I noticed that drinking coffee later in the day always affected the quality of my sleep at night. No surprise here. What I didn’t realize is how long caffeine actually stays in our system. It was only when I watched this video where Dr Rangan Chatterjee interviewed Matthew Walker, author of Why We Sleep.
The half-life (the amount of time it takes a drug, like caffeine, for half of that drug to be excreted out of your system) of caffeine of around 6 or 7 hours (depends on what type of gene you have to metabolize it). But it has a quarter-life of around 12 hours.
Which means if you have a cup of coffee at noon, about 25% of that caffeine is still circulating around your brain at midnight. That’s getting into bed and having a quarter cup of coffee.
Best to enjoy your coffee in the morning hours, so you get a good night’s sleep.
(You can watch the full interview here.)