How you wake up and feel alert in the hours after sleeping depends on how you slept, what you ate for breakfast, and how much exercise you did the day before.
In addition, an individual’s daily alertness setpoint is related to positive emotional state and age.
These are the findings of a new study that adds to the range of options available to those who want to sleep well and wake up feeling revitalised.
Scientists at the University of California, Berkeley, have discovered that you can wake up each morning without feeling sluggish by paying attention to three key factors: sleep, exercise and breakfast.
The findings come from a detailed analysis of the behavior of 833 people who, for two weeks, ate different breakfasts, wore wristwatches to monitor physical activity and sleep amount, quality, timing and regularity, diary food consumption, and tracked wakefulness levels throughout the day.
Twins – identical and fraternal – were included in the study to disentangle the influence of genes from environment and behavior.
The researchers found that the secret to alertness is a three-part prescription requiring substantial exercise the previous day, sleeping longer and later into the morning, and eating a breakfast high in complex carbohydrates, with limited sugar.
The researchers also discovered that a healthy controlled blood glucose response after eating breakfast is key to waking up more effectively.
“All of these have a unique and independent effect,” said UC Berkeley postdoctoral fellow Raphael Vallat, first author of the study.
Walker, the author of the international bestseller, Why We Sleep, runs one of the world’s preeminent sleep research labs, the Center for Human Sleep Science, and is a member of the Helen Wills Neuroscience Institute at UC Berkeley.
Walker and Vallat teamed up with researchers in the U.K., U.S. and Sweden to analyze data from a U.K.-based company, Zoe Ltd., that followed hundreds of people for two weeks to learn how to predict individual metabolic responses to food based on a person’s biological characteristics, lifestyle factors and the foods’ nutritional composition.
The participants were given preprepared meals, with different proportions 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, was 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.”
Vallat and Walker also 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.
We sleep for about 1/3 of our lives: during this time many essential processes ensure that we can live the other 2/3.
What happens in our bodies during sleep is crucial for survival and not taking this into account can cost us a very high price.
Other co-authors of the paper are Sarah Berry, Paul Franks and Tim Spector of King’s College London; Neli Tsereteli of Lund University in Malmö, Sweden; Joan Capdevila, Haya Al Khatib and Jonathan Wolf of Zoe Ltd.; Ana Valdes of the University of Nottingham in the U.K.; and Linda Delahanty, David Drew and Andrew Chan of Massachusetts General Hospital and Harvard Medical School in Boston. The study was funded by Zoe Ltd. and the Department of Twin Studies at King College London.
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For more information
How people wake up is associated with previous night’s sleep together with physical activity and food intake (Nature Communications)
Center for Human Sleep Science
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