Obesity and high blood pressure of 12-hour night shift female clean-room workers

Behavioral-Social Rhythms and Cardiovascular Disease Risk in Retired Night Shift Workers and Retired Day Workers

OBJECTIVE

Stability in the timing of key daily routine behaviors such as working/doing housework, sleeping, eating, and engaging in social interactions (i.e., behavioral-social rhythms) contributes to health. This study examined whether behavioral-social rhythms were associated with cardiovascular disease (CVD) risk factors in retired night shift workers and retired day workers and explored whether past night shift work exposure moderated this association.

METHODS

A total of 154 retired older adults participated in this study. Multiple logistic regression models were used to examine associations between behavioral-social rhythms and CVD risk factors. Independent variables included Social Rhythm Metric (SRM)-5 score and actigraphy rest-activity rhythm intradaily variability (IV) and interdaily stability (IS). Dependent variables were metabolic syndrome prevalence and its five individual components.

RESULTS

More regular behavioral-social rhythms were associated with lower odds of prevalent metabolic syndrome (SRM: odds ratio [OR] = 0.57, 95% confidence interval [CI] = 0.35-0.88; IV: OR = 4.00, 95% CI = 1.86-8.58; IS: OR = 0.42, 95% CI = 0.24-0.73) and two of its individual components: body mass index (SRM: OR = 0.56, 95% CI = 0.37-0.85; IV: OR = 2.84, 95% CI = 1.59-5.07; IS: OR = 0.42, 95% CI = 0.26-0.68) and high-density lipoprotein cholesterol (SRM: OR = 0.49, 95% CI = 0.30-0.80; IV: OR = 2.49, 95% CI = 1.25-4.96; IS: OR = 0.35, 95% CI = 0.19-0.66). Past shift work history did not moderate the association between behavioral-social rhythms and metabolic syndrome.

CONCLUSIONS

Behavioral-social rhythms were related to CVD risk factors in retired adults regardless of prior night shift work exposure. Older retired workers may benefit from education and interventions aiming to increase behavioral-social rhythm regularity.

Impaired Melatonin Secretion, Oxidative Stress and Metabolic Syndrome in Night Shift Work

Metabolic syndrome has been associated in many studies with working in shifts. Even if the mechanistic details are not fully understood, forced sleep deprivation and exposure to light, as happens during night shifts, or irregular schedules with late or very early onset of the working program, lead to a sleep-wake rhythm misalignment, metabolic dysregulation and oxidative stress. The cyclic melatonin secretion is regulated by the hypothalamic suprachiasmatic nuclei and light exposure. At a central level, melatonin promotes sleep and inhibits wake-signals. Beside this role, melatonin acts as an antioxidant and influences the functionality of the cardiovascular system and of different metabolic processes. This review presents data about the influence of night shifts on melatonin secretion and oxidative stress. Assembling data from epidemiological, experimental and clinical studies contributes to a better understanding of the pathological links between chronodisruption and the metabolic syndrome related to working in shifts.

Association between Shift Work and Metabolic Syndrome: A 4-Year Retrospective Cohort Study

(1) Background: Previous studies on the association between shift work and metabolic syndrome have had inconsistent results. This may be due to the cross-sectional study design and non-objective data used in those studies. Hence, this study aimed to identify risk factors for Metabolic syndrome using objective information provided by the relevant companies and longitudinal data provided in health examinations. (2) Methods: In total, 1211 male workers of three manufacturing companies, including shift workers, were surveyed annually for 4 years. Data on age, smoking, drinking, physical activity, length of shift work, type of shift, past history, waist circumference, blood pressure, blood sugar, triglyceride, and high-density cholesterol (HDL) were collected and analyzed using generalized estimating equations (GEE) to identify the risk factors for Metabolic syndrome. (3) Results: In the multivariate analysis of Metabolic syndrome risk factors, age (OR = 1.078, 95% CI: 1.045–1.112), current smoking (OR = 1.428, 95% CI: 1.815–5.325), and BMI (OR = 1.498, 95% CI: 1.338–1.676) were statistically significant for day workers (n= 510). Additionally, for shift workers (N = 701), age (OR = 1.064, 95% CI: 1.008–1.174), current smoking (OR = 2.092, 95% CI: 1.854–8.439), BMI (OR = 1.471, 95% CI: 1.253–1.727) and length of shift work (OR = 1.115, 95% CI: 1.010-1.320) were statistically significant. Shift work was associated with a higher risk of Metabolic syndrome (OR = 1.093, 95% CI: 1.137–2.233) compared to day workers. For shift workers, shift work for more than 20 years was associated with Metabolic syndrome (OR = 2.080, 95% CI: 1.911–9.103), but the dose–response relationship was not statistically significant. (4) Conclusions: This study revealed that age, current smoking, BMI, and shift work are potential risk factors for Metabolic syndrome. In particular, the length of shift work (>20 years) is a potential risk factor for Metabolic syndrome in shift workers. To prevent metabolic syndrome in shift workers, health managers need to actively accommodate shift workers (especially those who have worked for more than 20 years), current smokers, and obese people. A long-term cohort study based on objective data is needed to identify the chronic health impact and the risk factors of shift work.

Prediction of risk of coronary artery disease based on the Framingham risk score in association with shift work among nurses

Objectives. This study aimed to determine the prediction of risk of coronary artery disease (CAD) based on the Framingham risk score (FRS) in association with shift work among nurses.Methods. This cross-sectional and descriptive-analytic study was conducted with nurses working in three hospitals located in Abadan, southwest Iran. The sample size was 120 participants, divided into 60 shift workers and 60 day workers (non-shift workers). Demographic data and medical and occupational history were collected through a checklist and interviews. CAD risk assessment tools used to estimate the 10-year cardiovascular disease (CVD) risk included the FRS. Data were analysed by Mann-Whitney U test, χ² test and one-way analysis of variance (ANOVA) using SPSS version 22.0.Results. There were statistically significant differences between blood pressure (BP), total cholesterol (TC), body mass index (BMI) and shift work (p ≤ 0.001). There was a statistically significant difference between prevalence of CAD risk and shift work based on the FRS (p = 0.04).Conclusion. The study findings showed that shift work is a risk factor for CAD disturbances. Therefore, particular follow-up of shift workers should be recommended for screening and preventing CAD.

Monochromatic visible lights modulate the timing of pre-adult developmental traits in Drosophila melanogaster

Light exposure impacts several aspects of Drosophila development including the establishment of circadian rhythms, neuroendocrine regulation, life-history traits, etc. Introduction of artificial lights in the environment has caused almost all animals to develop ecological and physiological adaptations. White light which comprises different lights of differing wavelengths shortens the lifespan in fruit flies Drosophila melanogaster. The wavelength-specific effects of white light on Drosophila development remains poorly understood. In this study, we show that different wavelengths of white light differentially modulate Drosophila development in all its concomitant stages when maintained in a 12-h light: 12-h dark photoperiod. We observed that exposure to different monochromatic lights significantly alters larval behaviours such as feeding rate and phototaxis that influence pre-adult development. Larvae grown under shorter wavelengths of light experienced an altered feeding rate. Similarly, larvae were found to avoid shorter wavelengths of light but were highly attracted to the longer wavelengths of light. Most of the developmental processes were greatly accelerated under the green light regime while in other light regimes, the effects were highly varied. Interestingly, pre-adult survivorship remained unaltered across all light regimes but light exposure was found to show its impact on sex determination. Our study for the first time reveals how different wavelengths of white light modulate Drosophila development which in the future might help in developing non-invasive therapies and effective pest measures.

