Consuming caffeine affects our sleep. An association has been found between how much caffeine is ingested daily and a reduced quality of sleep as well as an increase in sleepiness during the day.
The most documented effects of caffeine on sleep are primarily about less total sleep time overall, waking up more frequently, prolonged sleep latency, poorer quality of sleep, lighter sleep, and less time spent in deep sleep. Rapid eye movement (REM) sleep stage seems to be less affected by caffeine consumption. REM sleep is the stage of sleep when we dream, our eyes move rapidly from side to side, we lose our reflexes, and our brain activity and heart rate increase.
How caffeine affects our sleep depends on how much caffeine we consume near bedtime as well as how much caffeine we’ve consumed throughout the day.
Our sensitivity to caffeine and its effects on sleep varies, but the exact basis for this is still in debate. In 2016 a comprehensive review of research on caffeine, coffee, and sleep found that people have different responses to caffeine based on genetic factors, age, regularity of caffeine and coffee consumption, sensitivity levels, and time of consumption.
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Human sleep cycles
Humans normally experience periods of REM sleep and nREM sleep, with nREM sleep divided into three stages, each one progressively deeper. When we first fall asleep, we are in the first stage of nREM sleep. As it gets deeper, we enter REM sleep, which occurs 80-100 minutes later. Then we cycle through nREM and REM sleep for about 90 minutes.
How caffeine affects sleep
Sleep studies show that consuming caffeine definitely can affect our sleep, however its effects vary among individuals. A number of factors affect how people who consume caffeine respond and how that affects their sleep:
There has only been limited research in this particular area, however it suggests that genetics play a role in how we metabolize caffeine. Researchers have identified several genes that affect how sensitive an individual is to caffeine:
- The concentration of caffeine in each individual’s plasma after ingesting a certain amount of caffeine was different among the studied subjects. This suggests that slow metabolizers are more sensitive.
- One of the identified genes that affect how sensitive someone is to caffeine has to do with how the adenosine A2A receptor gene, specifically ADORA2A, differs among people who rate themselves as sensitive to caffeine with poorer sleep quality and individuals who rate themselves as insensitive to caffeine. The PRIMA1 and the DARPP-32 genes also seem to play a part in caffeine induced insomnia and caffeine sensitivity. Therefore consuming the same amount(s) of caffeine can have a different effect on two similar individuals, depending on each one’s genetic makeup.
- In a similar vein, the likelihood of having an additional genetic variation of the ADORA2A genotype goes down as habitual caffeine consumption goes up, which suggests that people with this genotype may be less prone to becoming dependent on caffeine.
There have only been a few studies that looked at the age-related effects that caffeine may have on sleep, and the results are a bit confusing. Some studies indicate that older adults may be more affected by caffeine. But the level of caffeine exposure may depend on an individual’s body weight. Although older adults generally ingest caffeine in the same amounts as younger adults, they tend to weigh less. Older adults may also voluntarily limit their caffeine intake because of a perceived sleep problem. These studies found the following:
- One study showed that caffeine generally affected 20-30 years old and 45-60 years old adults in similar ways. There seemed to be several EEG spectral frequency bins that showed a stronger effect from caffeine in middle-aged adults than in young adults.
- The same group conducted another study in the morning hours investigating daytime recovery sleep after spending 25 hours awake. It found that caffeine lowered the efficiency and duration of sleep, REM and slow-wave sleep throughout daytime recovery sleep in similar ways in both age groups. Middle-aged subjects showed more decrements in the duration and efficiency of sleep than young subjects throughout daytime recovery with a placebo compared to nighttime sleep. With age and caffeine related lower brain synchronization these subjects experienced more difficulty combatting the circadian waking signal throughout daytime sleep, which resulted in very fragmented sleep.
- A study of 24 middle-aged and 22 young adults found that caffeine raised sleep latency, reduced sleep efficiency, and shortened the duration of sleep.The effects of caffeine were more dramatic for middle-aged subjects at a higher dose than in the younger subjects. Higher doses of caffeine increased stage 1 nonREM sleep in the younger adults, but decreased stage 2 nonREM sleep in the middle-aged adults. This suggests that middle-aged adults are in general more sensitive to high doses of caffeine than younger adults when it comes to quantity and quality of sleep.
Habitual consumption of caffeine
Research indicates that caffeine has less effect on people who drink coffee on a regular basis than on those who drink it occasionally.
Research published in 2015 found that people who perceived themselves as dependent on caffeine had poorer quality of sleep, especially women. This study showed that dependence on caffeine was associated with higher levels of nightly disturbance, increased dysfunction during the day, and poorer quality of sleep overall.
