Sleep: The Chemical Force and Circadian Force
By Mike Hazle, Sep 15, 2021
Part 1 in the series: Re-Engineering Human Performance Through Sleep
The Chemical Force: Adenosine
- Adenosine builds up the longer we are awake. When you wake up, adenosine levels are low, then begin to slowly rise until they reach very high levels at the end of the day. Higher adenosine levels drive sleep hunger.
- Caffeine blocks adenosine (antagonist) as it binds to the adenosine receptor and will not allow adenosine to park there. When caffeine wears off, adenosine rushes in and almost doubles in its binding power causing “the crash”.
- Caffeine increases dopamine, the "feel good and motivated" neurotransmitter. As dopamine goes up, epinephrine goes up as well, and the end result is energy.

The Circadian Force: The Internal 24-hour Clock
- If you “pull an all-nighter” you may feel sleepy as the night goes on, but if you stay up longer, you will feel alert again. This is due to the circadian force or circadian rhythm.
- When adenosine is low because we have slept, a hormone called cortisol is released from your kidneys and a little pulse of epinephrine as well. Think of cortisol as nature's built-in alarm system. This can be stimulated from an alarm or natural waking but it’s important that cortisol release happens earlier in the day.
- A natural timer is set in your body and your nervous system, so that melatonin gets secreted from the pineal gland about 12-14 hours after the initial cortisol release.

- The Pineal gland is the organ that produces melatonin. That’s the only place it can come from. Melatonin will help you fall asleep but not stay asleep in most cases.
- Cortisol and melatonin are endogenous, meaning it happens automatically, even if we were in a cave in total darkness.

- Sunlight is a huge, influential element that affects your nervous system and sleep process. Exposure to sunlight at dawn and dusk is key to setting your internal rhythm.
- When sun light comes into the eye (into the Retinal ganglion cells, which are brain neurons in the eye) those cells receive the signal from the light and then distribute that signal to every cell of your body.
- These cells respond best to sunlight and most sensitive to low solar angle light (yellow and blue contrast that is only available at early sunlight and sunset).
- Light is 50x less effective when viewed through sunglasses or a window, yet 10-50k lux is sufficient to set the circadian clock.
- Your circadian rhythms are set on averages based on when you are seeing the brightest blue lights.
- By viewing sunlight in the evening (sunset), the melanopsin cells signal to the brain that it’s the end of the day. This can help to increase melatonin and protect the body’s mechanisms against negative effects of light exposure later in the day.
- Phase advance and phase delays: Light exposure in the middle of the night will make it harder for you to wake up in the morning and harder to go to bed later, and vice versa. It is important to give your neurons and internal mechanisms an anchor to hold onto for timing and rhythm as these systems run on averages.
- Naps can be beneficial if they are less than 1 ultradian sleep cycle and you don’t go into REM sleep, with 20-40 minutes being the sweet spot.