Focus on Fatigue

Shift Work and the Metabolism

By January 10, 2019 No Comments

Welcome to Focus on Fatigue!

It’s a brand new year and that means a fresh start! Every January provides a great opportunity to reflect on the habits of the previous year, and plan for ways we can improve over the coming twelve months. For example, if you haven’t been getting enough sleep, then committing to some extra shuteye is an easy way to increase energy, improve focus and maintain health. So, let’s all get the year off to a great start… by taking a nap!

Before you grab that blanket and pillow, this month’s Focus on Fatigue will be investigating the how and why of the metabolic disturbances that are often associated with shift work.

Best wishes for the year ahead,
The FRMS Team



InterDynamics Pty Ltd
320 Adelaide Street Brisbane Qld 4000
Tel +61 7 3229 8300

Views expressed in articles and links provided are those of the individual authors, and do not necessarily represent the views of InterDynamics (except where directly attributed).


Shift Work and the Metabolism

All humans are wired by nature to be awake during the day and asleep at night. This fundamental truth, set by our circadian rhythm, is something we cannot ever truly escape. However, our society requires that a sizable portion of us work in shifts through both the day and night. One of the major consequences of this requirement is the increase in metabolic disorders seen among shift workers.

How does shift work disrupt the metabolism?

Shift work disrupts the metabolism in several ways, for example:

  • Ghrelin/Leptin – Ghrelin is a hormone produced when we need food. Leptin is produced when we have eaten enough. Shift work produces a desynchrony between these hormones. This leads to feelings of hunger in the middle of the night, especially for unhealthy food, without the stop needed to prevent overeating. Hence, the increased risk of obesity seen in shift workers.
  • Estrogen/Testosterone – There is an ageing component to these hormones. Older people have more difficulty adapting to shift work than younger people.
  • Inflammation – The HPA axis regulates stress hormones (the fight or flight response), so disruption makes people less able to deal with stress. This produces a state of chronic inflammation in the system. Obesity plays into inflammation (through fat tissue signalling) and makes it worse.
  • DNA Damage – Melatonin is believed to be a scavenger of free radicals. When the regulation of melatonin is upset it causes damage to the DNA, which the body then has less ability to repair. This leads to increased cancer risk.

In other words, there are many parts and players in this very complex system. They are all supposed to be in sync. Shift work, however, can upset the balance.

Study of Food Timing and Metabolomics in Shift Workers

A study conducted by Washington State University examined the effects of simulated shift work on the circadian rhythm and metabolic processes. Participants (stereotypically healthy people without sleep disorders) were separated into two groups. Those who underwent a series of three simulated night shifts, and those who underwent days shifts. Meals were timed at regular intervals throughout the night or day depending on which shift schedule the participants followed. Following the three ‘shifts’, all participants were kept awake for 24-hours in a constant environment (ie. lighting, posture, food, food timing, etc was kept constant) with regular blood samples taken to test hormone levels.

The Results

At the end of the three days of simulated night shifts, the onset of the hormone melatonin (a major indicator of the body’s circadian rhythm) shifted by only 1.5 hours. This is far short of the 12-hour shift that would be necessary for true ‘adjustment’ to the night shift hours. This was also true for a number of other hormones known to be closely related to the circadian rhythm, such as cortisol.

However, many of the hormones involved in the metabolic processes flipped their readings by the full 12 hours, lining up with the night shift schedule.

This produced a profound desynchrony between the circadian rhythm and the metabolic system. One system was convinced it was day, while the other had decided it was night.

What does this mean?

It has been thought that the metabolic disruption experienced by shift workers was due primarily to the misaligned biological clock. However, this may not be the whole story. It may be that other ‘clocks’ within the body are also involved.

This study showed that hormones involved in the metabolic processes may quickly align themselves to different sleep/wake and feeding/fasting schedules, even though the circadian rhythm is not so easily shifted.

Therefore, during night shifts it is possible that the biological clock will appear to be signalling night-time, where other peripheral oscillators (other clocks within the body) are signalling day-time, causing internal desynchronization.


  • van Dongen, H. (2018) Metabolomics: A new window on peripheral oscillators. Sleep Down Under 2018. 17-20 October 2018. Brisbane, Australia.


In the News

Provided below are a selection of articles from around the web on the issues associated with fatigue. We hope you find them useful and interesting.

Video: Researchers gain new perspectives on how shift work disrupts metabolism
KXLY, YouTube (13 July 2018)
A new study impacts millions of people who don’t work a typical nine to five job. KXLY4’s Ariana Lake reports. Including an interview with Dr Hans van Dongen of the WSU Elson S. Floyd College of Medicine.

Article: How shift work disrupts metabolism
Science Daily (9 July 2018)
A new study has brought scientists closer to finding out why working night shifts increases your risk of developing diabetes and other metabolic disorders. The study revealed that just three days of being on a night shift schedule will disrupt metabolism. This disruption appears to be driven by separate biological clocks (so-called peripheral oscillators) in the liver, gut and pancreas, rather than the brain’s master clock.

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