Shift Work and Obesity Risk-Are There Sex Differences?

PURPOSE OF REVIEW

Shift work is prevalent among the working population and is linked to an array of adverse health outcomes. This review summarizes current evidence on the relation between shift work and risk of obesity, with a particular emphasis on potential sex differences.

RECENT FINDINGS

Observational data strongly point towards an association between shift work and heightened risk of prevalent and incident obesity, and particularly abdominal obesity. Circadian misalignment and unhealthy lifestyle behaviors are the primary culprits mediating such association. As it pertains to sex differences in the impact of shift work on obesity, few studies have examined this aspect, and findings are conflicting. Shift work is an important risk factor for obesity, with likely multiple biological and behavioral mediators. However, whether there is a sex-dependent vulnerability to the obesogenic effects of shift work is unclear. This area presents opportunities for future research.

Nightshift Work and Nighttime Eating Are Associated With Higher Insulin and Leptin Levels in Hospital Nurses

BACKGROUND

Circadian misalignment between behaviors such as feeding and endogenous circadian rhythms, particularly in the context of shiftwork, is associated with poorer cardiometabolic health. We examined whether insulin and leptin levels differ between dayshift versus nightshift nurses, as well as explored whether the timing of food intake modulates these effects in nightshift workers.

METHODS

Female nurses (N=18; 8 dayshift and 10 nightshift) completed daily diet records for 8 consecutive days. The nurses then completed a 24-h inpatient stay, during which blood specimens were collected every 3 h (beginning at 09:00) and meals were consumed at regular 3-h intervals (09:00, 12:00, 15:00, and 18:00). Specimens were analyzed for insulin and leptin levels, and generalized additive models were used to examine differences in mean insulin and leptin levels.

RESULTS

Mean insulin and leptin levels were higher in nightshift nurses by 11.6 ± 3.8 mU/L (p=0.003) and 7.4 ± 3.4 ng/ml (p=0.03), respectively, compared to dayshift nurses. In an exploratory subgroup analysis of nightshift nurses, predominately eating at night (21:00 - 06:00) was associated with significantly higher insulin and leptin levels than consuming most calories during the daytime (06:00 - 21:00).

CONCLUSIONS

In our study of hospital nurses, working the nightshift was associated with higher insulin and leptin levels, and these effects were driven by eating predominately at night. We conclude that although nightshift work may raise insulin and leptin levels, eating during the daytime may attenuate some of the negative effects of nightshift work on metabolic health.

Metabolic health measurements of shift workers in a national cross-sectional study: Results from the Canadian Health Measures Survey

BACKGROUND

Shift work exposure may be a concern for a range of health effects, including metabolic health outcomes such as insulin resistance, high body weight, and abdominal obesity.

METHODS

We analyzed shift work and indicators of metabolic health (overweight/obesity defined by body mass index, self-reported changes in body mass index (BMI) in previous 1 and 10 years, waist circumference, waist-to-hip ratio, and insulin resistance assessed by the homeostasis model assessment 2 (HOMA-2-IR)) in the cross-sectional Canadian Health Measures Survey (CHMS). We analyzed descriptive characteristics of shift workers (regular night, evening, and rotating shift) and used multivariable linear regression to examine the association between two definitions of shift work exposure and measures of metabolic health, adjusted for age, sex, daily energy expenditure, sleep, and poor dietary quality.

RESULTS

5470 anthropometry (2637 fasting) participants in CHMS Cycles 1 and 2 were included, of whom 16.5% worked regular evening, night, or rotating shifts. Shift workers were younger and slept longer hours than non-shift workers. Bivariate associations showed inverse relationships between shift work and BMI, waist circumference, waist-to-hip ratio, and HOMA-2-IR. In adjusted analyses, BMI was inversely related to shift work, and other metabolic health outcomes showed no significant associations.

CONCLUSIONS

Healthy worker effects (including self-selection of exposure) could explain inverse relationships, particularly as the cross-sectional design only allowed assessment of current exposure. Key strengths include the population-based design and measurement of metabolic health indicators. Results underscore the importance of consideration of the health of shift workers following departure from the exposed population.

Association between shift work and risk of metabolic syndrome: A systematic review and meta-analysis

AIMS

A comprehensive assessment of the association of shift work with risk of metabolic syndrome (MetS) through a systematic review and meta-analysis has not been reported. We aimed to evaluate the relationship from observational studies.

DATA SYNTHESIS

We searched PubMed, Embase, and Web of Science databases from inception to December 16, 2020. Articles were chosen according to established inclusion criteria. Studies with data on men and women and different types of shift work were treated as independent studies. Relative risks (RRs) and 95% confidence intervals (CIs) were pooled by using random-effects models with heterogeneity (I²) > 50%; otherwise, a fixed-effects model was used. A total of 7192 articles was searched from PubMed, Embase and Web of science. Finally, we included 23 articles (38 studies) in this meta-analysis. The pooled RRs and 95% CI of MetS risk with shift work, 1-shift work, 2-shift work, and 3-shift work versus non-shift work were 1.30 (95% CI 1.19-1.41), 0.95 (95% CI 0.82-1.11), 1.19 (95% CI 0.91-1.56) and 1.17 (95% CI 1.00-1.37), respectively. The results from subgroup analyses stratified by sex, age, and region supported our overall findings that shift work is a risk factor for MetS.

CONCLUSIONS

This meta-analysis suggests that shift work increases risk of MetS. Higher risk of MetS was found in the shift workers who were 2-shift or 3-shift or women or Asian workers.

The Impact of Different Types of Shift Work on Blood Pressure and Hypertension: A Systematic Review and Meta-Analysis

Shift work (SW) encompasses 20% of the European workforce. Moreover, high blood pressure (BP) remains a leading cause of death globally. This review aimed to synthesize the magnitude of the potential impact of SW on systolic blood pressure (SBP), diastolic blood pressure (DBP) and hypertension (HTN). MEDLINE, EMBASE and CENTRAL databases were searched for epidemiological studies evaluating BP and/or HTN diagnosis among shift workers, compared with day workers. Random-effects meta-analyses were performed and the results were expressed as pooled mean differences or odds ratios and 95% confidence intervals (95% CI). The Newcastle-Ottawa Scale was used to assess the risk of bias. Forty-five studies were included, involving 117,252 workers. We found a significant increase in both SBD and DBP among permanent night workers (2.52 mmHg, 95% CI 0.75-4.29 and 1.76 mmHg, 95% CI 0.41-3.12, respectively). For rotational shift workers, both with and without night work, we found a significant increase but only for SBP (0.65 mmHg, 95% CI 0.07-1.22 and 1.28 mmHg, 95% CI 0.18-2.39, respectively). No differences were found for HTN. Our findings suggest that SW is associated with an increase of BP, mainly for permanent night workers and for SBP. This is of special interest given the large number of susceptible workers exposed over time.

