All human beings follow a specific pattern of activity and rest that more or less corresponds with the 24-hour period of the day. This specific pattern is guided by our circadian rhythms.
What are circadian rhythms?
These are the natural rhythms by which our body processes are tuned. Both internal and external factors play a part in maintaining them.
These rhythms regulate several familiar "drives" such as hunger, but also play an important part in temperature control and hormone release. Our sleep drive is perhaps the most prominent drive affected by the circadian system.We spend a third of our lives sleeping, and this usually takes place in consolidated blocks of time at night. There's a reason for that.
All living things have a rhythm which matches up in some way with the Earth's 24-hour orbit around the sun, providing important rhythmic regulation through exposure to both sunlight and darkness. This synchronicity between our body rhythms and the planet's light-dark cycles is referred to as entrainment.
The patterns of sleep and wake we experience are further defined by two key systems: the Sleep Wake System and the Circadian System.
The Sleep Wake System
We tend to get sleepy after our bodies signal to our brains that we have been awake for long enough. This is part of what is known as our "sleep drive." Likewise, when we sleep at night, our sleep wake system eventually wakes us up when we've acquired adequate sleep.
There are complex parts to this internal system which work in tandem with hormone release and body temperature which are key to maintaining a functional sleep wake pattern.
The Circadian System
This external system relies on time cues such as light availability, physical activity, and hunger to help keep the body's clocks balanced.
Circadian rhythms are especially attuned to the availability of light; light reception through the eyes is directly channeled to the circadian center to help maintain daytime wakefulness or nighttime somnolence.
Morningness vs. Eveningness
Circadian rhythms have a genetic, heritable component; we get our preferences from our parents. This explains why some people are called "morning larks" (or morningness) while others prefer a later "night owl" schedule (or eveningness).
What causes circadian rhythm disorders?
There are a number of factors that can lead to disruption of circadian rhythms.
Age brings changes to circadian rhythm functions that can result in the development of sleep disorders.
Advanced sleep phase delay mostly happens to older people, who find they need to retire earlier in the evening than they did when they were younger.
Delayed sleep phase delay happens to teens as a part of the final neurological development that comes with adolescence; as such, they tend to not be "wired" for sleep until well past what is considered a "normal" bedtime. Usually, they grow out of this phase shift, but not always.
It could be your work schedule, your school schedule, or a travel schedule that puts you off your rhythms.
Shift work disorder is a kind of sleep disorder which happens in those who work evening or overnight shifts—precisely the time when they should be sleeping.
People with irregular sleep-wake rhythms or non-24 sleep-wake disorder have circadian rhythms that are nearly impossible to adapt to the typical work or school schedule.
If you must travel across time zones frequently, you could suffer from jet lag disorder, in which your rhythms are confused by frequent trips across several clocks you can no longer physically synchronize with your internal clock.
When we encounter a time shift such as Daylight Saving Time, this poor synchronization of even one hour of time, leading to sleep deficit, is evidence of a circadian imbalance.
Treatments for circadian rhythm disorders
The main approaches for treating these dysfunctions of the sleep clock are:
Light therapy (also called phototherapy): A specific schedule for intentional exposure to bright light can be set up for a patient trying to reset their rhythms.
Chronotherapy: Following a preset sleep-wake schedule is one path for recalibrating confused circadian cycles. These might include "naps" to bank time or slight shifts in bed time and rise time until your schedule is corrected.
Sleep hygiene and behavior therapies: Sometimes, problems with circadian rhythm disruption are caused by poor sleep hygiene or sleep behaviors, both which can be corrected with coaching from a sleep specialist.
Medications: Some types of drugs can be useful for facilitating sleep, while others are helpful for maintaining alertness. Keep in mind, sometimes the effectiveness of specific kinds of medication can depend on the time of day you take them.
Other medical problems: An underlying physical or mental health problem might be at the root of a circadian rhythm problem. Identifying and treating these health issues may help correct sleep wake cycle imbalances.
If you find your daily rhythms are out of synch with your normal routine, it might be worthwhile to talk to your doctor. Any imbalance in your system suggests an underlying issue that needs to be assessed.
American Academy of Sleep Medicine
National Institute of General Medical Sciences
National Sleep Foundation
UCLA Sleep Disorders Center