Today's three-minute lesson

Caffeine Has a Longer Memory Than You Think

Caffeine can make you feel more alert, but it does not create energy.

Throughout the day, your brain uses energy to keep you awake, thinking and active. As it does, a substance called adenosine gradually builds up in your brain. You can think of adenosine as a natural tiredness signal: the longer you have been awake, the more of it collects.

Adenosine attaches to special receptors in your brain, signalling that your body has been awake for long enough and needs sleep. As more adenosine builds up, the pressure to sleep becomes stronger. While you sleep, your brain clears much of it away, which helps explain why you usually feel more alert after a restful night.

Caffeine temporarily blocks adenosine from making you feel sleepy.

The important word is temporarily.

Caffeine does not remove the sleep pressure that has been building. It simply makes it harder for you to notice it for a while.

Caffeine also has what is known as a half-life. This is the amount of time it takes your body to process half of the caffeine you have consumed.

The average half-life of caffeine is around five or six hours, although it varies considerably from person to person. This means that if you consume 200mg of caffeine at 3pm - roughly the amount in a typical medium latte - you could still have around 100mg in your system at 8 or 9pm. Several hours later, around half of that may still remain.

Your body does not suddenly become caffeine-free once the immediate boost wears off.

That means an afternoon coffee could still be influencing your brain when you go to bed - even if you no longer feel its effects and have no difficulty falling asleep.

Falling asleep is not the only measure that matters. Caffeine later in the day may reduce the depth or quality of your sleep, leaving you feeling less refreshed the following morning.

That can create an unhelpful cycle:

You feel tired, so you reach for caffeine.
The caffeine affects your sleep.
You wake feeling tired and reach for caffeine again.

This does not mean you need to give it up altogether.

Instead, choose a caffeine cut-off time that gives your body enough time to process it before bed. For many people, stopping around eight hours before bedtime is a sensible place to begin.

Remember that caffeine is not only found in coffee. Tea, soft drinks, pre-workout supplements and chocolate can all contribute to your daily intake.

If you usually rely on caffeine during the afternoon, do not simply remove it without considering what will replace it. When your energy dips, try getting outside, taking a short walk, drinking some water or accepting that a temporary lull in alertness is a normal part of the day.

You may even intentionally plan less demanding work for that period rather than repeatedly trying to override it.