Biological sleep rhythms

In order to sleep, we need to be physiologically sleepy. Two physiological processes that are influenced by our behavior. Most important influences:

A regular sleep wake schedule

An optimal balance of wake and sleep time

Maintain an optimal sleep window

• An appropriate duration (not too short and not too long)

• A regular bedtime and rise time 

Physiological Sleep Rhythms

Two physiological processes work together to create the conditions for good sleep and daytime functioning. The diagram below is an example of a person who needs 8 hours of sleep per night and maintains a sleep schedule of 10pm to 6am.1     

Circadian rhythm: There is a “biological clock” in the brain that regulates alertness levels over a 24-hour cycle. When it is working well, our alertness level follows the pattern depicted in the diagram. To fall asleep, our alertness levels need to fall below a certain threshold and to stay asleep they need to stay low. 

Sleep pressure: When we are awake and active, we accumulate a neurotransmitter called adenosine and this eventually produces pressure to sleep. To sleep well, we need to accumulate enough sleep pressure (e.g., ~16 hours of being awake promotes ~8 hours of being asleep). We deplete sleep pressure when we sleep or nap.

The influence of behavior on sleep rhythms

Maintaining a regular sleep schedule helps to preserve consistent physiological sleep rhythms. Going to bed too early, sleeping in too late, spending more than 8 hours in bed, or excessive napping can result in higher levels of alertness during the night and insufficient sleep pressure. Both significantly increase the chances of insomnia.  

Light (specifically the blue portion of the spectrum) plays a significant role in the timing of our circadian rhythm. Blue light suppresses the body’s release of endogenous melatonin which results in a higher level of alertness. To keep the biological clock in time, keep ambient light levels low in the evening and take measures to limit exposure to blue light produced by electronic screens. Being exposed to light at a consistent time in the morning also helps to maintain a consistent circadian rhythm.

Caffeine suppresses sleep drive and so it is best to limit caffeine intake overall and avoid it at least 6 hours before bedtime.

The two process-model of sleep-wake regulation

Two biological processes work together to regulate our sleep and wakefulness: circadian rhythm and homeostatic sleep drive. These are depicted in the diagram below. The squiggly line is the likelihood that we will be able to stay awake or remain asleep. The 8-hour period in gray shows the optimal to sleep.1

1Keep in mind that most adults need between 7-8 hours of sleep for optimal functioning, and not all adults need a full 8. 

Circadian rhythm & sleep drive

Circadian rhythm: There is a “biological clock” in the brain that regulates alertness levels over a 24-hour cycle. When it is working well, our alertness level follows the pattern depicted by the upward arrows in the diagram above. To fall asleep, our alertness levels need to fall below a certain threshold and to stay asleep they need to stay low. 

Sleep drive: The longer we are awake, the more sleep drive we accumulate. We deplete our store of sleep drive when we sleep. This is depicted by the downward arrows in the diagram above. To sleep well, we need to have accumulated enough sleep drive (e.g., 16 hours of being awake promotes 8 hours of being asleep).

Behavior and biology

Several behavioral factors influence our biological sleep rhythms, and three of the most significant include: (1) Our sleep-wake schedule; (2) light exposure, and (3) caffeine intake. 

(1) Our sleep-wake schedule: Maintaining a regular sleep schedule keeps us in time with our biological rhythms and synchronizes them with each other. Going to bed too early, sleeping in too late, spending more than 8 hours in bed, or excessive napping throws the whole system off and increases the chances of insomnia. 

(2) Light exposure: The timing of our exposure to light also plays a significant role in influencing the timing of our biological clock. Light (specifically the blue portion of the spectrum) sends a signal to our brain to keep the alertness levels high. To keep the clock in time, keep ambient light levels low in the evening and at night and take measures to limit your exposure to the blue light produced by electronic screens. The most effective way to reduce light exposure in the evening is to wear “blue-blocking” amber-colored glasses (for example: Uvex s0360x). Getting light exposure at the same time every morning also helps to keep the biological clock in time. 

(3) Caffeine: Caffeine suppresses sleep drive and so it is best to limit caffeine intake overall and avoid it at least 6 hours before bedtime.

Other biological factors

Digestion, metabolism, body temperature

Circadian chronotypes: Night owls and early birds

Genetics; Circadian Rhythm Sleep Disorders

[sleep-wake schedule]

Reset your biological sleep rhythms 

Step 2: Attend to your sleep-wake schedule

How much sleep do you need: 7-8 hours.

Maintaining a regular sleep schedule keeps us in time with our biological rhythms and synchronizes them with each other. Going to bed too early, sleeping in too late, spending more than 8 hours in bed, or excessive napping throws the whole system off and increases the chances of insomnia. 

Set a regular wake time, don’t go to bed too early, and limit napping

[light exposure]

Reset your biological sleep rhythms 

Step 3: Attend to your exposure to light

The timing of our exposure to light plays a significant role in influencing the timing of our biological clock. Light (specifically the blue portion of the spectrum) sends a signal to our brain to keep the alertness levels high. To keep the clock in time, keep ambient light levels low in the evening and at night and take measures to limit your exposure to the blue light produced by electronic screens. 

The most effective way to reduce light exposure in the evening is to wear “blue-blocking” amber-colored glasses (for example: Uvex s0360x). Getting light exposure at the same time every morning also helps to keep the biological clock in time. 

[limit substances]

Reset your biological sleep rhythms 

Step 4: Limit substances that interfere with sleep

Caffeine: Caffeine suppresses sleep drive and so it is best to limit caffeine intake overall and avoid it at least 6 hours before bedtime.

Alcohol; heavy foods; water. Foods that may promote.

[supplemental melatonin]

Reset your biological sleep rhythms 

Step 5: Determine whether supplemental melatonin may be beneficial

[systematic sleep scheduling]

Reset your biological sleep rhythms 

Step 5: Determine whether the "Systematic Sleep Scheduling" protocol is warranted.