Céline Vetter

Mismatch of Sleep and Work Timing and Risk of Type 2 Diabetes

OBJECTIVE To examine whether a mismatch between chronotype (i.e., preferred sleep timing) and work schedule is associated with type 2 diabetes risk. RESEARCH DESIGN AND METHODS In the Nurses’ Health Study 2, we followed 64,615 women from 2005 to 2011. Newly developed type 2 diabetes was the outcome measure (n = 1,452). A question on diurnal preference ascertained chronotype in 2009; rotating night shift work exposure was assessed regularly since 1989. RESULTS Compared with intermediate chronotypes, early chronotypes had a slightly decreased diabetes risk after multivariable adjustment (odds ratio 0.87 [95% CI 0.77–0.98]), whereas no significant association was observed for late chronotypes (1.04 [0.89–1.21]). Among early chronotypes, risk of type 2 diabetes was modestly reduced when working daytime schedules (0.81 [0.63–1.04]) and remained similarly reduced in women working <10 years of rotating night shifts (0.84 [0.72–0.98]). After ≥10 years of shift work exposure, early chronotypes had a nonsignificant elevated diabetes risk (1.15 [0.81–1.63], Ptrend = 0.014). By contrast, among late chronotypes, the significantly increased diabetes risk observed among day workers (1.51 [1.13–2.02]) appeared largely attenuated if their work schedules included night shifts (<10 years: 0.93 [0.76–1.13]; ≥10 years: 0.87 [0.56–1.34]; Ptrend = 0.14). The interaction between chronotype and shift work exposure was significant (Pinteraction = 0.0004). Analyses restricting to incident cases revealed similar patterns. CONCLUSIONS In early chronotypes, type 2 diabetes risk increased with increasing duration of shift work exposure, whereas late types had the highest diabetes risk working daytime schedules. These data add to the growing body of evidence that workers could benefit from shift schedules minimizing interference with chronotype-dependent sleep timing.

Human Activity and Rest In Situ

Our lives are structured by the daily alternation of activity and rest, of wake and sleep. Despite significant advances in circadian and sleep research, we still lack answers to many of the most fundamental questions about this conspicuous behavioral pattern. We strongly believe that investigating this pattern in entrained conditions, real-life and daily contexts-in situ-will help the field to elucidate some of these central questions. Here, we present two common approaches for in situ investigation of human activity and rest: the Munich ChronoType Questionnaire (MCTQ) and actimetry. In the first half of this chapter, we provide detailed instructions on how to use and interpret the MCTQ. In addition, we give an overview of the main insights gained with this instrument over the past 10 years, including some new findings on the interaction of light and age on sleep timing. In the second half of this chapter, we introduce the reader to the method of actimetry and share our experience in basic analysis techniques, including visualization, smoothing, and cosine model fitting of in situ recorded data. Additionally, we describe our new approach to automatically detect sleep from activity recordings. Our vision is that the broad use of such easy techniques in real-life settings combined with automated analyses will lead to the creation of large databases. The resulting power of big numbers will promote our understanding of such fundamental biological phenomena as sleep.

Sleep and need for recovery in shift workers: do chronotype and age matter?

This study examined associations of chronotype and age with shift-specific assessments of main sleep duration, sleep quality and need for recovery in a cross-sectional study among N = 261 industrial shift workers (96.6% male). Logistic regression analyses were used, adjusted for gender, lifestyle, health, nap behaviour, season of assessment and shift schedule. Shift workers with latest versus earliest chronotype reported a shorter sleep duration (OR 11.68, 95% CI 3.31–41.17) and more awakenings complaints (OR 4.84, 95% CI 4.45–11.92) during morning shift periods. No associations were found between chronotype, sleep and need for recovery during evening and night shift periods. For age, no associations were found with any of the shift-specific outcome measures. The results stress the importance of including the concept of chronotype in shift work research and scheduling beyond the concept of age. Longitudinal research using shift-specific assessments of sleep and need for recovery are needed to confirm these results. Practitioner Summary: Chronotype seems to better explain individual differences in sleep than age. In view of ageing societies, it might therefore be worthwhile to further examine the application of chronotype for individualised shift work schedules to facilitate healthy and sustainable employment.

