Hydration effects on cognition of pilots

Hydration effects on cognition of pilots

This study was carried out by Lindseth et al to explore the effects of different level of fluid intake and even dehydration on cognitive performance of pilots during flights. This article provides a further analysis based on the original one.
As shown in the table 1, the potential influences of high and low fluid intake on cockpit operation, memory and spatial cognition can be examined directly by recoding the simulator errors, Stemberg Short-term Memory response time and Vandenberg Mental Rotation scores. Using statistic analysis method, p-value can be obtained for each item based on a two-tail hypothesis statistic test, which was calculated by using each of those paired means and standard deviations under high and low fluid intake conditions respectively from 40 participants. In this study, the null hypothesis was set as there is no difference for hydration levels on the effect of cognitive functions. According to the sampling distribution, the locations of t-statistic can also illustrate the probability of determining whether to reject the null hypothesis of this research when comparing with 0.05 significant level (by finding out whether it located at the area of 5%). Or their relationships can be expressed through comparing p-values of each paired recorders to the 5% significant level (which was used generally). Depending on the results from table 1, it can be concluded that there was no difference between high and low fluid intake for cockpit operation (p=0.97), memory (p=0.23) and spatial cognition (p=0.12) as p>0.05 (for a two-tail hypothesis statistic test which was defined as no direction appointed, significant probability was the sum of two directions), for which we do not reject the null hypothesis (we only reject null hypothesis when p<0.05, which was known as significant difference between the two variables).

Table 1. Significant Differences in Cognition and Cockpit Operation When Comparing High and Low Fluid Intakes

Cognition measures Level of fluid intake Mean SD p-value
Simulator Errorsa High 278,986.8 194,077.3
Low 231,600.5 315,627.7 0.97
Stemberg Short-term Memory Response Timea High 772.3 198.8
Low 706.8 179.2 0.23
Vandenberg Mental Rotation (Situational Awareness) Scoresb High 14.2 5.7
Low 17.6 5.1 0.12

N = 40. aHigher score = poorer performance. bHigher score = better performance.

For further research, Lindseth et al also studied on the dehydration conditions, attempting to find out any significant difference between hydration (with low fluid intake) and dehydration, which were measured based on the weight change (1-3% of weight loss was considered as dehydration in this experiment) on participants. Sample sizes were different between the two groups in this experiment for which there were only 12 participants showing weight loss during diet period of low fluid intake. As the statistic results shown in table 2, there was significant difference between the two means in spatial cognition scores while p=0.03 (<0.05), and even highly significant in cockpit operation as p=0.002. Therefore, we can conclude that the dehydration did affect cockpit behaviour and spatial cognition from this statistic analysis. However, the result showed no significant difference in short-term memory for which p=0.13. In this further research, a two-tail test was still being used as the exact effect on dehydration was unclear. The result showed that memory was not a noteworthy factor influenced by dehydration. Comparing these two analyses, short-term memory can initially considered not being influenced by amount of fluid intake.

Table 2. Significant Differences in Cockpit Operation and Cognition When Experiencing Low Fluid Intake and Dehydration

Cognition measures Weight change Mean SD p-value
Simulator Errorsa No Weight Loss 193,234.9 72,055.9
1-3% Weight Loss 449,005.2 43,909.0 0.002
Stemberg Short-term Memory Response Timea No Weight Loss 688.7 184.5
1-3% Weight Loss 809.5 104.6 0.13
Vandenberg Mental Rotation (Situational Awareness) Scoresb No Weight Loss 18.26 4.2
1-3% Weight Loss 13.50 8.2 0.03

N = 40. aHigher score = poorer performance. bHigher score = better performance.

Scope of the Study

This study was conducted in a particular area in USA and the participants’ selection was restricted by several criteria, thus, there were few pilots take part in due to their right of freedom, resulting in a narrow range of application. From the demographic result, it could be concluded that participants involved in this study was concentrated upon young and inexperienced pilots. Hence, the result can only be generalized to the similar population as there was unclear whether the age and gender were confounding variables.


Research approach

A within-subjects design was used based on the experimental research to explore the impact of hydration on pilots. Counterbalancing was used with this experimental design to mitigate the order effect.


40 participants were selected randomly from 89 volunteer pilots who match all conditions for the experiment (including exclusive medical and healthy criteria). Most of the participants were young (M=20.3) due to the small dispersion (SD=1.5), with a little number of average total flight time and total instrument time (145.5hrs and 45.7hrs respectively). The average body mass index (weight-to-height measurements) was shown in a healthy range. During the 10-week experimental period, they were randomized to two groups, taking contrary sequences of high and low fluid intake diet respectively (high-low and low-high), and each period last for 2 weeks. There was a 2-week washout period to separate them.


Lindseth et al established the experiment by defining the level of fluid intake as the independent variable and the pilots’ responses which were expressed through cockpit operation, spatial cognition and short-term memory as the dependent variables, trying to conduct causality between those variables under different conditions for exploration of impact of hydration on their cognition. In the second further statistic analysis, weight change was treated as another independent variable that indicated the dehydration with low fluid intake.
Besides, there were several extraneous variables had to be concerned during the experiment to ensure the validity of the result. During the diet period, calorimetry measurement needed to be monitored carefully to prevent weight gain from excess calorie intake through the food and beverages restrictions, which ensured the exact amount of fluid intake meanwhile matching daily nutrition requirements. However, there was no exercise control to prevent excess water consumption. Moreover, caffeine consumption was strictly restricted but not forbidden in this study, giving rise to the uncertainty of precision of the results as it might affect the performance of pilots rather than hydration. Alcoholic beverages were not allowed during both diet periods since it might impact the hydration level within the body. In addition, adequate kidney function and sleep activity were monitored regularly to ensure normal metabolism and avoid fatigue, contributing to the precision and validity of the result. Furthermore, all participants were measured under a stable environment with appropriate noise level and temperature.


There were some limitations in this study. First, in the second experiment, the sample size were greatly different, which had a negative influence on the result since there might be some phenomenon occurred by accident that cannot be ignored via such a little sample. Second, further research was needed for this study because the exact effect of hydration was ambiguous as there was not enough evidence to prove that whether performance and cognition would be worse or better by the level of hydration and dehydration. Third, data collected were not precise enough as it ignored the influence of gender.

1. Lindseth, P. D., Lindseth, G. N., Petros, T. V., Jensen, W. C., & Caspers, J. (2013). Effects of hydration on cognitive function of pilots. Military Medicine, 178(7): 792-8.
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