Shift Work, Chronotype, and Melatonin Rhythm in Nurses

Night shift work, genetic risk, and the risk of depression: A prospective cohort study

BACKGROUND

Genetic factors and night shift work both contribute to the risk of depression, but whether the association of night shift work with depression varies by genetic predisposition remains unclear.

OBJECTIVES

To assess whether night shift work is associated with a higher risk of depression regardless of genetic predisposition.

METHODS

We used data from the UK biobank of 247,828 adults aged 38-71 free of depression at baseline from March 13, 2006, to October 1, 2010. Genetic predisposition to depression was assessed using polygenic risk scores (PRS) weighted sums of genetic variant indicator variables and classified as low (lowest tertile), intermediate (tertile 2), and high (highest tertile). Night shift work exposures were collected using a touchscreen questionnaire and were divided into four categories.

RESULTS

After a median follow-up of 12.7 years, 7315 participants developed depression. Compared with day workers, HRs (95 % CIs) of depression were 1.28 (1.19-1.38) for shift work, but never or rarely night shifts, 1.32 (1.20-1.45) for irregular night shifts, and 1.20 (1.07-1.34) for permanent night shifts. Considering lifetime employment and compared with never shift workers, >8 nights/month (HR: 1.40; 95 % CI: 1.19-1.66) and <10 years (HR: 1.30; 95 % CI: 1.09-1.54) of night shift work were associated with a higher risk of depression. In joint effect analyses, compared to participants with low genetic predisposition and day workers, the HRs (95 % CIs) of depression were 1.49 (1.32-1.69) in those with high genetic predisposition and shift work, but never or rarely night shifts, and 1.36 (1.20-1.55) for those with high genetic predisposition and irregular/permanent night shifts. In addition, there was neither multiplicative nor additive interaction between genetic predisposition and night shift work on the risk of depression.

CONCLUSIONS

Night shift work was associated with an increased risk of depression regardless of genetic risk.

Use of melatonin supplements and risk of type 2 diabetes and cardiovascular diseases in the USA: insights from three prospective cohort studies

BACKGROUND

Use of melatonin supplements has been increasing substantially in both children and adults in the USA; however, their long-term cardiometabolic effects remain unclear. We aimed to assess the associations between regular use of melatonin supplements and the risk of developing type 2 diabetes or cardiovascular disease in adults.

METHODS

In this study, we included individuals from three US cohorts: the Nurses' Health Study (women only), the Health Professionals Follow-up Study (men only), and the Nurses' Health Study II (women only). Women aged 25-55 years and men aged 45-75 years at baseline, who had no diagnosis of cancer at baseline, and who responded to the question about melatonin supplement use (yes or no) were included. We excluded baseline prevalent cardiovascular disease and baseline prevalent type 2 diabetes for the main analyses. The main outcomes were cardiovascular disease and type 2 diabetes incidence. In secondary analyses, we stratified by duration of rotating night shift work in the Nurses' Health Study and Nurses' Health Study II to examine whether the associations with melatonin supplement use differed by rotating night shift work.

FINDINGS

For the cardiovascular disease analysis, we included 67 202 women from the Nurses' Health Study (follow-up 1998-2019, mean age at baseline: 63·6 years [SD 7·1]), 26 629 men from the Health Professionals Follow-up Study (1998-2020, 62·9 years [8·8], and 65 241 women from the Nurses' Health Study II (2003-19, 48·2 years [4·7]). Follow-up for incident type 2 diabetes was from 1998 to June 30, 2021, for the Nurses' Health Study; 2003 to Jan 31, 2023, for the Nurses' Health Study II; and from 1998 to Jan 31, 2020, for the Health Professionals' Follow-up Study. Melatonin supplement use in the study cohorts doubled over recent decades from less than 2% in 1998-2007 to 4% or higher in 2014-15 (4·0% in men and 5·3% in women). We documented 16 917 incident cardiovascular disease events during 2 609 068 person-years of follow-up and 12 730 incident cases of type 2 diabetes during 2 701 830 person-years of follow-up. In a pooled analysis of the three cohorts, comparing users with non-users of melatonin supplements, the pooled multivariable-adjusted hazard ratios were 0·94 (95% CI 0·83-1·06, p=0·32) for cardiovascular disease and 0·98 (0·86-1·12, p=0·80) for type 2 diabetes. In secondary analyses, melatonin supplement use appeared to attenuate the positive association between long-term shift work (>5 years) and risk of cardiovascular disease (pinteraction=0·013) among the female nurses.

INTERPRETATION

With up to 23 years of follow-up of three large prospective cohorts of middle-aged and older men and women, self-reported melatonin supplement use was not associated with risk of type 2 diabetes or cardiovascular disease. Further research is warranted to assess if melatonin supplement use could mitigate the potential risks of type 2 diabetes and cardiovascular disease associated with rotating night shift work.

FUNDING

US National Institutes of Health.

Associations of Chronotype, Work Schedule, and Sleep Problems With Work Engagement Experiences in Middle Age-The Northern Finland Birth Cohort 1966

OBJECTIVE

The aim of the study is to investigate the role of chronotype for work engagement in middle age.

METHODS

We used data from the Northern Finland Birth Cohort 1966 study ( N = 5341) to analyze associations of self-reported chronotype (morning, intermediate, and evening type) with work engagement and its dimensions (vigor, dedication, absorption). We conducted multivariate analyses of variance to examine whether work schedule or sleep problems moderate these associations.

RESULTS

Evening types showed lower scores in work engagement and its dimensions than intermediate and morning types, even when work schedule and sleep problems were controlled. Sleep problems emphasized the chronotype-work engagement and chronotype-dedication linkages.

CONCLUSIONS

Chronotype may play a role in employees' work engagement. In addition, sleep problems seem relevant in terms of chronotype-work engagement linkage.

Prevalence and associated factors of insomnia symptoms after ending China's dynamic zero-COVID policy: a cross-sectional survey of frontline nursing staff in Chinese hospitals

Background

After the Chinese government announced the end of the dynamic zero-COVID policy on January 8, 2023, the COVID-19 pandemic peaked. Frontline nursing staff are at high risk of infection transmission due to their frequent contact with COVID-19 patients. In addition, due to the ending of China's dynamic zero-COVID policy, frontline nursing staff have grappled with increased workload, fatigue, and more. This study aimed to explore the prevalence of insomnia symptoms in frontline nursing staff and its influencing factors following the end of the policy.

