Caffeine and sleepPrint this page
Sleep in humans is readily affected by caffeine. There is an association between the daily intake of caffeine, sleep problems and daytime sleepiness49.
The most marked effects of caffeine on sleep, even at levels equivalent to those of a single cup of coffee, have been well documented. They consist principally of prolonged sleep latency, shorter total sleep time, increases in light sleep and shortening of deep sleep time, as well as more frequent awakenings. Rapid Eye Movement (REM) sleep* is less affected. These effects depend not only on the amount of caffeine ingested at bedtime, but also on the amount of caffeine ingested over the whole day. A 2012 study assessed the impact on sleep of caffeine consumption at different times of day, suggesting that caffeine consumed up to six hours before sleep may have disruptive effects on sleep50. Further work published in 2013 also suggested that coffee consumption decreases sleep time in physically active males (51). The effects of caffeine are smaller in habitual versus occasional coffee drinkers52.
*a stage in the normal sleep cycle during which dreams occur and the body undergoes marked changes, including rapid eye movement, loss of reflexes, and increased pulse rate and brain activity
Human sensitivity to the effects of caffeine on sleep is variable and its exact basis is still debated.
- The plasma concentration of caffeine after the ingestion of a given amount of caffeine may largely vary between subjects suggesting a greater sensitivity of slow metabolizers53.
- Studies in mice show that sleep disturbance after caffeine is mediated by blockade of adenosine A2A receptors. In humans, the distribution of distinct genotypes of the adenosine A2A receptor gene (ADORA2A) differs between self-rated caffeine-sensitive individuals with reduced sleep quality, and caffeine-insensitive individuals54.
- Similarly, another genetic variation of the ADORA2A genotype is associated with different amounts of caffeine intake55.
Thus, future studies are needed to take into account these genetic variations, habitual caffeine consumption and sensitivity on age-related changes.
The effects of age
Only a few studies have evaluated the age-related effects of caffeine on sleep.
- Overall, caffeine produced similar effects in young adults (20-30 year old) and middle-aged subjects (45-60 year old). Only a few EEG spectral frequency bins were more affected by caffeine in middle-aged than in young subjects56.
- A further study, by the same group, investigated daytime recovery sleep in the morning after 25 hours of wakefulness. Caffeine decreased sleep efficiency, sleep duration, slow-wave sleep and REM sleep during daytime recovery sleep similarly in both age groups. Middle-aged subjects showed greater decrements in sleep duration and sleep efficiency than young subjects during daytime recovery under placebo, compared to nocturnal sleep. Due to lower brain synchronization related to age and caffeine, these subjects had greater difficulty in overriding the circadian waking signal during daytime sleep and, as a result, had fragmented sleep57.
A 2008 systematic review, including randomised trials, suggests that caffeine abstinence for a whole day could improve sleep quality and could be recommended by health practitioners when giving sleep hygiene advice58.
- In one trial, caffeine abstinence significantly lengthened sleep duration and improved sleep quality.
- In another trial, subjects had less difficulty falling asleep on days when they drank decaffeinated coffee.
Caffeine use in young people
Caffeine helps restore better levels of wakefulness and counteracts degraded cognitive task performance due to sleep deprivation. However, caffeine may produce detrimental effects on subsequent sleep, resulting in daytime sleepiness, which may be a matter of concern, especially in adolescents59. Many adolescents use multiple forms of technology late into the night and concurrently consume caffeinated beverages to stay alert.
- A study looking at the effects of caffeine and technology on sleep duration and daytime functioning, in young people60, showed that sleep was significantly related to the multi-tasking index. Teenagers who scored 1.5-2 fold higher on multi-tasking indices slept less than 8-10 hours on school nights. Among the 33% of teenagers who fell asleep during school, caffeine consumption tended to be 76% higher than in those not falling asleep. The study suggests that, as a consequence, these teenagers were not fully functional throughout the day due to excessive daytime sleepiness, rather than because of the daytime effects of caffeine.
- Likewise, in a survey looking at adolescent caffeine use, it appeared that 95% used caffeinated drinks – soft drinks/soda primarily but also coffee. In contrast with high soda users, mixed users who drank more coffee expected more energy enhancement from caffeine, and they were more likely to get up early and report more daytime sleepiness, which led to the use of caffeine to ‘get through the day’61.
Caffeine, jet lag and shift work
Jet lag and shift work sleep disorder* can result in sleepiness and increase the risk of injury. According to the results of a systematic review62, caffeine may be effective at improving performance in people who work shifts, or in those who are suffering from jet lag. However, there are no data for subjects over the age of 40, who represent a population more likely to be affected. This research gap limits the conclusions that can be drawn and calls for more studies in this field.
In the same way, for short stopovers (1-2 days), adapting the circadian clock is not the best strategy and sensible naps, combined with caffeine and short-term hypnotics, appear to be the most effective way to maintain alertness and sleep in these situations63.
*A circadian rhythm sleep disorder characterized by insomnia and excessive sleepiness, affecting people whose work hours are scheduled during the typical sleep period
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