Coffee, caffeine, and sleep: A systematic review of epidemiological studies and randomized controlled trials.
Level 1 - systematic review of randomized trials
Systematic review of randomized controlled trials and epidemiological studies
PubMed 26899133 · doi:10.1016/j.smrv.2016.01.006
What was done
Systematic review of epidemiological studies and randomized controlled trials evaluating the effects of coffee and caffeine on objective and subjective sleep parameters, sleep architecture, dose- and timing-response relationships, and genetic factors.
What was found
The abstract reports no numerical values, confidence intervals, or effect sizes. It reports that caffeine typically prolonged sleep latency, reduced total sleep time and sleep efficiency, and worsened perceived sleep quality. Slow-wave sleep and EEG slow-wave activity were typically reduced, while stage-1 sleep, wakefulness, and arousals were increased. Dose- and timing-response relationships were observed, with older adults and individuals carrying specific adenosine-related gene polymorphisms showing greater susceptibility to caffeine-induced sleep disruption.
Why it matters
Synthesizes evidence showing that caffeine consistently degrades multiple objective and subjective sleep metrics, with effects modulated by timing, dosage, age, and genetics.
Limits
The abstract reports no quantitative estimates or study counts (n = ?). Generalizability is limited because most included studies evaluated male adults in Western countries. Longitudinal data evaluating downstream health impacts remain lacking.
Cited by
- supports Consuming 200 mg of caffeine in the evening reduces deep slow-wave sleep by approximately 20%.