The Science Behind Oura
Oura Crew | Sep 21, 2017

What the Clock?! | A Quick Introduction to Circadian Rhythms

Did you know that each of our organs operates with its own rhythm? And that consequently, we all have our own unique rhythms that drive our activities and rest. In this first part of our guest blog series, our prestigious visiting writer Dr. Benjamin Smarr leads you through the basics of circadian rhythms, and tells you why they are so important.

What You’ll Learn In This Article

What Are Biological Rhythms?

All our bodies have a unique shape. You wouldn’t buy a shirt from me if all I told you was that it’s “human sized.” Even a shirt of the right size-category might be short in the arms or fit at the shoulders but not the waist.

Well, we don’t only have unique arrangements in space. We also have unique shapes in time. When we get hungry or sleepy, when we’re most attentive or creative – these are not random events, nor are they just responses to our environment.

Our physiology – both body and mind – are built on multiple scales of overlapping cycles. Each of us may differ from others, but within ourselves these rhythms are persistent, and if you learn to hear them, then you can make your schedule fit like a finely tailored shirt.

Each of us may differ from others, but within ourselves these rhythms are persistent

Biological rhythms evolved to let organisms anticipate the environment. When a rhythm comes from within the organism, we call it endogenous, and we apply a name to that rhythm, to make it clear when we’re discussing the biological rhythm instead of the environmental pattern it matches.

Circadian and Circannual Rhythms

The most well-studied rhythms may also be the most intuitive to everyone: seasonal change (circannual rhythms) and daily change (circadian rhythms) (of course there are also ovulation cycles, but I’ll focus on those in a future blog post).

I tend to get tired around the same time each day, and unless I have deadlines or am at a party, I tend to go to sleep around the same time too. That time changes in the winter, when I tend to sleep more. Other people sleep on a different schedule, and maybe some don’t change as much with the year, but for all our differences, we all maintain individual daily snooze patterns. That’s because our circadian rhythms affect the brain centers that drive our sleep.

How Do Circadian Rhythms Work?

Circadian rhythm affects much more than sleep. In fact, every cell in our body has its own clock-work of genes that go up and down throughout the day.

It makes sense that circadian rhythms are in every part of our body because circadian rhythms were one of the first traits to evolve in life on Earth. As cells started combining to form organisms – eventually animals like us – each of these cells came with their own clocks. The result is that every organ and every process has a time.

The result is that every organ and every process has a time

Healthy living, and healthy aging, depend on letting each process happen when it wants to, because when they do that, all those processes line up in time: the pancreas can make the right amount of insulin, the stomach the right amount of acid, and the liver the right quantity of enzymes for optimal digestion of the food your brain makes you hungry for at “the time to eat.” And they can do this even if they can’t talk to each other because they all know when “the time to eat” is.

In the wild, both the day and the year can be predicted based on the sun. It rises with a predictable time each day, and since that time changes over the year, the length of the day serves as an accurate cue for our internal calendars. The brain, therefore, evolved to use light like villages used church bells – as a timing signal to send through the body and make sure every cell stays lined up in time.

Circadian Rhythm Disruptions

Our biology did not evolve with computers, or street lamps, or midnight deadlines. When light cues come in at unnatural times, our brain’s clocks get very confused, and the result is misalignment throughout our bodies. Some organs work to keep up with the brain, some run more on their own momentum, and some just can’t deal with noon-time bells at 11PM, and their rhythms fall apart.

While light at night is good for short-term productivity, it’s a long-term health risk. Similarly, changes in daily schedules (tonight I stay up late, tomorrow I sleep in, etc.,) make internal alignment harder and pose a long-term health risk.

While light at night is good for short-term productivity, it’s a long-term health risk

To use the earlier example, if our stomachs can’t predict when “the time to eat” will be, then they may make acid with no food incoming.

This is one reason why some shift-workers get ulcers. And the pancreas makes too little insulin for an unpredicted snack, and so irregular meals increase the risk of obesity and diabetes. When sleep rhythms fall apart, that’s a predictor for the earlier onset of dementia.

None of these problems kill you out right, so they can be easy to ignore, but the errors from internal circadian misalignment add up over time.

Living Up to Your Circadian Rhythm Schedule

Knowledge should be useful, not just scary. I don’t tell you about circadian rhythms to give you one more thing to worry about; I do it to empower you.

Just like you know to buy shirts that fit, you should seek out a schedule that fits you. Try sleeping without an alarm, and see when you naturally wake up. Try eating when you’re hungry rather than powering through another dozen emails. Keep track of when you go to sleep, and try to make it close to the same time every day. Same for when you work out, eat breakfast, and drink coffee or alcohol.

The more you can align your daily schedule, the easier it will be for your internal clocks to line up too. That will not only make you feel physically, mentally, and emotionally better, but it will help you live longer and age better too.

_That’s all well and good,” you say, “but I go to sleep at 2AM every day, and there’s no way I can make my job fit that routine. I’ve been misaligned since high school! Am I broken?_ Good question, imaginary owl. No, you’re normal, and you’re the poster-child for a social movement just starting to germinate.

My next blog post will be all about the natural distribution of circadian alignments people have, called chronotypes. I’ll talk about where they come from, and how understanding our chronotypes, and adjusting our society to accommodate them, can help reinvigorate global work, health, and education.


Dr. Smarr received his Ph.D. in Neurobiology and Behavior at the University of Washington in Seattle, and is currently a National Institutes of Health Fellow at UC Berkeley, where he works with with Professor Kriegsfeld in the Psychology Department. His work focuses on understanding how biological timeseries carry information useful for predictive medicine and personalized wellness. His specialties include circadian rhythms, sleep, female reproductive rhythms, and computational signal processing.


If you’re interested in tracking your sleep and you don’t yet have the tools for it, have a look at the Oura ring in the Oura Shop. If you have an Oura ring, read this article to get to know the Oura sleep metrics, or dig deep into your data in the Oura Cloud Beta.


What Kind of Bird Are You? | An Introduction to Chronotypes

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