Methods

Between January and February 2023, this study was conducted by the Wenjuanxing platform to survey frontline nursing staff in a hospital in Wuhu City, Anhui Province. All the nursing staff included in this study had a COVID-19 infection. The questionnaires included the Athens Insomnia Scale (AIS), PC-PTSD-5 Chinese Version Scale, the Fear of COVID-19 Scale, The 2-item Connor-Davidson Resilience Scale (CD-RISC-2) Scale, and the burden of COVID-19 Scale. Binary logistic regression methods were used to identify variables associated with insomnia symptoms.

Results

Among the 694 frontline nursing staff, 74.5% (517/694) exhibited insomnia symptoms. Fear of COVID-19 (p < 0.001), the burden of COVID-19 (p < 0.05), PTSD (p < 0.001), and higher technical titles (p < 0.008) were highly correlated with insomnia symptoms in frontline nursing staff. Psychological resilience (p < 0.001) was a protective factor for insomnia symptoms among frontline nursing staff.

Conclusion

After ending China's dynamic zero-COVID policy, the prevalence of insomnia symptoms among frontline nursing staff is generally higher. This study highlights the association between insomnia symptoms and PTSD, fear of COVID-19, COVID-19 burden, and resilience. Psychological assistance is needed for frontline nursing staff to prevent insomnia symptoms and protect the mental health of frontline nursing staff after the end of China's dynamic zero-COVID policy.

Environmental, social, and behavioral challenges of the human circadian clock in real-life conditions

Urban environments, in which ambient light has become a less-reliable entrainer, are challenging for the biological clock to maintain performance. As a consequence, human circadian rhythms are less robust and more variable among individuals. Assessing the individual phase of entrainment, as well as its plastic shifts in response to disturbances of the physical and social environment, is a way to measure circadian disruption. However, this is still difficult to address in real-life scenarios in which several factors modulate the circadian phase not always in a concerted manner. In this perspective, we present the contribution of two real-life situations, in which the circadian system is challenged by important alterations in entraining signals: 1) a trip to the Antarctic summer (socio-environmental challenge), and 2) dancers trained in morning/night shifts (socio-behavioral challenge). Both natural chronobiological experiments are helpful in exploring the functioning and plasticity of the circadian clock and allow for considering individual characteristics and history.

Significance of Melatonin in the Regulation of Circadian Rhythms and Disease Management

Melatonin, the 'hormone of darkness' is a neuronal hormone secreted by the pineal gland and other extra pineal sites. Responsible for the circadian rhythm and seasonal behaviour of vertebrates and mammals, melatonin is responsible for regulating various physiological conditions and the maintenance of sleep, body weight and the neuronal activities of the ocular sites. With its unique amphiphilic structure, melatonin can cross the cellular barriers and elucidate its activities in the subcellular components, including mitochondria. Melatonin is a potential scavenger of oxygen and nitrogen-reactive species and can directly obliterate the ROS and RNS by a receptor-independent mechanism. It can also regulate the pro- and anti-inflammatory cytokines in various pathological conditions and exhibit therapeutic activities against neurodegenerative, psychiatric disorders and cancer. Melatonin is also found to show its effects on major organs, particularly the brain, liver and heart, and also imparts a role in the modulation of the immune system. Thus, melatonin is a multifaceted candidate with immense therapeutic potential and is still considered an effective supplement on various therapies. This is primarily due to rectification of aberrant circadian rhythm by improvement of sleep quality associated with risk development of neurodegenerative, cognitive, cardiovascular and other metabolic disorders, thereby enhancing the quality of life.

Adiposity, Weight Change, and Urinary Melatonin Levels among Men in the Multiethnic Cohort

BACKGROUND

Low levels of 6-sulfatoxymelatonin, the primary urinary metabolite of melatonin, have been linked to cancer and cardiometabolic outcomes in White and female populations.

METHODS

We examined the association between adulthood adiposity and 6-sulfatoxymelatonin levels in a racially and ethnically diverse population. Our study included 4,078 men in the Multiethnic Cohort with adiposity measurements at enrollment (1993-1996) and biomarkers measured in urines collected in 1995 and 2005. Multivariable linear regression models were used to estimate the percent change in 6-sulfatoxymelatonin levels and 95% confidence intervals (CI). Associations were examined separately by racial/ethnic group.

RESULTS

The prevalence of obesity varied by race and ethnicity, from 10% for Japanese American men to 34% for Native Hawaiian men. Compared with men with normal body mass index (BMI), men who were overweight (-7.8%; 95% CI, -11.9 to -3.5%) and obese (-18.1%; 95% CI, -23.2 to -12.6%) had significantly lower 6-sulfatoxymelatonin levels adjusting for potential confounding factors. Increasing weight gain in adulthood was also associated with lower 6-sulfatoxymelatonin (Ptrend < 0.0001). The inverse associations for BMI and weight change were qualitatively similar across racial and ethnic groups.

CONCLUSIONS

Obesity is inversely associated with melatonin in a racially diverse population. This finding is relevant given higher rates of obesity among Black, Native Hawaiian, and Latino men, as well as potential racial and ethnic differences in circadian function.

IMPACT

Melatonin may be a relevant biomarker among obesity-associated malignancies and could shed light on a potential mechanism of cancer disparities.

Association between nocturnal light exposure and melatonin in humans: a meta-analysis

BACKGROUND

Night shift workers are more susceptible to circadian rhythm disturbances due to their prolonged exposure to nighttime light. This exposure during abnormal periods causes inappropriate suppression of melatonin synthesis and secretion in the pineal gland, thereby disrupting circadian rhythms. While it is believed that nocturnal light exposure is involved in suppressing melatonin secretion, research findings in this area have been inconsistent.

METHODS

Thirteen publications retrieved from PubMed and Web of Science databases were included to compare the differences between night shift workers and controls using aggregated mean differences (MD) and 95% confidence intervals (CI).

RESULTS

After a comprehensive review, 13 publications were included and data on urinary melatonin metabolite 6-sulfameoxymelatonin(aMT6s) were collected for meta-analysis. The results showed that the morning urinary aMT6s levels were significantly lower in the exposed group than in the non-exposed group (MD = -3.69, 95%CI = (-5.41, -1.98), P < 0.0001), with no significant heterogeneity among the original studies (I2 = 42%, P = 0.13). In addition, night shift workers had significantly lower mean levels of 24-h urinary aMT6s than day shift workers (MD = -3.38, 95%CI = (-4.27, -2.49), P < 0.00001, I2 = 0). Nocturnal light was correlated with nocturnal urine aMT6s secretion and inhibited nocturnal aMT6s secretion (MD = -11.68, 95%CI = (-15.70, -7.67), P < 0.00001, I2 = 0). Additionally, nocturnal light inhibited the secretion of melatonin in the blood, with no significant heterogeneity between studies (MD = -11.37, 95%CI = (-15.41, -7.33), P < 0.00001, I2 = 0).

