Biological Clocks and Shift Work: Circadian Dysregulation and Potential Long-term Effects

Abstract

Long-term epidemiologic studies on large numbers of night and rotating shift workers have suggested an increase in the incidence of breast and colon cancer in these populations. These studies suffer from poor definition and quantification of the work schedules of the exposed subjects. Against this background, the pathophysiology of phase shift and phase adaptation is reviewed. A phase shift as experienced in night and rotating shift work involves desynchronization at the molecular level in the circadian oscillators in the central nervous tissue and in most peripheral tissues of the body. There is a change in the coordination between oscillators with transient loss of control by the master-oscillator (the Suprachiasmatic Nucleus, SCN) in the hypothalamus. The implications of the pathophysiology of phase shift are discussed for long-term health effects and for the design of ergonomic work schedules minimizing the adverse health effects upon the worker.

The Model of Changes in the Psychomotor Performance of the Production Workers

“…Limits which are sometimes organisationally imposed on coffee consumption cause workers' dissatisfaction together with a related stress, as well as demotivation and a sensation of excessive fatigue in workers. Studies confirm that the incidence of diseases of the digestive system is several times greater in workers working on night shifts than in the rest of the staff [14,21,27,32,35,36]. This is associated with the impaired intestinal peristalsis and the irregular secretion of digestive juices.…”

“…Depending on a number of different conditions of the worker's working environment and seniority, these may produce symptoms, such as sleep disorders, lack or excess of appetite and problems with excretion of products of metabolism [30][31]. Many years of study in different scientific centres suggests that the populations of workers employed on night shifts suffer from diseases of the circulatory system, gastrointestinal dysfunction, peptic ulcers, diabetes, obesity [32][33], states of chronic fatigue, anxiety, sleep disturbances and depression [21,27,[34][35] more often than people who work only during the day. Night work disrupts the eating cycle, as well.…”

Work at night and breast cancer – report on evidence-based options for preventive actions

“…The degree of circadian adjustment varies significantly in relation to shift schedules, although the evidence is still limited (36)(37)(38)(39). Factors influencing the degree of circadian disruption are mostly related to specific shift characteristics like timing, speed (ie, number of consecutive night shifts), duration and direction of shift rotation as well as factors related to the actual light exposure (intensity, wavelength and timing).…”

Sleep duration and cancer risk: time to use a “sleep-years” index?

“…To provide but one example, studies for which Drs. Haus and Smolensky called in a widely cited article [33] in the Journal to investigate suggested causal links between disrupted natural sleep-wakefulness cycles and an increased cancer incidence in shift-workers could also benefit from the SYI approach.…”