Rotating Night Shift Work Research Articles

Abstract 007: Actigraphy-Measured Sleep Regularity and Risk of Incident Cardiovascular Disease: The Multi-Ethnic Study of Atherosclerosis

Background: Prior studies have linked rotating night shift work to increased risk of cardiovascular disease (CVD). Irregular sleep schedules, characterized by high day-to-day variability in sleep duration or timing, represent possibly milder but much more common/chronic disruption of circadian rhythms in the general population. However, no prospective study to date has examined the association between sleep regularity and CVD outcomes. Methods: In the Multi-Ethnic Study of Atherosclerosis, 1,993 participants who were free of CVD completed 7-day wrist actigraphy at home for objective monitoring of sleep duration and quality between 2010 and 2013, and were prospectively followed through 2015. We assessed sleep regularity using the standard deviation (SD) of actigraphy-measured sleep duration and sleep onset timing across 7 days. Incident CVD was defined as total cardiovascular events including coronary heart disease, stroke, congestive heart failure, and cardiovascular death. Cox proportional hazards model was used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for incident CVD according to SD of sleep duration and timing, adjusted for traditional CVD risk factors (e.g., sociodemographic factors, lifestyles and CVD biomarkers) and other sleep-related factors (e.g., average sleep duration, insomnia symptoms, daytime sleepiness, sleep-disordered breathing, chronotype and work schedules). Results: During a median follow-up of 4.0 years, 95 participants developed CVD events. Compared to participants with a 7-day sleep duration SD ≤60 min, the multivariable-adjusted HR (95% CI) for CVD was 1.12 (0.61, 2.07) for 61-90 min, 1.71 (0.94, 3.09) for 91-120 min, and 2.20 (1.22, 3.96) for >120 min. Every 1-hour increase in sleep duration SD was associated with 23% higher CVD risk (95% CI: 1.05, 1.45; p-trend=0.01). In contrast to this linear association with sleep duration variability, there appeared to be a threshold pattern for the association with SD of sleep onset timing. Compared to participants with a sleep timing SD ≤30 min, the multivariable-adjusted HR (95% CI) for CVD was 1.13 (0.60, 2.13) for 31-60 min, 1.15 (0.58, 2.31) for 61-90 min, and 2.07 (1.09, 3.94) for >90 min. CVD risk was 87% higher comparing sleep timing SD >90 min versus ≤90 min (95% CI: 1.19, 2.96; p=0.007). These associations did not differ significantly by age, sex, race/ethnicity, sleep duration or work schedules. Exclusion of current shift workers yielded similar results. Conclusion: Irregular sleep duration and timing may be novel risk factors for CVD, independent of traditional CVD risk factors and sleep quantity/quality. Given the increased prevalence of irregular sleep (e.g., due to mobile device use), our findings have important public health implications for CVD prevention and suggest value in evaluating the impact of sleep hygiene interventions aimed at improving sleep pattern consistency.

Rotating night shift work and menopausal age.

