Background: Few studies examining alcohol's effects consider prior sleep/wake history and circadian timing. We examined introspective and physiological sleepiness on nights with and without moderate alcohol consumption in well-rested young adults at a known circadian phase.
Methods: Twenty-nine adults (males=9), ages 21 to 25 years (M=22.6, SD=1.2), spent 1 week on an at-home stabilized sleep schedule (8.5 or 9 hours), followed by 3 in-lab nights: adaptation, placebo, and alcohol. Alcohol (vodka; 0.54 g/kg for men; 0.49 g/kg for women) or placebo beverage was consumed over 30 minutes ending 1 hour before stabilized bedtime. In addition to baseline, 3 sleep latency tests (SLTs) occurred after alcohol/placebo ingestion (15, 16.5, and 18 hours after waking). Stanford Sleepiness Scales (SSS) and Visual Analog Scales (VAS) of sleepiness were completed before each SLT and approximately every 30 minutes. The Biphasic Alcohol Effects Scale (BAES) was administered a total of 4 times (baseline, 5, 60, and 90 minutes postalcohol/placebo). Subjects' circadian phase was determined from melatonin levels in saliva samples taken at approximately 30-minute intervals.
Results: All sleepiness and sedation measures increased with time awake. Only SSS and BAES sedation measures showed higher levels of sleepiness and sedation after alcohol compared with placebo. The mean circadian phase was the same for assessments at both conditions.
Conclusions: Alcohol did not increase physiological sleepiness compared with placebo nor was residual sedation evident under these conditions. We conclude that the effects on sleepiness of a moderate dose of alcohol are masked when sleep-wake homeostatic and circadian timing influences promote high levels of sleepiness.