Circadian Rhythm Disorders and Corresponding Functional Brain Abnormalities in Young Female Nurses: A Preliminary Study

Objective: Shift work is associated with a decrease in melatonin level and perturbation of the circadian rhythm; however, it is unknown if these lead to functional brain changes. In this study, we investigated whether circadian rhythm disorders caused by shift work are related to changes in brain functional connectivity (FC) and regional homogeneity (ReHo) using whole-brain resting-state functional magnetic resonance imaging (fMRI).

Methods: This prospective case-control study included nine female night shift nurses and nine age-matched female day work nurses with normal sleep rhythms. To assess sleep quality and mood, participants were asked to complete questionnaires. Serum melatonin and cortisol levels were measured. ReHo of whole-brain resting-state function and seed-based FC of the bilateral hypothalamus were compared between groups. Variables that differed significantly between groups were used to examine the association between questionnaire scores and hormone levels and fMRI data.

Results: The night shift nurses had significantly lower sleep quality and melatonin levels; lower ReHo activation in the bilateral cerebellar hemisphere and higher ReHo in the bilateral occipital lobe and left parietal lobe; and higher FC from the hypothalamus to the right cingulate gyrus, right putamen, and vermis than did the day shift nurses. Activation of the right cerebellar hemisphere left superior parietal gyrus, and the right superior occipital gyrus was correlated with sleep quality scores. Moreover, activation of the right cerebellar hemisphere (r = 0.583, P = 0.011) was correlated with melatonin levels, and higher sleepiness scores were associated with stronger FC between the hypothalamus and vermis (r = 0.501, P = 0.034).

Conclusions: Circadian rhythm disorder caused by night shift work can lead to a decrease in sleep quality and melatonin level, as well as a series of changes in brain FC and ReHo.

Association between shift work or long working hours with metabolic syndrome: a systematic review and dose-response meta-analysis of observational studies

This meta-analysis investigates the relationship between both shift work and long working hours and risk of developing metabolic syndrome (MetS). PubMed, EMBASE, and Web of Science databases were searched from the outset to December 10, 2019. Two reviewers independently screened studies, extracted data, and assessed the risk of bias of included studies. A total of 36 (30 cross-sectional, 5 cohort, and a nested case-control) studies, involving 274,263 participants, were included. The pooled odds ratio of shift work and development of MetS was 1.35 (95% confidence interval: 1.24-1.48), and the pooled odds ratio of long working hours and development of MetS was 1.19 (95% confidence interval: 0.97-1.46). In the subgroup analysis stratified by gender, the pooled odds ratios for male and female shift workers were 1.25 (95% confidence interval: 1.14-1.37) and 1.47 (95% confidence interval: 1.18-1.82), respectively. The dose-response (number of years of shift work and development of MetS) analysis showed the pooled odds ratio for 5 years of shift work was 1.07 (95% confidence interval: 1.05-1.09) and for 10 years of shift work 1.11 (95% confidence interval: 1.06-1.15). Our meta-analysis confirmed shift work is significantly associated with risk of metabolic syndrome, but the relationship between long working hours and MetS was not substantiated. Additionally, there was a nonlinear dose-response relationship between the number of years of shift work and risk of MetS, showing positive relationship to about 20 years of shift work but not for longer than 20 years. Prospective cohort studies regarding specific shift work schedules are needed to confirm these results.

A systematic review and meta-analysis of the association between shift work and metabolic syndrome: The roles of sleep, gender, and type of shift work

This study was conducted to investigate the association between shift work and metabolic syndrome (MetS) and quantify the roles of sleep, gender, and type of shift work. We searched online databases, including PubMed, Scopus, and Web of Science on November 17, 2019. Of the 821 articles identified, 38 observational studies (27 cross-sectional, 10 cohorts, and one nested case-control), conducted on 128,416 participants, met our eligibility criteria. The pooled Odds ratio (OR) and 95% Confidence interval (CI) of MetS in shift-versus day-workers were estimated as 1.14 (1.07, 1.21) and 1.11 (1.06, 1.17) for the unadjusted and adjusted models. This association remained significant only for the studies with a cross-sectional design. There was a significantly higher odds of MetS in the studies conducted only on females (1.13 [1.06, 1.20]) or males (1.12 [1.02, 1.21]). The pooled adjusted OR (95% CI) for the studies without and with sleep adjustment was calculated as 1.14 (1.08, 1.21) and 1.29 (1.06, 1.52). We observed that rotating shift workers had stronger odds of MetS than the other shift workers. In conclusion, our findings revealed the significant odds of an association between shift work and MetS and different effects for sleep, gender, and type of shift work.

Effect of frequency and pattern of night shift on hypertension risk in female nurses: a cross-sectional study

OBJECTIVES

Understanding the effect of night shift on hypertension risk in nurses is important to improve the health of nurses and ensure patient safety. This study aimed to evaluate the effect of the frequency and pattern of night shift on hypertension risk and the interaction of them in female nurses.

METHODS

This cross-sectional study constituted 84 697 female nurses in 13 cities in China. The main contents of the survey included SBP, DBP, the frequency and pattern of night shift, and some other factors that might be associated with hypertension. Logistic regression analyses were used to calculate ORs and 95% CIs to estimate the effect of the frequency and pattern of night shift on hypertension risk and the interaction of them in relation to hypertension risk.

RESULTS

Having more than 5 to 10 or more than 10 night shifts per month were significantly more likely to be hypertensive (OR 1.19, 95% CI 1.10-1.28; OR 1.32, 95% CI 1.13-1.54), whereas having less than or equal to 5 night shifts per month was not (OR 1.05, 95% CI 0.95-1.16). The patterns of night shift were all associated with a higher probability of hypertension and participants engaging in rapidly rotating night shift had a lower OR (1.14) than those having slowly rotating night shift (1.23) and permanent night shift (1.46). No significant interaction was observed between the frequency and the pattern of night shift (Pinteraction = 0.281).

CONCLUSION

The frequency and pattern of night shift were associated with hypertension risk in female nurses and no significant interaction was observed between them.

Use of a Canadian Population-Based Surveillance Cohort to Test Relationships Between Shift Work and Breast, Ovarian, and Prostate Cancer

OBJECTIVES

Shift work with circadian disruption is a suspected human carcinogen. Additional population-representative human studies are needed and large population-based linkage cohorts have been explored as an option for surveillance shift work and cancer risk. This study uses a surveillance linkage cohort and job-exposure matrix to test relationships.

METHODS

We estimated associations between shift work and breast, ovarian, and prostate cancer using the population-based Canadian Census Health and Environment Cohort (CanCHEC), linking the 1991 Canadian census to national cancer registry and mortality databases. Prevalence estimates from population labour survey data were used to estimate and assign probability of night, rotating, or evening shifts by occupation and industry. Cohort members were assigned to high (>50%), medium (>25 to 50%), low (>5 to 25%), or no (<5%) probability of exposure categories. Cox proportional hazards modelling was used to estimate associations between shift work exposure and incidence of prostate cancer in men and ovarian and breast cancer in women.

