There might be more truth to the maxim "Just don't drink and drive" than most people think.

Because of weight and gender diffferences—as well as a range of other factors that can affect alcohol absorption and metabolization in humans—groups like MADD Canada simply advise people "Don't drink and drive", in order to avoid impairment when one is behind the wheel of any vehicle .

Now a new study, published as a research paper in the Journal of Physiology on December 17, has shown that skills strongly associated with driving ability can be "seriously" impaired by the equivalent of less than half a beer.

Scientists with the National Aeronautics and Space Administration's (NASA) California-based  Ames Research Center and San José State University found "for the first time" that hand-eye coordination is much more sensitive to alcohol than previously thought, with even a 0.015 percent blood-alcohol concentration (BAC) impairing certain measures of coordination by more than 20 percent.

The Criminal Code of Canada sets the legal impairment limit for driving as any measuremeent that exceeds 80 milligrams of alcohol in 100 millilitres of blood, or 0.08 percent. (Provinces may mandate variations on that level; B.C. has a "warning range" starting at 0.05 percent BAC that can lead to driving prohibitions, vehicle impoundment, and fines.)

The NASA scientists determined that for a 165-pound person, the ability to process visual motion—which is critical for hand-eye coordination while driving, among other tasks—is impaired after drinking an amount of alcohol equal to less than half a beer.

The researchers were trying to develop sensitive methods to detect even mild brain impairment in people working in low-gravity aerospace or on-Earth conditions, and alcohol was administered to test subjects as a proxy for stressors such as illness, sleep deprivation, and head injuries.

The research results provide new information to those trying to determine the effects of even small amounts of alcohol intake on people engaged in "high-risk human activities that rely on keen visual and visuomotor control, like driving, piloting, or working heavy machinery", according to a December 21 news release by the London-based Physiological Society, which publishes the Journal of Physiology and two other scientific publications.

The society, founded in 1876, claims more than 4,000 scientist members from more than 60 countries.

In the experiments, subjects' performance deficits were measured by an extremely sensitive test involving eye measurements.

The study's first author, Terence Tyson, said the results mean that people who think they are fine after just one drink or less are mistaken, even though they may be well within the legal limit.

“Our findings provide a cautionary tale that the subjective experience of drunkenness is often not aligned with objective impairment of sensorimotor coordination," Tyson said in the December 21 release. "In other words, most people feel they are unimpaired after one drink, yet they are to a significant degree.”