We’ve all been there: you’ve devoured a three-course meal, it’s 10pm and the waiter asks if you want a coffee. The rest of the table is ordering cappuccinos so you do too. Fast forward three hours and you’re lying in bed with eyes wider than a set of saucers.
Why does this happen? Because caffeine interferes with the action of adenosine, a compound found in the brain which slows down nerve activity and makes you sleepy. As the day progresses, levels of adenosine increase. But when you have coffee, caffeine binds to adenosine receptors in the brain and prevents you from becoming tired.
Dr Irshaad Ebrahim from Harley Street’s London Sleep Centre explains: “When caffeine binds to the adenosine receptors, the brain doesn’t detect the adenosine so neural activity does not slow down. You have increased activity in the brain, which stimulates the pituitary gland to signal to the body to increase activity. You then have more adrenaline, your heart accelerates and your breathing increases. As a result of this, you end up more alert.”
If you want to get a good night’s sleep, Dr Ebrahim advises not to drink coffee any time after 2pm. So that 10pm cappuccino is definitely not advised.