Older adults should not drink and drive at all, according to a new study which found that a single serving can make those aged 55 or older dangerous drivers.
The findings suggest it could be time to reassess legal blood alcohol levels for all drivers, researchers said.
Sara Jo Nixon, a professor in the departments of psychiatry and psychology at the University of Florida and researcher Alfredo Sklar tested how drinking legally non-intoxicating levels of alcohol affect the driving skills of two age groups: 36 people ages 25 to 35 and 36 people ages 55 to 70.
They found that although neither age group imbibed enough alcohol to put them over the legal driving limit, a blood alcohol level of 0.08, just one drink can affect the driving abilities of older drivers.
In the study, both groups completed a driving task completely sober. The task took the drivers down a simulated winding 4.8-km stretch of country road.
The drivers stared straight ahead at a large computer monitor. Two computer monitors flanked the first, mimicking the side windows of a car and what the drivers would see in their peripheral vision.
A stereo system played driving sounds. A console included a steering wheel and brake and gas pedals. Occasionally, the drivers would encounter an oncoming car, but they did not encounter other distractions.
Researchers assessed the drivers' ability to stay in the centre of their lane and maintain a constant speed. They also looked at how rapidly they adjusted their steering wheel.
On a later day, the groups were further separated into groups. The first imbibed a placebo - a diet lemon-lime soda misted with a negligible amount of alcohol to mimic the experience of drinking alcohol.
A second group's drink was strong enough to produce a 0.04 per cent breath alcohol level, and a third group's drink gave them a breath alcohol level of 0.065 per cent - still below the federal legal level for drinking of 0.08.
Participants then completed the same driving task they performed when they were sober. Researchers timed the task so participants' alcohol levels were declining to mimic a situation in which individuals have a drink with dinner and then drive home.
In younger adults, the researchers found alcohol consumption did not affect their measured driving skills at all - a finding that Nixon called a "bit surprising".
She warned that the absence of effects in this laboratory setting does not mean that young adult drivers' driving wouldn't be affected in normal circumstances, driving in a typical, real-world setting.
But for the older drivers, the small, legal levels of intoxication did affect their driving, researchers said.
The study is published in the journal Psychopharmacology.
