Dehydration & Cognitive Performance Deteriorates with Age

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Dehydration & Cognitive Performance Deteriorates with Age

Well documented is the crucial role that proper hydration plays in human homeostasis and all forms of optimal cognitive performance. Also well documented in recent posts is how driver hydration affects driver performance – in a study done by Loughborough University, mild dehydration (quantified as a mere 1% loss in body mass) led to double the amount of driver errors, along with a reduced ability to concentrate and lower levels of alertness.

Another factor which impacts driver hydration is that of age. According to Skills for Logistics the average age of an HGV driver is 53 years, and studies have shown that as we age, our ability to feel thirst (the body’s natural trigger to replenish lost fluids) diminishes after the age of 50; which means that the older the driver, the more dehydrated they may be without even knowing it – potentially exacerbating driver performance even further.

To look more closely at the effects of dehydration on older individuals, Ohio University ran a study to determine ‘the relation of hydration status to cognitive performance in healthy older adults’.

Analysis of the study can be split into hypothesis, methodology and results.


Prior data showed that dehydration led to a decrease in cognitive ability in young healthy adults, particularly in the areas of attention, processing speed and memory. While the thirst sensation is normally a sufficient stimulus to trigger fluid intake to compensate for fluid loss, a number of stressors can negate this trigger leading to involuntary dehydration. According to a Davis & Minaker (1994) study cited in the Ohio University research ‘age related decreases in muscle mass, renal function, and thirst sensation, in addition to limited access to fluids … lead to an overall decrease in total body water [dehydration] in older adults’.

The hypothesis of this study was then that ‘lower levels of hydration would be significantly related to slowed psychomotor processing speed and poorer performance on measures of attention and memory’ in older adults.


The test group comprised 28 participants ranging in age from 50 to 82 years – they were all living independently, and healthy without any prior neurological history (stroke or significant head injury) or global cognitive impairment.

Participants were randomly assigned to one of two groups:

Group 1: was asked to refrain from drinking or eating after dinner the night before they were due to participate in the study.

Group 2: was asked to eat and drink normally on the day prior to the study, as well as consume an additional 16 ounces of fluid – ideally water, but at the very least non-caffeinated and non-alcoholic fluids – throughout the day.

On the morning of the study (which lasted approximately 90 minutes) participants were given a general health overview, completed physiological measures, and then completed neuropsychological measures (including list learning and recall; story memory; copy and recall of complex drawing; spatial judgements; word fluency; attention; and psychomotor processing speed) to determine overall cognitive performance.


As predicted, the level of hydration significantly impacted ability and performance in processing speed, attention and memory skills.

‘Individuals who were less hydrated performed more slowly across several measures of psychomotor processing speed and more poorly on attention/memory tasks, even after controlling for the effects of demographic variables and blood pressure on cognition.’

This provides further proof that while dehydration adversely affects everyone – the younger participants, aged on average 22 years, in the Loughborough study showed that poor driver hydration led to increased instances of driver errors, along with changes in concentration and levels of alertness – this impaired cognitive function and mental performance is exacerbated in older individuals. And if one considers that the average age of the HGV vehicle is in his 50s, then the necessity of sufficient hydration becomes even more apparent.

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