CIRCADIAN RHYTHMS

Healthy from the Start Resources for Shiftworkers

Circadian rhythms are like clocks that live in every cell, keeping you on a 24-hour schedule. Shiftwork, with its irregular light exposure and non-traditional eating and sleeping times, can disrupt the individual circadian rhythms throughout your body, as well as the overall circadian system.

Circadian rhythms are driven by the in-built clocks that exist in every cell of your body, running on a roughly 24-hour cycle. Circadian is from Latin - circa means ‘about’ and dian means ‘day’.

Circadian rhythms play a key role in regulating body functions throughout the day and night, including (15):

  • Hormone Production and Release: timing the release of various chemicals in your body.

  • Hunger and Metabolism: regulating when you feel hungry and how your body processes food.

  • Vital Signs: controlling body temperature, heart rate, and blood pressure.

A clock isn’t very useful if it doesn’t keep time accurately. The same is true for your circadian rhythms – things that you do every day (and night) help your circadian rhythms to align with a 24-hour cycle.

For shiftworkers, maintaining synchronisation is a challenge. Irregular work schedules mean exposure to light, eating, and sleeping often happen at times that conflict with your natural circadian rhythms – this is called circadian disruption (16).

This circadian disruption can impact not just individual cellular rhythms, but also the overall coordination of the circadian system. As a result of this disruption, shiftworkers are at higher risk of a range of issues related to sleep, health, and wellbeing (16). Read more about the impacts of poor sleep and circadian disruption here.

While each cell has its own rhythm, these need to be synchronised for optimal functioning. This is where the circadian system comes into play. It acts as the master coordinator, ensuring all these individual rhythms are in harmony – kind of like winding a clock or setting the correct time zone.

The circadian system includes the master clock in your brain, peripheral (outer) clocks throughout your body, as well as neural (nerve) and hormonal (chemical) pathways. The circadian system responds most strongly to the light (and darkness) cues that your eyes pick up, and this helps to keep all your daily rhythms aligned with the external environment and with each other (15).