Why Does Night Shift Work Increase Cancer Risk?

A new US study has offered insight as to why night shift workers are at an increased risk of developing certain types of cancer.

Conducted at Washington State University, and published in the Journal of Pineal Research, the study involved a controlled laboratory experiment that used healthy volunteers who were on simulated night shift or day shift schedules.

The researchers found that night shifts seem to disrupt the natural 24-hour rhythms in the activity of certain cancer-related genes.

This makes night shift workers more vulnerable to damage to their DNA while at the same time causing the body’s DNA repair mechanisms to be mistimed to deal with that damage.

“There has been mounting evidence that cancer is more prevalent in night shift workers, which led the World Health Organization’s International Agency for Research on Cancer to classify night shift work as a probable carcinogenic,” said co-corresponding author Shobhan Gaddameedhi, an associate professor at North Carolina State University.

“However, it has been unclear why night shift work elevates cancer risk, which our study sought to address.”

The study involved a simulated shift work experiment involving 14 young adults – half of which followed a night shift schedule for three days, and the other half a day shift schedule.

Analyses of white blood cells taken from blood samples showed that the rhythms of many of the cancer-related genes were different in the night shift condition compared to the day shift condition.

Notably, genes related to DNA repair that showed distinct rhythms in the day shift condition lost their rhythmicity in the night shift condition.

What’s more, after the researchers exposed isolated white blood cells to ionizing radiation at two different times of day, cells that were radiated in the evening showed increased DNA damage in the night shift condition as compared to the day shift condition.

This meant that white blood cells from night shift participants were more vulnerable to external damage from radiation, a known risk factor for DNA damage and cancer.

“Nightshift workers face considerable health disparities, ranging from increased risks of metabolic and cardiovascular disease to mental health disorders and cancer,” said co-senior author Hans Van Dongen, a professor, and director of the WSU Sleep and Performance Research Center.

“It is high time that we find diagnosis and treatment solutions for this underserved group of essential workers so that the medical community can address their unique health challenges.”

The researchers say the next step is to conduct the same experiment with real-world shift workers to determine whether the DNA damage builds up over time – increasing the risk further.

The work is expected to eventually be used to develop prevention strategies and drugs that could address the mistiming of DNA repair processes.