New Research Suggests Earlier Caffeine Cutoff for Better Sleep

Caffeine consumption, particularly in coffee and pre-workout supplements, may need to be curtailed significantly earlier than commonly believed to avoid disrupting sleep. New research analyzing 24 studies suggests that coffee should be consumed at least 8.8 hours before bedtime.

This means that for an individual going to bed at 10 p.m., their last cup of coffee should be finished before 1:12 p.m. The study further indicates that standard servings of pre-workout supplements, which often contain double the caffeine of coffee, should be consumed at least 13.2 hours before sleep. For the same 10 p.m. bedtime, this would translate to a cutoff time before 8:48 a.m.

According to the research published in Sleep Medicine Reviews, consuming caffeine closer to bedtime can reduce total sleep time by approximately 45 minutes. It also increases the time it takes to fall asleep, known as sleep onset latency, by about nine minutes. Additionally, wake after sleep onset, the time spent awake after initially falling asleep, increases by 12 minutes, and sleep efficiency—the proportion of time spent asleep while in bed—decreases by 7%.

The study also examined caffeine's impact on sleep stages. When caffeine was consumed closer to bedtime, the time spent in light sleep increased, while deep sleep decreased. No significant effects were observed on rapid eye movement (REM) sleep across the 10 studies that investigated this aspect.

The researchers found that the closer to bedtime higher doses of caffeine were consumed, the greater the reduction in subsequent sleep. For instance, drinking caffeine at 3 p.m. before a 10 p.m. bedtime could lead to 16 minutes less sleep compared to consuming it at 9 a.m.

An exception noted in the research is black tea. A single 250-milliliter cup of black tea, containing approximately 47 milligrams of caffeine, did not appear to significantly affect sleep, even when consumed close to bedtime.

Caffeine works by blocking adenosine, a naturally occurring chemical that promotes drowsiness. While 99% of caffeine is absorbed by the body within 45 minutes of consumption, its half-life—the time it takes for the body to reduce the caffeine amount by half—can range from 1.5 to 9.5 hours, varying significantly between individuals due to factors like genetics.

Experts also recommend delaying the first cup of coffee until 90 minutes after waking to help regulate cortisol levels, the body's primary stress hormone. Approximately 80% of U.S. adults consume caffeine daily, but its effects on sleep can be substantial if not managed carefully.