Adenosine, Sleep Pressure, and Caffeine - Matthew Walker
Some things I took away from Matthew Walkers great book Why We Sleep, on adenosine, sleep pressure, caffeine.
Adenosine is the chemical that builds up in your brain.
The longer you are awake, the more it builds up. This increases your desire to sleep. This is what is known as sleep pressure. After 12 to 16 hours this has built up enough for us to go to sleep.
Caffeine takes up the receptor sites of the adenosine which blocks and inactivates the receptors. This then blocks the sleeping signal normally communicated to the brain by adenosine.
Caffeine has a half life of 5 to 7 hours. So a coffee at 6pm could still have 50% of the caffeine in your system at 11pm to 1am. And that's only halfway of getting the caffeine out of the system, don't forget.
Whilst caffeine is in the system, adenosine is still accumulating. So once the liver clears out the caffeine, you now have the sleepiness you had 2 hours before the coffee plus the additional build up of adenosine whilst on the caffeine. Once the caffeine leaves the receptors, the adenosine rushes in and you feel more sleepy than before.