Before you head to your car after a long day at work, consider this recent finding: staying awake for 17 to 19 hours--a normal working day for many people--can dampen your mental and physical reaction times as dramatically as two drinks. The study, reported in the latest issue of Occupational and Environmental Medicine, recruited 39 people in their 30s and 40s, all of whom worked in transport. Twice reseachers tested them for drops in reaction times, accuracy, coordination and attention spans using a range of manual and congnitive tasks.

During the first series of tests, the subjects were served alcohol--up to a blood alcohol level of 100 milligrams/decaliter or .10 percent--over a period of 28 hours. Then the tests were repeated after a night's sleep and without alcohol. The scientists found that on certain tasks, the subjects did far worse after a long day than at a blood alcohol level of .05 percent. Indeed, among subjects awake for 17 to 19 hours, reaction times were up to 50 percent slower; accuracy scores also plummeted. And the longer the subjects stayed awake, the worse they did--reaching performance levels that would be expected from someone legally under the influence.