For the study, the researchers had participants undergo four highway driving tests, with at least one week between each. In one test, they drove for 1.5 hours during the day; in the other three, they drove between 2 a.m. and 3:30 a.m. -- once after a 30-minute nap, once after a cup of coffee, and once after a cup of decaffeinated coffee.
Compared with the drive on decaf, drivers of all ages performed better when they had caffeinated coffee or a nap -- being less likely to let their car cross over the lane lines during the late-night drive. Each driver was accompanied by a driving instructor who could take control of the car if necessary.
However, while coffee was as effective for older drivers as it was for younger ones, naps were not.
In general, the study found, younger study participants tended to have a deeper sleep, which may have made their nap more restorative.
In addition, research suggests that as people age, they become less responsive to "sleep pressure" -- the body's drive to catch some Zs when it's been kept up too late. This might help explain why middle-aged drivers benefited less from a quick nap, according to Dr. Pierre Philip, the senior researcher on the study.
Experts advise that people not drive at all when they are tired. But if it's necessary to be on the road, the new findings suggest that sleepy drivers should consider their age when choosing the best pick-me-up -- though, of course, individuals vary in their physiological responses.
"If you are 20, coffee or a nap is OK, even if some (people) are better coffee responders and others are better nap responders," Philip said.
On the other hand, he added, "if you are over 40, very probably coffee is better for you than a nap, potentially because sleep pressure decreases with age and you cannot benefit from the effects of the nap."
SOURCE: Sleep, December 1, 2007.
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