CONCLUSION

The findings of this study indicate that exposure to nocturnal light among night shift workers leads to inhibition of melatonin secretion.

Time-restricted eating for chronodisruption-related chronic diseases

The circadian timing system enables organisms to adapt their physiology and behavior to the cyclic environmental changes including light-dark cycle or food availability. Misalignment between the endogenous circadian rhythms and external cues is known as chronodisruption and is closely associated with the development of metabolic and gastrointestinal disorders, cardiovascular diseases, and cancer. Time-restricted eating (TRE, in human) is an emerging dietary approach for weight management. Recent studies have shown that TRE or time-restricted feeding (TRF, when referring to animals) has several beneficial health effects, which, however, are not limited to weight management. This review summarizes the effects of TRE/TRF on regulating energy metabolism, gut microbiota and homeostasis, development of cardiovascular diseases and cancer. Furthermore, we will address the role of circadian clocks in TRE/TRF and propose ways to optimize TRE as a dietary strategy to obtain maximal health benefits.

Night shift work and serum markers of bone turnover in male shift workers

Night shift work is related to sleep disorders, disruption of circadian rhythm and low serum levels of vitamin D. It is known that all these conditions can adversely affect bone mass. The rate of bone turnover can be assessed through the measurement of molecules called bone turnover markers, including C-terminal telopeptide fragment of type I collagen (CTX) and procollagen type I N-terminal propeptide (P1NP). In this study, we evaluated the serum levels of CTX, P1NP and 25-Hydroxy Vitamin D in 82 male subjects (42 daytime workers and 40 night shift workers) to assess the possible risk of osteoporosis in male shift workers. Serum levels of CTX and P1NP were found to be higher in night shift workers than in daytime workers. No significant difference was found in vitamin D levels between night shift and daytime workers. The increased CTX and P1NP levels reveal a higher rate of bone turnover in night shift workers and thus a possible increased risk of osteoporosis in this category of workers compared with daytime workers. In view of this, our results highlight the importance of further studies investigating the bone health in male night shift workers.

Effects of sleep pattern, duration, and quality on premenstrual syndrome and primary dysmenorrhea in korean high school girls

BACKGROUND

Sleep deprivation is known to be a risk factor for premenstrual syndrome and primary dysmenorrhea in adults. However, it has rarely been investigated in adolescents. The aim of this study was to investigate whether sleep pattern, duration, and quality independently affect premenstrual syndrome and primary dysmenorrhea in adolescent girls. An additional purpose was to investigate the sleep status in Korean adolescent girls during the COVID-19 pandemic.

METHODS

A cross-sectional survey study was conducted in 519 high school girls aged 15 to 18 years in Gyeonggido, South Korea, in 2021 during the COVID-19 lockdown. Menstrual pain intensity and menstrual symptoms were assessed using the visual analogue scale (VAS) and Cox menstrual symptom scale (CMSS), respectively. Premenstrual syndrome was assessed by the premenstrual symptoms screening tool (PSST). Sleep was assessed by the Pittsburgh Sleep Quality Index (PSQI). The known risk factors of dysmenorrhea, including menstrual and lifestyle characteristics and stress, were assessed as covariates.

RESULTS

During the pandemic, approximately 68% of girls slept 7 h or less, while about 60% reported poor sleep quality. Additionally, 64% of participants had a bedtime later after 1AM, and 34% woke up later after 8AM. Late bedtime significantly affected VAS (P = 0.05), CMSS severity and frequency (both P < 0.01), and PSST symptom (P < 0.01). Waking up late affected CMSS severity (P < 0.05), PSST symptom (P = 0.05), and PSST function (P < 0.05). However, the significance of these effects disappeared after controlling for covariates. Sleeping less than 5 h affected CMSS frequency (P < 0.05) and PSST symptoms (P < 0.001). After controlling for covariates, the significance of the effect on PSST symptom remained (P < 0.05). General sleep quality and PSQI components, including subjective sleep quality, sleep latency, sleep disturbance, use of sleeping medication, and daytime dysfunction, significantly affected CMSS frequency and severity and PSST symptom after controlling for covariates (P < 0.05, P < 0.01, or P < 0.001). The multiple regression analysis revealed that among sleep characteristics, sleep quality was the most important risk factor of premenstrual syndrome and dysmenorrhea.

CONCLUSION

Our study result heightens the importance of healthy sleep hygiene, especially sleep quality in the management of premenstrual syndrome and dysmenorrhea in adolescent girls.

Chronotype and Cardiometabolic Parameters in Patients with Bipolar Disorder: Preliminary Findings

Cardiometabolic alterations are very common in bipolar disorder (BD). The aim of this study was to investigate the relationship between chronotype and cardiometabolic parameters in patients with a primary diagnosis of BD. This study is an observational clinical investigation including 170 subjects consecutively admitted to the Psychiatric Inpatient Unit of the IRCCS Ospedale Policlinico San Martino (Genoa, Italy), recruited over a period of 48 months. A psychometric tool assessing chronotype was administered and blood tests were performed. Furthermore, the atherogenic coefficient ((total cholesterol-HDL cholesterol)/HDL cholesterol), and Castelli risk index-I (total cholesterol/HDL cholesterol) and -II (LDL cholesterol/HDL cholesterol) were calculated. Patients with BD and an eveningness chronotype showed a higher body mass index, total and low-density lipotrotein cholesterol compared to patients with BD and an intermediate or morning chronotype. Furthermore, the Atherogenic Coefficient and Castelli Risk-Index I-II were found to be higher in bipolar patients with an evening chronotype. The role of chronotype in the development of obesity and cardiovascular risk is, therefore, a relationship worth being investigated, especially in the context of BD, to ameliorate the clinical and therapeutic approach, aiming at increasing the quality of life and reducing the mortality.

Individual light history matters to deal with the Antarctic summer

The effect of light, main zeitgeber of the circadian system, depends on the time of day it is received. A brief trip to the Antarctic summer (ANT) allowed us to explore the impact of a sudden and synchronized increase in light exposure on activity-rest rhythms and sleep patterns of 11 Uruguayan university students, and to assess the significance of light history in determining individual circadian phase shift. Measurements collected in the peri-equinox in Montevideo, Uruguay (baseline situation, MVD) and in ANT, included sleep logs, actigraphy, and salivary melatonin to determine dim-light melatonin onset (DLMO), the most reliable marker of circadian phase. The increase in light exposure in ANT with respect to MVD (affecting both light-sensitive windows with opposite effects on the circadian phase) resulted in no net change in DLMO among participants as some participants advanced their DLMO and some others delayed it. The ultimate cause of each participant's distinctive circadian phase shift relied on the unique change in light exposure each individual was subjected to between their MVD and ANT. This study shows an association between the individual light history and the circadian phase shift.

