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.

Dr Neil Stanley, who has been involved in sleep research for more than 35 years, says caffeine can prolong the amount of time it takes you to fall asleep, decrease the amount of deep sleep you have and reduce the overall quality of your sleep. Of course, some people can still fall asleep after a coffee. It all depends on the sensitivity of the drinker.

Dr Stanley explains that the only way to judge your caffeine sensitivity is to “listen to your body”: If you find the days you struggle to sleep seem to correlate with whenever you’ve had more tea or coffee, there’s a high chance they’re linked and you should reduce your intake.

If you are having repeated issues getting to sleep, Dr Ebrahim recommends going further than avoiding coffee in the evening, by reducing your caffeine intake to almost nothing, as the delayed wake-up effect can happen hours after your last cuppa.

Stopping caffeine impacting your sleep is important as effects of sleep deprivation can range from negative processing of emotions to a change in the way that people make decisions. Lack of sleep has also been attributed to hopelessness, memory problems and irritability. While long-term health outcomes of chronic deprivation (repeatedly having less than seven hours of sleep) include increased susceptibility to obesity, type 2 diabetes, cardiovascular diseases and high blood pressure.

If you’re looking for a replacement for your evening cappuccino, tea is a bit of an improvement as it tends to contain far less caffeine than coffee.

It’s thought that your average cup of English breakfast tea contains half the amount of caffeine than a standard cup of coffee. However, it’s worth noting that this can vary. According to Bluebird Tea Co, the amount of caffeine which ends up in the body is influenced by factors such as the type of tea leaf, how old the leaf is, the water temperature and how long you’ve brewed it for.

Dr Stanley says, in comparison to coffee, people would usually need to drink more tea for it to negatively impact their sleep.

To give you the best opportunity for undisrupted sleep, Dr Stanley recommends switching your pre-bedtime caffeinated beverage for a hot milky drink (“there’s scientific proof of its effectiveness in aiding sleep”) or any other non-caffeinated drink that aids relaxation of the mind and body. Chamomile tea; hot honey, lemon and ginger; or even a small glass of sherry or whisky should do the trick.