The circadian rhythm is our body’s natural 24-hour cycle that regulates sleep, alertness, hunger, and energy. Acting as an internal biological clock, it profoundly impacts performance, metabolism, and overall health.
When aligned, we feel awake during the day and sleepy at night. When disrupted, we experience fatigue, grogginess, and sleep disturbances.
Researchers like Dr. Satchin Panda have extensively studied circadian rhythms, emphasizing how light exposure, meal timing, and sleep patterns influence metabolic health and cognitive function.
A key regulator of this rhythm is cortisol, a hormone essential for energy mobilization. Studies show that cortisol patterns shape daily energy levels, focus, and brain function (Oster et al., 2016; O’Byrne et al., 2021; Korshunov et al., 2017).
In the following steps, you will be guided through an exercise to align your calendar and daily activities with your circadian rhythm.
To understand the impact of your circadian rhythm on daily performance, take a moment to reflect on your energy fluctuations throughout the day.
Exercise: Take a piece of paper and draw your daily rhythm:
Figure 1: A sample daily energy curve from waking up (left side) to going to bed (right side). Yours may look different.
Most individuals experience a peak in energy and focus in the morning, followed by a noticeable dip after lunch. Some may experience a second and even a third peak later in the afternoon or in the early evening. This pattern closely aligns with the natural rhythm of cortisol secretion, which spikes within 30–45 minutes after waking, remains elevated until midday, and then gradually declines. The post-lunch dip is often compounded by physiological processes, such as increased blood flow to the digestive system (Monk, 2005).
Most peoples’ daily energy curve aligns relatively well with their daily cortisol rhythm.
The fluctuation of cortisol levels influences energy levels, cognitive performance, and mood regulation. When cortisol levels are dysregulated - whether due to chronic stress, irregular sleep patterns, or misaligned work schedules—individuals may experience fatigue, difficulty concentrating, and impaired recovery.
Cortisol, is a steroid hormone produced by the adrenal glands, which plays a crucial role in regulating metabolism, immune response, and the body's stress adaptation mechanisms. It follows a distinct daily rhythm, peaking in the early morning to promote alertness and gradually tapering off throughout the day. Circadian cortisol rhythms have been measured based on 100.000+ saliva samples (Miller et al., 2016).
Your daily energy curve is not solely driven by cortisol. Other neurotransmitters, such as dopamine and serotonin, play a role as well. Yet, for sake of simplicity, we are focusing on cortisol when explaining daily energy rhythms here as it is likely the major contributor.