by at least 7 days. In one trial, participants exercised to cause dehydration of ~2.5% body weight loss. For the other trials, participants were required to be in a rested and euhydrated state. A set volume of alcohol was then consumed in each trial and participants were monitored over a 4h period. Blood (BAC) and breath (BrAC) alcohol samples were collected throughout and analysed to calculate pharmacokinetic variables associated with the blood alcohol curve. Total urine production, estimates of BrAC, and subjective ratings of intoxication and impairment were also recorded throughout each trial. No difference was found in the pharmacokinetics of alcohol between any of the trial conditions. BrACs were higher than BACs for 2h following alcohol consumption, but lower at measures taken 3 and 4 h post ingestion. Participants' ratings of confusion and intoxication were significantly lower, and they were more willing to drive in the dehydration trial compared with one of the euhydration trials. These findings suggest that dehydration or other physiological changes associated with exercise may have an ability to influence the subjective effects of alcohol and increase the likelihood of risk-taking behaviours such as drink-driving. However, further research is required to examine the effects of alcohol under conditions of exercise-induced fluid loss in order to clarify these findings.

Effects of walnut consumption on cognitive performance in young adults

Walnuts contain a number of potentially neuroprotective compounds like vitamin E, folate, melatonin, several antioxidative polyphenols and significant amounts of n-3 α-linolenic fatty acid. The present study sought to determine the effect of walnuts on verbal and non-verbal reasoning, memory and mood. A total of sixty-four college students were randomly assigned to two treatment sequences in a crossover fashion: walnuts-placebo or placebo-walnuts. Baseline data were collected for non-verbal reasoning, verbal reasoning, memory and mood states. Data were collected again after 8 weeks of intervention. After 6 weeks of washout, the intervention groups followed the diets in reverse order. Data were collected once more at the end of the 8-week intervention period. No significant increases were detected for mood, non-verbal reasoning or memory on the walnut-supplemented diet. However, inferential verbal reasoning increased significantly by 11.2 %, indicating a medium effect size (P = 0.009; d = 0.567). In young, healthy, normal adults, walnuts do not appear to improve memory, mood or non-verbal reasoning abilities. However, walnuts may have the ability to increase inferential reasoning.

Dehydration affects brain structure and function in healthy adolescents

It was recently observed that dehydration causes shrinkage of brain tissue and an associated increase in ventricular volume. Negative effects of dehydration on cognitive performance have been shown in some but not all studies, and it has also been reported that an increased perceived effort may be required following dehydration. However, the effects of dehydration on brain function are unknown. We investigated this question using functional magnetic resonance imaging (fMRI) in 10 healthy adolescents (mean age = 16.8, five females). Each subject completed a thermal exercise protocol and nonthermal exercise control condition in a cross-over repeated measures design. Subjects lost more weight via perspiration in the thermal exercise versus the control condition (P < 0.0001), and lateral ventricle enlargement correlated with the reduction in body mass (r = 0.77, P = 0.01). Dehydration following the thermal exercise protocol led to a significantly stronger increase in fronto-parietal blood-oxygen-level-dependent (BOLD) response during an executive function task (Tower of London) than the control condition, whereas cerebral perfusion during rest was not affected. The increase in BOLD response after dehydration was not paralleled by a change in cognitive performance, suggesting an inefficient use of brain metabolic activity following dehydration. This pattern indicates that participants exerted a higher level of neuronal activity in order to achieve the same performance level. Given the limited availability of brain metabolic resources, these findings suggest that prolonged states of reduced water intake may adversely impact executive functions such as planning and visuo-spatial processing.

Cognitive function in hot environments: a question of methodology

The physiological responses of thermal stress and its consequences on health have been well documented. However, the effect on cognitive function remains equivocal despite a substantial number of studies conducted in the area. Methodological discrepancies across different studies have made it difficult to conclude whether or not heat exposure per se has an adverse effect upon cognitive function and under what specific environmental and physiological conditions these alterations appear. This article gives an overview of the different confounding factors that have made it difficult to make conclusive interpretations. In addition, the current state of knowledge is presented and discussed with reference to the Global Workspace theory. Although previously presented conclusions are promising, much remains to be completed before understanding the mechanisms that could explain the relationship between heat exposure and cognitive function. Finally, recommendations are presented for further research in this area.

