How to feel alert in the morning Original paper

In this study, higher self-reported alertness in the morning was partially predicted by being happier, older, sleeping better, eating fewer meals per day, and getting more physical activity the previous day. Eating a higher carbohydrate breakfast also seemed to increase morning alertness, at least in the short term.

This Study Summary was published on January 5, 2023.

Background

Upon waking from sleep, people experience a period of reduced cognitive performance and alertness, a phenomenon called “sleep inertia”.[1] Although sleep inertia is temporary, its duration is variable, ranging from minutes to hours. Therefore, many people experience reduced alertness for much of the morning, which can impair their ability to carry out important tasks during this period.

The study

This 2-week study was designed to investigate the factors that predict morning alertness. It involved two cohorts of 833 participants, one in the UK and one in the U.S. The UK cohort consisted of 749 people, including 340 monozygotic (identical) twins and 359 dizygotic (fraternal) twins. The U.S. cohort consisted of 84 people, none of whom were twins. The participants were 18–65 years old and were generally healthy, although participants were not excluded if they had a sleep disorder, circadian rhythm disorder, or cognitive disorder.

Every day during the study, the participants rated their morning alertness on a 100-point scale at several time points during the morning, averaging about 8 ratings per day. These data were used to assess the association between various factors and level of morning alertness.

The researchers assessed the following factors:

  • Happiness
  • Depression or anxiety diagnosis (past or present)
  • Age
  • Sleep quality, assessed using the Pittsburgh Sleep Quality Index
  • Meal frequency
  • Physical activity, assessed using an activity monitor
  • Sleep/wake patterns, assessed using an accelerometer
  • Blood sugar, assessed using a continuous glucose monitor

These factors were combined into a statistical model to assess whether and to what extent they predicted morning alertness.

Additionally, the researchers conducted an experiment to assess how different breakfasts of differing macronutrient compositions would affect alertness. On different mornings, participants were given several different breakfasts:

  • Standard meal: muffins, about 40% fat and 57% carbohydrates
  • High-carbohydrate meal: muffins, about 76% carbohydrates
  • High-fat meal: muffins, 63%–71% fat
  • High-fiber meal: muffins and fiber bars, 71% carbohydrates and 15 grams of fiber
  • High-protein meal: muffins and a milkshake, 57% carbohydrates and 33% protein

All meals contained about 500 calories, with the exception of the high-fiber meal, which contained 534 calories. On one morning, the participants were given an oral glucose tolerance test (OGTT), which consisted of 75 grams of glucose only and functionally served as a breakfast on that day.

The analyses were adjusted for several factors, including age, sex, BMI, twin status, sunrise time, and daylight saving time.

The results

The following factors were identified as predictors of morning alertness:

Mood: Higher levels of daily happiness were associated with higher morning alertness. However, a past or current diagnosis of depression or anxiety was associated with lower morning alertness.

Age: Older age was associated with higher morning alertness.

Sleep: Better sleep quality was associated with higher next-day morning alertness. Additionally, sleep offset (sleeping later than usual), but not sleep onset (going to sleep earlier than usual), was associated with higher next-day morning alertness.

Meal frequency: Morning alertness was lower among participants who reported eating more meals per day (at least 5 meals per day) compared to participants who reported eating fewer meals per day (either 1–2 or 3–4 meals per day).

Physical activity: More physical activity was associated with higher next-day morning alertness. More nighttime physical activity, however, was associated with lower next-day morning alertness.

Breakfast: Compared to the standard meal (mixed macronutrient composition), the high-carbohydrate breakfast (but not the high-carbohydrate, high-fiber breakfast) increased morning alertness, and the high-protein breakfast decreased morning alertness. Compared to all breakfasts, alertness was lower following the OGTT. For all breakfasts, a higher glucose response at 2 hours after breakfast was associated with reduced morning alertness.

Note

This study did not investigate light exposure, a potentially important confounding variable.

The big picture

Ingrained in all humans is a circadian rhythm, a process involving fluctuations in various physiological processes throughout the day.[2][3] Notably, the circadian rhythm regulates the sleep/wake cycle, which stimulates wakefulness during daytime and promotes sleep at night.

Beyond the sleep/wake cycle, the circadian rhythm influences an extensive number of other biological systems, resulting in daily fluctuations in blood pressure,[4] body temperature,[5] bowel movements,[6] muscle strength,[7] levels of various hormones,[8] hunger,[9] and macronutrient metabolism.[10][11] Although some variability is common, the general timing of some of these circadian rhythms is depicted in the graphic below.