RESULTS

The cohort included 1 098 935 men and 939 520 women. Hazard ratios (HRs) indicated null or inverse relationships comparing high probability to no exposure for prostate cancer: HR = 0.96, 95% confidence interval (CI) = 0.91-1.02; breast cancer: HR = 0.94, 95% CI = 0.90-0.99; and ovarian cancer: HR = 0.99, 95% CI = 0.87-1.13.

CONCLUSIONS

This study showed inverse and null associations between shift work exposure and incidence of prostate, breast, or ovarian cancer. However, we explore limitations of a surveillance cohort, including a possible healthy worker survivor effect and the possibility that this relationship may require the nuanced exposure detail in primary collection studies to be measurable.

Clocks in the Wild: Entrainment to Natural Light

Entrainment denotes a process of coordinating the internal circadian clock to external rhythmic time-cues (Zeitgeber), mainly light. It is facilitated by stronger Zeitgeber signals and smaller period differences between the internal clock and the external Zeitgeber. The phase of entrainment ψ is a result of this process on the side of the circadian clock. On Earth, the period of the day-night cycle is fixed to 24 h, while the periods of circadian clocks distribute widely due to natural variation within and between species. The strength and duration of light depend locally on season and geographic latitude. Therefore, entrainment characteristics of a circadian clock vary under a local light environment and distribute along geoecological settings. Using conceptual models of circadian clocks, we investigate how local conditions of natural light shape global patterning of entrainment through seasons. This clock-side entrainment paradigm enables us to predict systematic changes in the global distribution of chronotypes.

Circadian Clock, Time-Restricted Feeding and Reproduction

The goal of this review was to seek a better understanding of the function and differential expression of circadian clock genes during the reproductive process. Through a discussion of how the circadian clock is involved in these steps, the identification of new clinical targets for sleep disorder-related diseases, such as reproductive failure, will be elucidated. Here, we focus on recent research findings regarding circadian clock regulation within the reproductive system, shedding new light on circadian rhythm-related problems in women. Discussions on the roles that circadian clock plays in these reproductive processes will help identify new clinical targets for such sleep disorder-related diseases.

Healthy Diet and Reduction of Chronic Disease Risks of Night Shift Workers

BACKGROUND

The large increase in epidemiological studies on night shift work is due to the important effects of night shift work on workers' health and psychophysical wellbeing. The short-term effects-insomnia, difficulties in managing work and private life, lower work performance, and more work and extra-work accidents-are easily studied. However, there are several long-term effects that are difficult to study because of the need for detailed exposure assessment and the long latency periods of these diseases.

OBJECTIVE

The aim was to collect epidemiologic evidence of diseases in night shift workers, describing their biological pathways and a set of dietary guidelines.

METHODS

This is a review on diet and health effects in night shift workers.

RESULTS

Significant increases in the rate ratios and hazard ratios of different diseases were associated with modified eating behaviours and poor eating habits among night shift workers. Night shift work is a risk factor for disruption of the circadian rhythms and for some genetic deregulation because it produces the inversion of the sleep/wake cycle and modifies the alternation between activity and rest.

CONCLUSION

A healthy diet and improved dietary practices, together with other factors, can reduce shift workers' chronic disease risk. The literature showed the importance of eating behaviour in order to prevent diseases in these workers; therefore, educational programmes are necessary to encourage several important lifestyle changes. The target of our future research will be the role of food components in some dietetic habits for the prevention of disease in night shift workers.

Lifespan is unaffected by size and direction of daily phase shifts in Nasonia, a hymenopteran insect with strong circadian light resetting

Most organisms have an endogenous circadian clock with a period length of approximately 24 h that enables adaptation, synchronization and anticipation to environmental cycles. The circadian system (circa = about or around, diem = a day) may provide evolutionary benefits when entrained to the 24-h light-dark cycle. The more the internal circadian period (τ) deviates from the external light-dark cycle, the larger the daily phase shifts need to be to synchronize to the environment. In some species, large daily phase shifts reduce survival rate. Here we tested this 'resonance fitness hypothesis' on the diurnal wasp Nasonia vitripennis, which exhibits a large latitudinal cline in free-running period with longer circadian period lengths in the north than in the south. Longevity was measured in northern and southern wasps placed into light-dark cycles (T-cycles) with periods ranging from 20 h to 28 h. Further, locomotor activity was recorded to estimate range and phase angle of entrainment under these various T-cycles. A light pulse induced phase response curve (PRC) was measured in both lines to understand entrainment results. We expected a concave survival curve with highest longevity at T = τ and a reduction in longevity the further τ deviates from T (τ/T<>1). Our results do not support this resonance fitness hypothesis. We did not observe a reduction in longevity when τ deviates from T. Our results may be understood by the strong circadian light resetting mechanism (type 0 PRC) to single light pulses that we measured in Nasonia, resulting in: (1) the broad range of entrainment, (2) the wide natural variation in circadian free-running period, and (3) the lack of reduced survival when τ/T ratio's deviates from 1. Together this indicates that circadian adaption to latitude may lead to changes in circadian period and light response, without negative influences on survival.

Weight gain in public hospital workers: a retrospective cohort study

This study assessed changes in the nutrition profile of public hospital workers over a period of three decades and the association between nutritional status and occupational factors. A retrospective cohort study was conducted with staff taken on in 1980, 1990, and 2000 still working in the hospital in 2013. The following data was obtained from staff records: sociodemographic characteristics; and body weight and height, recorded during pre-employment and periodic medical examinations. The latter was used to calculate body mass index (BMI).The final sample consisted of 386 workers (76.4% women and 88.1% white) with a mean age of 29.3 ± 7.3 years. Mean body weight and BMI at admission were highest in the 2000 cohort (W = 66.3 ± 12.5kg; BMI = 21.3 ± 2.5 kg/m2), compared to 1980 (W = 56.7 ± 10.2 kg; BMI = 21.3 ± 2.5 kg/m2)and 1990 (W = 62.2 ± 11.5 kg; BMI = 22.9 ± 3.3 kg/m2) cohorts. Variation in weight and BMI between the pre-employment examination and final periodic examination was highest in the 2000 cohort. When stratified by sex, this difference in variation was observed only in men. No association was found between variation in body weight and BMI and work shift and occupation. The increase in weight and BMI reflects the nutritional transition in Brazil, underscoring the need for nutritional surveillance and the implementation of health education programs directed at staff.

Is shift work associated with a higher risk of overweight or obesity? A systematic review of observational studies with meta-analysis

Background

An increasing number of original studies suggest that exposure to shift work could be associated with the risk of overweight and obesity, but the results remain conflicted and inconclusive. This study aimed to quantitatively synthesize available epidemiological evidence on the association between shift work and the risk of overweight and obesity by a meta-analysis.

Methods

The authors searched PubMed, Embase and the reference lists of all included studies up to April 2017, with a verification search in December 2017. Inclusion criteria were original studies that reported odds ratios, relative risks or hazard ratios (ORs, RRs or HRs, respectively) of at least one outcome of overweight or obesity. Summary risk estimates were calculated by random-effect models.

