There’s a common belief that drinking coffee first thing in the morning, as opposed to waiting one-to-two hours, will lead to an afternoon ‘crash’. Let’s go through this claim and see if it stands up to criticism.
Introduction
There’s nothing like waking up, heading to the kitchen, and firing up the espresso machine for a warm cup of coffee. However, if you believe what you hear on the internet—or on your favourite podcast—this is to be avoided. There are two main theories as to why this is unwise:
Caffeine—the chemical in coffee that increases alertness—binds to adenosine receptors. When it wears off in the afternoon, the now built-up levels of adenosine bind to the adenosine receptors very rapidly and your energy levels drop (because adenosine is thought to influence tiredness, and contributes to the regulation of sleep (1)). According to this theory, delaying your coffee and allowing adenosine to interact with its receptors for the first 60–120 minutes in the morning can alleviate the afternoon ‘crash’ associated with drinking coffee first thing.
Caffeine interferes with the production of cortisol—a hormone that increases in the morning, helping to wake us up. In doing so, caffeine prolongs the waking peak in cortisol levels, which can lead to an afternoon ‘crash’ when the caffeine wears off and cortisol levels come down (because cortisol is lowest before the onset of sleep, a drop in levels could lead to this afternoon ‘crash’) (2).
Sounds logical, right? I agree, but while a simple story of biological mechanisms is a starting point, this is not enough to draw any firm conclusions regarding the truthfulness of a theory—we must dig deeper. With that, let’s whip out the shovel and get to work.
The evidence in this article is taken from a recent paper, published in the Journal of the International Society of Sports Nutrition, which discussed 15 common questions and misconceptions about caffeine supplementation (2). Do check that out for more!
Did you know that caffeine can improve exercise performance? Check out our previous article on this topic to learn more.
Caffeine and Adenosine
Like melatonin, adenosine is a key regulator of the sleep-wake cycle (3). Upon waking, adenosine levels immediately and rapidly build up, whereas upon sleeping, adenosine levels rapidly decrease (2,4). While caffeine is an adenosine receptor antagonist (3)—meaning that it can bind to adenosine receptors and prevent adenosine from binding, thus increasing alertness—it doesn't follow that when caffeine is eliminated from the body in the afternoon, we experience a drop in energy levels that would have been prevented if we delayed our coffee intake.
In fact, based on our understanding of how caffeine works (i.e., by binding to adenosine receptors), we would expect energy levels to drop once caffeine wears off no matter the time of the day. This is because once caffeine is no longer attached to adenosine receptors, adenosine can now attach and make us feel less alert. To reiterate, there is no evidence to suggest that delaying our coffee intake would somehow prevent this natural drop in energy levels when the caffeine has worn off.
Another rationale sometimes proposed for delaying the morning coffee is based on the idea that adenosine levels decline upon waking, suggesting there's no immediate need for caffeine in the morning since lower adenosine levels might naturally promote alertness (2). In reality, adenosine levels rise rapidly within minutes of waking and then stabilise (2,3). Therefore, this is likewise a poor rationale for delaying coffee consumption in the morning (2).
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Caffeine and Cortisol
Like adenosine, cortisol follows a 24-hour rhythm, and is highest upon waking and lowest at the onset of sleep (2,5). Cortisol’s rhythm is governed by the hypothalamic-pituitary-adrenal (HPA) axis, which helps to regulate alertness and sleep (2,6). It is true that caffeine can impact the HPA axis and thus cortisol levels: in a study of 47 men, the consumption of 3.3 mg/kg of caffeine (equivalent to ~2.5 cups of brewed coffee) increased cortisol by 30% over the following 60–120 minutes, relative to the placebo (7). Interestingly, this increase was observed despite the fact that the caffeine wasn’t consumed immediately upon waking, suggesting that this would occur regardless of the time of day (2,7). Despite this, there is other evidence that the rise in cortisol is blunted in habitual caffeine users (e.g., coffee drinkers) (8,9).
However, even if we grant that caffeine consumption increases cortisol levels through its effect on the HPA axis, there is no evidence that the normal daily pattern of cortisol is changed (10); therefore, it’s unclear how a morning coffee would cause an afternoon ‘crash’ due to a reduction in cortisol levels (2). Finally, if we were to be logically consistent, this line of reasoning would suggest that early morning exercise is to be avoided, as it also increases cortisol levels (2). In my opinion, this would be absurd.
Coffee consumption is associated with a range of health benefits, and little risks, which we covered in an earlier article.
