Is coffee consumption harmful to our sleep?
Coffee is an institution of our civilization. It is everywhere and has been consumed for centuries by almost all populations on the planet. It is the most consumed hot or cold drink in the world after water: 2.6 billion cups are drunk per day! This omnipresence of coffee in our lives as well as its high consumption have led doctors and the scientific community to question the effects of coffee on our health. How does our body react to the caffeine present in many everyday drinks? But above all, the existential question that burns on all our lips, the one that animates many meals (especially dinners!) without ever being really resolved: does drinking coffee in the evening prevent sleep? Everyone has asked themselves this question at least once, right?
At the restaurant, the bill is often asked for at the same time as the coffee and sometimes, it seems as if we bring back a little caffeine insomnia as a tip for the night! So, is caffeine really harmful to our sleep?
Would you like a bit of insomnia with your coffee?
Strictly speaking, it is not the coffee itself that would influence the body, but a substance contained in it: caffeine. Moreover, the latter is not only present in coffee. Without realizing it, caffeine is one of the most consumed psychotropic substances. It is found in tea, chocolate, but also and especially in all cola-based drinks. It is easy for each of us to find ourselves a little, or even a lot, in this short list of consumer products. Are we all therefore "addicted" to this psychotropic called caffeine? It is quite possible! In any case, a first indication is given to us regarding the famous evening coffee thanks to several studies, notably the one conducted in 20131 by members of the Sleep Disorders Research Center at Henry Ford Hospital in Detroit: "It is better to refrain from consuming a lot of caffeine for at least 6 hours before bedtime," concludes this study. Furthermore, Prof. Jean Costentin, member of the Academies of Medicine and Pharmacy, wrote in 2010 in his book (Coffee, tea, chocolate. The benefits for the brain and body, Odile Jacob Editions) "that a dose of 150 mg of caffeine, taken half an hour before bedtime, has the effect of greatly lengthening the time to fall asleep, significantly reducing sleep duration, but also affecting other elements of sleep architecture, particularly by reducing the time spent in the deepest stages of slow-wave sleep, the most restorative." That is clear enough.
Well, you can now reply at all your future dinners that it is obvious that coffee has a harmful effect on sleep quality. It is established! However, it may be desirable to push our investigation on this question a little further. We may not all be equal in the face of caffeine's effects on our circadian rhythm? And what if coffee also had unsuspected effects?
A coffee and addiction, please!
Coffee, besides its omnipresence, is also distinguished by the addiction it causes. The morning cup of coffee, the midday espresso (you know, the one that would wake the dead because it is so strong!), the famous "coffee break" at work, so many occasions to drink coffee that a true "coffee addict" knows it is impossible to do without. Throughout the day, caffeine stimulates and energizes. It is therefore difficult to do without it, both during the day and in the evening, as indicated by a 2018 study2: a coffee detox, and bad mood is guaranteed! This addiction even leads to a vicious circle since we consume coffee to be fit and perform well to compensate, often, for a lack of sleep... which can itself be caused by caffeine. Moreover, coffee has the more unexpected effect of disturbing restorative daytime sleep more than nighttime sleep by making it "more vulnerable to the circadian wake-up signal" according to an experiment conducted in 20193, for people working at night for example.
Thus, the impact of coffee on sleep quality, both day and night, seems as real as the addiction it causes. However, does coffee consumption have the same consequences for everyone?
To each their coffee!
Indeed, as with many things in health and nutrition, we are probably not all equal when it comes to our cup of coffee. The bill, as well as the addiction, is not the same for everyone! This is essentially what an article written by Dr. S.H. Onen published on the University of Lyon website4 reveals: "After 4 to 5 days of daily consumption, tolerance to the stimulating effects of caffeine may appear." Thus, in chronic coffee drinkers, sleep disturbances may disappear. It is also very interesting to note that a more recent study goes much further and even causes a lot of ink to flow (but not coffee!). Indeed, Dr. Christine Spadola (a specialist referenced in sleep study) from Florida Atlantic University conducted a study in association with Harvard Medical School in 2019. This study aimed to scientifically and longitudinally evaluate the combined and separate effects of three factors on sleep: alcohol, nicotine, and caffeine. According to the results5, it was surprisingly found that there was no association between caffeine intake within four hours before bedtime and any sleep parameter. This is the first renowned study to conclude that, unlike alcohol and tobacco, coffee would not prevent sleep.
So there is hope for all "coffee addicts" not to pay too heavy a bill for their guilty little evening coffees!
Sources :
[1] Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed, C. Drake, T. Roehrs et al, Journal of Clinical Sleep Medicine, November 2013 [2] Effects of caffeine on sleep quality and daytime functioning, F. O’Callaghan, O. Muurlink et al, Risk Manag Healthc Policy, December 2018 [3] Effects of caffeine on daytime recovery sleep: A double challenge to the sleep-wake cycle in aging, J. Carrier, J. Paquet et al, Sleep Medicine, October 2009 [4] La caféine, S.H. Onen, D. Bailly et al, Prévention et traitement des dysosmies par une hygiène du sommeil., 1994 [5] Evening intake of alcohol, caffeine, and nicotine: night-to-night associations with sleep duration and continuity among African Americans in the Jackson Heart Sleep Study, C. E. Spadola, N. Guo et al, Sleep, October 2019