How the circadian rhythm influences certain aspects of human biology

Adapted from: Masri and Sassone-Corsi., 2018,[12] Smith and Betts 2022,[9] Serin and Tek 2019,[13] and Poggiogalle et al. 2018.[14]

Although the circadian rhythm is an ingrained biological system, it can be influenced by various cues. These cues are often called zeitgebers, from the German for “time givers”.

Of the zeitgebers, the most important is probably light exposure.[15] When light, especially blue light, enters the eyes, a signal is sent to the pineal gland, which blocks melatonin synthesis. Conversely, a lack of light entering the eyes allows the pineal gland to produce melatonin. Melatonin is an important regulator of the circadian rhythm; its presence promoting sleep and its absence promotes wakefulness. As a result, when a person gets significant exposure to light during the day and minimal exposure to light during the night, the resulting effect is such that nighttime sleep and daytime alertness are promoted.[16][17][18][19][20]

Beyond light, there are several other factors that seem to affect the circadian rhythm, possibly explaining some of the findings of the current study. One commonly cited (although sometimes disputed) zeitgeber is food.[21] In general, eating food with calories is thought to stimulate the circadian rhythm in a similar manner as light, with some researchers suggesting that eating more during the morning and less at night can help entrain the circadian rhythm in a manner conducive to better health and wellbeing.

The current study tested the effect of different meal compositions (rather than meal timing) on morning alertness, finding that a high-carbohydrate breakfast (three muffins) resulted in the highest alertness and a high-protein meal (two muffins and a protein shake) resulted in the lowest alertness. Unfortunately, there is limited data available regarding the type of carbohydrates, protein, or fat making up the various meals, so it’s difficult to draw definitive statements from the findings. Similarly, it’s difficult to determine whether this finding would apply to any number of other possible meals and foods (beyond muffins and protein shakes) that a person might eat for breakfast. Also, because the current study was testing acute (postmeal) effects, it was too short to detect any potential long-term effects of these meals on alertness.

Only a few other studies have investigated how different macronutrient ratios affect energy levels and alertness, with findings somewhat divergent from the current one. In a clinical trial involving 21 healthy men, alertness was similar following a breakfast drink that was either high in protein (from whey protein) or high in carbohydrate (from glucose).[22] In another clinical trial involving 14 people, alertness was highest following a high-carbohydrate/high-fiber cereal compared to either a high-carbohydrate/low-fiber cereal, bacon and eggs, or a croissant with margarine and jam.[23] Ultimately, more research is needed to determine how different types of breakfast affect morning alertness.

Another potential zeitgeber is exercise.[24] In the current study, more physical activity the previous day was associated with higher morning alertness, which could be a result of exercise helping to synchronize the circadian rhythm. Conversely, the study found that physical activity during nighttime was associated with less morning alertness the next day. This is consistent with existing research indicating that, as with light, exercise can entrain the circadian rhythm depending on when it is performed.[24] However, a number of studies have reported no apparent negative effect of evening exercise on sleep or cognitive function.[25][26][27] It’s possible that, in the current study, evening physical activity was just a marker of people having a later chronotype — so-called “night owls” — who tend to have lower levels of alertness in the morning, independent of exercise.[28]

The current study found that happiness was associated with greater alertness and that a past or current diagnosis of depression or anxiety was associated with less alertness. This finding could be related to the fact that a disrupted circadian rhythm can also adversely affect mood. A clear example of this is seasonal affective disorder (SAD), a type of depression accompanying seasonal changes, which is believed to be at least partly the result of less sunlight availability disrupting a person’s circadian rhythm.[29] The link between mood and alertness might be explained by other factors as well, including higher inflammatory signaling promoting both worse mood and fatigue.[30]

Finally, sleep quality was associated with high morning alertness, a finding consistent with an extensive body of research and likely consistent with many people’s lived experiences.[31][32][33][34]

Sleeping in later than usual, as well as going to sleep earlier than usual, was associated with higher next-day morning alertness, independent of total sleep time. One theoretical possibility is that this could be related to the circadian rhythm of sleep cycles, with more rapid eye movement (REM) sleep occurring later during sleep, meaning that sleeping in increases the time spent in REM.[35] Because REM sleep appears to prime the body for wakefulness, it could result in greater alertness upon waking from this sleep stage.[36]

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This Study Summary was published on January 5, 2023.

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