For the laboratory-controlled, simulated shift work study, 14 healthy participants were split into two groups. The first group did the “day shift” sleeping from 10pm to 6am over a 72 hour period, while the second group did the “night shift” staying awake overnight and sleeping from 10am to 6pm. For the following 24 hours, the researchers tested the participants' blood every three hours to analyse levels of melatonin and cortisol (the hormones related to your body’s circadian rhythm) and metabolites associated with digestion.
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The results showed that the three night shifts moved the brain’s master clock by two hours on average, while the digestive system clock was moved by 12 hours. These findings demonstrate how diverse our internal biological clocks can be and although the brain utilises light changes to dictate sleeping patterns, other organs operate differently. Researchers knew that these different systems could fall out of sync, but said they were surprised at how much.
Debra Skene, the first author on the study, told The Guardian that the results will help further investigation into the harms of shift work, which has previously been associated with obesity, diabetes, heart disease and cancer. Research has also found that shift workers are more likely to develop Irritable Bowel Syndrome and abdominal pain, an association that's independent of sleep quality.
And given the essential role shift workers have in our society (hello, healthcare) it’s important to find ways to minimise the negative effects it has.
“Now that we know this, we can begin to design studies to see if we can minimise the detrimental effect of mistimed sleep and meals,” Skene said.
For a start, recent research out of the University of Adelaide suggests that committing to consistent meal times – regardless of work schedules – could help shift workers with weight maintenance.
