- Individuals tend to experience different levels of alertness from one day to another, while also differing from other individuals in their average daily alertness levels.
- A recent longitudinal study suggests that the prior night’s sleep profile, physical activity during the previous day, and the nutritional composition of breakfast were linked to the daily variation in a person’s morning alertness levels.
- The study also found that non-genetic factors, including mood, sleep quality, age, and daily food intake frequency, predicted differences in morning alertness among individuals.
- The study reported a modest effect of genetic factors on daily alertness, suggesting that interventions to modify non-genetic factors could help improve daily alertness levels.
Impaired alertness immediately after waking and over the course of the day can adversely 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 larger 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 alleviate the negative consequences associated with impaired alertness.
Impaired alertness and risk factors
Sleep inertia refers to the phase of impaired alertness and performance that occurs between sleep and wakefulness, and it can last between a few minutes to several hours after waking up.
Although it 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 decision-making by emergency service personnel, including healthcare workers and firefighters, which can influence the safety of others.
Likewise, reduced alertness over the course of the day due to inadequate sleep is associated with lower productivity and an increased risk of traffic accidents.
However, there is limited scientific evidence on the factors that influence the levels of alertness after waking up.
In the present study, the researchers assessed the factors associated with daily variation in morning alertness in the same individual.
They also examined the role of genetic versus non-genetic factors in influencing differences in average morning alertness levels among individuals.
Sleep duration and physical activity
The researchers first examined the impact of four prespecifiedfactors on the day-to-day variation in alertness observed within the same individual.
They assessed the impact of the previous night’s sleep profile, physical activity on the previous day, the nutritional composition of breakfast, and post-breakfast blood sugar levels on morning alertness. Participants recorded their dietary intake and alertness on the ZOE study app, through the study. The study was funded by ZOE Ltd.
To examine the impact of these factors, the researchers used data collected over a 2-week period from 833 individuals aged 18–65 years. The participants had to wear a wristwatch accelerometer throughout the entire study period to facilitate the collection of data on their sleep profile and physical activity levels.
For the evaluation of morning alertness levels, the participants recorded the levels of their alertness on an app on a scale of 0–100. They reported their first alertness rating at the start of breakfast and then intermittently over the subsequent 3 hours.
Based on each participant’s baseline sleeping profile, the researchers found an association between sleep duration and sleep timing with morning alertness levels.
Specifically, when a participant slept longer than usual or woke up later than their usual time, they were more likely to show higher levels of alertness the next morning.
Higher levels of physical activity during the previous day were also associated with increased morning alertness.
Only physical activity levels during the 10 most active hours of the previous day were positively correlated with morning alertness levels.
Conversely, physical activity during the nighttime was associated with lower morning alertness.
Morning meals and nutrition
The researchers then examined the impact of the macronutrient composition of breakfast on morning alertness. They provided calorie-matched standardized breakfasts of varying nutritional compositions, including high carbohydrate, high protein, and high fiber meals to each participant, which were consumed on different days.
The researchers compared the participants’ alertness levels after the consumption of each of these meals with that after a reference meal that provided moderate levels of carbohydrates and proteins.
Among the different standardized meals provided to the participants, consumption of a high carbohydrate breakfast was associated with higher levels of morning alertness than the reference meal.
In contrast, the high protein breakfast was linked to lower alertness levels than the reference meal.
The researchers also examined how the changes in blood glucose (sugar) levels after the consumption of breakfast influenced morning alertness levels.
Independent of breakfast composition, a lower blood glycemic load, a measure of the impact of food intake on blood glucose levels, after breakfast was associated with greater morning alertness.
Notably, these four factors influenced morning alertness levels independently of each other.
Jeff Kahn, CEO and co-founder of energy and sleep tracker subscription app Rise Science, who was not involved in this study, commented on the findings, telling Medical News Today that:
“The study helps to show that positive health and wellbeing outcomes, in this case, greater alertness, can be achieved through a variety of levers. The four independently impactful inputs they cite — longer than normal sleep duration, prior daytime exercise, carb-rich but still macronutrient-diverse breakfast composition, and a lower glycemic response in the hours following breakfast consumption are discrete tools in our performance toolbox that we can use and benefit from, even if we’re unable to achieve all four at all times.”
Differences between individuals
While these factors explained the day-to-day differences in morning alertness within the same individual, the authors were also interested in factors that could explain why certain participants had higher average alertness levels than others.
To put it differently, the researchers were interested in genetic and/ or lifestyle factors that could influence an individual’s characteristic or average daytime alertness levels.
The researchers found that positive mood, older age, lower frequency of eating during the day, and better sleep quality were predictors of an individual’s average daily alertness levels.
The present study consisted of both twins and genetically unrelated adults. This allowed the researchers to examine the extent to which genetic factors could influence daily alertness levels in twins.
The researchers found that genetic factors had a small impact on an individual’s alertness levels, suggesting a more significant impact of lifestyle factors that are amenable to modification.
Dr. Andrew McHill, a sleep researcher at Oregon Health & Science University, not involved in this study, commented that “[u]nique to this current study is the wide-ranging predictors that were collected — sleep, diet, and activity — and the ability to tease apart these behaviors versus genetic influences by use of the twin study.”
“Using this type of analysis allows for a more accurate assessment of potentially modifiable behaviors to improve next-day alertness. This is not only exciting for potential individual and society targets to improve safety and health, but also for the research community as it provides further testable hypotheses for future examinations to identify what exact mechanisms are causing these observed changes in alertness,” he added.
The researchers acknowledged that their study had a few limitations. For instance, the morning alertness levels in the study were based on self-reports and could be susceptible to bias.
The study also did not account for differences in light exposure during the morning, a factor known to significantly enhance alertness.
The researchers further noted that all standardized breakfasts consisted of carbohydrates, protein, and fat and only varied in the levels of these macronutrients.
They cautioned that these results should not be taken at face value and lead to the adoption of meals composed only of carbohydrates for breakfast.
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