How are rotating night shift schedules associated with age at menopause among a large, national cohort of shift working nurses? Our findings suggest that working rotating night shifts with sufficient frequency may modestly accelerate reproductive senescence among women who may already be predisposed to earlier menopause. Younger age at menopause has been associated with increased risk of adverse health outcomes, particularly those linked to reproduction. Night work has been associated with reproductive dysfunction, including disruption of menstrual cycle patterns. This cohort study was conducted among 80 840 women of the Nurses' Health Study 2 (NHS2), with prospective follow-up from 1991 through 2013. Loss-to-follow-up of the NHS2 is estimated to be <10%. We assessed the association between cumulative and current rotating night shift work and age at natural menopause over 22 years of follow-up (1991-2013). Cox proportional hazards models were used to estimate hazard ratios (HR) for menopause, adjusted for age, smoking status, body mass index, physical activity, alcohol consumption, reproductive factors and exogenous hormone use. Over follow-up, 27 456 women (34%) reached natural menopause. Women who worked 20 or more months of rotating night shifts in the prior 2-year had an increased risk of earlier menopause (multivariable-adjusted (MV)-HR = 1.09, 95% CI: 1.02-1.16) compared to women without rotating night shift work. This risk was stronger among women undergoing menopause or otherwise censored under age 45 years (MV-HR = 1.25, 95% CI: 1.08-1.46), than it was for those continuing in the study when >45 years old (MV-HR = 1.05, 95% CI: 0.99-1.13). Working 10 or more years of cumulative rotating night work was also associated with higher risk of menopause among women reaching menopause under age 45 (MV-HR10-19 years = 1.22, 95% CI: 1.03-1.44; MV-HR≥20 years = 1.73, 95% CI: 0.90-3.35), though not over the age of 45 years (MV-HR10-19 years = 1.04, 95% CI: 0.99-1.10; MV-HR≥20 years = 1.01, 95% CI: 0.89-1.15). The degree to which observed effects of rotating night shifts on age at natural menopause are due to circadian disruption, rather than fatigue and stress associated with working more demanding schedules, is uncertain due to potential residual confounding by these factors. This is the first study to assess the effects of night work on menopausal timing among a larger national cohort of shift working women. Women already prone to earlier menopause may further truncate their reproductive lifetime by working schedules comprising day as well as night shifts. This study was supported by Center for Disease Control and Prevention/The National Institute for Occupational Safety and Health Grant 5R01OH009803 (PI: Schernhammer E), as well as UM1 CA176726 from the National Institute of Health. The funding sources had no role in the design and conduct of the study; collection, management, analysis and interpretation of the data; preparation, review or approval of the article; and decision to submit the article for publication. The authors have no conflicts of interest.

Association between metabolic risk, oxidative stress and rotating shift work in a tertiary health care facility

ContextHealthcare industry employees, work in rotating shift duties to provide 24/7 services. Shift work is known to disrupt circadian rhythm and predispose the employees to metabolic risk and oxidative stress, subsequently increasing the risk for Non-Communicable Diseases. Present study attempts to evaluate this association. AimsTo evaluate the association between metabolic risk and oxidative stress among health care personnel working in rotating night-shift as compared to dayshift. Settings and designCross sectional study. Methods and materialsEligible 124 employees [(night shift (61), Day shift (63)] working in a tertiary care hospital in Bengaluru were randomly selected and tested for anthropometric and laboratory parameters pertaining to metabolic risk and oxidative stress and categorized accordingly using standard criteria. Statistical tests (student t-test) were applied to test for association between shift work, metabolic risk and oxidative stress. ResultsMetabolic risk and Oxidative stress were significantly higher in rotating night shift workers as compared to day shift (p < 0.001) and (p < 0.017) respectively. ConclusionRotating night shift work is associated with increase in metabolic risk and oxidative stress and there is a need to consider this enhanced risk during periodical medical examination and employee health interventions. There is a need for further research to quantify risk for metabolic risk and understand this association in other occupations as well.

The association between serum dehydroepiandrosterone sulfate (DHEAS) levels and job-related stress among female nurses.

BackgroundDehydroepiandrosterone sulfate (DHEAS) is an endogenous steroid hormone produced by the adrenal gland. DHEAS has been suggested to play a protective role against psychosocial stress. The aim of this study was to investigate the association between job-related stress and blood concentrations of DHEAS according to occupational stress factors among female nurses.MethodsA cross-sectional study was conducted among 118 premenopausal nurses from 4 departments (operating room, emergency room [ER], intensive care unit, and ward) of a university hospital. Participants were all rotating night shift workers who have worked for over a year and mean age of 33.5 ± 4.8 years. Data from structured questionnaires including the Korean Occupational Stress Score, Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), and Pittsburgh Sleep Quality Index (PSQI) were used.ResultsIn the high job-related stressor group, scores of BDI, BAI, and PSQI were significantly higher than low-stressor group. ER nurses had relatively more work-burden related stressors, but they had significantly lower levels of anxiety and depression than other groups. And, ER nurses showed higher levels of DHEAS than the other department nurses. The differences were significant (p = 0.003). Additionally, there was a statistically significant difference even after adjusting for factors that could affect level of DHEAS, such as age, body mass index, drinking, and physical activity (p = 0.039).ConclusionsThis result suggests the possibility that DHEAS may play a role as a marker of proper stress management. The capacity to secrete DHEAS is not simply due to workload or job stressor but could be determined depending on how individuals and groups deal with and resolve stress. Proper resolution of stress may affect positive hormone secretion.

Night shiftwork and prostate-specific antigen level in a tire manufacturing factory.