Reducing nighttime light exposure in the urban environment to benefit human health and society

Nocturnal light pollution can have profound effects on humans and other organisms. Recent research indicates that nighttime outdoor lighting is increasing rapidly. Evidence from controlled laboratory studies demonstrates that nocturnal light exposure can strain the visual system, disrupt circadian physiology, suppress melatonin secretion, and impair sleep. There is a growing body of work pointing to adverse effects of outdoor lighting on human health, including the risk of chronic diseases, but this knowledge is in a more nascent stage. In this Review, we synthesize recent research on the context-specific factors and physiology relevant to nocturnal light exposure in relation to human health and society, identify critical areas for future research, and highlight recent policy steps and recommendations for mitigating light pollution in the urban environment.

Circadian rhythm sleep-wake disorders and the risk of dyslipidemia among railway workers in southwest China: A cross-sectional study

Railway workers are more likely to have an irregular work schedule, which had an effect on their circadian rhythm of sleep, and may lead to circadian rhythm sleep-wake disorders (CRSWDs). The association between CRSWDs and dyslipidemia in railway workers is poorly understood. The objective of this research is to study the association between CRSWDs and the risk of dyslipidemia. This cross-sectional study was conducted among railway workers in Southwest China. CRSWDs were assessed by the morningness-eveningness questionnaire self-assessment version (MEQ-SA). The blood samples were collected in the morning and the lipids of participants were measured. Associations of CRSWDs with dyslipidemia and its components were analyzed. A total of 8079 participants were enrolled in this study, and the results revealed that shift work sleep disorder (SWD) and advanced sleep-wake phase disorder (ASWPD) were associated with a higher risk of dyslipidemia (OR 1.17, 95%CI 1.06-1.29, P < 0.01; OR 1.68, 95%CI 1.09-2.64, P < 0.05) after adjusting for sociodemographic characteristics and lifestyles, in comparison with the control group. As for its components, the SWD group was associated with a higher risk of elevated total cholesterol, triglycerides, and low-density lipoprotein than the control group, while the ASWPD group was associated with a higher risk of elevated total cholesterol, and low-density lipoprotein (P < 0.05). In summary, SWD and ASWPD participants were associated with a higher risk of dyslipidemia in railway workers in Southwest China.Abbreviation: TG: triglyceride; TC: Total cholesterol; LDL-C: low-density lipoprotein cholesterol; HDL-C: high-density lipoprotein cholesterol; FPG: fasting plasma glucose. MEQ-SA: morningness-eveningness questionnaire self-assessment version; IPW: inverse-probability weighting; HDS: healthy diet scores; FFQ: food frequency; PA: physical activity; IQAP-SF: international physical activity questionnaire short form; MET-min/wk: metabolic equivalent task minutes per week; BMI: body mass index; SBP: systolic blood pressure; DBP: diastolic blood pressure; HBP: hypertension; DM: diabetes; CVD: cerebrovascular disease; OR: odds ratios; CI: confidence intervals.

Consequences of Shift Work and Night Work: A Literature Review

Nonstandard work schedules such as shift work and night work tend to trigger problems for workers in different areas. To illustrate the diversity of areas affected and the relative interest of the scientific community, we conducted a literature review of the effects of shift work and night work on workers. In particular, we intended to identify the main variables addressed in the field of health, the family sphere, and the organizational context. The literature review was carried out using the Web of Science with the following terms: "shift work", "rotating shifts", and "night work". Inclusion criteria incorporated empirical studies and articles written in Portuguese or English published in 2019. We selected 129 of the 619 articles identified. Regarding the impacts of shift work and night work, there existed a high discrepancy of focus between the three defined areas: health, family life, and organizational context. Specifically, health-related variables were the most studied (83.4%), followed by organizational variables (9.2%), and, lastly, family variables (7.4%). Based on these results, it is essential to extend the study of the two underrepresented impacts to other crucial areas, not only for the worker but also for organizations.

The association between night shift work and breast cancer risk in the Finnish twins cohort

Breast cancer is highly prevalent yet a more complete understanding of the interplay between genes and probable environmental risk factors, such as night work, remains lagging. Using a discordant twin pair design, we examined the association between night shift work and breast cancer risk, controlling for familial confounding. Shift work pattern was prospectively assessed by mailed questionnaires among 5,781 female twins from the Older Finnish Twin Cohort. Over the study period (1990-2018), 407 incident breast cancer cases were recorded using the Finnish Cancer Registry. Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) adjusting for potential confounders. Within-pair co-twin analyses were employed in 57 pairs to account for potential familial confounding. Compared to women who worked days only, women with shift work that included night shifts had a 1.58-fold higher risk of breast cancer (HR = 1.58; 95%CI, 1.16-2.15, highest among the youngest women i.e. born 1950-1957, HR = 2.08; 95%CI, 1.32-3.28), whereas 2-shift workers not including night shifts, did not (HR = 0.84; 95%CI, 0.59-1.21). Women with longer sleep (average sleep duration > 8 h/night) appeared at greatest risk of breast cancer if they worked night shifts (HR = 2.91; 95%CI, 1.55-5.46; P_intx=0.32). Results did not vary by chronotype (P_intx=0.74). Co-twin analyses, though with limited power, suggested that night work may be associated with breast cancer risk independent of early environmental and genetic factors. These results confirm a previously described association between night shift work and breast cancer risk. Genetic influences only partially explain these associations.

UPLC-MS/MS simultaneous quantification of urinary circadian rhythm hormones and related metabolites: Application to air traffic controllers

