Some individuals may find that caffeine intake is associated with a reduced sleep quality and increased daytime sleepiness3,4.
The majority of documented effects of caffeine on sleep consist of prolonged sleep latency, shorter total sleep time, worsened perceived sleep quality, increased light sleep and shortened deep sleep time. Caffeine was also associated with more frequent awakenings, however Rapid Eye Movement (REM) sleep was less affected3.
Research suggested that feeling tired in the morning can lead to high caffeine consumption, which in turn may be associated with impaired subsequent sleep patterns, called a “coffee cycle”4. However, it has been proposed that after a period of overnight abstinence, the improvements associated with caffeine consumption may simply be associated with the reversal of caffeine withdrawal4 .
A 2020 meta-analysis also concluded that caffeine may have a significant effect on performance after sleep loss, through positive impacts on physical and cognitive functioning. The authors suggested that dose variability may explain some of the intra-individual differences observed2.
Variability in the effect of caffeine on sleep
Human sensitivity to the effects of caffeine on sleep is variable and its exact basis is still debated. A 2016 systematic review on coffee, caffeine and sleep concluded that individuals respond differently to caffeine based on a variety of factors, including age, sensitivity levels, regular coffee and caffeine intake, time of consumption, and genetic variability3.
It may be possible that people learn to regulate consumption to fit their individual patterns of response. A European study of 2,202 participants gathered data on sleep characteristics and the use of pharmacologically active compounds, including caffeine. Researchers found that caffeine consumption did not predict difficulties inducing sleep or other sleep disturbances when age, gender, smoking, and seasonal variations were controlled for4.
Although the research in this area is limited, research to date indicates that there is a genetic variability in the metabolism of caffeine, and several genes have been identified that affect an individual’s sensitivity to caffeine12.
A 2019 study noted ADORA2A genetic variations related to the duration of nocturnal sleep only in low caffeine consumers (< 50mg per day). The authors suggested that in moderate caffeine consumers (51–300mg per day) the nocturnal sleep decreases irrespective of genetic variants and when consuming caffeine above 300mg per day the genetic variants of ADORA2A seem not to influence the total sleep time, which remains significantly lower compared to low caffeine consumption12.
Only a few studies have evaluated the age-related effects of caffeine on sleep, and confounding factors are often present. Some research suggests that older adults may be more sensitive to the effects of caffeine. However, caffeine exposure may vary as a function of body weight. For example, older adults tend to consume the same amount of caffeine as younger adults, but typically weigh less. Older adults may also self-limit the amount of caffeine they consume due to perceived sleep problems3.
Habitual intake of caffeine
Research suggests that the effects of caffeine are less marked in those who regularly drink coffee when compared to occasional coffee drinkers13. Results from a 2015 research survey concluded that sleep quality was poorer in those who perceived themselves to be dependent upon caffeine, particularly amongst females. Caffeine dependence was associated with poorer sleep quality, increased daytime dysfunction, and increased levels of night-time disturbance14.
Time of consumption
Caffeine consumed closer to sleep time has the greatest potential for sleep disruption, although there are only limited studies that assess the timing of caffeine administration. Evening consumption of 200mg caffeine is suggested to be linked with an increased sleep latency (by 7 min), reduced sleep efficiency (by 5%), and decreased sleep duration and stage-2 sleep (by 28 min) in older and younger adults3.
The effects of caffeine abstinence
Some researchers have suggested that abstaining from caffeine for a whole day could improve sleep quality and could be recommended by health practitioners when giving sleep hygiene advice15. However, the effect may be complicated by the fact that caffeine consumption may be a response to fatigue as well as a cause of it. Some have suggested that following overnight avoidance of caffeine, improvements in performance the next day may simply be due to the reversal of the impact of caffeine withdrawal4.