Individuals tend to experience different levels of alertness from day to day, while also distinguishing themselves from other individuals by their average daily level of alertness.
A recent longitudinal study suggests that the previous night’s sleep pattern, the previous day’s physical activity, and the nutritional composition of breakfast are related to daily variation in a person’s morning alertness levels. The study also found that non-genetic factors, including mood, sleep quality, age and frequency of daily food intake, predicted differences in morning alertness between individuals. The study reports a modest effect of genetic factors on daily alertness, suggesting that interventions to modify non-genetic factors could help improve levels of daily alertness.

Impaired alertness immediately upon waking and throughout the day can negatively impact cognitive and motor performance and increase safety risks. A recent study published in Nature Communications suggests that various modifiable lifestyle factors, such as sleep quality and duration, may have a greater impact on morning alertness levels than genetic factors. These results suggest that interventions undertaken at the individual and societal level targeting these non-genetic factors could help to mitigate the negative consequences associated with reduced alertness.

Impaired alertness and risk factors

Sleep inertia refers to the phase of impaired alertness and performance that occurs between sleep and wakefulness, and which can last from a few minutes to several hours after waking. Although this is a common phenomenon, it can have a profound impact on the productivity and safety of individuals. Specifically, sleep inertia can impact the safety of workers in hazardous occupations or impair the decision-making of emergency service personnel, including caregivers and firefighters, which can impact safety. others.

Similarly, reduced vigilance during the day due to insufficient sleep is associated with lower productivity and an increased risk of road accidents. However, there is little scientific evidence on the factors that influence alertness levels after waking. In the present study, the researchers evaluated the factors associated with daily variation in morning alertness in the same individual. They also looked at the role of genetic and non-genetic factors in influencing differences in average morning alertness levels between individuals.

Sleep duration and physical activity

The researchers first examined the impact of four pre-specified factors on the daily variation in alertness observed in the same individual. They assessed the impact of the previous night’s sleep pattern, previous night’s physical activity, breakfast nutritional composition, and post-breakfast blood glucose levels on morning alertness. Participants recorded their food intake and alertness on an app.

To examine the impact of these factors, the researchers used data collected over a two-week period from 833 people between the ages of 18 and 65. Participants were required to wear a wristwatch accelerometer throughout the study to help collect data on their sleep profile and physical activity level. For the assessment of morning alertness levels, participants recorded the levels of their alertness on an app on a scale of 0 to 100. They reported their alertness rating first at the start of breakfast and then intermittently during the next three hours. Based on each participant’s baseline sleep profile, the researchers found an association between sleep duration and timing and morning alertness levels. Specifically, when a participant slept longer than usual or woke up later than usual, they were more likely to exhibit higher levels of alertness the next morning.

Higher levels of physical activity during the previous day were also associated with increased alertness in the morning. Only physical activity levels during the 10 most active hours of the previous day were positively correlated with morning alertness levels. Conversely, physical activity performed at night was associated with lower morning alertness.

Morning meal and nutrition

The researchers then looked at the impact of the macronutrient composition of breakfast on morning alertness. They provided each participant with standardized breakfasts matched in calories and nutritional composition, including meals high in carbohydrates, protein and fiber, which were eaten on different days. The researchers compared the participants’ alertness levels after consuming each of these meals with those of a reference meal containing moderate levels of carbohydrates and protein. Among the various standardized meals offered to participants, consumption of a carbohydrate-rich breakfast was associated with higher levels of morning alertness than the reference meal. In contrast, the high-protein breakfast was linked to lower levels of alertness than the benchmark meal. The researchers also looked at the influence of changes in blood glucose (blood sugar levels) after breakfast consumption on levels of morning alertness.

Regardless of breakfast composition, lower blood glycemic load, a measure of the impact of food intake on blood sugar, after breakfast was associated with greater morning alertness. In particular, these four factors influenced morning alertness levels independently of each other.

Differences between individuals

If these factors explain the daily differences in morning alertness in the same individual, the authors also looked at factors that could explain why some participants had higher average levels of alertness than others.

In other words, the researchers looked at genetic and/or lifestyle factors that might influence an individual’s characteristic or average levels of daytime alertness. The researchers found that positive mood, older age, less frequent meals during the day, and better quality of sleep were predictors of an individual’s average daily alertness levels.
The current study involved both twins and genetically unrelated adults. This allowed the researchers to examine the extent to which genetic factors could influence daily alertness levels in the twins. The researchers found that genetic factors had only a small impact on an individual’s alertness levels, suggesting a greater impact from lifestyle factors that can be changed.

This study allows a more precise evaluation of potentially modifiable behaviors to improve alertness the next day. This is not only exciting for potential targets of individuals and society to improve safety and health, but also for the research community as it provides further testable hypotheses for future examination to identify exact mechanisms that cause these observed changes in alertness.

Study limitations

The researchers acknowledged that their study had some limitations. For example, morning alertness levels in the study were based on self-reports and may be biased. The study also did not take into account differences in light exposure during the morning, a factor known to significantly improve alertness. The researchers also noted that all of the standardized breakfasts were made up of carbohydrates, proteins, and fats, and only the levels of these macronutrients varied. They cautioned that these findings should not be taken at face value and lead to the adoption of carb-only meals for breakfast.

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