Working Time Society consensus statements: Circadian time structure impacts vulnerability to xenobiotics—relevance to industrial toxicology and nonstandard work schedules

Abstract

The circadian time structure (CTS) has long been the subject of research in occupational medicine, but not to industrial toxicology, including methods of setting threshold limit values (TLVs) and employee biological monitoring. Numerous animal and human investigations document vulnerability to chemical, contagion, and other xenobiotics varies according to the circadian time of encounter. Permanent and rotating nightshift personnel are exposed to industrial contaminants in the same or higher concentration as dayshift personnel, and because of incomplete CTS adjustment to night work, contact with contaminants occurs during a different biological time than day workers. Thus, the amount of protection afforded by certain TLVs, especially for employees of high-risk settings who work night and other nonstandard shift schedules, might be inadequate. The CTS seems additionally germane to procedures of employee biological monitoring in that high-amplitude 24 h rhythms in biomarkers indicative of xenobiotic exposure may result in misjudgment of health risks when data are not gathered in sufficient frequency over time and properly interpreted. Biological reference values time-qualified for their rhythmic variation, currently of interest to laboratory medicine practice, are seemingly important to industrial medicine as circadian time and work-shift specific biological exposure indices to improve surveillance of personnel, particularly those working nonstandard shift schedules.

Does the compromised sleep and circadian disruption of night and shiftworkers make them highly vulnerable to 2019 coronavirus disease (COVID-19)?

“…The circadian structure of shiftworkers when working a night shift of several days duration must be reorganized to accommodate the unnatural routine of activity during the dark phase and sleep during the light phase of the day. The necessary biological adjustments result in a transient state of circadian disturbance, i.e., circadian disruption, that can increase vulnerability to chemical and other xenobiotic stressors (Smolensky et al 2019).…”

“…In the long term, rotating shiftwork may give rise to chronic adaptive stress, and as shown in Figure 1, with possible repercussions on the neuroendocrine-immune system (Shields 2002) that results in attenuation of immune responsiveness (Amati et al 2007;Boscolo et al 2009;De Gucht et al 1999;Endresen et al 1987;Okamoto et al 2008), evident by increased CD3 + CD16, CD56 + cell numbers, increased IL-6 plasma levels, reduced CD57 + , CD8 + , CD11b + cell numbers, reduced LT function (Curti et al 1982;Nakano et al 1982), and attenuated NK activity (Magrini et al 2006;Morikawa et al 2005;XU et al 1998). Accordingly, SD in combination with altered circadian time structure may result in increased vulnerability during night shift not only to industrial contaminants but contagions, such as viruses (Smolensky et al 2019).…”

International consensus statements on non-standard working time arrangements and occupational health and safety

“…They describe and evaluate the current evidence for chronic diseases such as cardiovascular and cancer, other physical effects such as metabolic syndrome, reproductive disorders and gastrointestinal illnesses, and mental health effects such as depression. Circadian time structure impacts vulnerability to xenobiotics—Relevance to industrial toxicology and nonstandard work schedules. Smolensky and colleagues23 ) consider human circadian rhythms and raise the question that if workplace threshold limits and biological monitoring methods for toxic exposures are based on studies of daytime workers, should they be revisited and adjusted for those working at night? Recommendations from the authors include considerations in improving measurements of circadian timing and its association with acute and chronic adverse health effects to inform workplace threshold limits. Psychosocial stressors relevant to the health and well-being of night and shift workers .…”

“…Circadian time structure impacts vulnerability to xenobiotics—Relevance to industrial toxicology and nonstandard work schedules. Smolensky and colleagues23 ) consider human circadian rhythms and raise the question that if workplace threshold limits and biological monitoring methods for toxic exposures are based on studies of daytime workers, should they be revisited and adjusted for those working at night? Recommendations from the authors include considerations in improving measurements of circadian timing and its association with acute and chronic adverse health effects to inform workplace threshold limits.…”

Important Difference between Occupational Hazard Exposure among Shift Workers and Other Workers; Comparing Workplace before and after 1980

“…According to the literature, this association between shift work and poorer health could be explained through the disruption of the circadian rhythms, perhaps as a result of physiological and psychological maladaptation to chronically shifted patterns [ 16 ]. Yet, since the circadian cycle is known to affect sensitivity to different stressors, exposure to hazardous substances may be worse for “non-standard hour” workers [ 17 ]. However, only few studies investigated and controlled for exposure to occupational health hazards among shift workers (e.g., noise, heat, dust, as well as chemical exposure at work).…”