Understanding your circadian rhythm
Key points
- We all have a circadian rhythm that is effectively our body’s inner wake/sleep programming.
- Exposure to artificial light may disrupt our normal circadian rhythms and sleep cycles.
- Some people are more sensitive to light exposure than others.
If you’ve ever done any research on how to sleep better, you’ve probably come across something called ‘circadian rhythm’. While it sounds like a dance move, it’s actually how our bodies are innately programmed by the earth’s cycle around the sun.
So, if you’re wondering ‘what is my circadian rhythm?’, sleep specialist Dr David Cunnington describes it like this:
“You could think of circadian rhythm as the rhythm of a day. You may think of it as a light/dark cycle. Or activity/rest. Or feeding/fasting. Or wake/sleep. Ideally, you want all those things to be in sync, so you’re awake, active and eating when it's light. When it’s dark, you're asleep, resting and fasting.”
The challenge, says Dr David, is that we no longer live in caves with the sun as the only source of light. Instead, we have all sorts of artificial lighting and distractions that could play havoc with our circadian rhythm. If you’re wondering, ‘why do I feel so tired?’, this may be the cause.
So, what happens when circadian rhythms are disrupted?
“Obviously, this may cause sleep/wake issues,” explains Dr David. “But it could also cause other issues. If you’re eating when your body is in fasting mode, the food is metabolised and processed differently. When it comes to circadian rhythm and exercise, your heart rate response may be different if you’re physically active when your body’s expecting to be resting.”
Your body also has a lot of other peripheral clocks, like a heart clock, vascular clock, gut clock and liver clock.
To help you understand your circadian rhythm and the importance of sleep, Dr David shares his valuable insights.
Circadian rhythm and heart rate
The human body never ceases to amaze. It’s incredible to think that it has this clever built-in clock to help you regulate things like sleep.
Dr David says you could think of your circadian rhythm as a kind of central clock that tells your body when it’s day or night.
“Your body also has a lot of other peripheral clocks, like a heart clock, vascular clock, gut clock and liver clock,”
he adds. “If your body is expecting to rest, sleeping and fasting, it may set lower blood pressure goals.”
“Things like catching up on sleep by taking a nap during the day or being active in the evening when your body is expecting rest. When you do this, it may feel like things aren’t working. And that’s how it could impact things like heart rate.”
Adult vs adolescent circadian rhythm
Everyone knows the stereotype of the teenager who wants to stay up all night and then sleep until lunchtime. Dr David says this isn't just a stereotype; it’s an actual thing. But the science is noncommittal on why it occurs.
While scientists haven’t pinpointed the exact reasons behind the adolescent circadian rhythm, Dr David suggests some social influences may also be at play.
“Adolescence is a time when you want to assert your independence. There are some things you can’t control, such as when school starts. But there are others you do have some power over, such as when you go to sleep. It’s revenge sleep procrastination.” he says.
The impact of coffee on circadian rhythm
If you enjoy your daily coffee, Dr David says that it generally doesn’t impact your circadian rhythm. But there may be an indirect impact.
“Coffee is a stimulant,” he explains. “It could potentially delay the onset of sleep or make you feel like you could ‘cheat sleep’ for longer. That, in turn, may affect your circadian rhythm by pushing it out longer.”
Determining your own circadian rhythm
Have you ever wondered what your circadian rhythm is?
Dr David explains that individuals have different timing and responsiveness to light and dark. This is partly mediated by our genes.
“Our clocks are about 24 hours, and they’re regulated by our genes. People who are early birds tend to have a clock that’s pretty much bang-on 24 hours. For people who are night owls, they might have a 24 hour and 30 minute clock. Unless they’re getting a bit of light each day to just slightly reset that 30 minute offset, they’ll tend to find it a bit tougher to get up in the morning.”
Some research shows there’s a 50 fold difference in sensitivity to light between individuals.
For people who are really sensitive to light, even a little bit of light after the sun has gone down may significantly impact their sleep schedule. For others, this post-sunset light exposure has no impact.
This is perhaps why blue light may affect sleep more for some people than others.
Dr David says the preference for morning or evening is referred to as a chronotype. If you want to understand yours, he suggests a method called the Morningness-Eveningness scale.
The difference between ultradian and circadian rhythm
While circadian rhythm happens over a day, ultradian rhythms have a shorter length and occur multiple times within a day.
“Even though we talk about a 24 hour sleep/wake cycle, there’s also ebbs and flows across the day. These are ultradian rhythms,” explains Dr David. “A sleep cycle, usually one or two hours in length, is an example of an ultradian rhythm. Many people may also relate to that little dip in productivity we often see after lunch.”
The rhythm of sleep
With all your new knowledge, you may need to find some new sleep hacks that align with your circadian rhythm. So, get your sleep hygiene sorted and start giving your body the sleep it needs.
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Dr David Cunnington is a specialist sleep physician who helps his clients to treat their complex sleep problems while also promoting sleep health through education, research and advocacy.
Reviewed by the healthylife Advisory Board March 2022