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What Are Circadian Rhythms and How Do They Affect Sleep?

by BetterSleep
Sep 3 • 3 min read

Circadian rhythms are essential to many aspects of optimal health and daily functioning. The most recognizable and well-known of these is the sleep-wake cycle. The more you can do to adhere to your body and your mind’s natural rhythms, the better you’ll sleep.

Circadian Rhythms – The Basics

Circadian rhythms describe the 24-hour cycle of behaviors and mental and physical changes you experience daily. Most animals have some version of this cycle, dictated largely by light and dark and coinciding with day and night.

The brain has something like a master clock that regulates daily changes. Known as the suprachiasmatic nucleus, it takes input from the eyes to keep time. The purpose is to optimize the body’s functions based on the time of day.

How Do Circadian Rhythms Affect Sleep?

One of the most important aspects of the 24-hour cycle of circadian rhythms is that we sleep at night and remain awake during the day. It does this in a few different ways:

  • Melatonin is a hormone that makes you sleepy. It is suppressed during the day, in daylight, and released as it gets dark at night.
  • Cortisol is a hormone that makes you more alert. Your body releases more of it in the morning.
  • Body temperature drops at night when you sleep and rises during the day.
  • Metabolic rates differ at night and during the day to match when you should be sleeping and when you should be eating.

The sleep-wake cycle is a crucial part of circadian rhythms. Many of the signals are directed at making you sleepy at night and alert during the day. The result should be that you get restorative, restful sleep every night, which in turn supports your daytime activities.

How Else Do Circadian Rhythms Affect Us?

Sleeping and waking are some of the most obvious effects of circadian rhythms, but they are not the only ones. Circadian rhythms also affect:

  • Weight and other dietary factors, like blood sugar, metabolism, and cholesterol
  • Mental health
  • The immune system
  • DNA repair processes, which impact cancer risk
  • Neurodegenerative diseases, like dementia

What Factors Can Change Circadian Rhythms?

Because circadian rhythms impact so many aspects of health, it is important to avoid or minimize disruptions to them. Many factors can change your circadian rhythms, disrupting the cycle and causing harm.

Anything that disrupts normal sleep patterns, for example, can be a problem. Working night shifts or traveling and having to cope with jet lag will change the cycle. Also problematic are any lifestyle changes that keep you up late or force you to rise well before the sun.

Stress and mental illness can impact the cycle, too, as can some physical health conditions. These include brain damage, head injuries, and blindness. Some medications can also be disruptive.

Even if you have none of these specific issues, poor sleep habits can damage your normal circadian rhythm. To sleep better and be healthier, stick to a regular, 24-hour routine that includes going to bed at the same time every night and getting up at the same time in the morning.

Get exposure to sunlight during the day. As a bonus, get exercise outdoors. Make sure your sleep environment is cool, relaxing, and dark. Avoid screens before bed as well as alcohol, caffeine, and heavy meals. Don’t nap in the afternoon or evening.

Circadian rhythms are essential to so many aspects of normal functioning. Follow that rhythm and practice good sleep habits, and you should feel rested and restored during the day.

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