Mild hypohydration increases the frequency of driver errors during a prolonged, monotonous driving task

The aim of the present study was to examine the effect of mild hypohydration on performance during a prolonged, monotonous driving task.

Eleven healthy males (age 22±4y) were instructed to consume a volume of fluid in line with published guidelines (HYD trial) or 25% of this intake (FR trial) in a crossover manner. Participants came to the laboratory the following morning after an overnight fast. One hour following a standard breakfast, a 120min driving simulation task began. Driver errors, including instances of lane drifting or late breaking, EEG and heart rate were recorded throughout the driving task

Pre-trial body mass (P=0.692), urine osmolality (P=0.838) and serum osmolality (P=0.574) were the same on both trials. FR resulted in a 1.1±0.7% reduction in body mass, compared to -0.1±0.6% in the HYD trial (P=0.002). Urine and serum osmolality were both increased following FR (P<0.05). There was a progressive increase in the total number of driver errors observed during both the HYD and FR trials, but significantly more incidents were recorded throughout the FR trial (HYD 47±44, FR 101±84; ES=0.81; P=0.006) CONCLUSIONS: The results of the present study suggest that mild hypohydration, produced a significant increase in minor driving errors during a prolonged, monotonous drive, compared to that observed while performing the same task in a hydrated condition. The magnitude of decrement reported, was similar to that observed following the ingestion of an alcoholic beverage resulting in a blood alcohol content of approximately 0.08% (the current UK legal driving limit), or while sleep deprived.