Cheat your body clock!

A good night's sleep can completely transform your day. Working shifts, late nights or travelling across time zones can turn a night of sleep into a nightmare. You are buzzing with adrenaline and really need to refresh your brain before your long day, exam or meeting tomorrow, but no matter how hard you try, sleep just will not come to you. A sleep-deprived brain feels foggy, slow and heavy and isn't something you want if you have something challenging on the next day. If we really want to know how to trick our sleep patterns, we need to turn to science.

Neuroscientific research has advanced so much in recent years that we suddenly have a whole lot of information on what makes us fall asleep and the signals our body clock responds to. Playing with these signals can help us trick our clocks into letting us fall asleep, whenever we want...So, what does the science say?

How you fall asleep

Two things make you fall asleep:

1. Your sleep ‘debt’.

2. The time on your body clock.

During every hour of being awake, we collect a ‘sleep debt'. When the debt becomes very big towards the end of the evening, our body tries to pay it back by trying to fall asleep immediately.

If you have gathered a huge 'sleep debt' from not getting enough sleep but it is not your usual bedtime, your body clock will prevent you from falling asleep. If your body clock is working perfectly but you have napped all day and don't have a big 'sleep debt' then you won't be able to fall asleep at your usual bedtime.

A few hours before you would usually sleep, your body starts wanting to sleep because you have clocked up a big 'sleep debt' all day. Your body clock overrides your body’s ‘fall asleep’ signal to keep you awake for another few hours.The opposite happens in the early hours of the morning. By about 4am, your body has repaid every cent of its sleep debt and wants to wake up. Your body clock again overrides this and keeps you asleep for another few hours.

The body’s clock acts like a security gate. You might want to enter the world of sleep or the world of wakefulness, but it will only let you do so if it thinks the time is right.

In order to sleep well, you need to have both a ‘sleep debt’ and a well-tuned body clock. The sleep debt part is easy. Not sleeping gives you a sleep debt. The body clock part needs to be hacked.

Identify where your clock can be hacked

Your clock can be hacked mainly through light, but also through food, exercise and heat. Light is the strongest player.

Light changes the levels of melatonin. Melatonin is a hormone we produce at night and it helps us sleep. Bright light during the day enhances melatonin production during the night. Dim light during the evening suppresses it.

There are several 'tricks' we can use to retune our body’s time.

Hack your clock with light

Light can change the time on the body’s clock, but whether it pushes the time forward or backward depends on the time at which your body is at its coolest. Your body cools down during the night and reaches a minimum temperature in the early hours of the morning. Exposure to light BEFORE this point pushes the clock back. Exposure AFTER this point, brings the clock forward. In many people who wake up at 7am, this dip takes place at around 4am. So, exposure to light at 3:30 will push the clock back, whereas exposure at 4:30 will bring the clock forward. The brighter the light and the longer it is shone for, the bigger the effect. Full spectrum white light actually works best, although blue light comes a close second. Light has the maximal effect on your body clock when used around the time of your temperature dip.

(Blue-blocking glasses are becoming available everywhere and have an orange tint to them. If you are concerned about how you look, the newer ones come in a variety of styles!)

Hack your clock with food

Of the non-light signals, food exerts the strongest effect. Eating a large meal after a long fast lasting at least 8 hours or longer tells the body that it has woken up after an overnight sleep and is taking breakfast. The timing of that meal sets the time for morning or ‘breakfast time’. A large meal at night suppresses the hormone ‘melatonin’ and keeps you awake.

Hack your clock with exercise

Exercise is another signal. When you exercise is crucial. Remember the two time windows when your body clock acts like a security guard? One window is about 3 hours before you fall asleep. The other is about 3 hours before you wake up. It is the evening 3 hour window that becomes important. If you exercise in the evening BEFORE the 3-hour time window during which your body wants to sleep but your clock won’t let you, you bring your clock forward. Exercising in the evening DURING that time window pushes the clock back. Exercise also affects your tiredness, so exercising lets you clock in more ‘sleep debt’ overall. You can make the biggest impact on your clock with exercise, bringing your clock forward, if you exercise 4 to 8 hours before falling asleep.

Hack your clock with heat

Heat is another signal. Our bodies get coldest during the night and become warmer as we wake up and start to move around. We are more likely to fall asleep as our core body temperature drops...but there is a catch! We all live in two bodies. One is our outer ‘shell’ of arms and legs and skin. The other is our inner ‘core’, the cavity inside us that houses our organs. It is the ‘core’ that gets colder as we drift off to sleep. All that heat has to go somewhere, so it is ‘shifted’ to the outer ‘shell’, which heats up. The ‘shell’ then dissipates the heat into the air around us.

This provides the opportunity for a clever hack: temporarily heating up our ‘shell’ confuses the brain and makes us fall asleep faster! Foot warming has been shown to rapidly bring on sleep! This heating process must not interfere with the body’s ‘core’ cooling down. Our ‘core’ needs to become cooler in order to sleep.

Hack your clock with caffeine

Taking caffeine in the evening will keep you awake for longer. In one experiment, about 200mg of caffeine given in the evening delayed sleep onset by 40 mins, even in dim light conditions. Remember, though that caffeine can cause harm, so if you resort to this option, it may be far safer to take caffeine in the form of a cup or two of tea or coffee, instead of the tablet form. Do not take too much. Taking too much caffeine is extremely dangerous for your health.

Clock-hacking protocol

To stay awake for longer and push your clock back:

1. Expose your eyes to bright light late in the evening. The later this exposure is, into your ‘usual’ night, the more powerful the effect, but it has to be BEFORE your usual 4am temperature dip.

2. Keep eating late into the day and eat a large meal in the evening to suppress melatonin.

3. Exercise. In order to be able to stay awake for longer, the best slot to exercise in would be within the few hours before you usually fall asleep.

4. Keep warm. Make sure your whole body stays warm, though, not just your feet!

5. Drink a cup of coffee in the evening. ​


1. For day/night reversal, wear blue light-blocking glasses in the morning and try to keep wearing them throughout the day. Take them off in the evening.

2. Have your largest meal of the day after an 8-10 hour fast, when you want it to be morning.

To make your clock go forward and fall asleep sooner:

1. Make your light dim in the hours before you want to fall asleep and block blue light.

2. Wear blue light-blocking glasses if you are watching movies on the plane or if you are working all night on your computer.

3. Wake up an hour or so before your usual waking up time and expose yourself to bright light.

4. Stop eating several hours before you want to fall asleep.

5. Exercise well to make yourself tired and accumulate ‘sleep debt’ but do this between 4 and 8 hours BEFORE you want to fall asleep.

6. Before you want to fall asleep, start to cool down your body with cool circulating air, but warm up small parts of your shell by wearing warm socks!

7. Avoid caffeine.​

Good Luck!


This site is for discussion only and should not be used as a source of medical information. Please consult your medical doctor before making any changes to your diet, lifestyle or medications.


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