A systematic review and meta-analysis of the effects of caffeine on sleep aimed to help determine clear guidelines.
To avoid sleep time reductions, coffee (107 mg/250 mL) should be consumed at least 8.8 hours before bedtime and a standard serving of preworkout supplement (217.5 mg) should be consumed at least 13.2 hours before bedtime, according to a review published in Sleep Medicine Reviews.
This study was conducted because the consumption of caffeine in response to inadequate sleep might weaken the onset and maintenance of ensuing sleep.
The researchers were trying to understand the effect of caffeine on the characteristics of night-time sleep, with the desire to recognize the time after which caffeine should not be consumed before bedtime in a systematic review and meta-analysis.
“The half-life of caffeine displays large variation across healthy adults (2 to 10 h), making it difficult to identify the appropriate time of day to discontinue caffeine intake to minimise disruptions to sleep,” explained the study authors.
The use of caffeine to stay awake might result in weakened onset and upholding of subsequent sleep and possibly creating a cycle of reduced sleep and ensuing caffeine dependance.
A systematic search of the literature was conducted with 24 studies included in the analysis.
Caffeine consumption diminished total sleep time by 45 minutes and sleep efficiency by 7%, with a rise in sleep onset latency of 9 minutes and wake after sleep onset of 12 minutes. Duration (+6.1 minutes) and proportion (+1.7%) of light sleep (N1) grew with caffeine intake and the duration (–11.4 minutes) and proportion (–1.4%) of deep sleep (N3 and N4) lowered with caffeine intake.
By quantifying the influence of the dose and timing of caffeine intake on subsequent sleep, the investigators highlighted, cutoff times for caffeine intake before bedtime can be initiated.
After evaluating sleep onset latency, the researchers found that there seemed to be a peak effect of caffeine on sleep onset latency that happens approximately 3 hours after consumption. The findings emphasized that the consumption of caffeine prolongs the onset of ensuing sleep. Caffeine consumption was linked with a 45-minute decrease in total sleep time over the subsequent evening.
Regarding the evaluation of REM onset latency, 10 studies explored the effects of caffeine on REM onset latency, and none showed significant effects.
Wake after sleep onset was examined in 13 studies, with 6 showing a significant increase when caffeine was consumed. In the current study, it could not be determined if the increase in wake after sleep onset was affected by the amount or timing of the final caffeine dose.
Upon review of sleep efficiency, 15 of 18 studies reported a significant decrease in sleep efficiency after caffeine consumption. Of the 3 studies finding no significant effect, 2 administered the caffeine dose over multiple days. Also, 1 study showed no effect after 1200 mg of caffeine given in 3 equal doses across the morning, afternoon, and evening.
When evaluating caffeine’s effect on sleep architecture, the effect of caffeine on absolute sleep architecture was examined in 12 studies. The findings suggested that no relationship exists between caffeine timing intake and alterations in sleep stage duration.
In terms of subjective sleep outcomes, 12 studies examined the effect of caffeine on the perceptions of sleep. Ultimately, it was determined that subjective sleep outcomes are an important metric and should be integrated alongside objective measures. Collective findings from the literature review for subjective sleep outcomes suggest that chronic caffeine exposure may increase tolerance.
Current study results give evidence-based guidance for the appropriate consumption of caffeine to alleviate the deleterious sleep effects.
The researchers recommend that consumers consider the cutoff times given as a starting point and adjust the amount and timing of when they consume caffeine in response to its effect on their subsequent sleep.
Some limitations of this study are that 3 studies employed activity monitors that may have underestimated wake duration, and so there might be variation in the calculation of some outcome measures. Secondly, caffeine was administered as a single daily dose or sustained dose across multiple days across studies, so there is potential for habituation.
“The results of the present study provide evidence-based guidance for the appropriate consumption of caffeine with respect to both dose and timing of consumption to mitigate the deleterious effects on sleep,” concluded the researchers.
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;69:101764. doi:10.1016/j.smrv.2023.101764