BackgroundRecent studies suggest that night shiftwork may increase the risk of prostate cancer and elevated serum prostate-specific antigen (PSA) level. The purpose of this study was to verify whether rotating night shiftwork affects serum PSA level.MethodsThis study included 3,195 male production workers who work in a large tire manufacturing factory. Serum PSA levels were measured and the data on related factors were obtained.ResultsThe mean serum PSA level was 0.98 ± 0.79 ng/mL. PSA levels were significantly lower in the younger age group, the obese group, and regular exercise group. PSA levels were lower in night shift workers (n = 2,832) compared to day workers (n = 363), but the difference was not statistically significant.ConclusionsUnlike previous studies, we did not find any evidence that night shiftwork results in an increase in serum PSA levels. Further research and consistent results are needed to elucidate the association between night shiftwork and the effect on the prostate.

Circadian disruption: What do we actually mean?

The circadian system regulates physiology and behavior. Acute challenges to the system, such as those experienced when traveling across time zones, will eventually result in re-synchronization to local environmental time cues, but this re-synchronization is oftentimes accompanied by adverse short-term consequences. When such challenges are experienced chronically, adaptation may not be achieved, as for example in the case of rotating night shift workers. The transient and chronic disturbance of the circadian system is most frequently referred to as "circadian disruption", but many other terms have been proposed and used to refer to similar situations. It is now beyond doubt that the circadian system contributes to health and disease, emphasizing the need for clear terminology when describing challenges to the circadian system and their consequences. The goal of this review is to provide an overview of the terms used to describe disruption of the circadian system, discuss proposed quantifications of disruption in experimental and observational settings with a focus on human research, and highlight limitations and challenges of currently available tools. For circadian research to advance as a translational science, clear, operationalizable, and scalable quantifications of circadian disruption are key, as they will enable improved assessment and reproducibility of results, ideally ranging from mechanistic settings, including animal research, to large-scale randomized clinical trials.

Rotating night shift work and adherence to unhealthy lifestyle in predicting risk of type 2 diabetes: results from two large US cohorts of female nurses

ObjectivesTo prospectively evaluate the joint association of duration of rotating night shift work and lifestyle factors with risk of type 2 diabetes risk, and to quantitatively decompose this joint association...

Rotating night shift work and colorectal cancer risk in the nurses' health studies.

Animal and human data have suggested that shift work involving circadian disruption may be carcinogenic for humans, but epidemiological evidence for colorectal cancer remains limited. We investigated the association of rotating night shift work and colorectal cancer risk in two prospective female cohorts, the Nurses' Health Study (NHS) and NHS2, with 24 years of follow‐up. In total, 190,810 women (NHS = 77,439; NHS2 = 113,371) were included in this analysis, and 1,965 incident colorectal cancer cases (NHS = 1,527; NHS2 = 438) were reported during followup (NHS: 1988–2012, NHS2: 1989–2013). We used Cox proportional hazards models adjusted for a wide range of potential confounders. We did not observe an association between rotating night work duration and colorectal cancer risk in these cohorts (NHS: 1–14 years: Hazard Ratio (HR) 1.04, 95% CI: 0.94, 1.16; 15+ years: HR 1.15, 95% CI: 0.95, 1.39; P trend = 0.14 and NHS2: 1–14 years: HR 0.81, 95% CI: 0.66, 0.99; 15+ years: HR 0.96, 95% CI: 0.56, 1.64 and P trend = 0.88). In subsite analysis in NHS, rectal cancer risk increased after long‐term (15+ years) rotating night shift work (proximal colon cancer: HR 1.00, 95% CI: 0.75, 1.34, P trend = 0.90; distal colon cancer: HR 1.27, 95% CI: 0.87, 1.85, P trend = 0.32; rectal cancer: HR 1.60, 95% CI: 1.09, 2.34, P trend = 0.02). We found no overall evidence of an association between rotating night shift work and colorectal cancer risk in these two large cohorts of nurses. Risk for rectal cancer significantly increased with shift work duration, suggesting that long‐term circadian disruption may play a role in rectal cancer development.

Night Shift Work Before and During Pregnancy and Offspring Weight Outcomes Through Adolescence.