Impacto da desidratação na geração de força de atletas de arco e flecha durante competição Indoor e Outdoor

INTRODUÇÃO: O arco e flecha é um esporte estático que requer força e resistência da parte superior do corpo, sendo que a habilidade do arqueiro é definida pela capacidade de atirar a flecha no alvo em um intervalo de tempo com precisão. A contração muscular gerada durante a execução do gesto esportivo propicia o aumento da temperatura corporal, da oxidação de glicose e da sudorese, podendo esta ser potencializada pelas condições climáticas às quais o atleta é exposto. Todos estes fatores alteram a percepção de esforço e a própria geração de força, impondo um estresse negativo à performance. OBJETIVOS: Avaliar e relacionar o estado de hidratação de atletas de arco e flecha com alterações fisiológicas e de força intervenientes no rendimento competitivo. MÉTODOS: Participaram 11 arqueiros em duas competições distintas (indoor e outdoor). Foram mensurados parâmetros relacionados ao estado de hidratação, glicemia, percepção de esforço subjetivo e alteração na força de preensão palmar. RESULTADOS: Os atletas analisados apresentaram alterações significativas nos parâmetros relacionados ao estado hídrico em diferentes dias, provavelmente relacionadas às condições climáticas adversas na competição outdoor (34ºC e 60% URA) em relação à competição indoor (22ºC e 90% URA). O mesmo não foi observado para a glicemia. CONCLUSÃO: Este trabalho é o primeiro a comprovar a relação direta entre fatores climáticos e de rendimento em arqueiros de alto nível durante evento competitivo, assim como a evidenciar quais métodos não invasivos seriam os mais indicados para a avaliação do impacto destas alterações.

Heat exposure in the Canadian workplace

Exposure to excessive heat is a physical hazard that threatens Canadian workers. As patterns of global climate change suggest an increased frequency of heat waves, the potential impact of these extreme climate events on the health and well-being of the Canadian workforce is a new and growing challenge. Increasingly, industries rely on available technology and information to ensure the safety of their workers. Current Canadian labor codes in all provinces employ the guidelines recommended by the American Conference of Governmental Industrial Hygienists (ACGIH) that are Threshold Limit Values (TLVs) based upon Wet Bulb Globe Temperature (WBGT). The TLVs are set so that core body temperature of the workers supposedly does not exceed 38.0 degrees C. Legislation in most Canadian provinces also requires employers to install engineering and administrative controls to reduce the heat stress risk of their working environment should it exceed the levels permissible under the WBGT system. There are however severe limitations using the WGBT system because it only directly evaluates the environmental parameters and merely incorporates personal factors such as clothing insulation and metabolic heat production through simple correction factors for broadly generalized groups. An improved awareness of the strengths and limitations of TLVs and the WGBT index can minimize preventable measurement errors and improve their utilization in workplaces. Work is on-going, particularly in the European Union to develop an improved individualized heat stress risk assessment tool. More work is required to improve the predictive capacity of these indices.

Heart Rate Responses and Fluid Balance of Competitive Cross-Country Hang Gliding Pilots

Purpose:

To evaluate the physiological challenges of competitive cross-country hang gliding.

Methods:

Seventeen experienced male pilots (age = 41 ± 9 y; mean ± SD) were fitted with a monitor that recorded heart rate and altitude at 0.5 Hz throughout a competitive fight. Fluid losses were evaluated by comparing pilot pre- and postfight mass.

Results:

The pilots’ displacement was 88.4 ± 43.7 km in 145.5 ± 49.4 min. Mean fight altitude was 1902 ± 427 m (range = 1363-2601 m) with a maximum altitude of 2925 ± 682 m (1870-3831 m). The mean in-fight heart rate of the pilots was 112 ± 11 bpm (64 ± 6% predicted HRmax). For all except one subject, heart rate was highest while launching (165 ± 12 bpm, 93 ± 7% predicted HRmax), followed by landing (154 ± 13 bpm, 87 ± 7% predicted HRmax). No statistically significant relationship was observed between heart rate during the launch and reported measures of state anxiety. Heart rate was inversely related (P < .01) to altitude for all pilots except one. Fluid loss during the fight was 1.32 ± 0.70 L, which approximated 0.55 L/h, while mean in-fight fluid consumption was 0.39 ± 0.44 L. Six pilots consumed no fluid during the fight.

Conclusions:

Even among experienced pilots, high heart rates are more a function of state anxiety than physical work demand. Fluid losses during fight are surprisingly moderate but pilots may still benefit from attending to fluid balance.