Effects of Shift Work on Toxicology and Carcinogenesis

Abstract

The existence of biological clocks that control many of our daily activities and physiological functions has always been part of tacit knowledge. Biological clocks tuned to the earth's 24‐h light/dark cycles are a fundamental property of all life on earth. We now understand that essentially every cell in our body has a free‐running molecular clock with an intrinsic periodicity of ∼24 h. These peripheral clocks are synchronized by a central timekeeper in the brain whose periodicity is determined by the amount of light entering the eyes. The central pacemaker coordinates peripheral clocks with the earth's rotation cycle. Social activities, occupations, and environmental exposures (e.g., light pollution, working at night, stress, conflict, illness, social pressures, chemical exposures, noise, and lifestyle) that disrupt biological clocks affect the quality of our sleep, our sense of well‐being, as well as our ability to function, perform tasks and learn. More importantly, chronic circadian disruption negatively impacts our health and susceptibility to chronic diseases and aging. An estimated 20–30% of the modern workforce is employed in jobs that require working night shifts associated with circadian disruption, putting a significant fraction of the workforce at increased risk of poor performance, errors, accidents, and decreased quality of life and health. To address this increasing public health issue, toxicologists, industrial hygienists, and occupational health clinicians must understand mechanisms by which exposures disrupt biological clocks, and use this knowledge to develop and implement targeted preventive, interventions, and mitigation strategies to reduce risks.