Circadian Rhythms: What Are They & How to Improve Yours

7 min read

Last Modified 31 August 2023 First Added 14 January 2021

By Liam Porter

Circadian rhythm definition:

any periodic variation in physiological or behavioural activity that repeats at approximately 24-hour intervals, such as the sleep–wake cycle.

Source: APA dictionary

If you’ve ever spoken about your body clock, you’ve actually referred to one of your circadian rhythms. But what exactly are these rhythms? And why should they be considered when looking to improve your approach to sleep? Here, we take a look at this important biological cycle with some tips on how to get yours in sync and achieve better sleep health.

What are circadian rhythms?

Circadian rhythms are 24-hour cycles which make up the body’s internal clock. There are three other types of biological rhythms: diurnal, ultradian, and infradian. But it’s circadian rhythms which have the most impact – at least in terms of sleep. That’s because one circadian rhythm is our sleep-wake cycle, responsible for why we wake up in the morning and fall asleep at night.

What are the other biological rhythms?

Aside from circadian rhythms, there are three other types of biological rhythm: diurnal, ultradian and infradian.

1. Diurnal

Closely linked to the circadian rhythm, these biological rhythms centre around day and night. Unlike the circadian rhythm, they can’t be kicked out of sync. Rather, it refers to whatever cycle our body goes through in the daytime and night. So, for sleep chronotypes who don’t follow a typical sleep routine, their diurnal rhythm will be different from the norm.

2. Ultradian

These rhythms complete over a much shorter time period than circadian or diurnal. For example, they can refer to the lifespan of a heartbeat. They repeat in a loop throughout the day and are what keep us going all day and night.

3. Infradian

These rhythms are the opposite of ultradian and stretch way beyond 24 hours. They can refer to breeding and hibernation in mammals, menstruation, hair growth and more. At it’s most basic, infradian refers to any rhythms that are those which last more than a day.

Circadian rhythms and the link to sleep

As experts on all things sleep, we thought it’s time to take a look into the science behind circadian rhythms, specifically focusing on the sleep-wake cycle. We’ve touched on this before, with our visual graphic on how to reset your body clock.

What can disrupt your circadian rhythm?

There are numerous factors that can affect and disrupt your circadian rhythm. If you’re struggling to sleep or keep a sleep routine, it’s worth exploring the below factors and considering whether they are affecting you.

1. Light at night

We’ve all heard about the dangers of blue light before bed. Typically, this comes in the form of screens. The lights emitted from phones, laptops and tablets trick our body into thinking it’s still daytime. This makes it more difficult to sleep. And beyond our sleep, it also impacts our mood and can cause health issues later in life. Here’s what the science journal Translational Psychiatry had to say on the matter:

“When exposure to light is mistimed or nearly constant, biological and behavioural rhythms can become desynchronized, leading to negative consequences for health. The relationship among mood disorders, light, and circadian rhythms have long been recognized.”

2. Shift work sleep disorder

Shift work disorder is a risk for those whose work activity begins, or ends, outside of the standard daytime working hours of 7am to 7pm. And with the always-on nature of the 21st century, the number of people working in these industries is increasing. For bartenders in late licence bars, healthcare workers on night shifts, and countless other irregular hours workers, the body will find it difficult to differentiate between sleep time and work time. A big factor that affects shift work disorder is the production of melatonin. This hormone is what kicks in our sleep routine but it is only produced at night. For those trying to sleep in the day, a focus on your melatonin levels could be key. Read more in our guide to melatonin and sleep.

How can I fix this?

Obviously, you can’t just leave your job and take on new shifts. So, combatting shift work disorder through other means is important. Here are some tips:

  • Wear blue light blocking glasses when working with screens
  • Incorporate foods which boost melatonin into your diet – read more in the diet and nutrition section further on in this article.
  • Embrace the outdoors to help realign your body clock with the natural world.
  • Create and stick to an exercise routine
  • Avoid alcohol and caffeine for at least 8 hours before you plan to go to sleep.

3. Social jet lag

If the only downside of holidays abroad is jet lag, then the downside of weekends is a phenomenon called social jet lag. In scientific circles, this term refers to how we alter our sleep cycle to account for social events. Coined by German researcher Till Roennenberg in 2006, this theory largely centres on the discrepancies between our sleep and wake routines on weekdays and weekends. Here’s how he describes social jet lag:

“We proposed SJL as a concept that describes and quantifies the chronic discrepancy between an individual’s biological clock and the social clock. As such, we envisioned SJL as a measure of circadian misalignment.”

In the study for Translational Psychology, further research was undertaken on how sleep is impacted by discrepancies between work or school and our social lives:

“A large scale epidemiological study confirmed that both sleep timing and duration are substantially challenged by work and school schedules or other social events. To align sleep and wake times with social obligations, 80% of the population uses alarm clocks on school or workdays. Early school and work schedules are particularly difficult for individuals with late chronotypes.”

How can I combat social jet lag?

Fortunately, we’re not here to advocate for missing social events. After all, socialising is important for our mental health. It’s quite simply about balance. Try to ensure you aren’t staying up late multiple times a week. If you can limit your late nights to one per weekend that should help. And on those nights where you’re getting to bed late, set your alarm for a reasonable time the next day. Try not to sleep into the afternoon as this will kick your circadian right out of sync.

4. Diet and nutrition

It’s common knowledge that caffeinated and alcoholic drinks are bad for our sleep routine. Put simply, they’re loaded with chemicals that make it difficult for our body to nod off. But when it comes to diet and nutrition for your circadian rhythm, there is more that can be taken into account.

For example, there are plenty of foods which can help boost melatonin, a crucial hormone for sleep. Most commonly, there are plenty of foods which contain the following sleep-inducing minerals and vitamins:

  • Tryptophan – an amino acid which turns into serotonin and then melatonin
  • Magnesium – a natural relaxant that helps reduce adrenaline
  • Calcium – a mineral widely known for its sleep-inducing properties, indicated to help those who suffer from insomnia
  • Vitamin B6 – a vitamin which helps produce serotonin and melatonin
So, what should I be eating to help realign my circadian rhythm?

Here’s a starter pack for what to include in your diet to help boost melatonin and kick-start your circadian rhythm. Hopefully, you’ll already have incorporated some of these into your diet:

Tryptophan-rich foods: dairy, poultry, nuts and seeds, grains
Magnesium-rich foods: bananas, soybeans, cashews, almonds, salmon, low-fat yoghurt, wheat
Calcium-rich foods: low-fat milk, cheese, broccoli, enriched bread and grains
Vitamin B6-rich foods: pistachio nuts, flaxseed, dried prunes, spinach, bananas



There’s quite a lot to circadian rhythms! Especially the one which controls your sleep-wake cycle. First and foremost, it’s important to understand that it’s a real thing, and the connection to light and the time of day are key. For those struggling to keep a sleep routine, it’s important to do all you can to get yours back in order. Avoiding blue light and eating sleep-inducing foods is a good start. Try our Sleep Cycle Calculator to find out how many sleep cycles you need to feel truly rested.

About the author

More from the Sleep Matters Club