Effects of caffeine on daytime recovery sleep: A double challenge to the sleep-wake cycle in aging.
Level 2 - randomized trial
Individual double-blind randomized crossover trial.
PubMed 19342294 · doi:10.1016/j.sleep.2009.01.001
What was done
Young (20–30 years) and middle-aged (45–60 years) subjects participated in a double-blind crossover study comparing caffeine against placebo, with conditions spaced one month apart. In each condition, subjects completed an initial nocturnal laboratory sleep episode followed by 25 hours of sustained wakefulness. Subjects took 200 mg total of caffeine (or placebo) administered as 100 mg three hours prior and 100 mg one hour prior to morning daytime recovery sleep, during which sleep parameters and NREM EEG power were measured.
What was found
The abstract reports directional findings without providing exact numbers, p-values, or effect sizes. Under placebo, middle-aged subjects showed greater reductions in sleep duration and sleep efficiency during daytime recovery sleep compared to nocturnal baseline than young subjects. Caffeine decreased sleep efficiency, sleep duration, slow-wave sleep (SWS), and REM sleep similarly in both age groups. Caffeine also decreased NREM sleep EEG synchronization (reduced delta, theta, and alpha power; increased beta power).
Why it matters
This study demonstrates that caffeine and advancing age additively impair daytime recovery sleep when attempting to sleep against the circadian wake-promoting signal. It indicates that middle-aged individuals using caffeine to manage shift work or jet lag may experience severe sleep fragmentation.
Limits
The abstract omits sample size (n), participant sex, baseline caffeine intake habits, and all quantitative metrics. Findings from acute 25-hour sleep deprivation in a controlled laboratory setting may not fully generalize to chronic shift work or varied dosing schedules.
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