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Everyone has already felt it: sleep pressure is this irresistible need to fall asleep, after a long period of being awake. How does it appear? Here is the origin of this force, which encourages us to close our eyes.
After a long party or a sleepless night, our eyes tend to close almost automatically. This force that pushes us to go to bed is what we call sleep pressure, known as homeostatic pressure in medical jargon.
Sleep pressure, essential for wanting to sleep
Our sleep is regulated by two processes: the circadian rhythm and homeostatic pressure. We go through different phases during the day, during which we are more or less alert. This is explained by the regulation of the day/night alternation, which is the circadian rhythm. This internal biological clock implies that our body is not “able to get quality sleep at any time of the 24 hours” explains the Réseau Morphée, an Ile-de-France network for the management of sleep disorders.
On the other hand, our body, during our waking phases, accumulates hypnogenic substances, real natural sleeping pills. A bit like a bathtub filling up to a certain level, you would have to pull the plug to empty it and thus reduce the level of these substances. This is what we call homeostatic pressure, the force that pushes us to go to sleep when the body feels the need. At the end of a good night’s sleep, this pressure is “reset”, the need for alertness increases and we wake up, ready to start a new day.
Adenosine, the key molecule that allows this functioning
This cycle is enabled by the presence of a particular molecule, called adenosine. It is one of the hypnogenic substances indicated previously and begins to be produced upon awakening.
Its accumulation in our brain would subsequently promote sleep at the end of the day, by generating this famous homeostatic pressure. It is then eliminated during the night, and so on. According to scientists, the greater the lack of sleep, the higher the level of adenosine, a coherent reasoning in relation to the functioning of this substance in our body.
Beware of caffeine and naps that are too long or too late
To maintain good sleep pressure and have no (or almost!) difficulty falling asleep in the evening, experts advise against taking a nap that is too long or too late. Indeed, sleeping too long during the day or too late (after 3 p.m.) reduces the quantity of adenosine in our brain, which will also reduce the desire to sleep once we go to bed.
Pay attention to caffeine too, which plays a role as an antagonist of adenosine receptors and therefore promotes alertness. Physical exercise, on the contrary, increases adenosine levels and will create a need for sleep, but be careful not to practice a sporting activity too late, in the evening, otherwise the expected effect will be reversed.
Consult a doctor online for your sleep problems
Homeostatic pressure and circadian rhythm, a duo that works
Our sleep is therefore regulated by the “homeostatic pressure/circadian rhythm” duo. This is why it is recommended to sleep at the most regular times possible, even on weekends, so as not to disturb their balance.
On average, specialists estimate that a two-hour delay between getting up during the week and getting up on the weekend would be the maximum that our body can tolerate. A “too late” morning on Sunday will prevent you from having the sleep pressure necessary to fall asleep peacefully in the evening. And you risk starting the week with too few hours of sleep… And not necessarily in a very good mood.