Civil aviation flight crew and civil aviation air traffic controllers are prone to circadian rhythm abnormalities, which can lead to a slew of other maladies. It could endanger people's health and provide a serious threat to the safety of civil aviation flights if it is not appropriately evaluated and addressed. Early detection of rhythm irregularities and prompt treatment for particular populations that are vulnerable to rhythm disorders are crucial for enhancing civil aviation safety. In general, monitoring of the classical circadian rhythm biomarkers (melatonin or cortisol) in plasma or saliva is an effective way to evaluate the rhythm status. Due to the challenging sample procedure and the trauma of plasma, urine sample testing has received an increasing amount of attention. While, urine circadian rhythm biomarkers have seldom been examined, and the relationship between urinary steroid hormones and melatonin is still poorly understood. In most cases, hormones are determined by immunoassays respectively, mainly enzyme-linked immunosorbent assay (ELISA) or radioimmunoassay (RIA). There are also reports describing the liquid chromatography with tandem mass spectrometry (LC-MS/MS) technique as a method of melatonin or few steroid hormones quantification, however, the simultaneous detection of multiple rhythmic hormones in human urine is rarely reported. For the quantification of the rhythmic hormones in human urine, an accurate approach using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was devised in this work. Nine endogenous hormones (melatonin, 6-hydroxymelatonin, 6-sulfatoxymelatonin, cortisol, corticosterone, cortisone, testosterone, epitestosterone and androsterone), in human overnight urine, were quantified after solid phase extraction (SPE). A reverse phase HSS C18 column was used for chromatographic separation with a 9-minute gradient elution and deuterated analogues of each analyte were applied as internal standards. This method was successfully applied to the analysis of 596 overnight urine samples (23:00-9:00) collected from 84 air traffic controllers in the Beijing area during shift work. This study's findings showed a clear correlation not only between melatonin and its metabolites; cortisol-related metabolites, but also between melatonin metabolites and endogenous metabolites upstream and downstream of cortisol, implying that these two categories of hormones can be used as potential biological rhythm indicators to provide circadian rhythm data support for future studies on circadian rhythm disorders.

Alterations in Pregnenolone and Testosterone Levels in Male Shift Workers

Steroid hormone levels are closely related to the endogenous circadian rhythm induced by sleep-wake and dark-light cycles. Shift work that disrupts the circadian rhythm may influence the levels of steroid hormones. The association between shift work and alterations in female sex steroid hormone levels has been studied, but little is known about testosterone and its precursor pregnenolone levels in male shift workers. The present study investigated serum pregnenolone and testosterone levels in a group of shift and daytime male workers. All participants were sampled at the beginning of the morning shift. Lower levels of serum pregnenolone and total testosterone were found in the shift workers compared to the daytime workers. Variations in pregnenolone levels may have consequences for well-being, and they might produce consequences for the levels of hormones downstream of the steroid hormone cascade, such as testosterone. The low levels of testosterone found in shift workers demonstrate the perturbative effect of shift work on testosterone serum levels, which may be independent and/or related to pregnenolone synthesis.

To what extent is circadian phase predictive of subjective jet lag in long-haul cabin crew pre- and post-trip?

Long-haul cabin crew regularly report misalignment between their circadian phase and the external world (i.e. jet lag). The extent to which changes in circadian phase relate to reported levels of jet lag remains unclear. The main aim of the present study was first to evaluate the relationship between objective (circadian phase) and subjective jet lag and second to explore the relative role of both subjective and objective psycho-behavioural factors in predicting the subjective experience of jet lag. Twenty-eight long-haul cabin crew completed questionnaires measuring diurnal preference, trip characteristics and subjective jet lag as a single and as a multidimensional measure. Sleep was monitored using actigraphy and urinary melatonin peak time was measured, at baseline (T1), e.g. before a long-haul trip and post-trip on the crew's first recovery day (T2). Subjective jet lag was also measured at both time points. At T1, later circadian phase related to increased unidimensional jet lag, however, a post-trip discrepancy was found between objective and subjective uni- and multidimensional jet lag measured at T2 and change from T1 to T2. After controlling for direction and size of circadian phase, increased uni- and multidimensional subjective jet lag was predicted by depressed mood states. The regression models including phase, diurnal preference, departure time on the outbound sector and arousal levels accounted for 28% of the variance in unidimensional jet lag and 53% of the variance in multidimensional jet lag. It was concluded that there is a discordance between objective and subjective jet lag post-trip. Further, subjective jet lag in long-haul cabin crew is better explained by mood impairment than circadian phase. The results are discussed with reference to the gap between subjective and objective jet lag and the role of psychology rather than just biology in the jet lag experience. The implications for improving health and safety in the workplace, through a better understanding of the role of human factors in the management of jet lag, are discussed.

Analysis and mapping of global research publications on shift work (2012-2021)

BACKGROUND

The main objective of the study was to identify research trends, collaboration patterns, and the most impactful publications in the field of shift work.

METHODS

Documents published in scientific journals indexed in the Scopus database on shift work were retrieved and analyzed using the title/abstract search methodology. The study period was from January 1st, 2012, to December 31st, 2021.

RESULTS

Two thousand three hundred twenty-eight documents were retrieved with an h-index of 71 and an average number of 4.5 authors per document. The cumulative number of publications showed a linear growth pattern, while that of citations showed an exponential pattern. The most frequent author keywords, excluding keywords related to shift work, were sleep, fatigue, and nursing. The average annual growth rate was 4.3, and the average doubling time was 3.2. No significant correlation was found between the number of publications and national income among prolific countries. Cross-country research collaboration was weak while the degree of author-author collaboration was relatively high. The Chronobiology International journal was the most prolific, while Harvard University was the most active institution in the field of shift work.

CONCLUSIONS

Given the volume and the negative health impact of shift work, better human resource management is needed to create safer and healthier working schedules.

Association between shift work and inflammatory markers in workers at an electronics manufacturing company

Background

Shift work is known to be associated with cardiovascular disease (CVD). It has been found that inflammatory reactions are involved in the onset and progression of CVD. Therefore, the purpose of this study was to investigate the association between shift work and inflammatory markers.

Methods

Among workers at an electronics manufacturing company, 2,329 workers who had a health checkup from January 2019 to December 2019 were targeted. The general and biochemical characteristics of daytime workers and shift workers were compared through the Independent-test and the χ² test. Through multiple linear regression analysis, the association with shift work and inflammatory markers was investigated. Through multiple logistic regression analysis, the association with shift work and high inflammatory markers.

Results

The mean total leukocytes, neutrophils, monocytes, lymphocytes of shift workers were significantly higher than those of daytime worker. The mean high-sensitivity C-reactive protein (hs-CRP) of shift workers was also higher than that of daytime workers but not significantly. In multiple linear regression, shift work was associated with increase of total leukocyte count (β = 0.367, p < 0.001) and hs-CRP (β = 0.140, p = 0.005) after adjusting for all variables. In multiple logistic regression analysis, shift work showed 2.27 times risk of high leukocyte count and 1.8 times risk of high hs-CRP level compared to daytime work after adjusting for all variables.

Conclusions

This study confirmed that shift work is associated with high inflammatory markers. Considering that high inflammatory markers is independent indicator of CVD, the association between shift work and high inflammatory markers may help to understand the CVD risk of shift workers.

