Researchers from Washington State University (WSU), in collaboration with the United States Department of Energy’s Pacific Northwest National Laboratory (PNNL) have recently published results of a study investigating why night-shift work is potentially carcinogenic. The study hypothesised that some oncogenic genes are expressed in 24-hour rhythmic cycles, and that the disruption of this 24-hour cycle through night-shift pattern work can damage these genes, as well as their corresponding DNA repair mechanisms, increasing the risk of cancer.
Testing this hypothesis, the study enrolled 14 participants to spend 7 days at the sleep laboratory of WSU Health Sciences Spokane. 7 participants completed a 3-day simulated night-shift schedule, meanwhile the remaining 7 completed a 3-day day shift schedule. On completion of these protocols, all participants were kept on a routine monitoring schedule to measure their internally generated biological rhythms. This included being kept awake for 24 hours under constant light exposure in a semi-reclined position, with identical snacks given every hour, and blood samples drawn every 3 hours.
Analysis of the white blood cells in the patient blood samples showed that the rhythmic expression of some oncogenic genes was different in the 7 participants who completed the simulated night-shift schedule, and that importantly, the DNA repair mechanisms associated with these genes had also lost their rhythmic expression, meaning that DNA repair was sub-optimal at these gene loci. Unsurprisingly, the white blood cells of these night-shift samples displayed more DNA damage than samples collected from day-shift participants. Furthermore, when exposed to radiation twice a day, white blood cells from night-shift participants showed increased DNA damage compared to white blood cells from day-shift samples, indicating that night-shift pattern workers are more susceptible to DNA damage from radiation.
Moving forward, the research team plans to upscale the study to real-world setting, enrolling participants who have been on day and night-shift pattern work for years. If this real-world evidence is true to the study results, then this data could be used to develop prevention strategies and develop drugs that mitigate or remove this risk. Furthermore, this information could be used to optimise the timing of cancer therapy administration.
Koritala B et al., Night shift schedule causes circadian dysregulation of DNA repair genes and elevated DNA damage in humans. J of Pineal Res. 2021. [epub].