Effects on vigilance performance and sleepiness of alcohol given in the early afternoon ('post lunch') vs. early evening.
Level 2 - randomized trial
Individual randomized repeated-measures crossover trial
PubMed 2009851 · doi:10.1080/00140139108967289
What was done
Eight women completed a double-blind, randomized repeated-measures study evaluating the interaction between circadian timing and alcohol intake. Participants consumed zero, two, or four units of alcohol with food at either 1300h (early afternoon) or 1830h (early evening), reaching approximate peak blood alcohol concentrations of <5, 35, and 70 mg/100 ml blood, respectively. After consumption, participants completed a 1-hour vigilance test and self-reported sleepiness scores every 30 minutes. Outcomes assessed were reaction time, hit rate, and subjective sleepiness.
What was found
Significant main effects of dose and time of day were observed for reaction time, hits, and subjective sleepiness scores. A significant dose by time of day interaction was found for reaction time and hits, with two and four units of alcohol producing greater performance impairment in the early afternoon than in the early evening. The abstract reports these significant main effects and interactions but provides no numerical point estimates, variance, or exact p-values.
Why it matters
These findings suggest that the circadian post-lunch dip magnifies the soporific and impairing effects of alcohol, meaning sub-legal doses may carry higher performance risks in the early afternoon than in the evening.
Limits
The sample size was very small (n = 8) and included only female subjects. Testing was restricted to two times of day, and the abstract omits exact numerical performance metrics, effect sizes, and p-values.
Cited by
- supports Humans are biologically crepuscular, experiencing higher alertness in the morning and evening and a physiological increase in sleep pressure after lunch.