Results

Twenty-six studies (7 cohort studies, 18 cross-sectional studies and 1 case-control study) involving 311 334 participants were identified. Among these studies, the cut-off points of overweight and obesity varied greatly, so the heterogeneity was substantial; however, the results were stable. Shift work was found to be positively associated with the risk of overweight [RR: 1.25; 95% confidence interval (95% CI): 1.08-1.44] and obesity (RR: 1.17; 95% CI: 1.12-1.22).

Conclusions

Individuals involved in shift work are more likely to become overweight or obese. Appropriate preventive interventions in the organization of shift schedules according to ergonomic criteria would allow shift workers to avoid potential health impairment.

Night and rotational work exposure within the last 12 months and risk of incident hypertension

Objectives Shift work, such as alternating day and nights, causes chronobiologic disruptions which may cause an increase in hypertension risk. However, the relative contributions of the components of shift work ‒ such as shift type (eg, night work) and rotations (ie, switching of shift times; day to night) ‒ on this association are not clear. To address this question, we constructed novel definitions of night work and rotational work and assessed their associations with risk of incident hypertension. Methods A cohort of 2151 workers at eight aluminum manufacturing facilities previously studied for cardiovascular disease was followed from 2003 through 2013 for incident hypertension, as defined by ICD-9 insurance claims codes. Detailed time-registry data was used to classify each worker's history of rotational and night work. The associations between recent rotational work and night work in the last 12 months and incident hypertension were estimated using adjusted Cox proportional hazards models. Results Elevated hazard ratios (HR) were observed for all levels of recent night work (>0-5, >5-50, >50-95, >95-100%) compared with non-night workers, and among all levels of rotational work (<1, 1-10, >10-20, >20-30, and >30%) compared with those working <1% rotational work. In models for considering the combination of night and rotational work, workers with mostly night work and frequent rotations (≥50% night and ≥10% rotation) had the highest risk of hypertension compared to non-night workers [HR 4.00, 95% confidence interval (CI )1.69-9.52]. Conclusions Our results suggest recent night and rotational work may both be associated with higher rates of incident hypertension.

Association between night-shift work, sleep quality and metabolic syndrome

Objectives

Occupational factors, particularly night-shift work, are attracting growing interest as a possible determinant of metabolic syndrome (MetS). This study aimed to determine the association between night-shift work and MetS, and assess whether sleep quality is a mediating factor.

Methods

A cross-sectional study was conducted among Malaysian manufacturing workers, aged 40–65 years old. They completed a self-administered questionnaire on sociodemographics, lifestyle and family history, and the Pittsburgh Sleep Quality Index (PSQI) questionnaire. Waist circumference, blood pressure, fasting blood sugar, triglycerides and high-density lipoprotein levels were measured. Baron and Kenny’s method, Sobel test and multiple mediation models with bootstrapping were used to determine whether the PSQI global score or its components mediated the association between night-shift work and MetS.

Results

Of the 494 participants, 177 (36%) worked night shift and 51% were men. The prevalence of MetS was 37%. Night-shift work was independently associated with a twofold increase in the risk of MetS (adjusted OR: 1.92, 95% CI 1.24 to 2.97). However, the association between night-shift work and MetS did not appear to be modified by sex. Night-shift workers also reported significantly poorer sleep quality, longer sleep latency, shorter sleep duration, sleep disturbances and daytime dysfunction. Robust mediation analysis nonetheless showed that neither PSQI global score nor its components mediated the association between night-shift work and MetS.

Conclusion

Early screening and management of MetS and the development of programmes to improve sleep quality should be carried out among night-shift workers. Future research should investigate other modifiable mediators linking night-shift work and MetS.

Night shift work exposure profile and obesity: Baseline results from a Chinese night shift worker cohort

AIMS

This study aimed to evaluate the associations between types of night shift work and different indices of obesity using the baseline information from a prospective cohort study of night shift workers in China.

METHODS

A total of 3,871 workers from five companies were recruited from the baseline survey. A structured self-administered questionnaire was employed to collect the participants' demographic information, lifetime working history, and lifestyle habits. Participants were grouped into rotating, permanent and irregular night shift work groups. Anthropometric parameters were assessed by healthcare professionals. Multiple logistic regression models were used to evaluate the associations between night shift work and different indices of obesity.

RESULTS

Night shift workers had increased risk of overweight and obesity, and odds ratios (ORs) were 1.17 (95% CI, 0.97-1.41) and 1.27 (95% CI, 0.74-2.18), respectively. Abdominal obesity had a significant but marginal association with night shift work (OR = 1.20, 95% CI, 1.01-1.43). A positive gradient between the number of years of night shift work and overweight or abdominal obesity was observed. Permanent night shift work showed the highest odds of being overweight (OR = 3.94, 95% CI, 1.40-11.03) and having increased abdominal obesity (OR = 3.34, 95% CI, 1.19-9.37). Irregular night shift work was also significantly associated with overweight (OR = 1.56, 95% CI, 1.13-2.14), but its association with abdominal obesity was borderline (OR = 1.26, 95% CI, 0.94-1.69). By contrast, the association between rotating night shift work and these parameters was not significant.

CONCLUSION

Permanent and irregular night shift work were more likely to be associated with overweight or abdominal obesity than rotating night shift work. These associations need to be verified in prospective cohort studies.

Associations of rotational shift work and night shift status with hypertension: a systematic review and meta-analysis

BACKGROUND

The reported risks of hypertension (HTN) in rotating shift and night shift workers are controversial. The objective of this meta-analysis was to assess the association between shift work status and HTN.

METHODS

A literature search was performed using MEDLINE, EMBASE and Cochrane Database from inception through October 2016. Studies that reported odds ratios (OR) comparing the risk of HTN in shift workers were included. A prespecified subgroup analysis by rotating shift and night shift statuses were also performed. Pooled OR and 95% confidence interval (CI) were calculated using a random-effect, generic inverse variance method. The protocol for this study is registered with International Prospective Register of Systematic Reviews; no. CRD42016051843.

RESULTS

Twenty-seven observational studies (nine cohort and 18 cross-sectional studies) with a total of 394 793 individuals were enrolled. The pooled ORs of HTN in shift workers in cohort and cross-sectional studies were 1.31 (95% CI, 1.07-1.60) and 1.10 (95% CI, 1.00-1.20), respectively. When meta-analysis was restricted only to cohort studies in rotating shift, the pooled OR of HTN in rotating shift workers was 1.34 (95% CI, 1.08-1.67). The data regarding night shift and HTN in cohort studies was limited. The pooled OR of HTN in night shift workers in cross-sectional studies was 1.07 (95% CI, 0.85-1.35).

CONCLUSION

Based on the findings of our meta-analysis, shiftwork status may play an important role in HTN, as there is a significant association between rotating shift work and HTN. However, there is no significant association between night shift status and risk of HTN.

