Effects of caffeine are more marked on daytime recovery sleep than on nocturnal sleep.
Level 2 - randomized trial
Individual randomized double-blind crossover trial
PubMed 16936703 · doi:10.1038/sj.npp.1301198
What was done
Thirty-four moderate caffeine consumers participated in a double-blind crossover trial comparing 200 mg caffeine (administered as 100 mg 3 h before bedtime and 100 mg 1 h before bedtime) against lactose placebo. Seventeen subjects followed their habitual sleep-wake cycle and slept during the night, while 17 subjects were sleep-deprived for one night and took recovery sleep starting in the morning.
What was found
The abstract reports no exact numerical values or effect sizes. Compared to placebo, caffeine lengthened sleep latency, increased stage 1, and reduced stage 2 and slow-wave sleep in both groups. Caffeine reduced sleep efficiency more strongly in the daytime recovery group, and decreased sleep duration and REM sleep exclusively in that group.
Why it matters
These findings indicate that caffeine interacts with circadian wake drive and sleep pressure dissipation, making daytime recovery sleep (such as after night shift work) particularly vulnerable to caffeine-induced disruption compared to normal night sleep.
Limits
Small sample size (n = 34 total, 17 per group) restricted to moderate caffeine consumers. The abstract does not report specific numerical values, variances, or p-values, tests only a single total dose (200 mg), and does not measure daytime functional or cognitive outcomes after recovery sleep.
Cited by
- supports Consuming 200 mg of caffeine in the evening reduces deep slow-wave sleep by approximately 20%.