Shift Work Studies Research Articles

Critical reviews of exposure assessment in carcinogenic hazard identification: the IARC Monographs experience

ObjectivesTo summarise the rationale, workflow and recommendations for the conduct of exposure assessment critiques in key human studies evaluated for International Agency for Research on Cancer (IARC) Monographs on the...

Eating on the Night Shift: A qualitative study to understand what is important to UK night workers when designing nutritional research

The night-time economy contributed £93.7bn to the total UK economy in 2023(1) and relies on extensive employment of night workers. There is strong evidence to support the association between shift work, predominately involving night shifts, and adverse cardiometabolic health(2). However, there are limited evidence based dietary guidelines available for night workers or nutritional practitioners(3). Simulated shift work studies have significantly contributed to understanding how eating at night impacts physiology however, real world research is needed among shift workers. Engaging end users in research design is key to inform acceptable and feasible interventions.The aim of the Eating on The Night Shift study (King’s College London Ethics:LRM-22/23-35745) is to understand how UK night workers view working at night in relation to nutritional health and wellbeing and the barriers and enablers to participating in nutritional research studies.Semi-structured qualitative interviews were undertaken with a convenience sample (n=18) of UK night workers between June and September 2023. Interviews were held virtually and covered experiences of working night shifts, perceptions about night work and health, and perceptions of, and barriers and facilitators of engagement with, nutritional research. All interviews were audio recorded and transcribed verbatim. Transcripts were coded using an inductive thematic analysis approach to identify overarching themes and sub-themes(4).Of the final sample 13 were female (72%), 39% worked a rotating shift pattern, 50% had worked night shifts for between one to three years and 39% were employed in the healthcare sector. Four overarching themes were identified 1) The consequences of night work on health and wellbeing: this theme included concerns about the impact on physical and psychological wellbeing and on cognitive function during night shifts, 2) Eating at night means a less healthy diet: this theme highlighted the concerns about less healthy diets at night and how night work impacts meal planning and eating patterns, 3) Working at night has wider knock-on effects: sub themes were related to the negative impact on physical activity, sleep and social networks and 4) Nutritional research is perceived as important but there are barriers – barriers discussed were related to workload and the ability to change eating patterns, identified enablers were clear study instructions and financial compensation.The results suggest that night workers are aware of the negative long-term consequences working nights has on their health. Furthermore, efforts to maintain a healthy lifestyle are impeded by the nature of night work and its disruptions to the circadian rhythm. Although night workers support research to understand how diet during night work can impact long-term health, several barriers to taking part in research need to be considered in the design of research studies. This will ensure that studies are acceptable and feasible to the night shift population.

Circadian Disruption and Colorectal Cancer Incidence in Black Women.

Animal and experimental studies suggest circadian disruption increases colorectal cancer risk, but evidence in humans is limited. We examined night shift work, chronotype, and residential position within a time zone, proxies for circadian disruption, in relation to colorectal cancer risk. Participants in the Black Women's Health Study, a prospective cohort of 59,000 Black American women established in 1995, reported history of night shift work and chronotype on follow-up questionnaires. Residential position within a time zone was estimated using participant addresses at each questionnaire cycle. Number of colorectal cancer cases and follow-up duration varied by analysis depending on timing of exposure assessment, ranging from 204 over the 2005 to 2018 night shift work study period to 452 over the 1995 to 2018 residential position study period. Cox proportional hazards regression was used to estimate multivariable-adjusted HRs and 95% confidence intervals (CI). Compared with never having worked a night shift, working a night shift for ≥10 years was associated with increased colorectal cancer risk (HR = 1.64; 95% CI, 1.01-2.66). However, shorter duration was not. The HR for evening versus morning chronotype was 0.96 (95% CI, 0.73-1.27). Westward position of residence within a time zone was not associated with colorectal cancer risk (HR per 5-degree longitude increase: 0.92; 95% CI, 0.82-1.03). Our findings suggest a possible increased risk of colorectal cancer associated with long duration night shift work; however, results require confirmation in larger studies. Circadian disruption from long-term night shift work may contribute to colorectal cancer development in Black women.

