Yes, caffeine can keep you awake, even when you need to sleep.
It does this by using a hormone called adenosine, which masks the urge to sleep.
Adenosine continually builds up in your brain while you’re awake. This buildup is called “sleep pressure.” The longer you stay awake, the higher the concentration of adenosine.
Adenosine has one essential function. The greater the buildup of adenosine in your brain, the greater the need to sleep – hence the expression, sleep pressure.
Sleep pressure builds to such an extent that there’s an overpowering urge to sleep for most people after being awake for 12-16 hours. You simply can’t stay awake any longer and must sleep.
However, when it comes to a cup of coffee, the adenosine’s sleep signal is artificially muted, thereby making you feel more awake and alert than you otherwise would be.
It works by the caffeine latching onto the brain’s adenosine receptor sites, thereby blocking the sleep signal that gets communicated to the brain. In this way, caffeine tricks you into feeling alert and awake, even though sleep pressure continues to build.
Caffeine can keep you awake because of its half-life
Now, there’s nothing wrong with taking caffeine. The problem is, how long before bedtime do you have a coffee because caffeine has a very long half-life.
Firstly, half-life simply refers to the length of time it takes for the body to remove 50 percent of the caffeine. The half-life of caffeine is four to six hours for a small 8 oz (250 ml) cup of coffee.
So, one cup of coffee after your evening meal at 8 pm means that your body has only processed half the coffee by 2 am. Not good, and a difficult night’s sleep is ahead for most people.
There are other factors at play, though. The main one is the amount of caffeine consumed during the day. The other is how quickly or slowly it’s metabolized by the body.
The caffeine crash
Caffeine is removed from your body by an enzyme within your liver that degrades it over time.
Eventually, when the caffeine finally exits, your concentration and energy levels drop rapidly, and the urge to sleep is great. This phenomenon is known as a “caffeine crash.”
What’s happened is the caffeine has blocked the feelings of tiredness caused by adenosine, which continues to build in concentration in your body. Once your body is free of caffeine, the adenosine level, or sleep pressure, will be higher than before you drank the coffee.
Coffee in the morning
For sure, caffeine makes you feel more awake or alert. That’s because it masks the continuing build-up of the sleep pressure chemical adenosine.
It makes sense that coffee after dinner, or even in the late afternoon, is not a great idea, given caffeine’s half-life.
But what about coffee in the morning?
For me, I like strong coffee. I also like being able to get to sleep relatively quickly. So I just have one, occasionally two, cups of coffee before 11 am, and that works just fine for a good night’s sleep.