Large, population-based studies have identified robust links between shift work and increased cancer risk. Much of this risk is associated with disruptions in the body’s circadian rhythms, the 24-hour cycles of biological, hormonal, and behavioral patterns. A recent study suggests that circadian dysregulation of DNA repair mechanisms drives the increased cancer risk associated with shift work.

Circadian rhythms influence many physiological pathways associated with cancer, such as regulation of the cell cycle, cell proliferation, and inflammation. These rhythms also influence mechanisms that repair DNA damage – which can drive mutations that promote cancer.

The study involved 14 healthy men and women (22 to 34 years old) who participated in a simulated shift work experiment at a sleep laboratory. Half of the participants completed a simulated night shift schedule for three nights in which they were awake from 6 p.m. to 10 a.m. The other half completed a simulated day shift schedule for three days in which they were awake from 6 a.m. to 10 p.m. The study participants received a snack and provided blood samples every three hours. After completing their three days of respective shift work schedules, they underwent a 24-hour study protocol in which they were kept awake for 24 hours in low light in a semi-recumbent posture and received hourly snacks. Every three hours the study investigators took a blood sample from the participants. They analyzed the white blood cells from the samples and then exposed the cells to radiation in the morning and evening.

The authors found that the rhythms of many of the cancer-related genes in the white blood cells were different among the night shift workers compared to the day shift workers. Notably, genes related to DNA repair that showed distinct rhythms of expression during the day shift lost their rhythmicity during the night shift. They also found that the night shift workers' cells that were exposed to radiation in the evening showed more DNA damage – an indication that they were more vulnerable to external stressors.

These findings suggest that night shift work alters circadian DNA repair mechanisms and promotes DNA damage, thereby increasing cancer risk. One strategy for ameliorating the harmful effects of night shift work is time-restricted eating. Learn more in this episode featuring circadian rhythm expert Dr. Satchin Panda..

• Link to study abstract.