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That disruptions of the body's internal clockwork can lead to negative health consequences, including cancer, is a plausible hypothesis. Yet, despite strong mechanistic and animal support, the International Agency for Research on Cancer (IARC) experts considered epidemiological evidence as limited regarding the carcinogenicity of "shift-work involving circadian disruption" (2007) and "night shift work" (2019). We use directed acyclic graphs (DAGs) to outline a concept of circadian causes that discloses challenges when choosing appropriate exposure variables. On this basis, we propose to move beyond shift-work alone as a direct cause of disease. Instead, quantifying chronodisruption as individual doses can lead to interpretable circadian epidemiology. The hypothesis is that doses of chronodisruption cause disrupted circadian organisation by leading to desynchronization of circadian rhythms. Chronodisruption can be conceptualized as the split physiological nexus of internal and external times. Biological (or internal) night – an individual's intrinsically favoured sleep time window – could be the backbone of circadian epidemiology. In practice, individual doses that cause disrupted circadian organisation are derived from the intersection of time intervals of being awake and an individual's biological night. After numerous studies counted work shifts, chronobiology may now advance circadian epidemiology with more specific dose estimation – albeit with greater challenges in measurement (time-dependent individual data) and analysis (time-dependent confounding). [ABSTRACT FROM AUTHOR]

Planned burning is a preventative strategy aimed at decreasing fuel loads to reduce the severity of future wildfire events. During planned burn operations, firefighters can work long shifts. Furthermore, remote burning locations may require firefighters to sleep away from home between shifts. The existing evidence surrounding firefighters’ sleep during such operations is exclusively anecdotal. The aims of the study were to describe firefighters’ sleep during planned burn operations and evaluate the impact of the key operational factors (shift start time, shift length and sleeping location) that may contribute to inadequate sleep. Thirty-three salaried firefighters were recruited from Australia’s fire agencies and sleep was measured objectively using wrist actigraphy for four weeks. All variables were examined in two conditions: (1) burn days, and (2) non-burn days. Time in bed, total sleep time, sleep latency and sleep efficiency were evaluated objectively. Subjective reports of pre- and post-sleep fatigue, sleep location, sleep quality, sleep quantity, number of times woken and sleep timing were also recorded. Analyses revealed no differences in measures of sleep quantity and quality when comparing non-burn and burn days. Total sleep time was less when planned burn shifts were >12 h. However, on burn days, work shift start time as well as sleeping location did not impact firefighters’ sleep quantity. Self-reported levels of pre- and post-sleep fatigue were greater on burn days compared to non-burn days. These findings indicate that sleep quantity and quality are not compromised during planned burn operations <12 h in duration. [ABSTRACT FROM PUBLISHER]

Studies have shown a relationship between circadian rhythm disruptions and type-2 diabetes. This investigation examined the effects of circadian disruption (6-h phase advances) on the progression of diabetes in a type-2 diabetic mouse model –TALLYHO/JngJ – and whether wheel-running can alleviate the effects of the phase advances. 6-h advances alter fasting glucose, glucose tolerance and insulin production. Wheel-running reduced body mass, improved glucose tolerance and reduced insulin in TALLYHO/JngJ and alleviated some of the changes in diabetic symptoms due to 6-h advances. These results indicate that individuals with type-2 diabetes can benefit from physical activity and exercise can be a countermeasure to offset the effects of an acute phase advance. [ABSTRACT FROM PUBLISHER]

