Des chercheurs de l’Université de Californie à Berkeley ont découvert que l’on peut se réveiller frais et dispos chaque matin en se concentrant sur trois éléments clés : le sommeil, l’exercice et le petit-déjeuner.
Conseils trouvés par les chercheurs : Dormez plus longtemps et plus tard, faites de l’exercice la veille et prenez un petit-déjeuner faible en sucre et riche en glucides.
Vous sentez-vous somnolent jusqu’à ce que vous ayez pris votre café du matin ? Souffrez-vous de somnolence pendant la journée de travail ?
Si vous avez du mal à vous réveiller le matin, vous n’êtes pas seul. Cependant, une nouvelle étude de l’Université de Californie à Berkeley montre que se réveiller reposé n’est pas qu’une question de chance. Les scientifiques ont découvert que prêter attention à trois facteurs – le sommeil, l’exercice et le petit-déjeuner – peut vous aider à commencer votre journée sans vous sentir somnolent.
Les résultats proviennent d’une analyse détaillée du comportement de 833 personnes qui ont reçu une variété de petits déjeuners sur une période de deux semaines ; portaient des montres-bracelets pour enregistrer leur activité physique et la quantité, la qualité, le moment et la régularité de leur sommeil ; journaux tenus de leur apport alimentaire; et enregistré leur niveau de vigilance à partir du moment où ils se sont réveillés et tout au long de la journée. Des jumeaux – identiques et fraternels – ont été inclus dans l’étude pour démêler l’influence des gènes sur l’environnement et le comportement.
Dans la nouvelle étude, Vallat, Walker et leurs collègues ont examiné l’influence des gènes et des facteurs non génétiques, y compris l’environnement, sur la vigilance au réveil. En mesurant comment la vigilance varie entre les individus et chez la même personne à différents jours, ils ont pu démêler le rôle de l’exercice, du sommeil, du type de petit-déjeuner et de la réponse glycémique post-prandiale d’une personne. Crédits : Raphael Vallat et Matthew Walker, UC Berkeley
Les chercheurs ont découvert que le secret de la vigilance est une recette en trois parties : faire beaucoup d’exercice la veille, dormir plus longtemps et plus tard le matin et un petit-déjeuner riche en glucides complexes et faible en sucre. Les chercheurs ont également découvert qu’une réponse saine et contrôlée de la glycémie après le petit-déjeuner est essentielle pour se réveiller plus efficacement.
« Tous ces éléments ont un effet unique et indépendant », a déclaré Raphael Vallat, boursier postdoctoral à l’UC Berkeley, premier auteur de l’étude. « Si vous dormez plus longtemps ou plus tard, vous verrez une augmentation de votre vigilance. Si vous augmentez votre exercice la veille, vous verrez une augmentation. Vous voyez des améliorations dans chacun de ces facteurs.
La somnolence matinale est plus qu’une simple gêne. Elle a des conséquences sociales majeures : de nombreux accidents de voiture, accidents industriels et catastrophes de grande ampleur sont causés par des personnes incapables de se débarrasser de la somnolence. La marée noire de l’Exxon Valdez en Alaska, la fusion de Three Mile Island en Pennsylvanie et un accident nucléaire encore pire à Tchernobyl, en Ukraine, en sont des exemples bien connus.
« Beaucoup d’entre nous pensent que le sommeil du matin est une gêne bénigne. Cependant, il coûte aux pays développés des milliards de dollars chaque année en raison de la perte de productivité, de l’utilisation accrue des soins de santé et de l’absentéisme. Cependant, il a plus d’un impact qu’il tue – il tue, » déclare l’auteur principal Matthew Walker, professeur de neurosciences et de psychologie à l’UC Berkeley. « Des accidents de voiture aux accidents liés au travail, le coût de la somnolence est mortel. En tant que scientifiques, nous devons comprendre comment nous pouvons aider la société à mieux se réveiller et comment nous pouvons aider à réduire le coût mortel de la lutte actuelle de la société pour se réveiller efficacement chaque jour.
Vallat, Walker et leurs collègues ont récemment publié leurs découvertes dans la revue
Walker and Vallat teamed up with researchers in the United Kingdom, the U.S, and Sweden to analyze data acquired by a U.K. company, Zoe Ltd., that has followed hundreds of people for two-week periods in order to learn how to predict individualized metabolic responses to foods based on a person’s biological characteristics, lifestyle factors, and the foods’ nutritional composition.
The participants were given preprepared meals, with different amounts of nutrients incorporated into muffins, for the entire two weeks to see how they responded to different diets upon waking. A standardized breakfast, with moderate amounts of fat and carbohydrates, as compared to a high protein (muffins plus a milkshake), high carbohydrate, or high sugar (glucose drink) breakfast. The subjects also wore continuous glucose monitors to measure blood glucose levels throughout the day.