0217 Is the Timing of the Endogenous Circadian Rhythm of Neurobehavioral Functioning Inherently Task-Dependent?

Abstract Introduction Changes in waking neurobehavioral functioning (NF) over time are governed by homeostatic and circadian processes. It has been reported that peak circadian timing varies inherently between tasks, such that the optimal timing for NF would be task-dependent. Here we investigated this idea with a simulated shift work study protocol followed by a 24h constant routine (CR) protocol to experimentally and statistically separate the circadian from the homeostatic process. Methods N=13 healthy adults (ages 25.5±3.2y; 9 men) completed a 7-day/6-night in-laboratory study. They were randomized to a 3-day simulated day shift condition (n=7) with nighttime sleep (22:00–06:00) or a 3-day simulated night shift condition (n=6) with daytime sleep (10:00–18:00). They then underwent a 24h CR protocol, during which they stayed awake under constant behavioral and environmental conditions and blood was collected at 1–3h intervals for the assessment of dim light melatonin onset (DLMO). During scheduled wakefulness, subjects completed three functionally distinct NF tasks at ~2h intervals: the Karolinska Sleepiness Scale (KSS), Digit Symbol Substitution Test (DSST), and Psychomotor Vigilance Test (PVT). Data from these tasks taken during the CR protocol were analyzed with non-linear mixed-effects regression to separate endogenous circadian effects from the homeostatic process. Results Following simulated night shift, compared to simulated day shift, on average there was a modest, 1.4h (±0.8h SE) delay in DLMO (F1,11=3.68, p=0.082). As such, the simulated night shift condition produced a 10.6h shift in alignment of the homeostatic process relative to the circadian process. Regardless of prior shift condition, the peak of the circadian rhythm effect on NF occurred post-DLMO by 16.8h (±1.0h) for KSS, 15.9h (±1.4h) for DSST, and 18.6h (±1.0h) for PVT, which was not significantly different (F2,9=1.55, p=0.26). Conclusion As proof of principle, we studied three distinct NF assays, and found only small, non-significant differences between them in the timing of underlying circadian rhythmicity. While a larger sample could have yielded statistical significance in our comparison of circadian peak times, the small magnitude of the observed difference does not support the idea of inherent task-dependent differences in the timing of the endogenous circadian rhythm’s influence on NF. Support (If Any) CDMRP W81XWH-16-1-0319 and W81XWH-20-1-0442

Simulated Night-Shift Schedule Disrupts the Plasma Lipidome and Reveals Early Markers of Cardiovascular Disease Risk.

IntroductionThe circadian system coordinates daily rhythms in lipid metabolism, storage and utilization. Disruptions of internal circadian rhythms due to altered sleep/wake schedules, such as in night-shift work, have been implicated in increased risk of cardiovascular disease and metabolic disorders. To determine the impact of a night-shift schedule on the human blood plasma lipidome, an in-laboratory simulated shift work study was conducted.MethodsFourteen healthy young adults were assigned to 3 days of either a simulated day or night-shift schedule, followed by a 24-h constant routine protocol with fixed environmental conditions, hourly isocaloric snacks, and constant wakefulness to investigate endogenous circadian rhythms. Blood plasma samples collected at 3-h intervals were subjected to untargeted lipidomics analysis.ResultsMore than 400 lipids were identified and quantified across 21 subclasses. Focusing on lipids with low between-subject variation per shift condition, alterations in the circulating plasma lipidome revealed generally increased mean triglyceride levels and decreased mean phospholipid levels after night-shift relative to day-shift. The circadian rhythms of triglycerides containing odd chain fatty acids peaked earlier during constant routine after night-shift. Regardless of shift condition, triglycerides tended to either peak or be depleted at 16:30 h, with chain-specific differences associated with the direction of change.DiscussionThe simulated night-shift schedule was associated with altered temporal patterns in the lipidome. This may be premorbid to the elevated cardiovascular risk that has been found epidemiologically in night-shift workers.