Association between rotating night shift work and metabolic syndrome in Korean workers: differences between 8-hour and 12-hour rotating shift work

This study aimed to analyze the association between the shift work schedule and metabolic syndrome (MetS). This is a retrospective longitudinal study based on the 2015 health checkup data of 2,090 workers evaluated for MetS in 2010 at a general hospital in Korea. The participants were divided according to their shift work schedule into daytime, three-shift (8-h rotation), and two-shift (12-h rotation) workers. The index that indicates the association between the shift work schedule and MetS is the odds ratio (OR) calculated using multivariate logistic regression. The analysis for the entire group of workers indicated that there was positive association between two-shift rotation and MetS (OR=1.58, 95% confidence interval [CI]: 1.09, 2.29). In the analysis of rotating night-shift workers, the years of rotating night shifts, frequency of night-shift work, and sleep disturbance were added to the confounding variables, and two-shift work remained positively associated with MetS (OR=1.72, 95% CI: 1.10, 2.70). The risk of MetS differs based on the shift work schedules they engage in. Hence, structural changes to the shift work schedules are required to prevent MetS in night-shift workers.

Meta-analysis on shift work and risks of specific obesity types

AIMS

This systematic review and meta-analysis evaluated the associations between shift work patterns and risks of specific types of obesity.

METHODS

PubMed was searched until March 2017 for observational studies that examined the relationships between shift work patterns and obesity. Odds ratio for obesity was extracted using a fixed-effects or random-effects model. Subgroup meta-analyses were carried out for study design, specific obesity types and characteristics of shift work pattern.

RESULTS

A total of 28 studies were included in this meta-analysis. The overall odds ratio of night shift work was 1.23 (95% confidence interval = 1.17-1.29) for risk of obesity/overweight. Cross-sectional studies showed a higher risk of 1.26 than those with the cohort design (risk ratio = 1.10). Shift workers had a higher frequency of developing abdominal obesity (odds ratio = 1.35) than other obesity types. Permanent night workers demonstrated a 29% higher risk than rotating shift workers (odds ratio 1.43 vs. 1.14).

CONCLUSION

This meta-analysis confirmed the risks of night shift work for the development of overweight and obesity with a potential gradient association suggested, especially for abdominal obesity. Modification of working schedules is recommended, particularly for prolonged permanent night work. More accurate and detailed measurements on shift work patterns should be conducted in future research.

Daily rhythms count for female fertility

Female ovulation depends on a surge in circulating luteinizing hormone (LH) which occurs at the end of the resting period and requests high circulating estradiol. This fine tuning involves both an estradiol feedback as an indicator of oocyte maturation, and the master circadian clock of the suprachiasmatic nuclei as an indicator of the time of the day. This review describes the mechanisms through which daily time cues are conveyed to reproductive hypothalamic neurons to time the pre-ovulatory surge. In female rodents, neurotransmitters released by the suprachiasmatic nuclei activate the stimulatory kisspeptin neurons and reduce the inhibitory RFRP neurons precisely at the end of the afternoon of proestrus to allow a full surge in LH secretion. From these findings, the impact of circadian disruptions (during shift or night work) on female reproductive performance and fertility should now being investigated in both animal models and humans.

Association of Sleep Duration, Sleep Quality and Shift-Work Schedule in Relation to Hypertension Prevalence in Chinese Adult Males: A Cross-Sectional Survey

Background: Previous studies indicated that measurement of sleep only by duration and quality may be biased. This study aimed to investigate the interactive association of self-reported sleep duration, quality and shift-work schedule with hypertension prevalence in Chinese adult males. Methods: A total of 4519 Chinese adult males (≥18 years) were enrolled into the cross-sectional survey. Sleep attributes were measured from the responses to the standard Pittsburgh Sleep Quality Index and relevant questions in a structured questionnaire survey. The association of sleep duration, quality and shift-work schedule with hypertension prevalence was analyzed using multivariate logistic regression, considering the interaction between them or not. Results: Taking the potential interaction of the three aspects of sleep into consideration, only short sleep duration combined with poor sleep quality was found to be related to hypertension prevalence in Chinese adult males (odds ratio (OR): 1.74, 95% confidence interval (CI): 1.31–2.31), which could be modified by occasional and frequent shift-work schedule (OR: 1.43, 95% CI: 1.05–1.95; OR: 1.97, 95% CI: 1.40–2.79). Conclusions: Short sleep duration was not associated with the prevalence of hypertension in Chinese adult males unless poor sleep quality exists, which could be further modified by shift-work schedule. Assessment of sleep by measuring sleep duration only was not sufficient when exploring the association of sleep with hypertension.

The impact of meal timing on cardiometabolic syndrome indicators in shift workers

The aims of this study were to 1) compare the inflammatory potential of night- and day-shift nurses' diets with regard to time of day and work status and 2) explore how the timing of food intake during work and off-work is associated with cardiometabolic syndrome (CMS) risk factors between these two groups. Female nurses (N = 17; 8 day-shift and 9 night-shift) reported food intake over 9 days. On a middle day off of work, metabolic parameters were measured after an overnight fast. Energy/macronutrient intake and inflammatory potential of dietary intake (as assessed via the Dietary Inflammatory Index^TM) were calculated for nurses' workdays, work nights, off-work days, and off-work nights. Work-night total food intake (grams) accounted for a significant amount of variance in CMS risk factors for night-shift nurses only. Increased total gram consumption during night-shift nurses' work nights was associated with increased lipid levels - independent of the macronutrient composition of the food consumed. Alternatively, for night-shift nurses, work-day intake of several food parameters accounted for a significant proportion of variance in HDL cholesterol levels, with higher intake associated with higher HDL levels. For both day- and night-shift nurses, food intake during the day was more pro-inflammatory regardless of shift type or work status. Our novel approach of combining time-of-day-specific and work-day-specific analyses of dietary inflammatory factors and macronutrient composition with measurement of CMS risk factors suggests a link between meal timing and cardiometabolic health for shift-working nurses.

Prevalence of work-site injuries and relationship between obesity and injury among U.S. workers: NHIS 2004-2012

INTRODUCTION

Studies have reported associations between obesity and injury in a single occupation or industry. Our study estimated the prevalence of work-site injuries and investigated the association between obesity and work-site injury in a nationally representative sample of U.S. workers.

METHODS

Self-reported weight, height, and injuries within the previous three months were collected annually for U.S. workers in the National Health Interview Survey (NHIS) from 2004-2012. Participants were categorized as normal weight (BMI: 18.5-24.9kg/m(2)), overweight (BMI: 25.0-29.9), obese I (BMI: 30.0-34.9), and obese II (BMI: 35+). The prevalence of injury and prevalence ratios from fitted logistic regression models was used to assess relationships between obesity and injury after adjusting for covariates. Sampling weights were incorporated using SUDAAN software.

RESULTS

During the 9-year study period from 2004 to 2012, 1120 workers (78 workers per 10,000) experienced a work-related injury during the previous three months. The anatomical sites with the highest prevalence of injury were the back (14.3/10,000±1.2), fingers (11.5±1.3), and knees (7.1±0.8). The most common types of injuries were sprains/strains/twists (41.5% of all injuries), cuts (20.0%), and fractures (11.8%). Compared to normal weight workers, overweight and obese workers were more likely to experience work-site injuries [overweight: PR=1.25 (95% CI=1.04-1.52); obese I: 1.41 (1.14-1.74); obese II: 1.68 (1.32-2.14)]. These injuries were more likely to affect the lower extremities [overweight: PR=1.48, (95% CI=1.03-2.13); obese I: 1.70 (1.13-2.55); obese II: 2.91 (1.91-4.41)] and were more likely to be due to sprains/strains/twists [overweight: PR=1.73 (95% CI=1.29-2.31); obese I: PR=2.24 (1.64-3.06); obese II: PR=2.95 (2.04-4.26)].

