If you love coffee and want to sleep peacefully, it is not difficult. You only need one trick to solve it.

It's 4 p.m. and you're so sleepy that you can barely open your eyes. At this point, it seems like a difficult decision whether you should fight against fatigue and take a nap or drink a cup of coffee to cheer yourself up.

Let's first take a brief look at how coffee keeps you awake. Coffee contains a central nervous system stimulant called caffeine. There is a chemical called adenosine in our brain that can produce a substance that makes us sleep when we are awake. The longer we are awake, the more adenosine there is in the body. Caffeine is the enemy of adenosine and will reduce its sleep-inducing effect.

Simply put, the reason why caffeine can make us energetic is that it inhibits the secretion of substances in the human body that can make people fall asleep, so naturally you will not feel sleepy.

Caffeine is a bit like a nasty partygoer: You show up early with a bang when the party starts, party for a few hours, and then disappear after the party is over. For most people, the main stimulating effect of caffeine occurs about 15 to 45 minutes after drinking it, as caffeine levels in the blood reach peak levels, at which point you feel that energy rush.

But caffeine takes a long, long time to be completely metabolized. The half-life of caffeine is generally around 4 to 6 hours, which means that 4 to 6 hours after ingestion, about half of the caffeine is still in your body, at this time, you may still feel some of the stimulating effects of caffeine. Over time, it will take another 4 to 6 hours for the remaining half of the caffeine to be metabolized, and the side effects will gradually disappear.

If you drink a cup of coffee with 100 mg of caffeine at 10 a.m. (about one 250 ml cup of coffee), then when you lie down at 10 p.m., you may still have 25 mg of caffeine in your body. If you drink another cup of coffee with 200 mg (about two 250 ml cups of coffee) at 4 p.m., then about 100 mg of caffeine is still in your system at 10 p.m.

​Perhaps your current life experience has shown that you are the type of person who can drink coffee at any time and still sleep soundly. If so, congratulations, you don't need to make any changes, you are perfect. If you don't have trouble falling asleep and have plenty of energy during the day, then there is nothing wrong with drinking coffee in the late afternoon.

However, sleep is fundamental to good health, and if that 4 p.m. latte is disrupting your sleep, or you're not sure if caffeine is causing you to lose sleep, the first thing you should do is stop drinking coffee.

It is generally recommended that you drink your last cup of coffee at least 8 to 10 hours before bedtime, which gives you two half-lives of coffee. This puts the daily coffee cut-off for most people between 12 and 2 o'clock. In simple terms, no more coffee after lunch. If you're thinking of trying to get away with it and drink all the coffee you want in the morning and early afternoon, you're overthinking it. It won't work. Increasing your caffeine intake only means that your body will metabolize more caffeine later than it normally would, which cancels out the benefits of consuming it earlier.

​Since people react differently to caffeine, you can also explore your own patterns and find out what affects your sleep. The only way is to find the right balance for you. It often takes trial and error. You may find that drinking coffee at 10 am or 4 pm has no effect.

Another way to adjust your caffeine intake for better sleep is to cut back on your caffeine intake. Try drinking one less cup per day to see if your sleep improves. Or switch to decaffeinated coffee, although decaffeinated coffee still contains a small amount of caffeine.