Caffeine is good for mornings and workouts, but not as a sleep aid

© princeoflove - stock.adobe.com

Coffee, with 107 mg of caffeine per 250 mL (or approximately one cup), should be consumed at least 8.8 hours prior to bedtime to avoid reductions in total sleep time, according to a study published in Sleep Medicine Reviews.

Additionally, investigators found that a standard amount of pre-workout supplement at 217.5 mg of caffeine should be taken at least 13.2 hours before bedtime to avoid sleep disruptions; however, there was no cut-off time for a cup of black tea. According to the study authors, the current recommendation for sleep is seven to nine hours per night, however, they also reported that insufficient sleep is an increasing public health concern.

Another recommendation for sleep is to avoid caffeine too close to bedtime due to the psychostimulant effects of caffeine. There has not been a consensus on how close is “too close” to bedtime, according to the investigators, who aimed to determine the ideal time to stop consuming caffeine before it is time to go to sleep.

Four electronic databases (CINAHL MEDLINE, SPORTDiscus, and Web of Science) were used to gather studies until June 2021. The results were limited to include peer-reviewed journal articles in only humans published in English, which ultimately included 24 studies for inclusion in the review.

Investigators included studies that had a controlled crossover design and the intervention administered as an acute daily dose on the day of the measured sleep analysis. The exception was for 5 studies, which included the daily dose administered for consecutive days at 4 (2 studies), 6, 9, and 14.

The study authors reported that caffeine consumption was associated with approximately 45.3 minutes less of total sleep time when compared to the control group. There was a significant influence of timing of consumption and final dose of caffeine on total sleep time, according to the investigators.

Furthermore, they found that the difference in total sleep time between the control group and given dose of caffeine decreased by 2.8 minutes every additional hour caffeine was consumed before sleep time. In addition, the difference in total sleep time increased by 0.2 minutes per every 1 mg increase of caffeine.

Investigators also found that sleep onset latency was 9.1 minutes longer in the caffeine groups compared to the controls. They also found that the duration of wake after sleep onset was 11.8 minutes longer and sleep efficacy was reduced by 7%. There was no effect on rapid eye movement onset latency, the study authors reported.
Additionally, the results showed that the duration and proportion of light sleep increased by 6.1 minutes and 1.7%, respectively, due to caffeine intake. The duration and proportion of deep sleep decreased by 11.4 minutes and 1.4%, respectively.

When using a bedtime of 10 pm, the investigators’ model predicted that black tea could be consumed at any time without significantly reducing total sleep time, coffee could be consumed before 1:12 p.m. to avoid significant reductions, and pre-workout could be taken before 8:50 a.m. to avoid significant reduction.

The study authors said that because of the prevalence of caffeine consumption, there should be better awareness around the cut-off times to best optimize sleep and avoid disturbances. However, they caution that these should serve as a starting point for individuals as everyone is different and these results can very from person to person.