How Accurately Can We Recall the Timing of Food Intake? A Comparison of Food Times from Recall-Based Survey Questions and Daily Food Records

ABSTRACTBackgroundThere currently are no standard, low-cost, and validated methods to assess the timing of food intake.ObjectivesThe aim of this study was to validate simple, recall-based questions that can characterize food timing in free-living populations.MethodsThe concordance between recall-based survey questions and food times estimated from multiple daily food records was assessed in 249 generally healthy, free-living adults from the Shift Work, Heredity, Insulin, and Food Timing (SHIFT) Study. At baseline, participants were asked: “At what time do you first start and stop eating on weekdays/workdays and weekends/non-workdays?” and “At what time do you have your main meal on weekdays/workdays and weekends/non-workdays?” Participants were then asked to complete ≤14 d of food records noting the start time of each eating occasion. The timing of the first, last, and main (largest percentage calories) eating occasions were determined from food records. Wilcoxon matched pairs signed rank and Kendall's coefficient of concordance were used to compare differences and determine agreements between the methods for these food timing parameters, as well as for the midpoint between first and last eating occasion.ResultsEating occasions on work and free days showed significant agreements between the 2 methods, except for the main eating occasion on free days. Significant agreements were generally modest and ranged from 0.16 (workdays main eating occasion) to 0.45 (workdays first eating occasion). Generally, times based on recall were later than those estimated from food records, and the differences in estimated times were smaller on workdays compared with free days, and smaller for the first compared with the last eating occasion. Main eating occasions from food records often varied between lunch and dinner times, contributing to low concordance with recalled times.ConclusionsModest agreements were found between food times derived from simple, recall-based survey questions and food times estimated from multiple-day food records. Single administration of these questions can effectively characterize the overall timing of eating occasions within a population for chrononutrition research purposes.

Sleep disruptions and bone health: what do we know so far?

This review briefly summarizes the growing body of literature addressing the skeletal consequences of sleep and circadian disruption. The most recent data in the field suggest that the diurnal variation in bone turnover markers are because of endogenous circadian rhythmicity linked to clock genes in all bone cells; in a small human intervention study, cumulative sleep restriction with concurrent circadian disruption negatively alter bone turnover markers in a way that could explain the lower BMD and increased fracture risk identified in some prior night shift work studies; abnormal sleep duration and obstructive sleep apnea are associated with low BMD and increased fracture risk in some but not all studies. Normal physiology and some animal and human intervention studies suggest that sleep and circadian disruptions, such as night shift work, abnormal sleep durations and obstructive sleep apnea are detrimental to skeletal health. However, additional research in this area is needed to determine which sleep/circadian disturbances are most detrimental to skeletal health, the reversibility of such impairments, and underlying mechanisms.

095 Steering Wheel Angle Excursions as a Measure of Fatigue-Related Driver Performance Impairment

Abstract Introduction Fatigue from sleep loss and circadian misalignment causes automobile driving performance impairment. Metrics based on steering wheel angle, which is straightforward to measure, could be used to quantify this impairment. As the tail of the distribution of steering wheel angles (absolute magnitude of deviation from center) increases with fatigue, we investigated whether driving performance impairment could be quantified based on the prevalence of steering wheel excursions beyond a given angle threshold. We used data from two published laboratory studies of simulated shift work, in which fatigue remained low during day shifts but increased across time awake during night shifts. Methods N=37 healthy adults (ages 26.8±5.2y; 25 men) were assigned to a simulated night shift schedule (awake 20:00-10:00) or day shift schedule (awake 08:00-22:00; study 1 only). After an adaptation period, participants underwent two 5-day shift cycles with an intervening rest period. Driving performance was measured on a high-fidelity simulator during adaptation (data not used) and four times at 3h intervals during each shift day. Every drive involved 30min driving at 55mph, including ten 0.5mi uneventful straightaways being considered here. Steering wheel angle was measured at 72Hz (study 1) or 60Hz (study 2). A total of 1,471 drives (31,394,498 angle measurements) were available for analysis. Results We investigated angle thresholds across 0.01-0.25rad in 0.01rad intervals and counted the corresponding number of threshold excursions in each drive for each participant. For study 1, we applied mixed-effects ANOVA with fixed effects for condition and time awake, and their interaction, and determined the local effect size for interaction. A 0.03rad (1.7°) threshold yielded the greatest effect size, f²=0.031 (small). For this threshold, we repeated the analysis using the data from both studies, controlling for study. The interaction was significant (F[3,1428]=13.23, p<0.001), showing low driving impairment across time awake during day shifts but increasing impairment across time awake during night shifts. Conclusion The prevalence of steering wheel excursions beyond a 1.7° angle threshold yielded sensitivity to fatigue-related driving performance impairment during simulated night shifts. Further research will extend our results to driving through curves and with greater fatigue levels. Support (if any) FMCSA DTMC75-07-D-00006

Selection into shift work is influenced by educational attainment and body mass index: a Mendelian randomization study in the UK Biobank.