The Effect of Chronotype on Oppositional Behaviour and Psychomotor Agitation of School-Age Children: A Cross-Sectional Study

The aim of this study is to examine the relationship between chronotype, classroom behaviour and school performance in 140 healthy school-age children attending various levels of education during the 1st cycle during 2021 in Portugal. In this cross-sectional and quantitative study, the Chronotype Questionnaire for Children (to assess the chronotype) and the Conners Scale-a reduced version was presented to the teachers (to assess behaviours such as excessive movement, inattention and oppositional behaviours)-were used. The methodology of this study followed a comparative method since the independent variables were not controlled, and therefore, it was still possible to compare the differences between the morning and evening groups. Statistical methods were used such as multivariate analyses, inter-item correlations and reliability tests, and descriptive tests were used for the percentile analysis. The sample was divided into three groups based on the identification of the chronotype-morning, intermediate and evening types-to further study the relationship between these chronotypes, their academic performance and classroom behaviour were studied. A multivariate analysis of variance revealed that there was a higher rate of oppositional behaviour in the morning type and no differences in the school performance during the two semesters (covering all of the school periods) regarding the chronotype effect, even with the analysis of regression parameters and covariates. On the other hand, the morning-type children showed a greater amount of motor agitation and impulsivity after controlling for the gender covariate. Age had an effect on the chronotype, after controlling for the covariate parental education. This study highlights the need for further research on the chronotype of the morning children in order to regulate their behaviour. The data that were obtained raise questions that have not been yet considered in the literature in the area of education and infant development.

A matter of time: A systematic scoping review on a potential role of the circadian system in binge eating behavior

Background

Emerging research suggests that food intake timing, eating behavior and food preference are associated with aspects of the circadian system function but the role that the circadian system may play in binge eating (BE) behavior in humans remains unclear.

Objective

To systematically evaluate the evidence for circadian system involvement in BE behavior.

Methods

Systematic searches of PubMed, EMBASE, and Scopus were performed for reports published from inception until May 2020 (PROSPERO Registration CRD42020186325). Searches were conducted by combining Medical Subject Headings related to the circadian system, BE behavior, and/or interventions. Observational and interventional studies in humans with BE behavior published in peer-review journals in the English language were included. Studies were assessed using quality and risk of bias tools (AXIS, ROB 2.0, or ROBINS).

Results

The search produced 660 articles, 51 of which were included in this review. Of these articles, 46 were observational studies and 5 were interventional trials. Evidence from these studies suggests that individuals with BE behavior tend to have more food intake, more binge cravings, and more BE episodes later in the day. Hormonal and day/night locomotor activity rhythm disturbances may be associated with BE behavior. Furthermore, late diurnal preference ("eveningness") was associated with BE behavior and chronobiological interventions that shift the circadian clock earlier (e.g., morning bright light therapy) were found to possibly decrease BE behavior. Substantive clinical overlap exists between BE and night eating behavior. However, there is a significant knowledge gap regarding their potential relationship with the circadian system. Limitations include the lack of studies that use best-established techniques to assess the chronobiology of BE behavior, heterogeneity of participants, diagnostic criteria, and study design, which preclude a meta-analytic approach.

Conclusion

Current evidence, although limited, suggests that the circadian system may play a role in the etiology of BE behavior. Further mechanistic studies are needed to fully characterize a potential role of the circadian system in BE behavior. A chronobiological approach to studying BE behavior may lead to identification of its neurobiological components and development of novel therapeutic interventions.

Systematic review registration

[https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020186325], identifier [CRD42020186325].

Chronotype, circadian rhythm, and psychiatric disorders: Recent evidence and potential mechanisms

The circadian rhythm is crucial for physiological and behavioral functions. Chronotype, which represents individual preferences for activity and performance, is associated with human health issues, particularly psychiatric disorders. This narrative review, which focuses on the relationship between chronotype and mental disorders, provides an insight into the potential mechanism. Recent evidence indicates that (1) the evening chronotype is a risk factor for depressive disorders and substance use disorders, whereas the morning chronotype is a protective factor. (2) Evening chronotype individuals with bipolar disorder tend to have more severe symptoms and comorbidities. (3) The evening chronotype is only related to anxiety symptoms. (4) The relationship between chronotype and schizophrenia remains unclear, despite increasing evidence on their link. (5) The evening chronotype is significantly associated with eating disorders, with the majority of studies have focused on binge eating disorders. Furthermore, the underlying mechanisms or influence factors are described in detail, including clock genes, brain characteristics, neuroendocrinology, the light/dark cycle, social factors, psychological factors, and sleep disorders. These findings provide the latest evidence on chronotypes and psychiatric disorders and serve as a valuable reference for researchers.

Environmental disruption of reproductive rhythms

Reproduction is a key biological function requiring a precise synchronization with annual and daily cues to cope with environmental fluctuations. Therefore, humans and animals have developed well-conserved photoneuroendocrine pathways to integrate and process daily and seasonal light signals within the hypothalamic-pituitary-gonadal axis. However, in the past century, industrialization and the modern 24/7 human lifestyle have imposed detrimental changes in natural habitats and rhythms of life. Indeed, exposure to an excessive amount of artificial light at inappropriate timing because of shift work and nocturnal urban lighting, as well as the ubiquitous environmental contamination by endocrine-disrupting chemicals, threaten the integrity of the daily and seasonal timing of biological functions. Here, we review recent epidemiological, field and experimental studies to discuss how light and chemical pollution of the environment can disrupt reproductive rhythms by interfering with the photoneuroendocrine timing system.

Impact of shift work on irritable bowel syndrome and functional dyspepsia: A meta-analysis

BACKGROUND

The possible association between shift work with irritable bowel syndrome (IBS) and functional dyspepsia (FD) remains controversial. The purpose of the study is to conduct a meta-analysis to explore the potential association between shift work with IBS/FD.

METHODS

We searched relevant observational studies on Medline (PubMed) and Embase until June 30, 2021. Two different investigators extracted data and assessed the quality of each study independently. The meta-analysis was used to evaluate the pooled odds risk (OR) between shift work and IBS/FD.

RESULTS

Eight studies were included ultimately. Shift workers were more likely to suffer from IBS. The OR of shift work was 1.81 (95% confidence interval 1.42; 2.32) with low heterogeneity (P < .05, I2 = 0%) for IBS. However, no evidence of the association was observed between shift work and the risk of FD. The OR of shift work was 0.87 (95% confidence interval 0.62; 1.23) (P > .05) for FD.

CONCLUSIONS

There was a positive association between shift work and IBS. The prevalence of IBS was 81% higher among shift workers than among non-shift workers. Shift work was probably a risk factor for IBS. The low heterogeneity supports the reliability of the results. However, there was no significant association between shift work and FD. The strength of the evidence was limited and further prospective cohort studies were needed.

