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 similar to 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 similar 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.