Shift work is associated with increased cardiometabolic disease risk. This observation may be partly explained by cardiometabolic risk factors having a role in the selection of individuals into or out of shift work. We performed Mendelian randomization (MR) analyses in the UK Biobank (UKB) to test this hypothesis. We used genetic risk scores (GRS) to proxy nine cardiometabolic risk factors and diseases (including educational attainment, body mass index (BMI), smoking, and alcohol consumption), and tested associations of each GRS with self-reported frequency of current shift work among employed UKB participants of European ancestry (n = 190573). We used summary-level MR sensitivity analyses to assess robustness of the identified effects, and we tested whether effects were mediated through sleep timing preference. Genetically instrumented liability to lower educational attainment (odds ratio (OR) per 3.6 fewer years in educational attainment = 2.40, 95% confidence interval (CI) = 2.22-2.59, P = 4.84 × 10-20) and higher body mass index (OR per 4.7 kg/m2 higher BMI = 1.30, 95% CI = 1.14-1.47, P = 5.85 × 10-5) increased odds of reporting participation in frequent shift work. Results were unchanged in sensitivity analyses allowing for different assumptions regarding horizontal pleiotropy. No selection effects were evident for the remaining exposures, nor for any exposures on selection out of shift work. Sleep timing preference did not mediate the effects of BMI and educational attainment on selection into shift work. Liability to lower educational attainment and higher BMI may influence selection into shift work. This phenomenon may bias epidemiological studies of shift work that are performed in the UKB.

The relationship between alertness and spatial attention under simulated shiftwork

Higher and lower levels of alertness typically lead to a leftward and rightward bias in attention, respectively. This relationship between alertness and spatial attention potentially has major implications for health and safety. The current study examined alertness and spatial attention under simulated shiftworking conditions. Nineteen healthy right-handed participants (M = 24.6 ± 5.3 years, 11 males) completed a seven-day laboratory based simulated shiftwork study. Measures of alertness (Stanford Sleepiness Scale and Psychomotor Vigilance Task) and spatial attention (Landmark Task and Detection Task) were assessed across the protocol. Detection Task performance revealed slower reaction times and higher omissions of peripheral (compared to central) stimuli, with lowered alertness; suggesting narrowed visuospatial attention and a slight left-sided neglect. There were no associations between alertness and spatial bias on the Landmark Task. Our findings provide tentative evidence for a slight neglect of the left side and a narrowing of attention with lowered alertness. The possibility that one’s ability to sufficiently react to information in the periphery and the left-side may be compromised under conditions of lowered alertness highlights the need for future research to better understand the relationship between spatial attention and alertness under shiftworking conditions.

0781 Impact Of Suvorexant On Total Daytime Sleep Hours In Shift Workers: A Randomized, Double-blind, Placebo-controlled Clinical Field Trial

Abstract Introduction Many shift workers have an inability to sleep during the daytime following a night shift not due to insomnia or lack of sleep pressure, but because a circadian signal promoting wakefulness is hampering their ability to maintain sleep. We have previously hypothesized that the neuropeptide hypocretin-1 is, in part, responsible for the physiologic expression of this circadian wake signal. As such, it was our intent to determine whether a pharmacologic blockade of hypocretin would enable shift workers to obtain more daytime sleep. Methods Nineteen shift workers took part in a placebo-controlled, double-blind field study of suvorexant. Following two weeks of baseline, participants received 10 mg suvorexant/placebo for one week and were titrated upward to 20 mg suvorexant/placebo for an additional two weeks. Subjective (diaries) and objective (actigraphy) sleep were monitored throughout. No restrictions were placed on participants’ schedules. Results Both subjective and objective measures of total sleep time significantly improved in the active vs. the placebo condition, increasing by 2.08 ± 0.47 hours (diary) or 1.04 ± 0.53 hours (actigraphy) by the end of the 10 mg condition, and increasing by 2.97 ± 0.56 hours (diary) or 2.16 ± 0.75 hours (actigraphy) by the end of the 20 mg condition. Physician ratings of change in the severity of symptoms similarly improved in the active group. There were no adverse events reported in the active condition. Conclusion Robust changes in total sleep time were observed after administration of suvorexant, a dual-hypocretin antagonist, prior to daytime sleep in a field study of shift workers. The very large changes in total sleep time, coupled with the permissive nature of the therapeutic mechanism (i.e., suppressing wake rather than inducing sleep) indicate that this could be a viable and important therapy for shift workers. Support Merck Sharpe and Dohme investigator-initiated study #53236