Time of caffeine consumption
While there are only a few very limited studies evaluating the timing of caffeine consumption, they show that when caffeine is consumed closer to bedtime, it has the highest potential for disrupting sleep.
A study conducted in 2013 evaluated the effects of caffeine consumption on sleep at various times before sleep. The results suggest that consuming caffeine up to 6 hours before bedtime may reduce the quality of sleep as well as the total nightly sleep.
Abstinence from caffeine
A systematic review (including randomized trials) conducted in 2008 indicates that abstaining from caffeine for a day could enhance the quality of sleep and health practitioners providing advice on sleep hygiene could recommend this to patients. Researchers concluded that abstaining from caffeine significantly lengthened sleep and improved its quality. People had fewer problems falling asleep when they drank only decaffeinated coffee that day. However, people have varying sensitivities to caffeine and it may or may not affect the sleep of some individuals.
How caffeine affects young people’s sleep
Research indicates that caffeine consumption helps restore healthier levels of wakefulness and combats impaired performance on cognitive tasks due to lack of sleep. The problem is that caffeine may be detrimental to subsequent sleep. This may result in higher daytime sleepiness, which may be worrisome, especially in teens. Many teenagers use several types of technology well into the late hours of the night while drinking caffeinated beverages to stay alert.
- Research examining how caffeine and technology affect the duration of sleep and how well young people function during the day found that multitasking had a significant relationship to sleep. Adolescents who scored 1.5- to 2-fold on indices measuring multitasking normally got under 8-10 hours of sleep on school nights. In the 33% of adolescents who dozed off during school hours caffeine consumption was 76% higher than in students who hadn’t dozed off. The results of the study indicate that these teens were not able to function at their best throughout the school day because of excessive daytime sleepiness, not due to daytime effects of caffeine.
- Similarly, in a survey examining caffeine use among teens it appeared that 95% drank caffeinated beverages, mostly soda or soft drinks, but also coffee. Those who drank a lot of coffee, as opposed to teenagers who drank mostly soda, expected to gain more of an energy boost from caffeine, were more apt to wake up early, and experienced more sleepiness during the day, which drove them to drink more caffeine to make it through the day.
- A group of students were studied throughout an exam period and the results indicated that they drank less alcohol and slept significantly less. At the same time perceived stress significantly increased as did caffeine consumption. But although the students spent less time in bed and appeared to have insomnia, the researchers concluded that their age, gender, health, plus the amount of caffeine and alcohol consumed played no significant role in their overall quality of sleep.
How caffeine affects shift work and jet lag
Shift work and jet lag sleep disorders can cause an increase in sleepiness and raise the risk of making mistakes or getting injured. Shift work sleep disorder is basically a circadian rhythm sleep disorder that manifests in insomnia and extreme sleepiness. People who have a work schedule that requires them to work when they would normally be sleeping are often affected by this.
Research reveals that caffeine consumption may improve performance in shift workers and/or those with jet lag. But no data exist for people 40 years of age or older and these are the people more likely to be affected. This gap in research limits the ability to draw any real conclusions, which means that more studies are needed on this subject.
Caffeine and shift workers
- An intervention study evaluated a variety of counter measures that could be taken for sleep-wake problems linked to night work. Results indicated that a combination of caffeine consumption and napping worked best for increasing alertness. A decrease in sleepiness was observed in people who worked the night shift after they consumed caffeine.
- Additional research on how caffeine consumption affected people working night shifts indicated that caffeine does increase the level of alertness with clear-headedness after being awake for a period of time. But caffeine consumption can also be problematic for subsequent recovery sleep during daytime. Caffeine consumption is linked to a higher body temperature and this is linked to a lengthier latency of sleep. Moreover, sleep disturbances linked to caffeine consumed approaching the circadian alertness trough are apt to remain when it’s time for daytime recovery sleep (about 5 hours later) potentially causing sleep disturbances.
Caffeine and jet lag
- People often experience jet lag after a lengthy flight across several time zones. This can cause either excessive sleepiness or wakefulness at the wrong times. To combat jet lag a quick adjustment is recommended by sleeping, waking up, and eating at the appropriate times in that region of the world. Consuming coffee is linked to improved alertness and may be of help in managing the temptation to go to sleep when suffering from jet lag.
- Research indicates that caffeine may effectively enhance functioning in people with jet lag. But trying to adjust to the local time in each area may not be the best strategy for people taking 1-2-day stopovers in various time zones. One study implies that taking sensible naps in combination with drinking a moderate amount of caffeine at times when it is appropriate to be awake and alert plus the use of sleeping aids for a short period of time seem to be the most productive ways of staying alert and going to sleep during those short layovers.