The way we function and feel varies across the 24-h day/night cycle. Circadian (approximately 24-hour rhythms) are generated at the level of individual cells by a protein production feedback loop involving a small number of ‘clock genes’. Rhythms in cells, tissues and organs are synchronised throughout the body by a pacemaker, the circadian body clock, in the hypothalamus. The circadian clock receives information about light intensity from specialised cells in the retina, making it sensitive to the day/night cycle, and it programmes us to sleep at night.
Shift work can require people to be awake when the circadian clock dictates they should be asleep, and to try to sleep when they should be awake. Depending on the timing of shifts, this can lead to regular sleep restriction on work days. There is growing evidence that both sleep restriction and repeated disruption of the circadian time-keeping system can have adverse effects on metabolism. For shift workers, misalignment between meal patterns and circadian rhythms in tissues such as the pancreas and liver may also contribute to metabolic changes. Together, these factors are likely to contribute to shift workers being at greater risk of developing obesity and type 2 diabetes, compared to day workers.
Shift work and the gut microbiome (collaboration with Plant and Food Ltd)
Gut microbiota also have endogenous circadian rhythms that are synchronized by a person’s eating patterns. As a result, the functioning and composition (relative numbers of different organisms) in the gut biota change across the day. There is experimental evidence showing that disruption of the gut biota rhythms can cause metabolic disruption in the host (mice or humans) that can increase the risk of developing obesity and type 2 diabetes.
In 2016, the Sleep/Wake Research Centre collaborated with Plant and Food Ltd to conduct a small project to increase our understanding of the effect of shift work on metabolism and gut bacteria. This work is ongoing and involves recruitment of shift workers and their non-shift working partners to examine differences in gut health and metabolism.
The gut microbiome: a new pathway to obesity prevention and metabolic health
The Sleep/Wake Research Centre was also part of a multidisciplinary team led by Professor Bernhard Breier (Chair in Human Nutrition, College of Health, Massey University), which was working on a project to increase understanding of the key modifiable factors that help sustain metabolic health and prevent weight gain and increased body fatness. The study investigated associations between different body fat profiles and a wide of metabolic health risks and predictive factors including sleep patterns, among 20- to 40-year-old NZ European and Pacifica women. Data collection is completed and we are currently analyzing the sleep data derived from activity watches and questionnaires.
Funding: Health Research Council project grant ( 2015-2018) to Prof Bernhard Breier.