A systematic review and meta-analysis published in Sleep Medicine Reviews found that coffee should be consumed no more than 8.8 hours before bedtime to avoid negative sleep effects.
Investigators from the Australian Catholic University searched publication databases from inception through June 2021 for studies of the effects of caffeine on night-time sleep. A total of 24 controlled crossover studies were included in this analysis.
The studies used common caffeine products, such as a cup of black tea (approximately 47 mg caffeine per 250 mL), a cup of coffee (approximately 107 mg caffeine per 250 mL), and a standard preworkout supplement (approximately 217.5 mg caffeine).
In general, consuming caffeine associated with 45.3 (95% CI, 29.0-61.5 min; P <.001) fewer minutes of total sleep time compared with control. Significant interactions were observed for timing of caffeine consumption (P =.032) and final caffeine dose (P =.037). Together, total sleep time decreased by 2.8 (95% CI, 0.4-5.2) minutes for every additional hour caffeine was consumed closer to bedtime and by 0.2 (95% CI, 0.01-0.31) minutes for each 1-mg increase in caffeine dose.
Sleep onset was found to be 9.1 (95% CI, 3.8-14.4; P =.002) minutes later in the caffeine condition compared with control. Latency was not affected by timing of consumption (P =.071) or dose (P =.960).
Caffeine had additional effects on sleep efficiency (mean, 7.0%; 95% CI, 4.0%-10.0% decrease; P <.001), sleep architecture (mean, N1 duration: +6.1; 95% CI, 2.3-9.9 minutes; P =.012; N3 and N4 duration: -11.4; 95% CI, -4.3 to -18.5 minutes; P =.012), and wake-sleep onset (mean, 11.8; 95% CI, 2.5-21.0 minutes longer; P =.019).
A total of 6 studies included electroencephalogram data. Due to the small sample size no meta-analysis was performed. Individual studies reported significant effects of caffeine on spectral power within the delta and sigma frequencies. However, results were conflicting.
For subjective sleep outcomes, some studies reported a reduction in perceived duration of sleep and in perceived sleep quality and increased sleep onset latency and perceived wake duration after sleep onset. These subjective results were also conflicting.
Using these data, the investigators calculated cutoffs for caffeine consumption to avoid total sleep time reductions. They found that standard preworkout supplements should be consumed no later than 13.2 hours and a cup of coffee 8.8 hours prior to bedtime. There was no cutoff time for a cup of black tea. These data indicated that, assuming bedtime is at 10:00 pm, a preworkout supplement should not be consumed after 8:50 am and a cup of coffee after 1:12 pm to avoid total sleep time reductions.
The findings of this analysis may have been biased by combining data collected from differing sleep assessment tools.
Study authors concluded, “The consumption of caffeine impairs subsequent total sleep time, sleep onset latency, wake after sleep onset, sleep efficiency, and sleep architecture. The reduction in total sleep time is dependent on the final dose of caffeine and the time of day that it is consumed relative to bedtime.”
Gardiner C, Weakley J, Burke LM, et al. The effect of caffeine on subsequent sleep: a systematic review and meta-analysis. Sleep Med Rev. 2023;10164. doi:10.1016/j.smrv.2023.101764