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2 Biological Systems That Impact Your Sleep and Focus

You have more control over them than you might think.

Charlotte Grysolle
Charlotte Grysolle
7 min read
Photo by Bacila Vlad on Unsplash

For all of us, our days consist of two closely interconnected phases: sleep and wakefulness.

In our brain and body, there are certain hardwired, biological ‘mechanisms’ or ‘systems’ we can experiment with to improve the quality of our sleep and wakeful states.

We have more control over these mechanisms than we might think.

I’ve noticed that understanding the impact of my behaviour on my sleep and my focus, makes it easier to ‘justify’ the effort of better habits — and stick with them long term.

And the good news is:

You don’t need to be a scientist or a professor to understand any of this. The information I’ll share here is what I’ve picked up from Andrew Huberman’s popular podcast Huberman Lab. As in all his episodes, he explains the scientific research and medical concepts in a simple style, focusing on practical tools to enhance your mental and physical performance.

Alright, let’s dive into these 2 internal mechanisms that drive the quality of our sleep and wakeful state:

  1. A molecule called ‘adenosine’
  2. Our circadian rhythm

Adenosine: The Sleep Drive Molecule

Adenosine is a molecule in our nervous system that builds up the longer we’re awake, creating the drive for sleep towards the evening.

While we sleep, adenosine is pushed down.

Simply put:

If you’ve been awake for 12–14 hours, adenosine levels are going to be high because it’s been slowly creeping up.

If you’ve had a good night’s rest, adenosine is going to be low in your brain and body.

Now, here’s what’s interesting:

When you pull an all-nighter, as morning comes around, you’ll notice a sudden increase in energy and alertness, even though adenosine has been building up all night and is at its highest.

This happens because of an overriding 2nd internal force:

The circadian rhythm.

Before we go into that: a practical tip to manage the effects of adenosine (you might not be too happy about this one).

🤸‍♀️ Practical tip

As I mentioned, adenosine is pushed down while you sleep.

But, there will be some residual adenosine in your brain when you wake up in the morning.

If you’re a coffee drinker and you regularly experience afternoon crashes, feeling foggy and unfocused, it might have something to do with your morning coffee.

Here’s why:

Caffeine is considered an ‘adenosine antagonist’.

That means when you ingest caffeine, it binds to the adenosine receptor. This blocks the sleepiness signal, making you feel alert and awake.

Imagine it like caffeine stealing adenosine’s parking spot. Adenosine can’t get to work until caffeine leaves.

That’s of course the reason why we drink coffee first thing in the morning, but here’s the problem:

Once the caffeine wears off, adenosine will bind to the receptors, often with greater strength — kind of like an angry driver with screeching tires.

That causes the feeling of the afternoon crash.

Now, an afternoon dip is entirely normal as we’ll see further down, but the caffeine wear-off will augment the effect and cause a stronger feeling of ‘crash’.

So the solution is to give your body time to clear the adenosine surplus in the morning before caffeine intake.

The general advice is to avoid caffeine for the first 60–90 minutes after waking up.

(Sorry! I know, I wasn’t happy about this one either…)

For anyone experiencing afternoon crashes, this should have tremendous benefits.

Circadian Rhythm: Our Internal Clock

Back to the 2nd, overriding system: our circadian rhythm.

Have you ever thought about how your body knows when to feel awake and when to feel sleepy?

Think about it: it’s not like we feel like we need to sleep every 30 minutes and then feel wide awake again, and 30 minutes later sleepy, awake, sleepy, awake, and so on.

Our periods of sleep and periods of wakefulness are typically condensed into one block and move like a seesaw.

This rhythm is regulated by our internal circadian clock, a master clock inside the brain of every human and animal.

‘Circadian’ means recurring naturally on a twenty-four-hour cycle.

In humans, this master clock consists of about 20,000 neurons forming the ‘suprachiasmatic nucleus’. This is part of the hypothalamus, situated at the bottom of the brain, just above the roof of your mouth.

(As you read this, did you also touch the roof of your mouth with your tongue, as if to say hello to your circadian clock? No? Never mind, just me then.)

Now, this clock sits deep inside our dark skulls. To function, it relies on another piece of the brain to relay information.

Our eyes — the only pieces of our brain outside of the cranial vault

Yep, the eyes are considered an extension of the brain, containing nerve tissue in the retina, the light-sensitive in-side lining.

We typically think of eyes for seeing objects, colours, and movements.

Turns out, that’s a late-stage evolution of what eyes were designed for.

