‘It is unclear if there is a threshold of night shifts associated with circadian disruption’
Night shift work is attributable to hundreds of female workers who acquired breast cancer in 2011, according to a recent study.
Assuming a latency period of 10 to 50 years, The Impact of Night Shift Work on Breast Cancer: Results from the Burden of Occupational Cancer in Canada Study found that approximately two per cent to 5.2 per cent of all breast cancer cases diagnosed in women in 2011 were attributable to night shift work. The researchers came to the conclusion after looking at the total number of women who worked night shifts from 1961 to 2000 and were still alive in 2011. These numbers are comparable to data produced by recent studies on the topic in the United Kingdom and the United States.
Approximately 43 per cent of these attributable cases were diagnosed in female healthcare or social assistance professionals, 18 per cent were diagnosed in female accommodation and food services workers and 11 per cent were diagnosed each in trade employees and in manufacturing workers, the study said.
However, “it is unclear if there is a threshold of night shifts associated with circadian disruption,” the researchers said. Circadian disruption is the disruption of the internal body clock, which is “the key element believed to be associated with elevated breast cancer risk.”
The study also said exposure to night shift work can be eliminated, in theory. But in cases where it cannot be avoided, “there is evidence from workplace‐based interventions that forward‐rotating shifts that are rapid are associated with improved sleep quality and quantity.”
If shifts could be chosen based on an employee’s chronotype (individual biological clock) and previous shift work experience, their risk of acquiring breast cancer could possibly be reduced, the researchers said.