More than a third of French people say they are dissatisfied with the quality of their sleep, according to a survey conducted in March by the National Institute of Sleep and Vigilance and MGEN. The causes of bad nights are various (stress, exposure to screens, nightmares, noise pollution) but there are reflexes to counteract the harmful effects of a night that is not very restorative on the body. Among them, the famous nap, which, according to its followers, would allow you to recharge your batteries and make up for the fatigue accumulated during the previous shortened night. Oh, really?
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A minimum of time to recover physically and mentally
In reality, as Armelle Rancillac, a neuroscience researcher at Inserm and a sleep specialist, explains, napping is a physiological and individual need whose benefits depend above all on its duration. For example, the short nap format, also known as a "flash" nap and popularized by artist Salvador Dalí, lasts only a handful of seconds or minutes. We hold an object in our hand until it falls with a crash when we fall asleep and wake us up. The objective here is not the recovery of the body but rather to energize itself in order to stimulate its creativity, says the neuroscientist.
If, after a bad night's sleep, you want to fight drowsiness and regain energy, you should extend the nap time to at least 20 minutes. "Getting enough sleep in the middle of the day helps reduce the sleep pressure that has built up with the bad night's sleep," confirms the neuroscience researcher. During this time, we will produce a little slow-wave sleep, the phase that is supposed to help the body recover better. "Thanks to this type of nap, we will restore alertness, concentration and cognitive performance," says Armelle Rancillac.
Thanks to a nap of at least 20 minutes, we will restore alertness, concentration and cognitive performance
Armelle Rancillac, neuroscience researcher at Inserm and sleep specialist
In the event of a significant sleep deficit, for example after a sleepless night or after insomnia that would have halved our sleep quota, the neuroscientist advises (when possible) to sleep the equivalent of an entire cycle, i.e. between 90 and 120 minutes, in order to reproduce a "mini-night". In practice, "during a nap of one hour to 1 hour and 30 minutes, our body will produce more slow-wave sleep, which will regenerate the tissues and secrete the hormones necessary for the body, such as growth hormone," she explains. Another important stage of sleep will also be stimulated, the one called "REM sleep", a period when the brain will better consolidate learning and regulate its emotions.
A habit to monitor and adapt
Regardless of the length of the nap, the golden rule is not to do it too late in the day, at the risk of causing deleterious effects on the following night. "The ideal is not to take a nap after 17 p.m. to give adenosine, the hormone responsible for falling asleep, time to recharge sufficiently while waiting to be released in the evening," says Armelle Rancillac.
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To make sure that the daytime snooze is effective, you should also ask about your energy level after a nap. If you always feel tired, it could be a sign that the sleep debt is not being paid off enough, suggests the neuroscientist, or that you are suffering from a real sleep disorder. In this case, it is advisable to consult a health professional. Especially since there are many studies highlighting sleep deprivation as a risk factor for cardiovascular disease, type II diabetes, hypertension, overweight and, to a lesser extent, depression or anxiety.
Other reflexes are just as important as napping to protect your sleep. Starting with the times of getting up and going to bed. These must be regular, even on weekends, says the neuroscience researcher. During the day, it is also essential to activate the sleep-wake rhythm synchronizers by exposing yourself to natural light as much as possible. Forewarned is forearmed.