What Does 'Circadian Rhythm' Mean, Exactly?
How often do you check to see what time it is? Clocks—on our phones, watches and throughout the house—help guide our routines. They tell us when we should get up, when it’s time for bed, if our favorite show is about to come on TV or if it’s time for that meeting with our boss. Just as we rely on clocks to carry out different tasks, our body has its own internal clock, which is referred to as circadian rhythm.
Circadian rhythm is the body’s sleep-wake cycle, which takes place over the course of 24 hours. In other words, it’s tied to when it’s time to sleep and when it’s time to be awake. Many different factors can impact circadian rhythm. Sometimes, there are also dysfunctions and when that happens, health can be negatively impacted.
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What Is Circadian Rhythm and What Impacts It?
You know how at certain parts of the day you’re super alert and energized while other times you’re sleepy and fatigued? This is part of the circadian rhythm. As the body’s internal clock, it communicates to the brain when it’s time to be awake and when it’s time to be asleep.
The primary way that our circadian rhythm knows when it’s time to be awake versus when it’s time to be asleep is based on how light or dark it is. The sun serves as an external cue that it’s time to be awake while darkness indicates that it’s time to power down. Of course, the sun is not our only form of light; there’s a good chance that right now your room is being illuminated by light bulbs or you’re reading this from the glow of your phone or computer. External lights can impact circadian rhythm by reducing melatonin, a hormone that plays a role in the sleep-wake cycle. This reduction can lead to trouble sleeping.
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Feeling stressed can also impact circadian rhythm. This is because, like melatonin, cortisol (the body’s main stress hormone) plays a role in the body’s sleep-wake cycle. When we first go to sleep, cortisol levels are low and it reaches its peak right before we wake up. Being stressed can cause cortisol levels to stay high. This then impacts how well (or more accurately, how horrible) we sleep.
There are other factors that can impact circadian rhythm too: body temperature, traveling, shift work, hormones, exercise, aging and certain medications.
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What Happens When Circadian Rhythm Is Disrupted
Disruptions in circadian rhythm can lead to a cascade of health problems. The most obvious one is feeling tired yet not able to sleep. Other changes can include negatively impacting mood, digestive problems, problems with memory and concentration, increased risk for autoimmune disorders, higher likelihood of getting sick, and a higher risk of certain diseases and cancers. There is also a connection between disrupted circadian rhythm and obesity, diabetes and cardiovascular problems.
Shift workers are especially at-risk for experiencing a circadian rhythm disruption because they sleep during the day and are awake at night—the exact opposite of what circadian rhythm is telling the body to do. Because of this, it isn’t surprising that shift workers are more likely to experience all the health issues listed above. If you are a shift worker who must work at night, it can be beneficial to try to “trick” the body into thinking that it’s the night when you are trying to sleep during the day by using blackout curtains, avoiding bright lights on your way home after your shift and sticking to a consistent sleep-wake schedule.
As mentioned before, artificial lights can also cause circadian rhythm disruptions. This is why sleep experts often preach about the importance of “powering down” in the evening, putting away screens and dimming the lights as you make the transition to bedtime.
The importance of circadian rhythm cannot be minimized. Working against it can negatively impact health in myriad ways. This can include frustrating minor problems (such as trouble concentrating or feeling tired all the time) to increasing the risk of life-threatening conditions.
You might not have thought that having a good night and sleep routine is so important, but it truly is. Do what you can to rise and set with the sun and you’ll be doing your whole body a favor. It turns out that our internal clock is just as helpful as all our external ones.
Next up, find out how many hours of sleep you actually need a night.
Sources
Physiology, Circadian Rhythm. StatPearls.
I Can’t Sleep…Can you turn off the lights? Harvard University The Graduate School of Arts and Sciences.
Cortisol on Circadian Rhythm and Its Effect on Cardiovascular System. International Journal of Environmental Research and Public Health.
A look at the body’s natural time-keeping system. UCLA Health.
Health implications of disrupted circadian rhythms and the potential for daylight as therapy. Anesthesiology.
Shift Work and Health: Current Problems and Preventive Actions. Safety and Health at Work.
How Shift Works Affects the Circadian Rhythm—Can You Get a Sleep Disorder? Sleep Advisor