A unique, fast-forwards rotating schedule with 12-h long shifts prevents chronic sleep debt

ABSTRACT Sleep debt – together with circadian misalignment – is considered a central factor for adverse health outcomes associated with shift work. Here, we describe in detail sleep-wake behavior in a fast-forward rotating 12-h shift schedule, which involves at least 24 hours off after each shift and thus allows examining the role of immediate recovery after shift-specific sleep debt. Thirty-five participants at two chemical plants in Germany were chronotyped using the Munich ChronoType Questionnaire for Shift-Workers (MCTQShift) and wore actimeters throughout the two-week study period. From these actimetry recordings, we computed sleep and nap duration, social jetlag (a measure of circadian misalignment), and the daily timing of activity and sleep (center of gravity and mid-sleep, respectively). We observed that the long off-work periods between each shift create a fast alternation between shortened (mean ± standard deviation, 5h 17min ± 56min) and extended (8h 25min ± 72min) sleep episodes resulting in immanent reductions of sleep debt. Additionally, extensive napping of early chronotypes (up to 3 hours before the night shift) statistically compensated short sleep durations after the night shift. Partial rank correlations showed chronotype-dependent patterns of sleep and activity that were similar to those previously described in 8-h schedules; however, sleep before the day shift did not differ between chronotypes. Our findings indicate that schedules preventing a build-up of chronic sleep debt may reduce detrimental effects of shift work irrespective of shift duration. Prospective studies are needed to further elucidate the relationship between sleep, the circadian system, and health and safety hazards.

Not later, but longer: sleep, chronotype and light exposure in adolescents with remitted depression compared to healthy controls

The relationship between sleep and adolescent depression is much discussed, but still not fully understood. One important sleep variable is self-selected sleep timing, which is also referred to as chronotype. Chronotype is mostly regulated by the circadian clock that synchronises the internal time of the body with the external light dark cycle. A late chronotype as well as a misalignment between internal time and external time such as social jetlag has been shown to be associated with depressive symptoms in adults. In this study, we investigated whether adolescents with remitted depression differ from healthy controls in terms of chronotype, social jetlag and other sleep-related variables. For this purpose, we assessed chronotype and social jetlag with the Munich ChronoType Questionnaire (MCTQ), subjective sleep quality with the Pittsburgh Sleep Quality Index (PSQI) and used continuous wrist-actimetry over 31 consecutive days to determine objective sleep timing. Given the potentially mediating effect of light on chronotype and depressive symptoms, we measured light exposure with a light sensor on the actimeter. In our sample, adolescents with remitted depression showed similar chronotypes and similar amounts of social jetlag compared to controls. However, patients with remitted depression slept significantly longer on work-free days and reported a worse subjective sleep quality than controls. Additionally, light exposure in remitted patients was significantly higher, but this finding was mediated by living in a rural environment. These findings indicate that chronotype might be modified during remission, which should be further investigated in longitudinal studies.

A novel method to visualise and quantify circadian misalignment

The circadian clock governs virtually all processes in the human body, including sleep-wake behaviour. Circadian misalignment describes the off-set between sleep-wake cycles and clock-regulated physiology. This strain is predominantly caused by external (societal) demands including shift work, early school start times and fast travels across time zones. Sleeping at the ‘wrong’ internal time can jeopardise health and safety, and we therefore need a good quantification of this phenomenon. Here, we propose a novel method to quantify the mistiming of sleep-wake rhythms and demonstrate its versatility in day workers and shift workers. Based on a single time series, our Composite Phase Deviation method unveils distinct, subject- and schedule-specific geometries (‘islands and pancakes’) that illustrate how modern work times interfere with sleep. With increasing levels of circadian strain, the resulting shapes change systematically from small, connected forms to large and fragmented patterns. Our method shows good congruence with published measures of circadian misalignment (i.e., Inter-daily Stability and ‘Behavioural Entrainment’), but offers added value as to its requirements, e.g., being computable for sleep logs and questionnaires. Composite Phase Deviations will help to understand the mechanisms that link ‘living against the clock’ with health and disease on an individual basis.