ObjectiveThis study aimed to investigate associations between maternal history of rotating night shift nursing work before pregnancy and number of night shifts worked during pregnancy with offspring weight outcomes from early life through adolescence.MethodsMore than 4,000 children, enrolled in the second phase of the Growing Up Today Study between 2004 and 2013, and their mothers participating in the Nurses' Health Study II were included in our analyses.ResultsChildren of women with and without a history of rotating night shift work before pregnancy were similar in birth weight and body size at age 5. However, for mothers with night shift work before pregnancy, their children had a modestly elevated risk of having overweight or obesity (relative risk = 1.11; 95% CI: 1.02‐1.21), which was stronger for persistently having overweight or obesity during adolescence and early adulthood. Longer duration of rotating night shift work was not associated with any of these weight outcomes. Weight outcomes of children of women with versus without night shift work during pregnancy were similar, regardless of frequency of night shifts worked during pregnancy (all P > 0.09).ConclusionsOverall, nurses' night shift work before or during pregnancy did not affect offspring weight outcomes. Future larger studies should explore these associations in more detail.

Prospective study of chronotype and incident depression among middle- and older-aged women in the Nurses’ Health Study II

BackgroundPrior cross-sectional studies have suggested that being a late chronotype is associated with depression and depressive symptoms, but prospective data are lacking. MethodsWe examined the association between chronotype and incident depression (defined as self-reported physician/clinician-diagnosed depression or antidepressant medication use) in 32,470 female participants of the Nurses’ Health Study II cohort who self-reported their chronotype (early, intermediate or late) and were free of depression at baseline in 2009 (average age: 55 yrs). Women updated their depression status on biennial questionnaires in 2011 and 2013. We used multivariable (MV)-adjusted Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals (95%CI) for incident depression across chronotype categories (i.e., early, intermediate, and late chronotypes). ResultsAcross a follow-up period of 4 years, we observed 2,581 cases of incident depression in this cohort. Compared to intermediate chronotypes, early chronotypes had a modestly lower risk of depression after MV adjustment (MVHR = 0.88, 95%CI = 0.81–0.96), whereas late chronotypes had a similar risk of 1.06 (95%CI = 0.93–1.20); the overall trend across chronotype categories was statistically significant (ptrend<0.01). Results were similar when we restricted analyses to women who reported average sleep durations (7–8 h/day) and no history of rotating night shift work at baseline. ConclusionsOur results suggest that chronotype may influence the risk of depression in middle-to older-aged women. Additional studies are needed to confirm these findings and examine roles of both environmental and genetic factors to further our understanding of the role of chronotype in the etiology of mood disorders.

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.

Rotating night shift work, sleep, and colorectal adenoma in women.

This study aims to investigate the associations of rotating night shift work history and sleep duration with risk of colorectal adenoma. We evaluated 56,275 cancer-free participants of the Nurses' Health Study II, who had their first colonoscopy or sigmoidoscopy between 1991 and 2011; rotating night shift work and sleep duration were reported by mailed questionnaire. Multivariable-adjusted logistic regression was used to estimate relative risks (RR) of colorectal adenoma, with 95% confidence intervals (CI), across categories of rotating night shift work history (none, 1-4, 5-9, and ≥10years) and sleep duration (≤5, 6, 7, 8, and ≥9h/day). We found no association between duration of rotating night shift work and occurrence of colorectal adenoma (p-trend across shift work categories=0.5). Women with the longest durations of rotating night shift work (≥10years) had a similar risk of adenoma compared to women without a history of rotating night shift work (multivariable-adjusted RR=0.96, 95% CI=0.83-1.11). Similarly, there were no associations of shorter or longer sleep durations with adenoma risk (p-trend=0.2 across sleep durations of ≤5 through 7h/day and p-trend=0.5 across sleep durations of 7 through ≥9h/day). Results were similar when we examined associations according to adenoma location and subtype. Our results do not support an association between rotating night shift work or sleep duration and risk of colorectal adenoma in women.

Shift work, job strain and changes in the body mass index among women: a prospective study

ObjectivesThe effects of job strain and shift work on weight gain have not been studied jointly. Cross-sectional and longitudinal studies on shift work and weight gain have reported different results....

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

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

Night shift work and other determinants of estradiol, testosterone, and dehydroepiandrosterone sulfate among middle-aged nurses and midwives.

