Shift work and risk of cancer in women

Over the last 50 years, the shift working has increased significantly in all developed and developing countries such as Iran.1,2 According to the latest statistics, about a quarter of the workforce in the United States is shift working.3,4 From a scientific point of view, the definition of shift work is: “employment at work outside of normal working hours, that is, outside the time period (7 am to 6 pm)”.5,6 Despite the usefulness of the shift work for the general public, the workers themselves are mainly affected by the complications.7 Lighting the midnight environment causes physiological changes in the secretion of the melatonin hormone.8 In a number of epidemiological studies focusing on the relationship between shift work and cancer, attention was focused on the potential negative effects of shift work, with the special emphasis on nighttime light and melatonin. In these studies, there has been an inverse relationship between continuous exposure to light at night and melatonin level.8,9 This reduction in melatonin production is detailed in a hypothesis that light exposure results in an increase in the production and amount of hormones such as estrogen, as well as changes in the growth trend of hormones Tumors in the chest.9,10 According to the results of objective studies, the risk of lung and breast cancers is high in individuals who worked as shift workers.11 The results of laboratory studies and animal studies have shown that the effects of low production of melatonin are not limited to breast cancer.12,13 This review study details the recent systematically studies, and discusses the underlying mechanisms, assumptions, and results from epidemiological and laboratory studies on the incidences of cancer in women shift workers.