Many of us crave our morning coffee to give us the ‘energy and go’. Altogether, people in the world drink more than two billion cups of coffee every day.
You might think that coffee gives you the energy to get through the morning or day – but it’s not what you think. The main stimulant in coffee is caffeine. The main way caffeine works is by changing the way cells in our brain interact with a compound called adenosine.
Preoccupation with fatigue
Adenosine is part of the system that regulates our sleep-wake cycle and part of why activity levels rise to fatigue. As we continue to go about our days and get things done, adenosine levels rise because it is released as a by-product where energy is used in our cells.
Ultimately, adenosine binds to its receptors (parts of cells that receive signals) that tell cells to slow down, making us sleepy. This is why we feel tired after a day of activity. While we sleep, energy use decreases, which lowers adenosine levels as it is converted back into other forms. And you wake up in the morning feeling refreshed. Well, if you get enough sleep, this is the reality.
And if you’re still sleepy when you wake up, caffeine can help for a while. It works by binding to the adenosine receptor. But the process is not so similar that it triggers a sleepy-slowing signal like adenosine. Instead, it just fills in the spots and prevents adenosine from binding there. This prevents drowsiness.
And while it does feel energizing, that little caffeine intrusion is more of a loan to a feeling of alertness, rather than creating any new energy.
This is because the caffeine won’t stick around forever, and the adenosine that blocks it doesn’t go away. So eventually the caffeine breaks down, leaves the receptors and all that adenosine that’s been waiting and the sleepy feeling returns – sometimes all at once.
So, the debt you owe to caffeine always needs to be paid eventually, and the only real way to pay it off is to sleep.
Timing is everything
How much free adenosine is in your system that hasn’t bound to the receptors yet, and how sleepy you feel as a result will affect how much caffeine you drink to wake you up. So, the coffee you drink later in the day, when you have more signals of sleepiness, your system may feel more robust.
And if it’s too late in the day, caffeine can make it difficult to fall asleep at bedtime. The “half-life” of caffeine is about five hours. However, we all metabolize caffeine differently, so for some of us the effects wear off more quickly. And regular coffee drinkers may feel less “dose” of caffeine.
Caffeine can also raise levels of cortisol, a stress hormone that can make you feel more alert. This may mean that the caffeine becomes more effective later in the morning, because you already have a natural rise in cortisol when you wake up. And the effect of coffee straight from bed may not seem so strong for this reason.
And if the caffeinated drink you choose is also a sugary drink, this can exacerbate your high and crash. Because while sugar creates actual energy in the body, the free sugars in your drink can cause a spike in blood sugar, which can make you feel tired.
While there is no proven harm from drinking coffee on an empty stomach, coffee with or after a meal may hit you slower. This is because food may slow the rate of caffeine absorption.
How about strong tea or fizzy cola?
Coffee, of course, isn’t the only caffeinated beverage that can give you some energy.
The caffeine in tea, energy drinks, and other beverages still affects the body in the same way.
But because the ingredients come mostly from plants, each caffeinated beverage has its own profile of additional compounds that can have their own stimulant effect, or that can interact with the caffeine to alter its effects.
Caffeine can be helpful, but it’s not magic. To generate energy and re-energize our bodies, we need enough food, water and sleep.