The researchers believe that sleeping first fulfilled an evolutionary function, giving a definite advantage to animals that were able to do so (anchor future article sleep and evolution). The question then is, what was this initial function of sleep? Why do we spend a third of lives sleeping? How is sleep good for our health?
Truth is, scientists don’t really know. But there are scientifically backed theories.
Our first knowledge of the function of sleep comes from observing the consequences of sleep deprivation. One of the early discoveries and one of the most widely accepted by specialists is its crucial role in immunity. This is something you have necessarily already experienced: when you sleep too little, you are more likely to get sick. A scientific study has proved it by exposing healthy humans to a rhinovirus. It is responsible for rhinopharyngitis, the plain old cold. The volunteers who slept less than 5–6 hours the following night were more likely to “catch a cold” than those who had a good night’s sleep.
Yet another good reason to put you to bed early as soon as the first tickling starts in your throat! More strikingly, in a hepatitis B vaccination test, subjects who had not slept sufficiently produced lower amounts of antibody. It even leads to doubt about the efficacy of their immunization.
An opportunistic function
Conversely, large flu or even a simple cold will nail you to bed. It will significantly increase sleepiness and time spent sleeping too. No need to resist or feel guilty. Cytokines, the molecules secreted by your immune system to fight the viral or bacterial invader, act like sleeping pills.
They will cause an increase and an intensification of your slow, non-REM sleep (cf art1 part1 — phases of sleep), thus decreasing the amount of energy necessary for your body and especially your brain. This energy can be preserved to help the body recover, or spent to cause a fever that will help fight the infection. But nothing in this function justifies the need for loss of consciousness related to sleep. So it’s probably an opportunistic function.
Sleep: a public and individual health issue
Given the downward trend in the duration and quality of sleep in recent decades, this reciprocal relationship between sleep and immunity may well represent an important public and individual health issue in the years to come. Dreem has a role to play in this challenge: by improving the quality of your sleep, it supports your immune system and allows you to cope with the attacks of germs.