The aims of our study were to (i) investigate the association between rotating night shift work and blood concentrations of estradiol, testosterone and dehydroepiandrosterone sulfate (DHEAS) and (2) evaluate the role of their non-occupational determinants. A cross-sectional study was conducted on 345 premenopausal and 187 postmenopausal nurses and midwives (263 women working rotating night shifts and 269 women working during days). Data from in-person interviews were used, anthropometric measurements were performed, and body mass index (BMI) and waist- to-hip ratio were calculated. Morning blood and spot urine samples were collected. Multiple linear regression models were fitted with hormone concentrations as dependent variables, and night shift work characteristics and demographic, reproductive, lifestyle and anthropometric determinants as independent variables. Modification of the effect by chronotype was examined. Among postmenopausal women, we observed a statistically significant positive association between the total duration of night shift work >15 years and estradiol level (P<0.05 when compared to night work duration <5 years). Night shift work characteristics were significantly associated with estradiol among morning-type postmenopausal women. The well-established associations between hormones and their major determinants, such as age and BMI, were confirmed. The findings of our study imply that prolonged night shift work may be associated with increased estradiol levels among postmenopausal women, especially among the morning-type postmenopausal women.

Abstract 36: Light exposure at night influences host/cancer circadian regulatory dynamics, Warburg effect, and human prostate cancer progression in nude rats

Abstract Current evidence indicates that rotating night shift workers have an increased risk of developing breast and prostate cancers, which have been associated with light at night (LAN)-induced circadian disruption as the principal risk factor. Previously, we demonstrated that animal room dark phase light contamination with as little as 0.20 lux (0.08 μW/cm2) suppressed the nocturnal production of the circadian oncostatic neurohormone melatonin and stimulated human breast tumor growth and metabolism. The circadian melatonin signal suppresses tumor growth and metabolism via an MT1 melatonin receptor-mediated signaling mechanism involving inhibition of aerobic glycolysis (Warburg effect) and linoleic acid (LA) uptake and conversion to the mitogen 13-hydroxyoctadecadienoic acid (13-HODE) culminating in down-regulation of the epidermal growth factor and insulin-like growth factor-1 pathways. We developed a new tissue-isolated androgen-receptor positive (AR+), castration-sensitive VCaP prostate tumor model in adult male athymic nude rats (Crl:NIH-Foxn1rnu), to test the hypothesis that nocturnal melatonin levels inhibit, while dim LAN (dLAN)-induced suppression of nocturnal melatonin production stimulates, tumor signaling, metabolic and growth activity. VCaP xenograft-bearing rats (n = 6/group) maintained on either a control light/dark cycle (LD, 12:12; 300 lux light phase intensity) or an experimental light/dark cycle (LD, 12:12dLAN (0.2 lux; dark phase intensity) for 6 weeks resulted in a 2.5-fold decrease in latency-to-onset (time of implant to first palpable mass) and 2-fold increase in tumor growth rates in experimental animals lacking a nocturnal circadian melatonin signal as compared to control animals with an intact melatonin signal. In control animals, plasma melatonin levels were high in the mid-dark phase (183.4 ± 12.8 pg/mL) and low (2.2 ± 0.4 pg/mL) in mid-light phase, while they were low throughout the 24-hr period in dLAN-exposed animals. Tumors harvested during the mid-dark phase (2400 h) revealed that cAMP levels, Warburg effect (increased glucose uptake and lactate production), LA uptake, 13-HODE production, and DNA [3H]Thymidine incorporation were all significantly elevated (P &amp;lt; 0.001) in dLAN as compared with the controls. Signaling pathways AKT, MEK, ERK ½, STAT3, GSK3ß, and NFκß were all phospho-activated along with increased expression of Aldo-keto reductase family 1 member C3 (AKR1C3) under dLAN conditions. AKR1C3 has been associated with intratumoral androgen synthesis and the development of castration-resistance. These findings are the first to show that the nocturnal melatonin signal inhibits, while dLAN stimulates the Warburg effect, LA metabolism and growth activity, signaling activity and AKR1C3 expression in VCaP human androgen-sensitive prostate cancer. Citation Format: Robert T. Dauchy, Melissa A. Wren, Erin M. Dauchy, Steven M. Hill, Lin Yuan, Shulin Xiang, Yan Dong, Victoria P. Belancio, David M. Blask. Light exposure at night influences host/cancer circadian regulatory dynamics, Warburg effect, and human prostate cancer progression in nude rats. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 36.

