Why Dehydrated Driving May Be Just as Dangerous as Drunk Driving

Dehydration may increase driving errors in men

It's well-known that drinking alcohol and driving can be a deadly combination, but driving while dehydrated may be just as dangerous.

A new study from the UK found that men who had not had enough water to drink may make as many mistakes on the road as those who are under the influence of alcohol.

"The results...suggest that mild [dehydration], induced through a short-term period of fluid restriction, 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," wrote lead study author Phillip Watson, PhD, an exercise physiologist at Loughborough University in England, and colleagues.

According to Dr. Watson and team, some people limit fluids to avoid frequent bathroom stops on long car trips.

Mild dehydration, however, reduces the total amount of blood circulating in the body. This may result in fatigue and reduced mental ability.

Dr. Watson and team recruited 11 healthy men in their 20s to participate in two simulated driving experiments — each about a week apart — that tested their driving skills in a hydrated and dehydrated state.Each experiment was conducted over two days.

For both trials, the men ate and drank normally the first day.

In the first trial, they also drank 10.5 cups of water throughout the day. In the second trial, the men only drank 2.5 cups of water.

On the second day, the men in the first trial ate two cereal bars and drank two cups of water. Men in the second trial drank less than a cup of water. About two hours after eating and drinking, these men took the simulated driving test.

The men who were dehydrated made an average of 101 driving errors, while the men who were hydrated made only 47 errors.

According to Dr. Watson and team, the dehydrated error rate was similar to driving with a blood-alcohol level of 0.08 percent — the legal limit in most US states.

This study did not include women drivers.

This study will be published in the August issue of the journal Physiology & Behavior.

The European Hydration Institute funded this research.