Summary
To quote Antonio et al. (2): ‘...a fundamental basis for suggesting that delaying caffeine intake in the early waking hours would prevent an afternoon “crash” is completely lacking’. Therefore, if you like your coffee first thing in the morning, keep calm and carry on. However, if you prefer waiting 60–120 minutes, that’s also a perfectly reasonable way to enjoy your coffee. Ultimately, do what works for you.
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As always, thanks for reading. Have a lovely weekend!
Patrick Elliott, BSc, MPH
Health and Nutrition Science Communication Officer at Training121
Instagram: @just.health.info
Twitter/X: @PatrickElliott0
References
(1) Holst SC, Landolt, HP. Sleep Homeostasis, Metabolism, and Adenosine. Curr Sleep Medicine Rep. 2015;1:27–37. Available at: https://link.springer.com/article/10.1007/s40675-014-0007-3
(2) Antonio J, Newmire DE, Stout JR, Antonio B, Gibbons M, Lowery LM, Harper J, Willoughby D, Evans C, Anderson D, Goldstein E, Rojas J, Monsalves-Álvarez M, Forbes SC, Gomez Lopez J, Ziegenfuss T, Moulding BD, Candow D, Sagner M, Arent SM. Common questions and misconceptions about caffeine supplementation: what does the scientific evidence really show? J Int Soc Sports Nutr. 2024;21(1):2323919. Available at: https://www.tandfonline.com/doi/full/10.1080/15502783.2024.2323919
(3) Reichert CF, Deboer T, Landolt HP. Adenosine, caffeine, and sleep-wake regulation: state of the science and perspectives. J Sleep Res. 2022;31(4):e13597. Available at: https://onlinelibrary.wiley.com/doi/10.1111/jsr.13597
(4) Porkka-Heiskanen T, Kalinchuk AV. Adenosine, energy metabolism and sleep homeostasis. Sleep Med Rev. 2011;15(2):123–35. Available at: https://www.sciencedirect.com/science/article/abs/pii/S1087079210000663
(5) Krieger DT, Allen W, Rizzo F, Krieger HP. Characterization of the normal temporal pattern of plasma corticosteroid levels. J Clin Endocrinol Metab. 1971;32(2):266–84. Available at: https://academic.oup.com/jcem/article-abstract/32/2/266/2716306
(6) Buckley TM, Schatzberg AF. On the interactions of the hypothalamic-pituitary-adrenal (HPA) axis and sleep: normal HPA axis activity and circadian rhythm, exemplary sleep disorders. J Clin Endocrinol Metab. 2005;90(5):3106–14. Available at: https://academic.oup.com/jcem/article/90/5/3106/2837129
(7) Lovallo WR, Al'Absi M, Blick K, Whitsett TL, Wilson MF. Stress-like adrenocorticotropin responses to caffeine in young healthy men. Pharmacol Biochem Behav. 1996;55(3):365–9. Available at: https://www.sciencedirect.com/science/article/pii/S0091305796001050
(8) Lovallo WR, Whitsett TL, al'Absi M, Sung BH, Vincent AS, Wilson MF. Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels. Psychosom Med. 2005;67(5):734–9. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2257922/
(9) MacKenzie T, Comi R, Sluss P, Keisari R, Manwar S, Kim J, Larson R, Baron JA. Metabolic and hormonal effects of caffeine: randomized, double-blind, placebo-controlled crossover trial. Metabolism. 2007;56(12):1694–8. Available at: https://www.metabolismjournal.com/article/S0026-0495(07)00275-2/abstract
(10) Rieth N, Vibarel-Rebot N, Buisson C, Jaffré C, Collomp K. Caffeine and saliva steroids in young healthy recreationally trained women: impact of regular caffeine intake. Endocrine. 2016;52(2):391–4. Available at: https://link.springer.com/article/10.1007/s12020-015-0780-x
Technical Terms
Caffeine: Caffeine is a natural stimulant found in coffee, tea, and some sodas. It gives you a temporary boost in energy and alertness by blocking sleep-inducing chemicals in your brain.
Adenosine: Adenosine is a natural chemical in your body that builds up while you're awake and makes you feel sleepy. It helps regulate your sleep-wake cycle and promotes relaxation.
Cortisol: Cortisol is a hormone produced by your adrenal glands in response to waking and external stimuli (e.g., stress). It helps regulate metabolism, immune function, and the body's response to stress. Cortisol may also play a role in the sleep-wake cycle.
Melatonin: Melatonin is a hormone produced by the pineal gland in your brain. It helps regulate your sleep-wake cycle and signals to your body that it's time to sleep. Melatonin levels rise in the evening to promote sleep and decrease in the morning to wake you up.
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