More than 60% of Americans rarely feel rested or energized during the morning, and about 42% start feeling tired as early as noon. Daytime tiredness is an increasingly growing problem across the world, which isn’t normal at all. Humans are a diurnal species — we’re not bats, for crying out loud.
Poor daytime alertness isn’t only a mood killer, it can literally kill. Thousands of people die every year due to road traffic and occupational accidents caused by a lack of alertness. Economically speaking, impaired daytime alertness causes a massive loss in productivity quantified to nearly $411 billion in the U.S. alone, or roughly 2% of the nation’s GDP.
Despite the huge cost of lack of alertness, research into the unique factors that influence how each of us wakes up is lacking. Raphael Vallat from the University of California, Berkeley, and colleagues sought to fill this gap by embarking on an unprecedented study of 833 twins and unrelated adults to untangle the main factors that separate people who wake up feeling great from those that feel groggy and miserable first thing in the morning.
By including many pairs of twins in the study, the researchers could hone in on any genetic factors that might influence daytime alertness. The good news is that there were no such genetic factors, meaning anyone can dramatically change how well they wake up each morning by making lifestyle changes.
Rather than genetics, the authors found that morning alertness is tied to four main factors: sleep quantity/quality the night before, physical activity the day prior, a breakfast rich in carbohydrates, and a lower blood glucose response following breakfast.
Morning alertness is not fixed by genetics. Look to your lifestyle instead
During the course of the two weeks that the study ran, each participant had to eat different standardized breakfast meals with different nutritional compositions. For all of this time, they also had to wear wristwatches equipped with an accelerometer for tracking physical activity and sleep/wake detection, as well as a continuous glucose monitor. Participants recorded their food intake on a dedicated app designed specifically for this study, which also prompted users to rate their alertness levels on a scale from 1 to 100 at several time points throughout the day, starting with the morning just before breakfast.
After the researchers analyzed the data from the study, the first thing they noticed was how alertness was tied to sleeping patterns. Across the board, sleeping longer than one’s typical sleep duration was associated with significantly higher next-morning alertness. That’s not at all surprising, but a more interesting finding has to do with sleep offset. The researchers found that waking up later than one’s typical wake-up time was associated with higher daytime alertness even when the scientists controlled for sleep duration. Likewise, going to bed later than usual was associated with higher morning alertness.
“Sleep efficiency did not significantly predict morning alertness. Taken together, this first set of data demonstrates that sleeping longer and/or later than typical is associated with higher next-morning alertness,” the authors wrote in their study published in Nature.
The amount of physical activity during the prior day was directly correlated with morning alertness the following day. However, physical activity in the nighttime predicted worse next-day morning alertness.
Concerning diet, the researchers found that the high-carb breakfast meal, such as three muffins, was associated with a higher morning alertness relative to other meals consisting of a medium amount of fat and carbohydrates. By contrast, the high-protein meal (two muffins and a milkshake) was associated with the lowest alertness compared to the reference meal. The strongest next-morning alertness, however, was reported during the days that participants consumed pure glucose liquid for breakfast. Including breakfast caffeine intake did not change the significance of the other predictors, the researchers found.
The data from the glucose monitors showed that post-breakfast glucose levels were uniquely associated with subsequent morning alertness. A lower post-breakfast glycemic load predicted higher alertness.
“As a collective, analyses of this first component of the study demonstrate that morning alertness was significantly, and independently so, associated with the factors of (1) sleep (specifically a longer sleep duration, the offset timing of a later morning awakening and lower levels of movement during the night), (2) physical activity (increased activity on the previous day), (3) breakfast composition (high carbohydrates meal), and (4) post-breakfast blood glucose response (lower glycemic load),” the researchers found.
The researchers didn’t stop there and sought to also investigate what explains variance in daily morning alertness at an individual level. The findings suggest that between-individual variability in levels of alertness is best predicted by four key factors: mood, age, sleep, and eating frequency.
The happier a person felt during a week and the older they were, the higher their inherent levels of alertness turned out to be. Conversely, those who suffer from mood disorders, such as depression or anxiety, had lower levels of alertness.
Concerning food intake, those who ate only 1-2 times a day reported higher morning alertness than those consuming 3-4 times, who in turn reported higher alertness than those eating more than five times a day.
Many of the participants consisted of pairs of either identical or fraternal twins, which provided a baseline upon which the researchers could test the influence of genetics on alertness and sleep inertia. Identical twins share virtually all their germline DNA sequences whereas fraternal twins share about 50% of their inherited genetic material. Therefore, the degree to which monozygotic siblings have a higher correlation for a specific trait than fraternal siblings reflects the extent of genetic influence on this trait. But after adjusting for age and sex, the researchers could find no meaningful relationship between genetic inheritance and next-morning alertness, which was instead predicted by the four main factors outlined earlier.
“More broadly, our results reveal a set of key factors associated with alertness that are, for the most part, not fixed. Instead, the majority of factors associated with alertness are modifiable, and therefore permissive to behavioral intervention. Such findings may help inform public health recommendations towards reducing the non-trivial mortality, financial and societal burden caused by insufficient alertness,” the authors concluded.
