A prospective two-week study of twins and genetically-unrelated adults showed that how effectively an individual wakes up and regains alertness after a night’s sleep is determined by how well the person slept and the level of physical activity the previous day rather than by genetics. Having a breakfast rich in carbohydrates and a lower blood glucose response after breakfast also helps. Individual daily alertness set-point was related to the quantity of sleep, emotional state, and age. The study was published in Nature Communications.
Inability to maintain adequate levels of wakefulness through the day is a major cause of road traffic and occupational accidents. Impaired daytime alertness, often associated with insufficient sleep, is related to loss of productivity at work, absence from work, and greater use of healthcare services.
The inability to transition effectively to a state of cognitive alertness after awakening is known as “sleep inertia.” It is a serious safety risk for people performing hazardous tasks immediately after awakening, such as firefighters, pilots, military personnel, or healthcare workers, that can lead to injury or even death. However, factors determining effectiveness in regaining alertness after sleep and maintaining it throughout the day are not understood sufficiently.
“Every day, millions of individuals across the world struggle to wake up and feel fully alert in the morning — and, as a new parent, I can relate,” said study author Raphael Vallat (@RaphaelVallat), a postdoctoral researcher at the Center for Human Sleep Science at UC Berkeley.
“Battling sleepiness throughout the morning is not only unpleasant, it costs nations billions of dollars through loss of productivity, increased health care utilization and work absenteeism. Even more important, it costs human lives — from morning car crashes to work-related accidents. As scientists, it is therefore critical that we understand how to help society wake up better.”
To study effects of some of the factors that might affect the effectiveness in regaining alertness after sleep, Vallat and his colleagues analyzed data from The Personalized Responses to Dietary Composition Trial (PREDICT1), “a two country (UK, US) longitudinal study whose primary goal is to predict metabolic response to foods based on individuals characteristics.” They analyzed data from 833 twins and genetically-unrelated people.
Participants visited the researchers’ clinic at the start of the study and this was followed by a two-week at-home phase of the study. During this phase, they “consumed multiple standardized test meals differing in macronutrient composition, while wearing an accelerometer wristwatch and a continuous glucose monitor. The former was used to determine sleep/wake activity during the night and physical activity during the day. The continuous glucose monitor was used to measure postprandial (postprandial means after a meal) glucose response. Participants also recorded their dietary intake, satiety, mood, and exercise on the study app throughout the study,” the study authors explained. The meals were breakfast.
Participants also used an app to report their alertness level on a 0-100 scale at breakfast and at half-hour intervals in the 3 hours after. Participants were instructed to avoid any snacks or physical activity during this period. On average, participants ate breakfast at 8:12 AM, which was 1 hours and 8 minutes after waking, although there were substantial individual variations.
“How alert you feel each morning in the hours following awakening is not predetermined — it is not strongly genetic,” Vallat told PsyPost. “Instead, we have discovered that there are a set of specific factors that are very much under your control (unlike genes), which determine how efficiently you return to consciousness each day, and then maintain that alert concentration.”
For example, greater alertness was associated with doing more physical activity the day before. “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.
Nights when participants slept longer than usual and those when they woke up later than usual resulted in higher degrees of alertness in the following morning. The researchers explained this through bodily circadian rhythms and longer sleep providing a better chance for REM phases as both of these are known to reduce sleep inertia.
When individuals consumed a breakfast meal consisting of a higher amount of carbohydrates with limited sugar (compared to a standard breakfast with 40% of calories from fat, 50% from carbohydrates, and 10% from protein), they experienced higher levels of alertness after that. A high protein breakfast, on the other hand, resulted in diminished level of alertness following sleep compared to the standard breakfast.
“Beyond day-to-day fluctuations in alertness within an individual, we also found that there are large differences in baseline levels of morning alertness across participants,” Vallat said. “Interestingly, older individuals felt on average more alert than younger individuals. This was an interesting finding, which might be related to another strong relationship we found in this study, that of happiness and alertness. The happier you are, the more alert you feel, on average.”
“It is a well-known observation that older adults are happier than younger adults. In more scientific terms, there is a shift from negativity bias in younger age to positive thinking later in life, something referred to as the positivity effect. This is also why (healthy) older adults consistently rate their sleep quality higher than healthy young adults, even though they objectively sleep far worse than the latter.”
The study reveals important non-genetic, modifiable factors associated with daily alertness levels. However, it also has certain limitations. Notably, alertness was measured subjectively, through self-report measures and authors did not screen for sleep-disordered breathing. There could have been participants with sleep apnea and this could have influenced the results. Additionally, the study did not use sleep logs and light levels in the first hours of the morning were not measured.
“A noteworthy limitation of this study is that we did not measure light exposure,” Vallat said. “It is known that bright light exposure (e.g. natural sunlight) in the morning can give an energy boost, as well as improving subsequent sleep, and may thus represent another important modifiable factor which was not tested here.
“We hope that our findings may help inform public health recommendations to optimize alertness,” the researcher added. “This may be especially important in the context of education, where alertness is essential for effective knowledge acquisition in the classroom. Here, our results suggest that delaying school times and avoiding high-glycemic-response breakfast may lead to optimal alertness throughout the morning.”
The study, “How people wake up is associated with previous night’s sleep together with physical activity and food intake”, was authored 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. Walke.