Men who have worked night shifts for more than 20 years, or who work night shifts without daytime napping, or sleep for more than ten hours per night on average may have an increased risk of cancer, according to a study published in Annals of Medicine.
The study, led by scientists based at the Huazhong University of Science and Technology, Wuhan, China, reviewed data obtained via interviews with middle-aged and older Chinese in the Dongfeng-Tongji Cohort Study, a cohort of approximately 27,000 retired workers from the Dongfeng Motor Corporation.
The researchers sought to investigate the independent and combined effects of three sleep habits on cancer incidence; night shift work, daytime napping, and night time sleep. Via a questionnaire they ascertained individuals who had worked night shifts for over 20 years, had a habit of taking day time naps, and when they usually went to sleep at night and woke up in the morning.
Dr. Stegall’s Comments: I am not surprised by these results. The body’s natural circadian rhythm closely follows sun up and sun down: we are meant to sleep when it is dark outside, and be awake when it is light outside. Multiple studies have shown that we experience our most restful and restorative sleep at night, so night shift workers do not get the quality sleep that daytime workers do. We know from other studies that environmental stressors, including poor sleep, increases cancer risk. Thus, it makes sense that those who work the night shift for a prolonged period of time (in this case, years) will have an increased risk of cancer.