Caffeine Makes You Borrow Energy, But You Pay The Bill

Many of us want (or should I say need?) our morning coffee to give us our “get up and go”. Altogether, the people of the world drink more than two billion cups of coffee each day.¹⁾Surma, S., Oparil, S. Coffee and Arterial Hypertension. Curr Hypertens Rep 23, 38 (2021). https://doi.org/10.1007/s11906-021-01156-3 You might think coffee gives you the energy to get through the morning or the day – but coffee might not be giving you as much as you think.

The main stimulant in coffee is the caffeine. And the main way caffeine works is by changing the way the cells in our brain interact with a compound called adenosine.²⁾Timothy Roehrs, Thomas Roth, Caffeine: Sleep and daytime sleepiness, Sleep Medicine Reviews, Volume 12, Issue 2, 2008, Pages 153-162, https://doi.org/10.1016/j.smrv.2007.07.004.

Getting busy, getting tired

Adenosine is part of the system that regulates our sleep and wake cycle and part of why high levels of activity lead to tiredness.³⁾Tarja Porkka-Heiskanen, Lauri Alanko, Anna Kalinchuk, Dag Stenberg, Adenosine and sleep, Sleep Medicine Reviews, Volume 6, Issue 4, 2002, Pages 321-332, ISSN 1087-0792, https://doi.org/10.1053/smrv.2001.0201. As we go about our days and do things, levels of adenosine rise because it is released as a by-product as energy is used in our cells.⁴⁾Huang Z et.al. The Role of Adenosine in the Regulation of Sleep. https://doi.org/10.2174/156802611795347654

Eventually adenosine binds to its receptor (parts of cells that receive signals) which tells the cells to slow down, making us feel drowsy and sleepy. This is why you feel tired after a big day of activity. While we are sleeping, energy use drops lowering adenosine levels as it gets shuffled back into other forms.⁵⁾Bjorness T et.al. Adenosine and Sleep. https://doi.org/10.2174/157015909789152182 You wake up in the morning feeling refreshed. Well, if you get enough sleep that is.

If you are still feeling drowsy when you wake up caffeine can help, for a while. It works by binding to the adenosine receptor, which it can do because it is a similar shape.⁶⁾Fredholm B. Adenosine, Adenosine Receptors and the Actions of Caffeine. https://doi.org/10.1111/j.1600-0773.1995.tb00111.x But it is not so similar that it triggers the drowsy slow-down signal like adenosine does. Instead it just fills the spots and stops the adenosine from binding there. This is what staves off the drowsy feeling.

No free ride

But there is a catch. While it feels energising, this little caffeine intervention is more a loan of the awake feeling, rather than a creation of any new energy.

This is because the caffeine won’t bind forever, and the adenosine that it blocks doesn’t go away. So eventually the caffeine breaks down, lets go of the receptors and all that adenosine that has been waiting and building up latches on and the drowsy feeling comes back – sometimes all at once.

So, the debt you owe the caffeine always eventually needs to be repaid, and the only real way to repay it is to sleep.

Timing is everything

How much free adenosine is in your system, that hasn’t attached to receptors yet, and how drowsy you are as a consequence will impact how much the caffeine you drink wakes you up. So, the coffee you drink later in the day, when you have more drowsy signals your system may feel more powerful.⁷⁾Smith A. P. The effects of caffeine, impulsivity and time of day on performance, mood and cardiovascular function. https://doi.org/10.1177/026988119100500205

If it’s too late in the day, caffeine can make it hard to fall asleep at bedtime. The “half life” of caffeine (how long it takes to break down half of it) is about five hours.⁸⁾Caffeine for the Sustainment of Mental Task Performance. Formulations for Military Operations. Chapter 2. National Academies, 2001 That said, we all metabolise caffeine differently, so for some of us the effects wear off more quickly.⁹⁾Nehlig A. Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption. Pharmacol Rev. 2018 Apr;70(2):384-411. doi: 10.1124/pr.117.014407 Regular coffee drinkers might feel less of a caffeine “punch”, with tolerance to the stimulant building up over time.¹⁰⁾Ammon HP. Biochemical mechanism of caffeine tolerance. Arch Pharm (Weinheim). 1991 May;324(5):261-7. doi: 10.1002/ardp.19913240502.

Caffeine can also raise levels of cortisol, a stress hormone that can make you feel more alert.¹¹⁾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 Sep-Oct;67(5):734-9. doi: 10.1097/01.psy.0000181270.20036.06. This might mean caffeine feels more effective later in the morning, because you already have a natural rise in cortisol when you wake up. The impact of a coffee right out of bed might not seem as powerful for this reason.

If your caffeinated beverage of choice is also a sugary one, this can exacerbate the peak and crash feeling. Because while sugar does create actual energy in the body, the free sugars in your drink can cause a spike in blood sugar, which can then make you feel tired when the dip comes afterwards.

While there is no proven harm of drinking coffee on an empty stomach, coffee with or after a meal might hit you more slowly. This is because the food might slow down the rate at which the caffeine is absorbed.¹²⁾Caffeine. The Nutrition Source. Harvard School of Public Health

What about a strong tea or fizzy cola?

Coffee, of course, isn’t the only caffeinated beverage that can loan you some energy.

The caffeine in tea, energy drinks and other beverages still impacts the body in the same way. But, since the ingredients mostly come from plants, each caffeinated beverage has its own profile of additional compounds which can have their own stimulant effect, or can interact with caffeine to change its impacts.¹³⁾Barbara Penolazzi, Vincenzo Natale, Luigi Leone, Paolo Maria Russo, Individual differences affecting caffeine intake. Analysis of consumption behaviours for different times of day and caffeine sources, Appetite, Volume 58, Issue 3, 2012, Pages 971-977, ISSN 0195-6663, https://doi.org/10.1016/j.appet.2012.02.001.

Caffeine isn’t magic. To create energy and re-energise our bodies we need enough food, water and sleep.

For more information on the negative impacts of caffeine, continue with this article:
What Caffeine is doing to You and Your Child?

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This article is republished from The Conversation under a Creative Commons license. Read the original article.

Emma Beckett

Emma has a multi-faceted research background, with qualifications and experience in food science, nutrition, epidemiology, science management, biomedical sciences, immunology and microbiology. Her research focuses on molecular nutrition. Emma is also a passionate science communicator. She has written for newspapers and magazines, and appears regularly on local and national radio.

www.newcastle.edu.au/profile/emma-beckett