Fact Check: Caffeine… how it works and a few surprises

Yesterday, I was speaking with a friend about coffee and caffeine. I thought I had an idea of how it worked, though my friend, who always seems to have an opinion on everything, explained it differently than I imagined.

I thought it had something to do with releasing hormones, but he claimed it had to do with binding to some receptor in the brain which prevents the sleep inducing or tiredness hormones from being effective. I had some vague idea that it triggered a hormone to released a type of stimulant. I was surprised to realize, that although I love coffee and habitually drink 2-4 cups a day, I had no clear idea of how it worked.

So, time to consult the G(oogle).

Caffeine is a type of drug that promotes alertness. These drugs are called “stimulants.” Caffeine acts as an “adenosine receptor antagonist.” Adenosine is a substance in your body that promotes sleepiness. Caffeine blocks the adenosine receptor to keep you from feeling sleepy.


In reading the first two sentences I thought, “yeap, that’s what i thought…” However before, I must have stopped there, because it turns out that caffeine isn’t in-fact a “stimulant” as I had thought. It is the last two sentences which are key, and in-fact sounds a lot like what my friend had said.

Adenosine is a substance in your body that promotes sleepiness. Caffeine blocks the adenosine receptor to keep you from feeling sleepy

Looking back, I think I had caffeine mixed up with “stress” and how that works.

Ok, after going though various pages from Google, here’s the big picture of what I found:

During cellular energy production (happens in the mitochondria, cellular powerhouse), Adenosine Triphosphate (ATP) is broken down, leaving Adenosine. Throughout the day this builds up and binds to Adenosine Receptors. This action causes the brain the feel more relaxed and you feel a sense of being more tired. During sleep/recovery, the body builds back energy reserves and eliminates Adenosine. When you wake up, you will have low levels and feel refreshed. The daily cycle then begins again by breaking down ATP as your cells produce energy, increasing Adenosine which binds to waiting receptors.

But what about caffeine? Ok, here’s where it comes in. Caffeine, is similar to Adenosine in that it can bind to the Adenosine receptors, however it does not cause the receptors to trigger the sense of being tired. So, rather than your body feeling tired or sluggish as it normally would with increasing Adenosine levels, it doesn’t since the receptors are already occupied by caffeine. Remember caffeine has a half life of 3-5 hours, after witch there will be a buildup of Adenosine waiting to bind to the newly freed receptors.

Personal takeaway: I’m going to try to wait until after lunch before my first cup of caffeinated coffee. That’s the slowest part fo the day, which incidentally coincides with lunch digestion & my habitual morning coffee wearing off. In the morning, your body should have just eliminated the majority of the Adenosine during sleep anyway, so not much of it in your body yet anyway.

But, I do appreciate starting my day with a nice hot coffee with sugar and milk, so i’m going to try switching to the decaf variety :-p. Habits are hard to break 🙂

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