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Humanity’s first clock: Your sleep/wake cycle

Long before analog clocks were invented, each human body (and all other living things) has been regulated by its own internal clock. Our sleep/wake cycle, mental agility, appetite, body temperature, hormone production, and more all bow to the rule of a regular cycle, known as the circadian rhythm.

How the sleep/wake cycle works

Our body clocks adhere to a pretty consistent 24-hour cycle that aligns with the length of our days (although for some people, that cycle can be as long as 28 hours). Our circadian rhythms orchestrate the ebb and flow of alertness and drowsiness throughout the day.

This cycle is influenced by external cues, most notably light and darkness. When we see light—either daylight or blue light from screens—our eyes send signals to the brain, which suppresses the release of melatonin, a hormone that helps regulate sleep.

As the day begins, exposure to natural light suppresses melatonin production so we can wake up naturally. As evening approaches and light diminishes, melatonin levels rise, ushering in a sense of drowsiness and signaling to the body it’s time to settle down for the day and get ready for sleep.

Other factors affect the sleep/wake cycle, such as temperature, food, hormones, and even social interaction, but light has the biggest effect on how and when we sleep. Keeping this balance stable is crucial for helping us maintain overall good health, support energy levels, promote mental agility, and regulate appetite.

Larks and owls

While each of us has a body clock that tightly regulates our sleep/wake cycle, that clock is set a little differently for each of us. Some people are morning people—aka, the “larks”—while others are night people—aka, the “owls.” Morning larks are most energized in the mornings, while night owls are most active at night and tend to go to bed later.

Knowing your sleep chronotype, which is your body’s natural disposition to be awake or asleep at certain times, can help you manage your circadian rhythms and plan your days more effectively. Your chronotype can change over time too, so you may need to adjust your routine as you get older. If you’re not sure what your sleep chronotype is, take this quiz to find out!

What you can do to support a consistent sleep/wake cycle

In a world that never sleeps, sleep disruptions are common, from artificial lighting to irregular work schedules. So we may need to work a little harder these days to support our natural sleep rhythms, but it’s an achievable goal—one that’s definitely worth the effort.

Prioritize sleep hygiene. Good sleep doesn’t just happen. Your chances of a good night’s sleep greatly increase if you stick to a consistent sleep schedule, create a comfortable sleep environment, and take time to wind down or meditate each night before turning out the light.

Manage light exposure. Start your day with a burst of sunlight. Then, as the evening winds down, put your screens to rest an hour or two before you go to bed. Let your body follow the natural rhythms of the sun as much as possible.

Avoid eating before bed. It’s best to eliminate as many distractions as you can before bed, and this includes what you eat during the latter part of the day. A heavy meal right before bedtime can disrupt your sleep, and caffeine and alcohol too late in the day can keep you up far later than you want.

Exercise, but not too close to bedtime: Regular physical activity can help you sleep better at night, but try to save your intense workout for morning and mid-day. That being said, if exercise helps you relax, a short, leisurely walk or some stretches at night can help prepare you for some restful shut-eye.

For more best practices, see this post on essential tips for better sleep.


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