Work Around the Clock: How Work Hours Induce Social Jetlag and Sleep Deficiency

Relationship of Social Jetlag and Chronotype With the Risk of Diabetes Among Predominantly Male Japanese Daytime Workers: A Prospective Study

Greater social jetlag and late chronotypes have been linked to poor glucose metabolism, but their effects on diabetes risk in Asians remain unclear. This study investigated the prospective association between social jetlag, chronotype and diabetes risk among Japanese workers. We included 1681 workers (73% were daytime workers) aged 18-78 years who attended a nutritional survey in 2015 and 2016 and were followed for diabetes incidence until May 31, 2022. Social jetlag was defined as the absolute difference in the midpoint of sleep times between weekdays and weekends. Chronotype was estimated using the mid-sleep time on weekends that was corrected with sleep debt on weekdays. Following the American Diabetes Association criteria, diabetes onset was defined as the time when the participant first met any of the following conditions: HbA1c ≥ 6.5%, fasting plasma glucose ≥ 126 mg/dL, random plasma glucose ≥ 200 mg/dL or current use of antidiabetic medication. The Cox proportional hazards model was used to estimate hazard ratios (HRs) for diabetes incidence. Among the study participants, 88.8% were male, 5.0% experienced ≥ 2 h of social jetlag, and 7.6% were classified as having a late chronotype. During the 7-year follow-up, 107 individuals (6.4%) developed diabetes. Among daytime workers, social jetlag was not associated with diabetes risk: multivariable-adjusted HRs (95% CI) for diabetes were 1.00, 0.90 (0.52-1.55) and 1.08 (0.43-2.75) in participants with < 1.0, 1.0 to 1.9, and ≥ 2.0 h of social jetlag, respectively. Late chronotype was associated with higher diabetes risk, although not statistically significant, compared to early chronotype; multivariable-adjusted HRs (95% CI) were 1.32 (0.80-2.18) for intermediate chronotype and 1.98 (0.77-5.10) for late chronotype. In conclusion, this study suggests an association between late chronotypes and increased risk of diabetes among daytime workers and also highlights a mediating role of lifestyle-related behaviours on chronotype and their impact on metabolic health.

Individual associations of self-reported sleep duration, sleep quality, chronotype and social jet lag with infectious disease risk

Sleep deficiency is associated with infectious disease risk. However, little is known about the individual roles of different aspects of sleep, including sleep duration, sleep quality, sleep timing (assessed by chronotype) and sleep regularity (in the form of social jet lag) in this context. Here, we examined associations of the probability of reporting a cold or other infections with self-reported sleep duration, sleep quality and chronotype in a sample of 642 adults, and with social jet lag in a subsample of 274 adults. We found that short (≤ 6 h) and long sleepers (≥ 9 h) were more likely to report a cold in the past 30 days than average sleepers (7-8 h). Also, individuals with a definite evening chronotype were more likely to report a cold in the past 30 days than those with an intermediate chronotype, even when controlling for sleep duration. Finally, social jet lag was dose-dependently associated with the risk of reporting a cold in the past 12 months, independently of sleep duration, sleep quality and chronotype. No associations were found with sleep quality or with infections other than colds. The findings show that different aspects of sleep are independently associated with incidence of reported colds.This article is part of the Theo Murphy meeting issue 'Circadian rhythms in infection and immunity'.

Relationship between social jetlag and body mass index in nurses working shift schedules: a cross-sectional study