Association Between Rotating Night Shift Work and Risk of Coronary Heart Disease Among Women.

Prospective studies linking shift work to coronary heart disease (CHD) have been inconsistent and limited by short follow-up. To determine whether rotating night shift work is associated with CHD risk. Prospective cohort study of 189,158 initially healthy women followed up over 24 years in the Nurses' Health Studies (NHS [1988-2012]: N = 73,623 and NHS2 [1989-2013]: N = 115,535). Lifetime history of rotating night shift work (≥3 night shifts per month in addition to day and evening shifts) at baseline (updated every 2 to 4 years in the NHS2). Incident CHD; ie, nonfatal myocardial infarction, CHD death, angiogram-confirmed angina pectoris, coronary artery bypass graft surgery, stents, and angioplasty. During follow-up, 7303 incident CHD cases occurred in the NHS (mean age at baseline, 54.5 years) and 3519 in the NHS2 (mean age, 34.8 years). In multivariable-adjusted Cox proportional hazards models, increasing years of baseline rotating night shift work was associated with significantly higher CHD risk in both cohorts. In the NHS, the association between duration of shift work and CHD was stronger in the first half of follow-up than in the second half (P=.02 for interaction), suggesting waning risk after cessation of shift work. Longer time since quitting shift work was associated with decreased CHD risk among ever shift workers in the NHS2 (P<.001 for trend). [table: see text] Among women who worked as registered nurses, longer duration of rotating night shift work was associated with a statistically significant but small absolute increase in CHD risk. Further research is needed to explore whether the association is related to specific work hours and individual characteristics.

Fixed or Rotating Night Shift Work Undertaken by Women: Implications for Fertility and Miscarriage.

This review summarizes the evidence concerning effects of night shift work on women's reproductive health, specifically difficulty in conceiving and miscarriage. We distinguish between fixed night shift and rotating night shift, as the population subgroups exposed, the social and biological mechanisms, and the magnitude of effects are likely to differ; of note, women working fixed night shift are known to have high tolerance for this schedule. We identified two relevant systematic reviews with meta-analyses and five additional studies. Night shift work may give rise to menstrual cycle disturbances, but effect sizes are imprecise. Endometriosis may be elevated in night shift workers, but evidence is only preliminary. Adequate data are lacking to assess associations between night shift work and infertility or time to pregnancy. The weight of evidence begins to point to working at night, whether in fixed or rotating shifts, as a risk factor for miscarriage. There are many methodological problems with this literature, with substantial variation in the definitions of night shift and schedule types making comparisons between studies difficult and pooling across studies questionable. Nevertheless, there appears to be grounds for caution and counselling where women have concerns about night shift work and their reproductive health.

Evaluation of cognition using neurophysiological and neuropsychological tests in rotating night shift workers: a pilot study

Background: The modern lifestyle is changing the circadian rhythm of the body especially in rotating shift workers. The impact of this might impair cognitive performance of the rotating shift workers who are frequently exposed to unstable circadian rhythm. Aims and Objective: To evaluate cognitive functions using neurophysiological and neuropsychological methods in rotating night shift and day workers and to compare cognition between the two groups. Materials and Methods: Forty healthy male security guards (25–35 years) who did rotating night shifts at least for 6 months and 40 day workers ( 25–35 years) who did not do night shift in last 2 years were involved in the study. A battery of neuropsychological tests, latency, and amplitude of P300 were recorded. Result: Kolmogorov–Smirnov test for normalcy showed the latencies and amplitude of P300 to be normally distributed. Student’s unpaired t-test showed significant difference (p < 0.05) in the various neuropsychological tests and in the latency of P300 between night- and day-shift workers. There was no significant difference in the amplitude of P300. Conclusion: Night-shift workers who are prone to circadian rhythm alteration will have impaired cognitive performance.

Rotating night shift work and obesity among nurses and midwives in Poland

Background Results of some epidemiological studies suggest that night shift work may contribute to increased body weight and abdominal obesity. The aim of our study was to examine this association among nurses and midwives working in fast rotating system. Methods The cross-sectional study was carried out between 2008–2011 in Łodź and included as many as 724 women (354 …