How Accurately Can We Recall Food Timing? A Validity Study of a Novel Food Timing Questionnaire (P18-016-19)

ObjectivesEmerging epidemiological and experimental studies suggest that food timing associates with obesity, weight-loss success, and other adverse cardiometabolic health outcomes. Although anecdotally simple to ascertain, the validity of recalled food timing has not been evaluated against prospectively collected data and current methods do not account for day of the week. Our objective is to validate a novel, recall-based tool, the Eating Pattern Questionnaire (EPQ), aimed at assessing food timing in healthy, free-living populations for work/school days (WD) and non-work days (NWD), against up to 2 weeks of prospectively collected 24-hour food records (FR). MethodsA total of 95 participants (72% female; mean age: 33 ± 11 years) from the ongoing Shift Work, Heredity, Insulin, and Food Timing (SHIFT) Study (ClinicalTrials.gov: #NCT02997319) were included. On the EPQ, participants were asked to indicate whether food/beverages are always/sometimes/never consumed during every hour of a WD and NWD (hourly increments). On FR, participants were instructed by trained nutritionists to indicate type and time of all food/beverage items consumed. Food timing was averaged for WD and NWD separately across all completed FR. Five clock times in hour: minute were derived from the two tools: first/last eating episode and breakfast, lunch, and dinner. Concordance was quantified using Kendall’s correlation of concordance (W). ResultsA higher level of concordance was observed for clock time of first eating episode on WD (W = 0.867) compared to NWD (W = 0.568). Clock times for breakfast, lunch, and dinner had comparable concordance on WD and NWD, with highest concordance observed for lunch (WD: W = 1; NWD: W = 0.886), followed by breakfast (WD: W = 0.759; NWD: W = 0.745) then dinner (WD: W = 0.641; NWD: W = 0.665). Lastly, low concordance was found for clock time of the last eating episode for both WD and NWD (WD: W = 0.220; NWD: W = 0.313). ConclusionsBy comparing clock times estimated from a recall-based questionnaire against prospectively collected food timing data, we observe that individuals may more accurately recall the timing of meals earlier on in the day, particularly on work days, compared to meals later in the evening. These findings provide first insights into the accuracy of food timing data ascertained through self-reported in cohort studies. Funding SourcesNIH-R01DK105072.

Shift Work Patterns, Chronotype, and Epithelial Ovarian Cancer Risk.

Shift work causing circadian disruption is classified as a "probable carcinogen" and may contribute to the pathogenesis of hormone-sensitive cancers. This study investigated shift work exposure in relation to epithelial ovarian cancer (EOC) risk. In a population-based case-control study with 496 EOC cases and 906 controls, lifetime occupational histories were collected and used to calculate cumulative years of shift work exposure, average number of night shifts per month, and average number of consecutive night shifts per month. ORs and 95% confidence intervals (CI) for associations with EOC risk were estimated using logistic regression. Associations were also examined according to chronotype and menopausal status. More than half of the cases (53.4%) and controls (51.7%) worked evening and/or night shifts. There was no clear pattern of increasing EOC risk with increasing years of shift work; the adjusted OR of EOC comparing the highest shift work category versus never working shift work was 1.20 (95% CI, 0.89-1.63). This association was more pronounced among those self-identified as having a "morning" chronotype (OR, 1.64; 95% CI, 1.01-2.65). Associations did not greatly differ by menopausal status. These results do not strongly demonstrate a relationship between shift work and EOC risk. This study collected detailed shift work information and examined shift work patterns according to shift times and schedules. The findings highlight that chronotype should be considered in studies of shift work as an exposure.

Cardiac autonomic activity during simulated shift work.