This study aimed to explore the relationship between shift-working nurses' social jetlag and body mass index (BMI) and provide a theoretical basis for nursing managers to develop appropriate health interventions. Shift work is unavoidable in nursing and is associated with circadian rhythm disorders. Social jetlag is prevalent in shift-working nurses and is associated with adverse health outcomes (particularly metabolism-related indicators). BMI is a significant metabolic indicator, and research has demonstrated its effectiveness in predicting the formation of metabolic syndrome. The relationship between social jetlag and BMI can be explained by considering physiological, psychological, and behavioral factors. However, most studies on social jetlag and health status are focused on non-shift nurse populations, with fewer studies on shift workers. Five tertiary hospitals located at similar latitudes in Southwest China were selected for the study. We surveyed 429 shift-working nurses using sociodemographic data, the Munich Chronotype Questionnaire for Shift Workers, and BMI. The restricted cubic spline model was used to analyze the relationship between social jetlag and BMI among shift-working nurses, and segmented linear regression was performed around the inflection point using multiple linear regression analysis. The results revealed that social jetlag (82.0 [85.0] min) was experienced by 64.6% of the shift-working nurses. After controlling for confounding variables, the model with seven knots had the lowest accepted Akaike information criterion value, and there was a U-shaped relationship between shift-working nurses' BMI and social jetlag in this model; its inflection (lowest) point of 20.7 was considered the cut-off point. Segmented regression showed that for BMI < 20.7, BMI was significantly negative with standardized social jetlag; whereas with BMI > 20.7, BMI was significantly positive with standardized social jetlag. BMI has a U-shaped relationship with social jetlag, and attention should be paid to overweight or underweight shift-working nurses to detect early circadian rhythm disorder. Shift-working nurses with high social jetlag tended to have higher/lower BMI, which should be further investigated in the future, to minimize metabolic diseases among them.

Chronobioethics: Symphony of biological clocks observed by 7-day/24-hour ambulatory blood pressure monitoring and cardiovascular health

BACKGROUND

The high prevalence of desynchronized biological rhythms is becoming a primary public health concern. We assess complex and diverse inter-modulations among multi-frequency rhythms present in blood pressure (BP) and heart rate (HR).

SUBJECTS

and Methods: We performed 7-day/24-hour Ambulatory BP Monitoring in 220 (133 women) residents (23 to 74 years) of a rural Japanese town in Kochi Prefecture under everyday life conditions.

RESULTS

A symphony of biological clocks contributes to the preservation of a synchronized circadian system. (1) Citizens with an average 12.02-h period had fewer vascular variability disorders than those with shorter (11.37-h) or longer (12.88-h) periods (P<0.05), suggesting that the circasemidian rhythm is potentially important for human health. (2) An appropriate BP-HR coupling promoted healthier circadian profiles than a phase-advanced BP: lower 7-day nighttime SBP (106.8 vs. 112.9 mmHg, P=0.0469), deeper nocturnal SBP dip (20.5% vs. 16.8%, P=0.0101), and less frequent incidence of masked non-dipping (0.53 vs. 0.86, P=0.0378), identifying the night as an important time window.

CONCLUSION

Adaptation to irregular schedules in everyday life occurs unconsciously at night, probably initiated from the brain default mode network, in coordination with the biological clock system, including a reinforced about 12-hour clock, as "a biological clock-guided core integration system".

Sleep patterns in Metropolitan and Regional areas in Japan: Before and during COVID-19 social restrictions

Sleep timing is an important output of the circadian system. The COVID-19-mandated social restrictions significantly altered commuting time and sleep duration regionally in Japan. This study aimed to elucidate sleep patterns, especially chronotype and social jetlag (SJL), due to changes in social time pressure through the social restrictions between the Metropolitan and Regional areas in Japan. As part of the Global Chrono Corona Survey 2020 (GCCS), the data were collected during social restrictions (SR), but pre-COVID-19 behaviours were also queried retrospectively. We analyzed a cohort of 729 respondents representing both the Metropolitan and the Regional areas separately for workdays and work-free days. While the areas showed no difference in SJL before SR, the differential decrease was larger in the Metropolitan area during SR, resulting in a significant difference in SJL between the areas. The outdoor light exposure before SR was 30 min longer in the Metropolitan areas than in the Regional; during SR both areas showed similarly low (below 1 h) outdoor light exposures. The variables associated with decreased SJL were the Metropolitan areas, work-from-home, a no-usage alarm clock on workdays, and chronotypes (mid-sleep time on free days corrected for sleep deficit accumulated over the workweek, MSFsc) during SR. The results suggest that relaxed social schedules, as reflected in the increased frequency of work-from-home and reduced alarm clock use, and moving towards earlier MSFsc during SR were linked to decreased SJL and were more prominent in the Metropolitan areas. This study provides insights into sleep patterns and the social time pressure markers, by comparison between residential groups in Japan.