CONCLUSIONS

Among NHIS participants, overweight and obese workers were 25% to 68% more likely to experience injuries than normal weight workers.

PRACTICAL APPLICATIONS

Weight reduction policies and management programs may be effectively targeted towards overweight and obese groups to prevent or reduce work-site injuries.

Work schedule and self-reported hypertension - the potential beneficial role of on-shift naps for night workers

Data on the association between shift work and hypertension are controversial. Sleep restriction is hypothesized to be involved in this relationship. Since on-shift nap can partly compensate for sleep deprivation among night workers, this investigation is aimed at (i) comparing the prevalence of hypertension among workers considering both current and former night work, (ii) testing the association between on-shift naps and hypertension among night workers, and (iii) analyzing the influence of sleep complaints in the association between on-shift nap and hypertension. Nap was defined as a sleep episode with duration shorter than the average nighttime sleep. A cross-sectional study was performed at the 18 largest public hospitals in Rio de Janeiro, Brazil, in 2010-2011 (N = 2588 female registered nurses). Nurses were informally allowed to nap for up to three consecutive hours during working nights. Workers completed a multidimensional questionnaire including self-reported information on physician diagnosis of hypertension, napping, and sleep complaints (insomnia, diurnal sleepiness, and non-satisfactory sleep). Epidemiological and statistical treatment of data included binomial logistic regression and interaction tests. Higher chances of hypertension were observed for both current and former night workers compared with workers with no previous experience in night work, i.e. exclusive day workers (OR = 1.68; CI95% 1.22-2.33 and OR = 1.40; CI95% 1.01-1.96, respectively) after adjustment for age, race/ethnicity, physical activity, smoking, alcohol consumption, insomnia, weekly work hours, and BMI. Compared with exclusive day workers, both non-nappers and nappers were at a higher likelihood of reporting hypertension (OR = 1.93 CI95% 1.35-2.79 and OR = 1.41 CI95% 1.08-2.20, respectively). An interaction was observed between napping behavior and insomnia (p = 0.037). In the whole sample of night workers, the lower OR for nappers was confirmed when they were directly compared with non-nappers (OR = 0.76 CI95% 0.59-0.98). Analysis of night workers stratified by insomnia showed a significant reduction in OR for nappers (compared to non-nappers) only among insomniacs (OR = 0.58). Napping during night work may be a protective factor for hypertension, particularly among insomniacs. Factors related to melatonin secretion, blood pressure control, and blood pressure dipping patterns are likely to be involved in the relationship between on-shift napping and blood pressure.

Association between shift work and obesity according to body fat percentage in Korean wage workers: data from the fourth and the fifth Korea National Health and Nutrition Examination Survey (KNHANES 2008-2011)

BACKGROUND

Health problems in shift workers vary including obesity acting as a risk factor in cerebrovascular diseases. Recent studies have commonly determined the prevalence of obesity in shift workers on the basis of body mass index. The accuracy of BMI for diagnosing obesity are still limited apparently. Consequently, this study aimed to determine the relationship between shift work and obesity according to the total body fat percentage in Korean wage workers.

METHODS

From the Fourth and the Fifth Korea National Health and Nutrition Examination Survey (2008-2011), after military personnel were excluded, a total of 2952 wage workers (20 ≤ age ≤ 65) whose current jobs were their longest jobs were selected as subjects of the study. The total body fat percentage was used to determine the obesity standards (≥25.7 % in males and ≥36.0 % in females). The subjects were divided into groups by gender and work type (manual vs non-manual), and chi-squared test was used to evaluate the relationship between socio-economic, health behavior, and work-related factors, on the one hand, and obesity, on the other. In addition, multivariate logistic regression analysis was performed to examine the effects of shift work on obesity.

RESULTS

When other factors were controlled for, the risk of obesity in shift work showed a statistically significant increase (odds ratio = 1.779, 95 % confidence interval = 1.050-3.015) in the male manual worker group. However, there were no significant results in the male non-manual and female worker groups.

CONCLUSION

Shift work was related to a higher risk of obesity in the Korean male manual worker group.

Shift work and the risk of cardiovascular disease among workers in cocoa processing company, Tema

OBJECTIVE

Shift work has been implicated in cardiovascular disease (CVD), a major cause of death globally. The aim of this study was to evaluate the risk of developing CVD in shift work.

DESIGN

A cross-sectional study involving secondary analysis of shift and non-shift work from an industry in Ghana.

PARTICIPANTS

Two hundred (113 shift and 87 non-shift) consecutive workers who consented were recruited into the study. A structured questionnaire was administered to deduce information on participant's age, alcohol consumption pattern, smoking habits, history of diabetes, stroke and hypertension.

RESULTS

Shift workers were found to be associated with higher body mass index (26.9 ± 4.6 vs 25.2 ± 3.3, p = 0.013); fasting blood glucose (5.9 ± 1.8 vs 5.3 ± 0.8, p ≤ 0.0001); glycated haemoglobin (4.9 ± 0.9 vs 4.2 ± 0.8, p ≤ 0.0001); high sensitivity C-reactive protein (2.5 ± 1.1 vs 1.8 ± 1.1, p < 0.0001); total cholesterol (5.9 ± 1.3 vs 5.2 ± 1.7, p = 0.002); triglycerides (1.3 ± 0.8 vs 1.1 ± 0.6, p = 0.015) and LDL cholesterol (3.6 ± 0.9 vs 3.2 ± 1.3, p = 0.04) than controls. Shift work however, had no associations with HDL-cholesterol.

CONCLUSION

It can be concluded that shift work is associated with risk factors of CVD.

Association between night work and cardiovascular diseases: analysis of the 3rd Korean working conditions survey

OBJECTIVES

This study was conducted to investigate the relationship between night work and cardiovascular diseases among wage workers in Korea.

METHODS

The study was based on the 3rd Korean Working Conditions Survey (KWCS; 2011). This study included 29,711 wage workers. We used the chi-squared test and logistic regression to examine the association between cardiovascular diseases and night work and cumulative night work.

RESULTS

Among all of the paid workers, 12.5% reported doing night work ≥ 1 day per month. Night work was significantly associated with an increased risk of cardiovascular diseases (odds ratio [OR] 1.58, 95% confidence interval [CI] 1.11-2.25). Also, compared to the group that did not do night works, the group with higher cumulative night work demonstrated an increased risk for cardiovascular diseases (OR 1.81, 95% CI 1.19-2.74).

CONCLUSIONS

This study suggests that night work is significantly associated with cardiovascular diseases.

