Wakefulness may be driven by three key factors

A study has found a correlation between morning alertness and how people slept and moved the day prior, and what they had for breakfast.

“[Our] analyses revealed that three key factors significantly and independently predict how an individual awakens with alertness: 1) their prior sleep history, 2) levels of physical activity the day prior, and 3) what they first eat in the morning,” said the researchers.

 

Sleep history

Sleeping longer than one’s usual sleep duration was associated with higher next-morning alertness, as was waking up later than one’s usual wakeup time (after adjusting for sleep duration) and sleeping later than usual (p<0.001 for all). [Nat Commun 2022;13:7116]

“Sleeping later in the morning means that an individual is more likely to wake up farther away from their circadian nadir, shifting toward the circadian assent. Second, sleeping later will increase the likelihood of obtaining more (or even awaken from) REM* sleep,” the researchers explained.

These two factors have been associated with reduced sleep inertia, which is the inability to effectively transition to a state of functional cognitive alertness upon waking up. [Nat Sci Sleep 2019;11:155-165; Neuroimage 2019;184:266-278] “[Sleep inertia] is a serious safety risk for workers** performing hazardous tasks immediately upon awakening,” they noted.

The third potential underlying mechanism that could explain for the independent benefit of longer sleep involves the effective discharge of sleep pressure upon awakening. “[D]ischarging the sleep homeostat … is one of the most reliable predictors of diminished sleep inertia,” they said. “[Sleeping longer than] one’s own typical sleep amount may allow a fuller discharge of sleep pressure during the night, resulting in higher morning alertness from one day to the next.”

 

Previous day’s physical activity

The average acceleration value of the most active 10 hours of the previous daytime prior was associated with higher alertness (p=0.049). Conversely, night-time activity level was associated with worse next-day morning alertness (p=0.004). Hence, higher levels of daytime physical activity and lower levels of night-time movement predicted superior morning alertness.

 

Breakfast composition

Compared with a reference meal containing a medium amount of fats and carbs, consumption of a breakfast rich in carbohydrates was associated with higher morning alertness (p=0.002) but consuming a pure glucose liquid for breakfast (ie, OGTT***) was tied to marked reductions in subsequent alertness (p<0.001).

The high-carb breakfast also contained protein, fat, and fibre, which could have influenced the true synergistic effect of the meal on subsequent alertness. It also contained sucrose and had more calories. Whereas for OGTT, it was purely a carb and only contained glucose. Its lower calorie content could have led to a caloric deficit that could subsequently lead to post-consumption hunger and reduced levels of general alertness. [Nat Metab 2021;3:523-529]

The sedative effect associated with OGTT may have also been due to a surge in serotonin synthesis and brain-available tryptophan which has been tied to impaired alertness, and a surge in blood glucose levels that could inhibit wake-promoting hypothalamic neurons. [Neurosci Biobehav Rev 2019;101:45-67; Pflugers Arch 2007;454:19-27]

The findings associated with breakfast composition could be relevant in the context of education, given the growing trend of sugar-sweetened beverage intake among teens and young adults. “[This would] increase sleepiness in morning classes,” the researchers noted.

 

Productivity loss, occupational hazard

During the 2 weeks of the study, 833 participants (mean age 46.2 years, 72 percent female) consumed standardized breakfast meals with varying nutritional compositions. They were instructed to wear physical activity and continuous glucose monitors and to record their food intake and alertness on a dedicated study app.

Inadequate sleep leading to impaired daytime alertness could lead to loss of productivity and absenteeism at work and is a major causal factor of occupational accidents. [aaafoundation.org/prevalence-motor-vehicle-crashes-involving-drowsy-drivers-united-states-2009-2013, accessed January 28, 2023; Rand Health Q 2017;6:11; Postgrad Med 2009;121:86-95]

“[The] findings may help inform public health recommendations towards reducing the non-trivial mortality and financial and societal burden caused by insufficient alertness,” the researchers concluded.