The worst type of breakfast, on average, contained high amounts of simple sugar; it was associated with an inability to wake up effectively and maintain alertness. When given this sugar-infused breakfast, participants struggled with sleepiness.
In contrast, the high carbohydrate breakfast — which contained large amounts of carbohydrates, as opposed to simple sugar, and only a modest amount of protein — was linked to individuals revving up their alertness quickly in the morning and sustaining that alert state.
“A breakfast rich in carbohydrates can increase alertness, so long as your body is healthy and capable of efficiently disposing of the glucose from that meal, preventing a sustained spike in blood sugar that otherwise blunts your brain’s alertness,” Vallat said
“We have known for some time that a diet high in sugar is harmful to sleep, not to mention being toxic for the cells in your brain and body,” Walker added. “However, what we have discovered is that, beyond these harmful effects on sleep, consuming high amounts of sugar in your breakfast, and having a spike in blood sugar following any type of breakfast meal, markedly blunts your brain’s ability to return to waking consciousness following sleep.”
It wasn’t all about food, however. Sleep mattered significantly. In particular, Vallat and Walker discovered that sleeping longer than you usually do, and/or sleeping later than usual, resulted in individuals ramping up their alertness very quickly after awakening from sleep. According to Walker, between seven and nine hours of sleep is ideal for ridding the body of “sleep inertia,” the inability to transition effectively to a state of functional cognitive alertness upon awakening. Most people need this amount of sleep to remove a chemical called adenosine that accumulates in the body throughout the day and brings on sleepiness in the evening, something known as sleep pressure.
“Considering that the majority of individuals in society are not getting enough sleep during the week, sleeping longer on a given day can help clear some of the adenosine sleepiness debt they are carrying,” Walker speculated.
“In addition, sleeping later can help with alertness for a second reason,” he said. “When you wake up later, you are rising at a higher point on the upswing of your 24-hour circadian rhythm, which ramps up throughout the morning and boosts alertness.”
It’s unclear, however, what physical activity does to improve alertness the following day.
“It is well known that physical activity, in general, improves your alertness and also your mood level, and we did find a high correlation in this study between participants’ mood and their alertness levels,” Vallat said. “Participants that, on average, are happier also feel more alert.”
But Vallat also noted that exercise is generally associated with better sleep and a happier mood.
“It may be that exercise-induced better sleep is part of the reason exercise the day before, by helping sleep that night, leads to superior alertness throughout the next day,” Vallat said.
Walker noted that the restoration of consciousness from non-consciousness — from sleep to wake — is unlikely to be a simple biological process.
“If you pause to think, it is a non-trivial accomplishment to go from being nonconscious, recumbent, and immobile to being a thoughtful, conscious, attentive, and productive human being, active, awake, and mobile. It’s unlikely that such a radical, fundamental change is simply going to be explained by tweaking one single thing,” he said. “However, we have discovered that there are still some basic, modifiable yet powerful ingredients to the awakening equation that people can focus on — a relatively simple prescription for how best to wake up each day.”
It’s not in your genes
Comparisons of data between pairs of identical and non-identical twins showed that genetics plays only a minor and insignificant role in next-day alertness, explaining only about 25% of the differences across individuals.
“We know there are people who always seem to be bright-eyed and bushy-tailed when they first wake up,” Walker said. “But if you’re not like that, you tend to think, ‘Well, I guess it’s just my genetic fate that I’m slow to wake up. There’s really nothing I can do about it, short of using the stimulant chemical caffeine, which can harm sleep.
“But our new findings offer a different and more optimistic message. How you wake up each day is very much under your own control, based on how you structure your life and your sleep. You don’t need to feel resigned to any fate, throwing your hands up in disappointment because, ‘… it’s my genes, and I can’t change my genes.’ There are some very basic and achievable things you can start doing today, and tonight, to change how you awake each morning, feeling alert and free of that grogginess.”
Walker, Vallat, and their colleagues continue their collaboration with the Zoe team, examining novel scientific questions about how sleep, diet, and physical exercise change people’s brain and body health, steering them away from disease and sickness.
Reference: “How people wake up is associated with previous night’s sleep together with physical activity and food intake” by Raphael Vallat, Sarah E. Berry, Neli Tsereteli, Joan Capdevila, Haya Al Khatib, Ana M. Valdes, Linda M. Delahanty, David A. Drew, Andrew T. Chan, Jonathan Wolf, Paul W. Franks, Tim D. Spector and Matthew P. Walker, 19 November 2022, Nature Communications.
DOI: 10.1038/s41467-022-34503-2
The study was funded by Zoe Ltd.
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