Evaluation of environmental, social, and behavioral modulations of the circadian phase of dancers trained in shifts

The interplay of environmental, social, and behavioral factors influencing human circadian phase in ecological conditions remains elusive. The Uruguayan national dance school END-SODRE operating in two shifts (morning: 8:30–12:30 and night: 20:00–24:00) allowed us to evaluate how social demands, chronotype, environmental light, physical activity, and sleep patterns affected individual circadian phase measured by the onset of the nocturnal increase of melatonin (DLMO) in a single study. The DLMO was 1.5 h earlier in morning-shift dancers (n = 7) compared to night-shift dancers (n = 11). Sleep time and chronotype (only in night-shift dancers) were associated with the circadian phase. In training days, during each participant’s phase-advance and phase-delay time windows, light exposure was similar between morning and night-shift dancers and did not correlate with DLMO. In contrast, the time spent in moderate-vigorous physical activity during each participant’s phase-lag time window was higher in night-shift dancers than in morning-shift dancers and positively correlated with DLMO.

•

Circadian phase was earlier in morning than in night dancers in real-life conditions

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Sleep time (and night-shift chronotypes) correlated with the circadian phase

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In the phase-advance and phase-lag windows, light was not associated with DLMO

•

In the phase-lag time window, the longer the intense exercise the later the phase

Shift Work, Genetic Factors, and the Risk of Heart Failure: A Prospective Study of the UK Biobank

OBJECTIVE

To quantify the association of combined shift work and genetic factors with the incidence of heart failure (HF).

PARTICIPANTS AND METHODS

This study included 242,754 participants with complete shift work information in the UK Biobank. Participants were followed from baseline (2006 to 2010) through January 31, 2018. The association between shift work and HF incidence was investigated separately in males and females using a Cox proportional hazards model adjusted for covariates. In addition, we established a polygenic risk score and assessed whether shift work alters genetic susceptibility to HF.

RESULTS

The results showed a significant association of permanent night shift work with incident HF among females (hazard ratio, 2.25; 95% CI, 1.34 to 3.76; P=.002) after adjusting for age, and the association was attenuated in the fully adjusted model. Among men, we did not detect an association between shift work and HF. In addition, we observed that the association between the risk of HF and shift work was strengthened by high genetic risk. Permanent night shift work paired with high genetic risk, compared with low genetic risk, was suggested to be associated with the risk of HF in females (hazard ratio, 2.89; 95% CI, 1.05 to 7.94) but not in males.

CONCLUSION

Shift work, particularly permanent night shift work, may increase the risk of HF in females, especially in those with high genetic risk.

Perturbation of Circadian Rhythm Is Associated with Increased Prevalence of Chronic Kidney Disease: Results of the Korean Nationwide Population-Based Survey

Disturbances in circadian rhythms cause several health problems, such as psychosis, metabolic syndrome, and cancer; however, their effect on kidney disease remains unclear. This study aimed to evaluate the association between chronic kidney disease (CKD) and sleep disturbance in a Korean adult population. A total of 17,408 participants who completed the National Health and Nutrition Examination Survey from 2016 to 2018 were assessed for their sleep patterns and renal function. CKD was defined as an estimated glomerular filtration rate ≤ 60 mL/min/1.73 m² or a positive dipstick urinalysis. Sleep onset time and sleep duration showed significant differences between the control and CKD groups (p < 0.001). After adjusting for the covariates, sleep onset time rather than sleep duration was independently associated with incidence of CKD, and this association was more significant in people who were older, in women, and in those with low body mass index and no comorbidities. When comparing the prevalence of newly diagnosed CKD according to sleep onset time in a population with no CKD risk factors or no history of CKD, the early bedtime group showed an independent association with incidence of new CKD (odds ratio (OR), 1.535; 95% confidence interval (CI), 1.011−2.330) even after adjusting for covariates. Impaired circadian rhythm along with sleep disturbance could be associated with CKD development; therefore, sleep disturbance might be an important therapeutic target for CKD.

The Influence of Doing Shift Work on the Lifestyle Habits of Primary Care Nurses

Nurses’ lifestyle habits play a key role in promoting healthy lifestyles; although, they may not always be entirely healthy and can be influenced by working conditions. This paper aims to analyze the influence of doing shift work on nurses’ lifestyle habits. Participants (n = 219) were recruited from 27 primary health care centres in Spain. Data were collected on socio-demographic characteristics, working conditions and lifestyle behaviour, assessed by use of an adhoc questionnaire including validated measures. Descriptive analysis and logistic regression models were performed. A total of 95% of the nurses reported having an adequate diet; 45.2% did not engage in any type of physical activity; and 85.8% did not smoke, especially women. A total of 60.3% did shift work, especially the younger ones (80.8%; p < 0.001), these nurses being the ones with the worst food habits (81.8%). In contrast, nurses who did shift work, exercised more days a week (69.5%; p < 0.001). The dietary habits of the nurses were adequate. Low tobacco consumption and low adherence to physical activity were observed, especially among women. Shift work harmed eating habits and obesity rates, but was a protective factor in terms of adherence to physical exercise.

The relationship between night shift work and breast cancer incidence: A systematic review and meta-analysis of observational studies

The purpose of this study was to investigate the relationship between night shift work and breast cancer (BC) incidence. A search was performed in PubMed, EBSCO, Web of Science, and Cochrane Library databases before June 2021. The exposure factor of this study is night shift work, the primary outcome is the risk of BC. A total of 33 observational studies composed of 4,331,782 participants were included. Night shift work increases the risk of BC in the female population (hazard ratio [HR] = 1.20, 95% confidence interval [Cl] = 1.10–1.31, p < 0.001), especially receptor-positive BC, including estrogen receptor (ER)+ BC (HR = 1.35, p < 0.001), progesterone receptor (PR)+ BC (HR = 1.30, p = 0.003), and human epidermal growth factor receptor 2 (HER2)+ BC (HR = 1.42, p < 0.001), but has no effect on HER2− BC (HR = 1.10, p = 0.515) and ER−/PR− BC (HR = 0.98, p = 0.827). The risk of BC was positively correlated with night shift working duration, frequency, and cumulative times. For women who start night work before menopause, night work will increase the incidence of BC (HR = 1.17, p = 0.020), but for women who start night work after menopause, night work does not affect BC (HR = 1.04, p = 0.293). Night work can increase the incidence of BC in the female population. The effect of long working hours, frequency, and the cumulative number of night shifts on BC is influenced by menopausal status.