The aim of this pilot study was to explore the risk of metabolic abnormalities in steel workers employed in different shift-work rotations. Male workers in a steel factory [16 employed in a fast clockwise rotation (CW), 18 in slow counterclockwise rotation (CC), 9 day workers (DW); mean age 43.3 ± SD 6.8 years] with at least 5 years experience in their current work schedule participated. All workers provided fasting blood samples between 06:00 and 08:00 h for plasma glucose, insulin, apo-lipoproteins A and B (ApoA, ApoB), high- and low-density lipoproteins (HDL and LDL), total cholesterol (tCH), triglycerides (TG), minimally oxidized (mox) LDL, C-reactive protein (CRP), interleukin-8 (IL-8) and serum 25-hydroxyvitamin D (25(OH)D). HOMA index (homeostatic model assessment) was calculated to evaluate insulin resistance, beta cell function and risk of diabetes. Information on demographics, health, stimulants, sleep, social and work life, chronotype (phase of entrainment) and social jetlag (difference between mid-sleep on workdays and free days) as a surrogate for circadian disruption was collected by questionnaire. Neither chronotype nor social jetlag was associated with any of the metabolic risk blood markers. There were no significant differences in 25(OH)D, ApoA, ApoB, CRP, HDL, IL-8, insulin, LDL, mox-LDL, mox-LDL/ApoB ratio, tCH and TG levels between the three work groups. Although we did observe absolute differences in some of these markers, the small sample size of our study population might prevent these differences being statistically significant. Fasting glucose and HOMA index were significantly lower in CW compared to DW and CC, indicating lower metabolic risk. Reasons for the lower fasting glucose and HOMA index in CW workers remains to be clarified. Future studies of workers in different shift rotations are warranted to understand better the differential effects of shift-work on individual workers and their health indices. [ABSTRACT FROM AUTHOR]

The effects of shift and time-on-shift on alertness and perceived tension, as well as related physiological variables, were investigated in satellite controllers working a rapid forward rotating three-shift system. In controlled laboratory conditions, subjective tension and HR have been reported to display circadian variation and marked sensitivity to external factors. We examined whether circadian variations were masked for these particular variables in real-job conditions, unlike for alertness and body temperature, which have been repeatedly shown to display circadian variation in these conditions. This hypothesis was tested in a repeated-measures design by collecting alertness and tension self-reports and recording operators' sublingual temperature on three occasions on each shift and HR continuously throughout shifts. Alertness and body temperature varied according to a typical diurnal trend; subjective tension was only enhanced on the initial recording of each shift (compared to the remaining ones), while HR displayed an intermediary trend. Intra-subject correlations revealed a positive relationship between alertness, oral temperature, and HR, while no such relationship was found for subjective tension. These results support the hypothesis of a close dependence of alertness and temperature, and to a lesser extent for HR, on endogenous mechanisms in this job-situation. In addition, some situation-specific factors, such as job-demand, would affect subjective tension and partially mask the circadian variations in HR. [ABSTRACT FROM AUTHOR]

Relay operations are an important mode of freight transportation within Australia. Relay work requires multiple crews to drive the train continuously from one specified destination to another and return. Importantly, the nature of relay work requires train drivers to sleep on‐board during designated resting shifts. The main aim of the present study was to investigate the quality and quantity of sleep obtained in on‐board rest facilities (relay vans) during extended (four‐day) relay operations. Drivers (n=9) working the Port Augusta to Darwin relay operation volunteered to participate. The first leg of the trip typically took 40 h followed by an overnight stay in Darwin (between 8–12 h) prior to return. Two crews, each consisting of two drivers, changed every 8 h, giving the crew an 8 h rest in the relay van prior to each 8 h working shift. Using polysomnography, home sleep data were collected prior to and following each trip using a standard five‐channel EEG montage. All sleep periods during the relay trip (including Darwin) were also recorded. Additionally, subjective sleep quality ratings were recorded following each sleep period. Analyses revealed that the quantity of sleep obtained in the relay vans (3.3 h) was significantly reduced compared to home (6.8 h). In general, the total sleep time was increased at night and reduced during the day. In terms of quality, sleep onset latency, sleep efficiency, and amount of slow wave and rapid eye movement sleep did not differ significantly between home and the relay vans. The results of the study highlight sleep quantity as the main concern during extended relay operations. Future research should focus on investigating the subjective and objective impact of this sleep reduction on waking functions. [ABSTRACT FROM AUTHOR]