The science 

After you wake up, your body starts accumulating a chemical called Adenosine, which makes you sleepy. There are receptors in your brain that receives these chemicals, and they tell us when we should sleep. 

Imagine an elephant’s trunk taking in apples, and once it eats enough, it goes to sleep. This is like the receptor in your brain. Caffeine, living in your coffee, is like a huge plastic cube that forcibly sticks itself onto the elephant’s trunk (receptor), making the elephant (you) unable to take in apples (adenosine). 

As time goes on, there is a huge mass of apples on the ground. After some time, the elephant manages to shake off the plastic cube, and starts to eat all the apples greedily at one go. There comes the crash; a huge wave of sleepiness comes over you like a whale out of the water. This is called the ‘caffeine crash’. 

Caffeine’s half-life or effective time 

Caffeine has a half-life of about 7 hours, which means that half the morning cup of coffee at 7AM stays in your body at 2PM. If you find it hard to sleep at night, it is likely because there is still too much caffeine in your system, effectively blocking your ability to receive adenosine. You are tired but your brain doesn’t know it yet, as an army of caffeine is stopping the flood of adenosine from kicking in. 

By the way, caffeine is digested by your liver, and it is a slow process. 

How you can drink coffee and still sleep well

As you now know, each cup of coffee brings in a flood of caffeine that blocks the entry of adenosine. For most people, it means you should stop at 2 cups per day, especially if your job is desk-bound, like most people’s are. 

Given that most Singaporeans sleep by 10-11PM, we recommend your cup to be no later than 2PM. Remember, half a cup still remains at 9PM. It is worse if you haven’t been exposed to sunlight, which our body uses as an indicator of time. 

Depending on your health, weight, metabolism rate and work, we have found that it is perfectly alright to have a morning cup of coffee and another cup at lunch. You will still be able to sleep soundly at bed time, especially if you sleep on a King Koil. You can have your coffee (in moderation) and good sleep too.