Sleep hygiene is a term that’s been thrown around a lot lately as the awareness of the importance of sleep plays in our lives increases. It refers to the things you can do, to set yourself up for better sleep. It can essentially be broken down into two domains:
1. Daily Routine — the things you do before you go to sleep
2. Bedroom environment — how optimised your bedroom environment is to promote for sleep
You’ve most likely heard the common ones before such as:
sleeping and waking up at the same time every day
avoiding coffee or tea after a certain time
avoiding screen time before bed
avoiding naps
getting sunlight
But why do these strategies work? Most of what sleep hygiene does, is manipulating two biological mechanisms that regulate our sleep and wakefulness, circadian rhythm and sleep pressure.
Circadian Rhythm and Sleep Pressure
Here’s a fun graph spanning two days which we’ll use to look at these processes. Despite being two separate processes, they play off one another.
Circadian Rhythm
Circadian rhythm is our body’s internal clock, telling us when we should be awake, or when to be asleep. In the graph, it’s the green wavy line, and you can see that it goes up and down like a rollercoaster. You can think of it as when the line is going up, we tend to feel more alert and it’s telling us “hey, wake up, it’s time do stuff” and when it’s low, “hey i’m tired, let’s get ready to sleep”
While it may seem a bit abstract, you’ve most likely felt the circadian rhythm in action before if you have ever pulled an all nighter. You might notice you get a second wind at around 3–4am, because that’s when your circadian rhythm is rebounding back up, preparing us for the next day.
In the context of sleep hygiene, this is why it’s important to have a relatively stable routine where you go to sleep and wake up at the same time. It allows these two processes to remain in sync.
One thing to note with the circadian rhythm, is that it is mediated by melatonin, a hormone that promotes sleep. What a lot of people tend to do when they have trouble sleeping, is to buy melatonin. But, what they don’t know is that melatonin production is suppressed by natural and artificial light.
With sleep hygiene, that’s why it’s advised to have dim lighting or a dark bedroom environment when sleeping, and also to avoid electronics such as tv or phones before bed. You can think of taking melatonin as shifting our circadian rhythm forward, and exposure to light shifts our rhythm backwards. In reality, our rhythms are always adjusting back and forth.
You might have also heard of people telling you to sit in the sun for a few minutes in the morning, or to go for a walk outside. These are natural ways of fine tuning our circadian rhythm.
Sleep Pressure
When we’re awake, our body gradually builds up a chemical called adenosine within the brain. This build up is called sleep pressure, because the more we have it, the sleepier we become.
The adenosine graph is more straightforward, it just keeps going up — but once you go to sleep, the adenosine levels drop.
In the context of sleep hygiene, this is why you might not want to have caffeine in the late afternoon, as caffeine binds to the same receptors in the brain as adenosine. Our adenosine levels can keep building up, but we won’t be able to feel that sleep pressure. Caffeine can also last up to 10 hours in your bloodstream.
With napping, this can reduce our sleep pressure throughout the day, so when it comes time to sleep at night, our sleep pressure might not be strong enough to allow us to fall asleep, even if our circadian rhythm is telling us we should be sleepy.
Putting everything together, all sleep hygiene is really, is manipulating these two mechanisms to try and keep them in sync. You can have a healthy circadian rhythm, but if you’re loaded up on stimulants, you won’t be able to sleep well.