Does caffeine really interfere with sleep – and if so, why?

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Caffeine disturbs sleep, it is said again and again. Nevertheless, many like to drink an espresso after an extended dinner without lying awake all night afterwards. Others, on the other hand, can’t get any rest in the evening, even though it’s been hours since their last coffee. How can that be?

Some people are extremely sensitive to caffeine, while others can drink cola, coffee and the like just before going to bed without any problems. Is caffeine really “poison” for sleep or is that only partly true? And how does the substance actually work in the brain? Actually with everyone quite individually, knows the sleep researcher Dr. Christine flower. The fact that not everyone has the same experience with caffeine is not surprising for the expert.

How well we tolerate caffeine also depends on our genes
“Not everyone reacts the same way to caffeine. That’s where research has actually identified genetic variants as well. So there are people who don’t drink coffee at all because it stresses them out. Then there are people who are not sensitive at all, and still others are in the middle range,” explains the sleep expert. That something like “caffeine genes” actually exist sounds surprising at first, but they were identified in 2011 by Harvard researchers, among others.1 Their names: CYP1A2 and ADORA2A. Both are involved in how caffeine is metabolized, or docks with receptors in the brain. Depending on how well the genes “work” in the respective person, caffeine provides a pleasant to strong kick, nervousness, restlessness and stomach ache, or just not very much. That’s why, accordingly, some people can sleep wonderfully after a double espresso.

For the vast majority of people, caffeine is and remains a stimulant.
Nevertheless, caffeine would not be so famous and, above all, popular if it did not work for most people. “Caffeine is a stimulant. That means it causes certain effects to be triggered in the body. It increases the heart rate and blood pressure, it makes us breathe faster. All of this is opposed to the relaxation that is needed for sleep. So caffeine is not really compatible with sleep.” The body of research is quite clear on the question of whether or not caffeine interferes with sleep quality. In 2018, for example, an Australian study once again concluded that regular caffeine consumption in the evening reduces overall performance instead of increasing it.2 The reason: ongoing sleep deprivation, which at some point can no longer make up for the actually stimulating effect of caffeine.

What happens in the brain when we consume caffeine
Sleep researcher Dr. Blume also has an explanation for this: “In the course of the day, various metabolic products accumulate in the brain. One of them is called adenosine.” Adenosine ensures that we become tired in a comforting way over time. “That means it’s also a bit of a physiological marker of our accumulative state.” The trick: Caffeine “looks” a lot like adenosine, so it docks on the same receptors in the brain – but with the opposite effect. “Caffeine therefore ensures that adenosine no longer makes us tired. This then explains this wakefulness-keeping effect of caffeine.” In other words, caffeine fools the brain quite a bit, because it believes it recognizes in it the adenosine that makes us tired. How strong the effect is, however, is probably also a question of said “coffee genes.”

Determine your personal caffeine effect
“Three to five hours after your last cup of coffee, enough caffeine should have dissipated,” Blume asserts. “Then the disruptive effect on sleep should no longer be so drastic.” Nevertheless, the expert advises everyone to do without caffeine completely for a time. “You could also say for a whole week: ‘Okay, I’m going to look for a caffeine-free substitute drink and see what the effects on sleep are’. Then when you go back to coffee, you realize how well or how badly caffeine works for you.” Especially when it comes to stimulants like caffeine, for the expert, trial and error goes beyond study. “That’s the only way to find out what really does you good and what doesn’t.”

Sources
Cornelis MC, Monda KL, Yu K et al. Genome-Wide Meta-Analysis Identifies Regions on 7p21 (AHR) and 15q24 (CYP1A2) As Determinants of Habitual Caffeine Consumption. PLoS Genetics (2011, accessed September 7, 2021).
O’Callaghan F, Muurlink O, Reid N. Effects of caffeine on sleep quality and daytime functioning. Dovepress Risk Management and Healthcare Policy (2018, accessed September 7, 2021).