Plenty of people swear that coffee does not affect them, that they can drink an espresso at nine and sleep like a stone. They may even be telling the truth about falling asleep. The problem is what happens after that.
How caffeine works
Through the day a chemical called adenosine builds up in your brain and makes you feel sleepy. Caffeine works by blocking it, so you feel alert. The catch is that the adenosine does not go away, it just queues up behind the blockade. When the caffeine wears off, it floods back.
Caffeine also has a long tail. Half of it can still be in your system five or six hours after you drink it. That afternoon coffee at three is still half-present at nine.
The hidden cost
Even when caffeine does not stop you falling asleep, it can lighten your sleep, reducing the deep stages that leave you genuinely rested. So you sleep your usual hours but wake up less refreshed, and reach for more coffee, and the loop continues.
- Try a cut-off time, often around early afternoon
- Remember that tea, cola, energy drinks and chocolate all count
- Switch to decaf or herbal later in the day
- Notice that sensitivity varies hugely between people
What I changed
I moved my last proper coffee to lunchtime and switched to decaf in the afternoon. I did not feel dramatically different in the day, but I woke up clearer. The coffee was not stopping me sleeping. It was quietly making the sleep worse, which is harder to notice and easy to fix.