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Introduction
The definition of shift work usually encompasses work time arrangements outside of conventional daytime hours, which includes fixed early morning, evening, and night work, as well as roster work and rotating three shift work. The term rotating three shift work implies that employees rotate (alternate) more or less regularly between a day, an evening, and a night shift. About 29% of workers in the United States have work time arrangements outside of the normal workday of 0600-1800, 1 and many of these work nights. EU statistics from 2015 showed that about 19% of all employees work nights at least once a month. 2
Shift work forcefully disrupts the normal sleep-wake cycle, leading to short sleep and excessive fatigue. 3 4 Evidence has suggested that shift work may also affect long term health and safety, with several studies reporting elevated risks for breast cancer and coronary heart disease. 5 The evidence is inconsistent, however, and it is now accepted that shift work is not a definite causal factor for chronic disease. 6 A critical problem preventing progress in the field concerns a poor understanding of the pathways and mechanisms by which shift work may lead to chronic health problems.
Robust support exists for insufficient sleep causing adverse immunological and metabolic changes, 7 causing cognitive impairments, 8 9 and increasing the risk for chronic diseases. 10 11 Thus, short sleep or poor sleep quality (that is, insomnia related symptoms) could be a mediator of the relation between shift work and adverse health effects. Although several narrative reviews have assessed how shift work affects sleep, very few discuss whether insufficient sleep could lead to impaired health.
The aim of this review is to critically evaluate the evidence for links between shift work, chronic health problems, and occupational accidents. A central theme concerns whether insufficient sleep is a plausible mechanism of adverse health outcomes among shift workers. To expose the role of sleep as a pathway for chronic disease and accidents in shift work, we also examined the epidemiological link between short sleep, as well as poor sleep quality, and the same health outcomes used in the review of shift work and health. Furthermore, we reviewed recent experimental models related to sleep loss, circadian disruption, and physiological changes...