Are chronotype, social jetlag and sleep duration associated with health measured by Work Ability Index?

ABSTRACT The present study investigates the impact of chronotype, social jetlag and sleep duration on self-perceived health, measured by Work Ability Index (WAI), within an industrial setting. Between 2011 and 2013, 2474 day and shift workers participated in a health check offered by an occupational health promotion program and filled out the Munich ChronoType Questionnaire (adapted to the rotational 12-h schedule for shift workers) and the WAI. We computed sleep duration on work and free days, chronotype, and social jetlag. We used linear regression models to examine chronotype, sleep duration and social jetlag for association with the WAI sum score, and proportional odds models to estimate the combined effect of social jetlag and sleep duration. Participants reported an average daily sleep duration of 7.35 h (SD: 1.2 h), had an average chronotype of 3:08 a.m. (SD: 1 h), and the average social jetlag corresponded to 1.96 h (SD: 2.05 h). Increasing social jetlag and shorter sleep duration were independently associated with a decreasing WAI, while chronotype per se was not associated with WAI. Short sleep duration combined with high social jetlag significantly increased the risk of poor WAI (OR = 1.36; 95% CI: 1.09–1.72), while long sleep duration and high social jetlag were not associated with poor WAI (OR = 1.09; 95% CI: 0.88–1.35). Our results add to a growing body of literature, suggesting that circadian misalignment, but not chronotype per se, may be critical for health. Our results indicate that longer sleep may override the adverse effects of social jetlag on WAI.

Dysregulated daily rhythmicity of neuronal resting-state networks in MCI patients

In young healthy participants, the degree of daily rhythmicity largely varies across different neuronal resting-state networks (RSNs), while it is to date unknown whether this temporal pattern of activity is conserved in healthy and pathological aging. Twelve healthy elderly (mean age = 65.1 ± 5.7 years) and 12 patients with amnestic mild cognitive impairment (aMCI; mean age = 69.6 ± 6.2 years) underwent four resting-state functional magnetic resonance imaging scans at fixed 2.5 h intervals throughout a day. Time courses of a RSN were extracted by a connectivity strength and a spatial extent approach performed individually for each participant. Highly rhythmic RSNs included a sensorimotor, a cerebellar and a visual network in healthy elderly; the least rhythmic RSNs in this group included a network associated with executive control and an orbitofrontal network. The degree of daily rhythmicity in aMCI patients was reduced and dysregulated. For healthy elderly, the findings are in accordance with results reported for young healthy participants suggesting a comparable distribution of daily rhythmicity across RSNs during healthy aging. In contrast, the reduction and dysregulation of daily rhythmicity observed in aMCI patients is presumably indicative of underlying neurodegenerative processes in this group.

Early, but not late chronotypes, are up during their biological night when working the night shift

Bhatti et al 1 recently examined the impact of chronotype on melatonin levels in shift-workers and concluded that ‘(…) morning type shift-workers were better able to maintain normal patterns of melatonin secretion (…), suggesting that morning types may be protected against the negative effects of shift-work related melatonin disruption’. However, their data show that, compared to daytime workers sleeping at night, early chronotypes have lower melatonin …

Shift work practices and opportunities for intervention

There is increasing evidence that shift work, an occupational exposure affecting about one-fourth of the working population, increases the risk of major chronic disease outcomes, such as cardiovascular disease and cancer.1–4 Currently, there is an open discussion on whether shift work should be included in national lists of occupational hazards for compensation purposes. Denmark was the first (and to date only) country to consider breast cancer an occupational disease in shift workers, and to compensate women with over 20 years of night work who developed breast cancer. Chronic disease risk reduction and prevention in shift workers is an emerging field, which points to the need for more intervention studies. Whether and how companies or governments translate existing evidence into real-world policy or preventive actions currently remains largely unknown. The study by Hall et al 5 is a unique effort and first step to investigate the extent to which companies from across occupational sectors in the Canadian province of British Columbia implement programmes with potential health impact for their employees. In …