Why Your Sleep-Wake Cycle Is the Key to Daily Energy

Like many people, you probably do your best to wake up early enough to be on time for work or school and try to avoid missing out on sleep by staying up too late. But beyond that, you might not give much thought to the exact time you get up in the morning or go to bed at night. But did you know the timing of your sleep-wake cycle — where it falls in your 24-hour day — can influence your energy levels?

The sleep-wake cycle is a predictable, repeating pattern, and it is part of the body’s internal clock, or circadian rhythm. When you understand your circadian rhythm, you can aim to match your schedule to its predictable and consistent sleep patterns and wake patterns — resulting in you having the energy your body needs. And when you have the energy you need, you’ll feel and perform your best.

In this article, we’ll discuss the sleep-wake cycle as it relates to your circadian rhythm and your sleep need as well as give you some recommendations on how to improve your sleep hygiene for better sleep and energy outcomes.  

What Is the Sleep-Wake Cycle?

Your sleep-wake cycle is simply your sleep pattern and wake pattern over a roughly 24-hour period. The timing of your sleep-wake cycle is unique to you, and it’s dictated by the two laws of sleep: sleep homeostasis and circadian rhythm.

While these two laws work independently of each other, they are interrelated. Both of them point you toward your ideal sleep schedule and wake schedule.

Sleep homeostasis, the first law of sleep, might sound like a complicated science term, but it really just means getting the sleep your body needs. Your sleep need is determined by genetics, so everyone won’t need the same amount of sleep. While your best friend may need 8 hours of sleep each night, you may need 8.5.

When you don’t get the sleep you need, you accumulate sleep debt. This is the amount of sleep you’ve owed your body over the past 14 days.

Your circadian rhythm is the second law of sleep. It’s your body’s internal clock that tells it when to be active and inactive over a roughly 24-hour cycle. This internal clock not only tells your body when to go to sleep and when to wake up, but it’s also responsible for predictable peaks and dips in energy throughout the day.

But this isn’t the only circadian game in town. Your body has other circadian rhythms that regulate things like appetite/eating habits, energy fluctuations, mood changes, hormone production and secretion, and almost every bodily function. Think of them as a network of clocks distributed across your organ systems and cells. But running the whole show is a master clock located in the brain.

How Light Rules Your Master Clock

In the brain’s hypothalamus, there’s a special group of neurons that serves as an information hub. Collectively referred to as the suprachiasmatic nucleus (SCN), it is attuned to the roughly 24-hour period of changing light we experience each day.

Although there are other factors at play, sunlight is the most important external influence on the SCN. When the eye’s optic nerve senses light — or the lack thereof — the SCN alerts the rest of the body’s clocks by releasing specific chemical signals at different times of day. 

Let’s look at how light affects your sleep-wake rhythm:

• Morning: When it senses daylight, the SCN releases cortisol, norepinephrine, and serotonin, which increase feelings of wakefulness and alertness. 
• Afternoon: As the day goes on, a naturally occurring compound called adenosine begins to accumulate in the brain, causing feelings of sleepiness. The first strong dip in energy usually falls somewhere between 1 p.m. and 4 p.m -- the exact time for you will depend on your unique circadian rhythm. Use the RISE app to know exactly when this is for you.. You may know it as your afternoon slump; on the RISE app’s Energy screen, we call it your afternoon dip. It’s the ideal time to take a nap, fit in a little exercise, or catch up on errands or administrative tasks.
• Nighttime: In the evening when the sunlight fades, the SCN prompts the pineal gland in the brain to secrete melatonin, a hormone that preps the body for sleep. At night, core body temperature (primarily regulated by the endogenous circadian pacemaker located in the SCN) begins to drop. Body temperature is one of the most reliable markers of circadian functioning, and it appears to be one of the primary signals used by the SCN to oversee the rest of the body’s clocks. 

Sleep-Wake Cycle Disruption and Effects

So if genetics and biological clocks are in charge of our sleep-wake cycle, we should all be getting the sleep we need and be able to perform and feel our best during the day, right? Not quite. There are factors that can disrupt your sleep-wake cycle — resulting in circadian misalignment and sleep debt.

Irregular sleep from social jetlag, travel jetlag, shift work, and sleep procrastination can all disrupt your circadian rhythm. It’s also possible to experience circadian misalignment from your daily and nightly habits, such as drinking caffeine too late in the day, exposing yourself to blue light at night, or working out too close to your bedtime.

Not only can circadian misalignment lead to insomnia and other sleep problems, it’s also associated with poor mental health and mood disorders, changes in metabolic function, and an increased risk of conditions such as diabetes and cancer.

The best way to avoid these negative effects — and in turn feel and perform your best — is to keep your sleep debt low and align your schedule with your circadian rhythm, especially when it comes to your bedtime and wake time. How do you achieve this? By improving your sleep hygiene.

Improve Your Sleep Hygiene

Sleep hygiene is the upkeep of daytime and nighttime behaviors that influence the way you sleep. With a few simple tweaks to your daily and nightly habits, you can optimize your sleep-wake cycle for better circadian alignment and less sleep debt. Here are a few simple steps you can take to improve your sleep hygiene:

• Get some sun soon after waking to send a signal to your brain that the day has begun. 
• Exercise daily; it can help you get the sleep you need at night. 
• Avoid excess alcohol and caffeine, both known sleep disruptors, especially in the later afternoon or evening. (The RISE app can remind you of these cutoff times.)
• To avoid disrupting your body’s natural melatonin production, try to limit light exposure after dark, especially bright light and blue light. (Or wear blue-light blocking glasses.)
• Try to stick to a consistent bedtime and wake time, as a regular sleep schedule can help with circadian alignment. 

It is crucial to make lighting and timing a central part of implementing these habits, because sleep hygiene recommendations that aren't paired to your circadian rhythm aren't nearly as effective as they could be. Sleep cannot be understood nor improved without knowledge of your circadian rhythm. Using it as a guide is the best way to optimize your sleep-wake schedule to give your body the sleep and energy it needs.

If your sleep hygiene is on point, but you’re consistently having trouble getting to sleep or waking up, consult a sleep medicine specialist. They may want to run tests to screen for or rule out a clinical sleep disorder, such as circadian rhythm sleep disorder, sleep wake disorder, sleep phase disorder, sleep apnea, or narcolepsy.

Go to Sleep and Rise at the Right Time

It’s hard to overstate the importance of being consistent with your sleep schedule and strategic about the timing of your light exposure. Thinking about your sleep-wake cycle within the context of the Two Laws of Sleep is the best way to design a schedule that will help you get the sleep you need — while avoiding the health issues associated with circadian misalignment.

It’s also important to note that the timing of your sleep-wake cycle is unique to you and can change from day to day based on all sorts of external inputs. A tool like the RISE app, which knows your biology and analyzes sleep data from your phone, can help you get on a better sleep schedule that aligns with your circadian rhythm and gives you optimal energy during the day.