THE EFFECTS OF CAFFEINE ON SIMULATED NIGHT-SHIFT WORK AND SUBSEQUENT DAYTIME SLEEP

Thirty healthy volunteers were randomly assigned to either a caffeine or a placebo group to investigate the alerting effects of caffeine at night. Subjects adhered to a simulated night-shift schedule for 5 cons ecutive nights. On the first 3 nights, 2 mg/kg caffeine was added to d ecaffeinated coffee at 2220 and 0120 hours for the caffeine group. On nights 4 and 5 both groups received placebo. Each night, subjects comp leted five 60-minute sessions of a computerized simulated assembly lin e performance task (SALT), a multiple sleep latency test (MSLT) and qu estionnaires. Daytime sleep was recorded in the laboratory between 090 0 and 1700 hours each day following nighttime testing. Caffeine decrea sed physiological sleep tendency on the night shift compared with plac ebo; however, the two groups performed at equivalent levels on the SAL T. On nights 4 and 5, when both groups received placebo, there were no differences between the groups on the MSLT, suggesting the absence of a discontinuation effect. There were no differences on daytime polyso mnograms between the groups.