BORDEAU, France, Dec. 3 (UPI) -- Coffee is an effective countermeasure to sleepiness for those young and middle-aged, but napping is more efficient in the young, a French study found.

Patricia Sagaspe, of the Clinique du Sommeil at CHU Pellegrin in Bordeaux, France, studied 24 people, 12 ages 20 to 25 and 12 ages 40 to 50, who drove 125 highway miles in the daylight. Then, in a test of the effects of coffee and napping on night-time driving, participants drove another 125 miles in the middle of the night after having a cup of coffee with 200 mg of caffeine, a cup of decaffeinated coffee with 15 mg of caffeine or a 30-minute nap.

Inappropriate line crossings, self-perceived fatigue and sleepiness were recorded.

The study, published in the journal Sleep, found compared with the placebo -- decaffeinated coffee -- both coffee and napping reduced the risk of inappropriate line crossings in young and middle-aged participants.

However, napping led to fewer inappropriate line crossings in younger than in middle-aged participants. During napping, young participants slept more and had more delta sleep than middle-aged participants.

Delta sleep is our deepest sleep, the point when our brain waves are least like waking.