Determination of the relationship between body composition and nutritional habits and chronotype in healthy Turkish adults

This cross-sectional study aims to determine the relationship between chronotype characteristics, dietary habits, and body composition in 110 adults, of which 75.5% are female, residing in Mersin, Türkiye. Data collection included a descriptive information form, the Morningness-Eveningness Scale for assessing chronotype, a detailed 24-hour dietary record for evaluating dietary intake, and Bioelectrical Impedance Analysis for accurate anthropometric measurements of body composition. The evening types had higher BMI, body weight, waist circumference, hip circumference, total fat mass, and lower body water ratio than the morning types. Positive correlations were found between sleep duration and body mass index, total fat mass, and fat percentage. The evening types tended to skip breakfast more frequently and had higher energy intake during dinners and snacks. Additionally, the evening types consumed more lipids, carbohydrates, sodium, and saturated and polyunsaturated fatty acids. These findings suggest that chronotype influences anthropometric measurements, nutritional habits, and meal energy distribution. These findings highlight the importance of considering chronotype characteristics to understand how body composition and dietary patterns interact, underscoring the need for customized interventions to promote healthier lifestyles.

A longitudinal study of rotating shift type and attention performance of acute and critical care nurses with chronotype as moderator variable

OBJECTIVES

To investigate whether chronotype is a moderator variable that also interacts with shift type and whether they jointly influence the attention performance of nurses working in acute and critical care units.

METHODS

We adopted a longitudinal research design focusing on nurses working rotating shifts in the emergency room and intensive care units at a medical center. A total of 40 complete samples were obtained. Data analysis was conducted using the generalized estimating equations in SAS 9.4.

RESULTS

The mean (SD) age of the participants was 26.35 (2.12) years. After controlling for age, gender, and sleep duration, an interaction effect was discovered between a specific chronotype and shift type; that is, the interaction effect between chronotype and shift type was only significant when comparing late-types working the night shift with early- and intermediate-types working the night shift (B = -18.81, P = .011). The least squares means of the mean reaction time of the interaction effects between the 2 chronotype groups and the 3 shift types found that the mean reaction time of late-types working the night shift was 11.31 ms (P = .044) slower compared with working the day shift.

CONCLUSIONS

The chronotype is a moderator variable between shift type and mean reaction time, such that matching the chronotype of nurses in acute and critical care units with the appropriate shift type improved their mean reaction time. It is hoped that the results of this study could serve as a reference for acute and critical care nurses when scheduling their shifts.

Physiological Rhythms and Biological Variation of Biomolecules: The Road to Personalized Laboratory Medicine

The concentration of biomolecules in living systems shows numerous systematic and random variations. Systematic variations can be classified based on the frequency of variations as ultradian (<24 h), circadian (approximately 24 h), and infradian (>24 h), which are partly predictable. Random biological variations are known as between-subject biological variations that are the variations among the set points of an analyte from different individuals and within-subject biological variation, which is the variation of the analyte around individuals’ set points. The random biological variation cannot be predicted but can be estimated using appropriate measurement and statistical procedures. Physiological rhythms and random biological variation of the analytes could be considered the essential elements of predictive, preventive, and particularly personalized laboratory medicine. This systematic review aims to summarize research that have been done about the types of physiological rhythms, biological variations, and their effects on laboratory tests. We have searched the PubMed and Web of Science databases for biological variation and physiological rhythm articles in English without time restrictions with the terms “Biological variation, Within-subject biological variation, Between-subject biological variation, Physiological rhythms, Ultradian rhythms, Circadian rhythm, Infradian rhythms”. It was concluded that, for effective management of predicting, preventing, and personalizing medicine, which is based on the safe and valid interpretation of patients’ laboratory test results, both physiological rhythms and biological variation of the measurands should be considered simultaneously.