Shift work leads to adverse health outcomes including increased risk of cardiovascular disease. Heart rate (HR) and heart rate variability (HRV) are measures of cardiac autonomic activity and markers of cardiovascular disease and mortality. To investigate the effects of shift work on cardiac autonomic activity, we assessed the influence of simulated night work on HR and HRV, and dissociated the direct effects of circadian misalignment from those of sleep displacement and altered physical activity patterns. A total of 29 subjects each participated in one of two in-laboratory, simulated shift work studies. In both studies, EKG was continuously monitored via Holter monitors to measure HR and the high frequency (HF) component of HRV (HF-HRV). We found endogenous circadian rhythmicity in HR and HF-HRV. Sleep and waking physical activity, both displaced during simulated night work, had more substantial, and opposite, effects on HR and HF-HRV. Our findings show systematic but complex, interacting effects of time of day, sleep/wake state, and physical activity on cardiac autonomic activity. These effects need to be taken into account when evaluating HR and HRV in shift work settings and when interpreting these measures of cardiac autonomic activity as markers of cardiovascular disease.

Examining Exposure Assessment in Shift Work Research: A Study on Depression Among Nurses.

Coarse exposure assessment and assignment is a common issue facing epidemiological studies of shift work. Such measures ignore a number of exposure characteristics that may impact on health, increasing the likelihood of biased effect estimates and masked exposure-response relationships. To demonstrate the impacts of exposure assessment precision in shift work research, this study investigated relationships between work schedule and depression in a large survey of Canadian nurses. The Canadian 2005 National Survey of the Work and Health of Nurses provided the analytic sample (n = 11450). Relationships between work schedule and depression were assessed using logistic regression models with high, moderate, and low-precision exposure groupings. The high-precision grouping described shift timing and rotation frequency, the moderate-precision grouping described shift timing, and the low-precision grouping described the presence/absence of shift work. Final model estimates were adjusted for the potential confounding effects of demographic and work variables, and bootstrap weights were used to generate sampling variances that accounted for the survey sample design. The high-precision exposure grouping model showed the strongest relationships between work schedule and depression, with increased odds ratios [ORs] for rapidly rotating (OR = 1.51, 95% confidence interval [CI] = 0.91-2.51) and undefined rotating (OR = 1.67, 95% CI = 0.92-3.02) shift workers, and a decreased OR for depression in slow rotating (OR = 0.79, 95% CI = 0.57-1.08) shift workers. For the low- and moderate-precision exposure grouping models, weak relationships were observed for all work schedule categories (OR range 0.95 to 0.99). Findings from this study support the need to consider and collect the data required for precise and conceptually driven exposure assessment and assignment in future studies of shift work and health. Further research into the effects of shift rotation frequency on depression is also recommended.

Personal light-at-night exposures and components of variability in two common shift work industries: uses and implications for future research.

Objectives Shift workers' increased risk of various adverse health outcomes has been linked to light-at-night (LAN) exposure, but few studies have measured LAN exposure in workplaces. To inform future research methods, this study aimed to (i) measure shift workers' exposures to LAN across industries, occupations, and work environments and (ii) assess components of variance across different exposure groupings and metrics. Methods Between October 2015 and March 2016, 152 personal full-shift measurements were collected from 102 night shift workers in emergency health services (paramedics, dispatchers) and healthcare industries (nurses, care aides, security guards, unit clerks, and laboratory, pharmacy, and respiratory therapy staff) in the province of British Columbia, Canada. Descriptive and variance component analyses were conducted for the 23:00-05:00 period to characterize exposures using multiple metrics of potential biological relevance (median lux, 90 thpercentile lux, sum of minutes ≥30 lux, and sum of minutes ≥100 lux). Results Average exposure levels were highest in the healthcare industry. By occupation, laboratory workers and care aides displayed the highest and emergency dispatch officers displayed the lowest levels for all LAN exposure metrics. Between-group variance was large relative to within-group variance for all exposure groupings and metrics, and increased as grouping specificity increased (moving from industry to occupation). Conclusions Results from this study suggest that high-level grouping schemes may provide a simple yet effective way of characterizing individual LAN exposures in epidemiological studies of shift work. Ongoing measurement of LAN exposures and assessment of exposure variability is needed in future studies of shift workers as a means to increase sampling efficiency, reduce measurement error, and maximize researchers' ability to detect relationships where they exist.

