Research provides information on how working night shifts increases the risk of cancer

SPOKANE, Washington. – A new study conducted at Spokane in Health Sciences at Washington State University presents new clues as to why night shift workers have a higher risk of developing certain types of cancer.

Published online at Journal of Pineal Research, the study included a controlled laboratory experiment that used healthy volunteers who were on simulated night or day shift schedules. The study’s findings suggest that night shifts disrupt 24-hour natural rhythms in the activity of certain cancer-related genes, making night workers more vulnerable to damage to their DNA and at the same time , make repair mechanisms deal with this damage.

Although more research is still needed, one day these findings could be used to help prevent and treat cancer in night shift workers.

“There has been growing evidence that cancer is more common in night shift workers, which led the World Health Organization’s International Agency for Research on Cancer to classify night shift work. night as a probable carcinogen, “said correspondent Shobhan Gaddameedhi, a former associate professor with the WSU College of Pharmacy and Pharmaceutical Sciences and now with the Department of Biological Sciences and the State University Center for Human Health and the Environment. North Carolina. “However, it’s not clear why working night shifts increases the risk of cancer, which our study tried to address.”

Study rhythms in genes related to cancer

As part of a partnership between the WSU Sleep and Performance Research Center and the Northwest Pacific National Laboratory of the U.S. Department of Energy (PNNL), Gaddameedhi and other WSU scientists worked with PNNL bioinformatics experts. to study the possible involvement of the biological clock, an integrated mechanism that keeps us in a 24-hour night and day cycle. Although there is a central biological clock in the brain, almost every cell in the body also has its own built-in clock. This cellular clock includes genes known as clock genes that have a rhythmic expression, meaning that their activity levels vary depending on the time of day or night. The researchers hypothesized that the expression of cancer-associated genes could also be rhythmic and that night shift work could alter the rhythmicity of these genes.

To test this, they conducted a simulated shift work experiment that resulted in 14 participants spending seven days in the WSU Health Sciences Spokane sleep lab. Half of them completed a three-day simulated night shift program, while the other half were on a three-day simulated day shift program. After completing their simulated changes, all participants remained on a constant routine protocol that is used to study the internally generated biological rhythms of humans regardless of any external influence. As part of the protocol, they were kept awake for 24 hours in a semi-reclining posture under constant exposure to light and room temperature and were given identical snacks every hour. A blood sample was taken every three hours.

White blood cell analyzes extracted from blood samples showed that the rates of many cancer-related genes were different in the night shift condition compared to the day shift condition. It should be noted that genes related to DNA repair that showed different rhythms in the day shift condition lost their rhythmicity in the night shift condition.

The researchers then examined what the consequences of changes in the expression of cancer-related genes might be. They found that white blood cells isolated from the blood of night shift participants showed more evidence of DNA damage than those of day shift participants. In addition, after the researchers exposed isolated white blood cells to ionizing radiation at two different times of the day, the cells that irradiated in the evening showed more DNA damage on the night shift compared to the day. . This meant that the white blood cells of night shift participants were more vulnerable to external damage caused by radiation, a known risk factor for DNA damage and cancer.

“Taken together, these findings suggest that night shift schedules eliminate the timing of the expression of cancer-related genes so as to reduce the effectiveness of the body’s DNA repair processes when they are most needed,” he said. say Jason McDermott, author correspondent, a computer scientist in the Division of Biological Sciences at the Pacific Northwest National Laboratory.

Potential to improve prevention and treatment

The researchers’ next step is to perform the same experiment with real-world shift workers who have been constantly on day or night shifts for many years to determine whether night workers accumulate unrepaired DNA damage over the course of the day. time, which could ultimately increase the risk of cancer. If what happens in real-world shift workers is consistent with current results, that work could eventually be used to develop prevention strategies and medications that could address the falsity of DNA repair processes. It could also be the basis for strategies to optimize the timing of cancer therapy so that treatment is administered when efficacy is greatest and side effects are minimal, a procedure called chronotherapy that should be adjust to the internal rhythms of night workers.

“Night shift workers face considerable health inequalities, ranging from increased risks of metabolic and cardiovascular disease to mental health and cancer disorders,” said co-senior author Hans Van Dongen, professor at WSU Elson S. Floyd College of Medicine and director of the WSU Sleep and Performance Research Center. “It’s time to find diagnostic and treatment solutions for this underserved group of essential workers so that the medical community can address their unique health challenges.”

In addition to Van Dongen, Gaddameedhi and McDermott, the study’s authors included Bala Koritala, Kenneth Porter, Osama Arshad, Rajendra Gajula, Hugh Mitchell, Tarana Arman, Mugimane Manjanatha and Justin Teeguarden.

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