How does sleep work?

Animated drawing of a person standing in front of a larger-than-life clock. Behind the clock, there is a representation of the night sky and the daylight.

Image by Freepik

Different factors regulate or control your sleep.

The circadian clock (from the Latin roots circa = about and diem = day) is your body’s internal clock. This controls the timing of your sleep patterns.

Thanks to the circadian clock, we feel sleepy at night and awake during the day. Usually, the longer you stay awake, the stronger your desire to sleep. This need to sleep is called your homeostatic sleep drive. We sleep best when we keep our clock on a stable rhythm. This is why healthy sleep routine tips encourage going to bed and waking up at the same time every day.

Chemicals in your brain, called neurotransmitters, are involved in making you feel sleepy or awake. A hormone called melatonin is produced by special cells in your brain and helps to control your circadian clock. Normally, the amount of melatonin in your body begins to increase in the mid- to late evening. It remains high for the most of the night and then drops to a lower level in the morning.

Light is also very important in controlling your sleep because it affects the amount of melatonin that your body produces.

During the winter months, when the days are shorter, your body may produce melatonin either earlier or later in the day than usual. This change can lead to changes in your sleep patterns. Many people who live in Northern countries such as Canada can be affected by seasonal problems with their sleep because they are exposed to very little light during the winter months. Talk to your healthcare team if you think this might be an issue for you.

A special chemical called adenosine is also very important in controlling how sleepy you feel. Without enough adenosine, it’s difficult for our bodies to reach the deepest parts of our sleep cycle. Deep sleep is very important because it’s the time when muscles repair themselves and the body secretes growth hormone.

Factors that can impair your sleep

A matrix of illustrated bottles of beverages such as cola.


Adenosine works by fitting into specific cell receptors, similar to a lock and key. The chemical caffeine, found in coffee, cola and energy drinks, fits the same cell receptors as adenosine. This means that consuming caffeine can block the adenosine receptors and prevent adenosine from creating the feeling of sleepiness.

The American Academy of Pediatrics recommends that teens (aged 19 and younger) get no more than 100 mg of caffeine a day. Adults (aged 20 and older) with a medical condition should get no more than 200 mg of caffeine per day.

A young person lying in bed , their expression distressed. There are bolts around their head, indicating stress.

Poor sleep hygiene

“Sleep hygiene” describes the routine you create for your sleep every night. It is important to avoid poor sleep hygiene so your brain can learn to associate your bed only with sleep. If you do activities that are keep you wide awake in bed, your brain will have a more difficult time settling down to rest when it’s sleep time. For this reason, it’s very important to avoid doing stressful activities right before bedtime or in bed. So instead of studying for a test in bed, for example, do your study in the living room.

A young person lying awake in bed late at night. They are holding a smartphone in their hand.

Electronic devices and TV

These devices can particularly disrupt your sleep routine. This is because these devices emit mostly blue light, which is very high intensity and associated with morning. This, coupled with the fact that handheld electronic devices are generally held very close to your eyes, means that the devices can confuse your brain into thinking that it’s time to start waking up instead of falling asleep.