0688 IMPACT OF CIRCADIAN MISALIGNMENT AND BMI ON GLUCOSE DYSREGULATION IN NIGHT-SHIFT WORKERS

Epidemiological studies suggests that night shift workers are at increased risk for obesity and diabetes, and simulated shift work studies in day workers have implicated circadian misalignment as a culprit for reduced glucose tolerance. However, this has not been tested in actual night shift workers. To better understand the role of circadian misalignment on glucose dysregulation, we examined glucose tolerance in a sample of fixed night shift workers. Thirty fixed night shift workers participated in this study. All subjects were given an eight-hour opportunity to sleep upon arrival at the lab, and remained under dim-light conditions for 24 hours. An oral glucose tolerance test was administered two hours after awakening. The change in glucose from fasting to one hour after glucose intake, and from fasting to two hours after glucose intake were measured. Melatonin was also assayed via hourly salivary samples, and circadian phase was indexed using the dim light melatonin onset (DLMO). Analyses included years of night shift work as a covariate. Partial correlations controlling for years of shift work indicated that DLMO was not significantly associated with change in glucose tolerance at one-hour, r(27) = .07, p>.05, or at two-hour, r(27) = -.24, p>.05. However, DLMO was significantly associated with glucose tolerance when accounting for weight. Specifically, overweight shift workers (BMI ≥ 26) with earlier DLMOs showed lower glucose tolerance at the two-hour time point, r (15) = -.46, p<.05, compared to subjects with healthy weight, r (9) = .06, p>.05. Results suggest that circadian misalignment alone may not be a significant predictor for glucose dysregulation, but instead may interact with other risk factors for diabetes, such as weight. Thus, increased risk for diabetes in night shift workers should not be generalized, but rather considered only when circadian disturbance is paired with pre-existing risk factors. Our project was funded by TEVA pharmaceuticals.

Shift work and cognitive aging: a longitudinal study.

Objectives The few studies of shift work and late life cognitive functioning have yielded mixed findings. The aim of the present study is to estimate the association between shift-work experience and change in cognitive performance before and after retirement age among older adults who were gainfully employed. Methods Five hundred and ninety five participants with no dementia were followed up for a mean of 17.6 standard deviation (SD) 8.8 years from a Swedish population-based sample. Participants had self-reported information on any type of shift-work experience (ever/never) in 1984 and measures of cognitive performance (verbal, spatial, memory, processing speed, and general cognitive ability) from up to 9 waves of cognitive assessments during 1986-2012. Night work history (ever/never) from 1998-2002 was available from a subsample (N=320). Early adult cognitive test scores were available for 77 men. Results In latent growth curve modeling, there were no main effects of "any-type" or night shift work on the mean scores or rate of change in any of the cognitive domains. An interaction effect between any-type shift work and education on cognitive performance at retirement was noted. Lower-educated shift workers performed better on cognitive tests than lower-educated day workers at retirement. Sensitivity analyses, however, indicated that the interactions appeared to be driven by selection effects. Lower-educated day workers demonstrated poorer cognitive ability in early adulthood than lower-educated shift workers, who may have selected jobs entailing higher cognitive demand. Conclusion There was no difference in late-life cognitive aging between individuals with a history of working shifts compared to those who had typical day work schedules during midlife.

Associations among rotating night shift work, sleep and skin cancer in Nurses' Health Study II participants

BackgroundNight shift work and sleep duration have been associated with breast and other cancers. Results from the few prior studies of night shift work and skin cancer risk have been...

Impact of Sleep and Circadian Disruption on Energy Balance and Diabetes: A Summary of Workshop Discussions.

A workshop was held at the National Institute for Diabetes and Digestive and Kidney Diseases with a focus on the impact of sleep and circadian disruption on energy balance and diabetes. The workshop identified a number of key principles for research in this area and a number of specific opportunities. Studies in this area would be facilitated by active collaboration between investigators in sleep/circadian research and investigators in metabolism/diabetes. There is a need to translate the elegant findings from basic research into improving the metabolic health of the American public. There is also a need for investigators studying the impact of sleep/circadian disruption in humans to move beyond measurements of insulin and glucose and conduct more in-depth phenotyping. There is also a need for the assessments of sleep and circadian rhythms as well as assessments for sleep-disordered breathing to be incorporated into all ongoing cohort studies related to diabetes risk. Studies in humans need to complement the elegant short-term laboratory-based human studies of simulated short sleep and shift work etc. with studies in subjects in the general population with these disorders. It is conceivable that chronic adaptations occur, and if so, the mechanisms by which they occur needs to be identified and understood. Particular areas of opportunity that are ready for translation are studies to address whether CPAP treatment of patients with pre-diabetes and obstructive sleep apnea (OSA) prevents or delays the onset of diabetes and whether temporal restricted feeding has the same impact on obesity rates in humans as it does in mice.