The purpose of the eyes, first and foremost, is to instruct the rest of the brain and set the overall arousal state.

The eyes are fundamentally the most powerful driver of what we think, what we feel, and ultimately what we can do, because they set the basic level of alertness or sleepiness.

So, the master clock relies on the direct input from our eyes and one of the key ways it does this is through our light viewing behaviour.

How, when & what type of light

In the retina, the light-sensitive in-side lining of the eye, there’s a specialised group of neurons.

These neurons send electrical signals to the circadian clock when they are triggered by light. Our clock has connections with every cell and organ of our body, and when activated, sets in motion a release of hormones.

For example, this is what happens when our eyes detect morning light:

  • Immediate: a release of cortisol, promoting wakefulness & focus
  • 12–14 hrs later: a release of melatonin, stimulating feeling of sleepiness

By viewing bright light first thing in the day, you are setting in motion these two timers: one for wakefulness that starts immediately, and one for sleepiness that starts later.

Now, we’re not talking about just any type of light.

The neurons are most triggered by natural light low in the sky, like at sunrise. They don’t get activated in an optimal way by say, the light from your phone screen.

How do these neurons to the difference between sunlight and artificial light?

Good question — they don’t.

They just respond best to the quality and intensity of light when the sun is low in the sky.

That’s because the neurons in our eyes that activate the internal clock reside mainly in the bottom half of our retina. The lens in front of our retina creating an inversion of the visual image means these neurons see our upper visual field and are designed to detect sunlight.

I know, Mother Nature’s a genius.

🤸‍♀️ Practical tips

Now, what does this mean for us practically?

It’s simple:

Light naturally regulates your circadian clock, so one of the most effective ways to improve your sleep during the night and your focus during the day is by managing when and how you see sunlight.


View bright light early in the day, as close to waking up as possible. Ideally, this is natural light.

As explained, this triggers the timed release of cortisol, which acts as a wake-up signal and promotes the ability to focus throughout the day.

You want this cortisol pulse to happen as early in the day as possible.

It also starts a timer for the release of melatonin, 12–14 hours later, which stimulates the feeling of sleepiness.

Go outside for a walk, or stand in your garden. It’s 50–100 times less effective when it’s through a window.

And don’t worry about cloud cover; you’ll still get the light energy coming through. Depending on how cloudy it is, you should aim to go outside for 10–30 minutes.

No, you don’t need the sunlight beaming into your eyes directly. There are a lot of photons scattered around from sunlight. Just don’t wear sunglasses (unless you have a medical condition, of course).

If there is no light when you wake up (hello winter in London), you can use artificial light. Turn on bright, overhead lights. I bought a Lumie Light Box for extra brightness. Andrew mentioned selfie ring lights also do the trick.

What’s the worst thing you can do?

Wake up, grab your phone and lie around in bed. The light of a screen is not bright enough to trigger the activation of the neurons in your eyes.


Then, during the day, try to go outside again to catch natural light and boost wakefulness. Light inhibits the release of melatonin, another hormone your brain produces in response to darkness.

Ideally, view natural light again in the late afternoon before the sun goes down. This will adjust your retinal sensitivity in a way that allows you to see more artificial light in the evening (e.g. from your computer screen) without disrupting your sleep patterns.


In the evenings, you want to avoid activating the light-sensitive neurons in your eyes.

The longer you’ve been awake, the more sensitive your retina and cells are to light. Even small amounts of light will trigger the activation of the clock, making you feel like you don’t want to go to sleep.

So, no bright, overhead lights. Make it cosy and romantic with dim lights placed low in your physical environment. Grab a book instead of your laptop when winding down in bed.

Bookend your day with morning and evening light

Giving your nervous system these anchors of natural morning and evening light, allows you to balance your sleep and wakefulness cycles, so you sleep better and feel more alert during the day.

According to Andrew, it will take 3–4 days of doing this to balance your system and start noticing a difference in your sleep and alertness during the day.

Treat Your Body Like a Mini-Laboratory

What’s most fascinating to me about this type of information is learning that we can do these little experiments on ourselves, and see the difference it makes in our daily lives.

You don’t have to accept that “you’re just not a morning person” or “you are always tired in the afternoon”. Be curious about how your body and systems work, and experiment with small changes in our habits and routines. Observe how you feel.

So, a few simple ideas to try:

  • Start with a morning walk immediately after waking up
  • Wait with having coffee until later in the morning
  • A quick walk over lunch
  • Finish the day with an afternoon walk

If anything, you’ll get more walks in and that’s a good thing to do anyway!

Resources for more info:


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