A Multi-Oscillatory Circadian System Times Female Reproduction

Rhythms in female reproduction are critical to insure that timing of ovulation coincides with oocyte maturation and optimal sexual arousal. This fine tuning of female reproduction involves both the estradiol feedback as an indicator of oocyte maturation, and the master circadian clock of the suprachiasmatic nuclei (SCN) as an indicator of the time of the day. Herein, we are providing an overview of the state of knowledge regarding the differential inhibitory and stimulatory effects of estradiol at different stages of the reproductive axis, and the mechanisms through which the two main neurotransmitters of the SCN, arginine vasopressin, and vasoactive intestinal peptide, convey daily time cues to the reproductive axis. In addition, we will report the most recent findings on the putative functions of peripheral clocks located throughout the reproductive axis [kisspeptin (Kp) neurons, gonadotropin-releasing hormone neurons, gonadotropic cells, the ovary, and the uterus]. This review will point to the critical position of the Kp neurons of the anteroventral periventricular nucleus, which integrate both the stimulatory estradiol signal, and the daily arginine vasopressinergic signal, while displaying a circadian clock. Finally, given the critical role of the light/dark cycle in the synchronization of female reproduction, we will discuss the impact of circadian disruptions observed during shift-work conditions on female reproductive performance and fertility in both animal model and humans.

The impact of sleep and circadian disturbance on hormones and metabolism

The levels of several hormones fluctuate according to the light and dark cycle and are also affected by sleep, feeding, and general behavior. The regulation and metabolism of several hormones are influenced by interactions between the effects of sleep and the intrinsic circadian system; growth hormone, melatonin, cortisol, leptin, and ghrelin levels are highly correlated with sleep and circadian rhythmicity. There are also endogenous circadian mechanisms that serve to regulate glucose metabolism and similar rhythms pertaining to lipid metabolism, regulated through the actions of various clock genes. Sleep disturbance, which negatively impacts hormonal rhythms and metabolism, is also associated with obesity, insulin insensitivity, diabetes, hormonal imbalance, and appetite dysregulation. Circadian disruption, typically induced by shift work, may negatively impact health due to impaired glucose and lipid homeostasis, reversed melatonin and cortisol rhythms, and loss of clock gene rhythmicity.

Sleep Strategies of Night-Shift Nurses on Days Off: Which Ones are Most Adaptive?

OBJECTIVES

To determine the off-shift sleep strategies of bi-ethnic night-shift nurses, the relationship between these sleep strategies and adaptation to shift work, and identify the participant-level characteristics associated with a given sleep strategy.

METHODS

African-American and non-Hispanic White female, night-shift nurses from an academic hospital were recruited to complete a survey on sleep-wake patterns (n = 213). Participants completed the standard shiftwork index and the biological clocks questionnaire to determine sleep strategies and adaptation to night-shift work. In addition, chronotype was determined quantitatively with a modified version of the Munich ChronoType Questionnaire. Most participants worked ~3 consecutive 12-h night-shifts followed by several days off.

RESULTS

Five sleep strategies used on days off were identified: (a) night stay, (b) nap proxy, (c) switch sleeper, (d) no sleep, and (e) incomplete switcher. Nap proxy and no sleep types were associated with poorer adaptation to night-shift work. The switch sleeper and incomplete switcher types were identified as more adaptive strategies that were associated with less sleep disturbance, a later chronotype, and less cardiovascular problems.

CONCLUSION

Behavioral sleep strategies are related to adaptation to a typical night-shift schedule among hospital nurses. Nurses are crucial to the safety and well-being of their patients. Therefore, adoption of more adaptive sleep strategies may reduce sleep/wake dysregulation in this population, and improve cardiovascular outcomes.

Protecting the melatonin rhythm through circadian healthy light exposure

Currently, in developed countries, nights are excessively illuminated (light at night), whereas daytime is mainly spent indoors, and thus people are exposed to much lower light intensities than under natural conditions. In spite of the positive impact of artificial light, we pay a price for the easy access to light during the night: disorganization of our circadian system or chronodisruption (CD), including perturbations in melatonin rhythm. Epidemiological studies show that CD is associated with an increased incidence of diabetes, obesity, heart disease, cognitive and affective impairment, premature aging and some types of cancer. Knowledge of retinal photoreceptors and the discovery of melanopsin in some ganglion cells demonstrate that light intensity, timing and spectrum must be considered to keep the biological clock properly entrained. Importantly, not all wavelengths of light are equally chronodisrupting. Blue light, which is particularly beneficial during the daytime, seems to be more disruptive at night, and induces the strongest melatonin inhibition. Nocturnal blue light exposure is currently increasing, due to the proliferation of energy-efficient lighting (LEDs) and electronic devices. Thus, the development of lighting systems that preserve the melatonin rhythm could reduce the health risks induced by chronodisruption. This review addresses the state of the art regarding the crosstalk between light and the circadian system.

Years worked at night and body mass index among registered nurses from eighteen public hospitals in Rio de Janeiro, Brazil

Background

Employees working night shifts are at a greater risk of being overweight or obese. Few studies on obesity and weight gain analyze the years of exposure to night work. The aim of this study was to determine the relationship between the years of exposure to night work and body mass index (BMI) among registered nurses.

Methods

A cross-sectional analysis was performed in 18 largest public hospitals in Rio de Janeiro, Brazil. A total of 2,372 registered nurses (2,100 women) completed a comprehensive questionnaire concerning sociodemographic, professional, lifestyle, and health behavioral data. Current and past exposures to night shifts as well as BMI values were measured as continuous variables. A gamma regression model was used with an identity link function to establish the association.

Results

The association between years of exposure to night work and BMI was statistically significant for both women and men after adjusting for all covariates [β = 0.036; CI95% = 0.009–0.063) and β = 0.071 (CI95% = 0.012–0.129), respectively]. The effect of night work was greater among men than women. For example, for those women who have worked at night for 20 years the estimated average BMI was 25.6 kg/m² [range, 25.0–26.2]. In relation to men, after 20 years of exposure to night work the estimated average BMI was 26.9 kg/m2 [range, 25.6–28.1].

Conclusions

These findings suggest that night shift exposure is related to BMI increases. Obesity prevention strategies should incorporate improvements in work environments, such as the provision of proper meals to night workers, in addition to educational programs on the health effects of night work.

Meta-analysis on night shift work and risk of metabolic syndrome

This study aims to quantitatively summarize the association between night shift work and the risk of metabolic syndrome (MetS), with special reference to the dose-response relationship with years of night shift work. We systematically searched all observational studies published in English on PubMed and Embase from 1971 to 2013. We extracted effect measures (relative risk, RR; or odd ratio, OR) with 95% confidence interval (CI) from individual studies to generate pooled results using meta-analysis approach. Pooled RR was calculated using random- or fixed-effect model. Downs and Black scale was applied to assess the methodological quality of included studies. A total of 13 studies were included. The pooled RR for the association between 'ever exposed to night shift work' and MetS risk was 1.57 (95% CI = 1.24-1.98, pheterogeneity  = 0.001), while a higher risk was indicated in workers with longer exposure to night shifts (RR = 1.77, 95% CI = 1.32-2.36, pheterogeneity  = 0.936). Further stratification analysis demonstrated a higher pooled effect of 1.84 (95% CI = 1.45-2.34) for studies using the NCEP-ATPIII criteria, among female workers (RR = 1.61, 95% CI = 1.10-2.34) and the countries other than Asia (RR = 1.65, 95% CI = 1.39-1.95). Sensitivity analysis confirmed the robustness of the results. No evidence of publication bias was detected. The present meta-analysis suggested that night shift work is significantly associated with the risk of MetS, and a positive dose-response relationship with duration of exposure was indicated.