What is a Circadian Rhythm?

Sleep conforms to a cycle that roughly conforms to a 24-hour period. Based on an individual’s circadian rhythm, the brain wants to sleep at a certain routine time every night and wake up at a certain routine time every morning. This process is partially mediated by a hormone called melatonin.



About 2 hours before natural sleep, the pineal gland in the brain starts secreting melatonin. As an example, let’s say you start your day at 6 AM and stay awake all day. At around 8 PM, melatonin starts to rise and continues to do so for about 2 hours. Around 10 PM, melatonin levels peak – roughly about the time you have been awake for about 16 hours. This dual effect of being awake for about 16 hours and the melatonin peak should allow for natural sleep to occur. Between 8-10 PM (during the 2-hour period when melatonin levels start to accumulate), the brain starts to sense that “darkness” is coming and prepares itself for sleep. It is important to note that any light source during this time can blunt the darkness effect, causing delay of sleep onset. This includes electronic devices (computers, cell phones, reading devices) which can suppress melatonin’s effects and contribute to difficulty falling asleep.

What are Circadian Rhythm Sleep Disorders?

Circadian rhythm sleep disorders occur when there is desynchronization of the physiological sleep-wake schedule from what is deemed socially acceptable. For example, let’s say your underlying circadian rhythm wants to go to sleep at midnight and wake up at 8 AM. However, you may need to wake up at 6 AM for work. If so, then the best sleep schedule would be 10 PM to 6 AM. However, attempts at falling asleep earlier or waking up earlier occurs because of this disconnect between your natural sleep rhythm and your desired sleep schedule.

Examples of Circadian Rhythm Sleep Disorders

Delayed Sleep Phase DisorderDSPD

If melatonin secretes later, the usual time to feel sleepy is later, or “delayed”. This often occurs naturally during puberty. As adults, most people start to entrain themselves to combat this delay. In others, the delayed sleep pattern becomes chronic. Delayed patterns of sleep are worsened by electronic usage in the evening and during sleep hours.

Advanced Sleep Phase Disorder

Conversely, if melatonin secrets earlier than usual, sleepiness occurs earlier in the evening – ahead of when others may feel sleepy. This can occur naturally during the aging process.

Shift Work Sleep Disorder

This circadian sleep disorder occurs when you try to force yourself to sleep during a time that isn’t “natural” to your endogenous sleep rhythm. For example, working night shifts or rotating shifts often leads to “forced” sleep during the day or afternoon. Shift work sleep disorder occurs when you are unable to fall asleep outside of your natural sleep time, have difficulty achieving the appropriate amount of sleep, feel that the sleep is poor quality, and/or have difficulty staying awake during the work shift.

Do I have a Circadian Rhythm Sleep Disorder?

If you suspect you have a circadian rhythm sleep disorder, see a sleep physician for evaluation and to discuss potential treatment options.

If you’d like to get a better idea if you have a Circadian Rhythm disorder, take our quick Sleep Disorder Quiz.


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