Chronotype Profile, Stress, Depression Level, and Temporomandibular Symptoms in Students with Type D Personality

Background: Despite a growing interest in the types of human circadian activity, different chronotypes and personality-related issues have been rarely studied. It has already been emphasized that ‘stress personality’ is considered a risk factor for certain psychosomatic diseases and may be a temporomandibular disorders (TMDs) predictor. Therefore, an attempt has been made to analyze the chronotypes, stress levels, stress factors, and the occurrence of depression and TMDs in students with type D personalities. People with this personality trait tend to experience negative emotions more—depression, anxiety, anger, or hostility—yet may have a negative image of themselves and report somatic complaints. Aim: The aim of this study was to analyze the importance of the chronotype profile for the level of stress perceived, as well as for the occurrence of depression and TMDs in people with type D personalities. Material and Methods: The study has been conducted on a group of 220 physical therapy students. The study group G1 consisted of 110 participants with type D personalities, the control group G2 consisted of the same number of participants without the stress personality. All participants have been analyzed for the chronotype (MEQ), stress perception (PSS10), the occurrence of depression (Beck scale-BDI), the occurrence of TMDs symptoms and have completed the stress factor assessment questionnaire during the study, followed by DS14 questionnaire—a tool for assessing the prevalence of type D personality. Results: In students with type D personalities (G1), the definitely evening and evening chronotypes have been significantly more predominant than in the control group (G2). A significantly higher number of stressors and TMDs symptoms have been observed in the respondents from the G1 group than in the control group (<0.001). Univariate logistic regression analysis showed that type D personality was strongly associated with a more frequent occurrence of all TMD symptoms. Additionally, a significant influence of the evening chronotype on the occurrence of type D personality was observed. Among the potential confounding variables, female gender and a mild and moderate degree of depression have an impact on the occurrence of type D personality (p < 0.05). In the multivariate model, adjusted with the above-mentioned factors, an increased risk of the type D personality trait was found. Conclusion: The evening chronotype and type D personality may imply greater feelings of stress, greater depression, and more frequent symptoms of TMDs in young adults.

Systematic review of drugs that modify the circadian system's phase-shifting responses to light exposure

We searched PubMed for primary research quantifying drug modification of light-induced circadian phase-shifting in rodents. This search, conducted for work published between 1960 and 2018, yielded a total of 146 papers reporting results from 901 studies. Relevant articles were those with any extractable data on phase resetting in wildtype (non-trait selected) rodents administered a drug, alongside a vehicle/control group, near or at the time of exposure. Most circadian pharmacology experiments were done using drugs thought to act directly on either the brain's central pacemaker, the suprachiasmatic nucleus (SCN), the SCN's primary relay, the retinohypothalamic tract, secondary pathways originating from the medial/dorsal raphe nuclei and intergeniculate leaflet, or the brain's sleep-arousal centers. While the neurotransmitter systems underlying these circuits were of particular interest, including those involving glutamate, gamma-aminobutyric acid, serotonin, and acetylcholine, other signaling modalities have also been assessed, including agonists and antagonists of receptors linked to dopamine, histamine, endocannabinoids, adenosine, opioids, and second-messenger pathways downstream of glutamate receptor activation. In an effort to identify drugs that unduly influence circadian responses to light, we quantified the net effects of each drug class by ratioing the size of the phase-shift observed after administration to that observed with vehicle in a given experiment. This allowed us to organize data across the literature, compare the relative efficacy of one mechanism versus another, and clarify which drugs might best suppress or potentiate phase resetting. Aggregation of the available data in this manner suggested that several candidates might be clinically relevant as auxiliary treatments to suppress ectopic light responses during shiftwork or amplify the circadian effects of timed bright light therapy. Future empirical research will be necessary to validate these possibilities.

Exposure to night-time light pollution and risk of prolonged duration of labor: A nationwide cohort study

BACKGROUND

Light pollution (LP) is a ubiquitous environmental agent that affects more than 80% of the world's population. This large nationwide cohort study evaluates whether exposure to LP can influence obstetric outcomes.

METHODS

We analyzed Austrian birth registry data on 717 113 cases between 2008 and 2016 and excluded cases involving day-time delivery, <23 + 0 gestational weeks, and/or birthweight <500 g, induction of labor, elective cesarean, or cases with missing data. The independent variable, that is, degree of night-time LP, was categorized as low (0.174 to <0.688 mcd/m² ), medium (0.688 to <3 mcd/m² ), or high (3 to <10 mcd/m² ). Duration of labor and adverse neonatal outcomes served as outcome measures.

RESULTS

Cases in regions with high LP (odds ratio [OR], 1.43; 95% confidence interval [CI], 1.30-1.57) and medium LP (OR, 1.22; 95% CI, 1.14-1.31) showed increased odds of prolonged labor (P < .0001 each). Newborns born in regions with high LP (OR, 1.12; 95% CI, 1.07-1.16) and medium LP (OR, 1.07; 95% CI, 1.04-1.10) showed increased odds of experiencing adverse outcomes (P < .0001 each). Preterm delivery <28 + 0 weeks was also associated with the degree of LP (P = .04).

CONCLUSIONS

Night-time LP negatively interferes with obstetric outcomes. The perceived influence of LP as an environmental agent needs to be re-evaluated to minimize associated health risks.

Autonomic nervous system activity under rotational shift programs: effects of shift period and gender

Rotational shifts perturb homeostatic mechanisms in a sexually dimorphic way and may compromise the activity of the autonomic nervous system during day- and night-shifts. Heart rate variability (HRV) is a non-invasive measure to assess autonomic control of the heart. Our aim in this study was to assess HRV by short-term continuous electrocardiogram in female (n=40, average age: 31, average working year: 7) and male (n=40, average age: 29, average working year: 6) nurses under rotational shift programs, HRV is derived from short-term electrocardiogram recordings, carried out both at day- and night -shifts, and included time-domain [e.g., standard deviation of NN intervals, SDNN (ms); percentage of successive RR intervals that differ by more than 50 ms, pNN50 (%); root mean square of successive RR interval differences, RMSSD (ms)] and frequency-domain [very low frequency, VLF; low frequency, LF; high frequency, HF; LF/HF] parameters. Heart rates were similar across the groups but males had lower SDNN (p=0.020), RMSSD (p=0.001). pNN50 (p=0.001), VLF (p=0.048) and HF (p=0.001) but had higher LF/HF ratio (p=0.000) than females. In general, these parameters did not differ between day- and night-shifts (p<0.05). Lower HRV parameters and higher LF/HF in males suggest that they may be under greater threat for disease progression.

A Growing Link between Circadian Rhythms, Type 2 Diabetes Mellitus and Alzheimer's Disease

Type 2 diabetes mellitus (T2DM) patients are at a higher risk of developing Alzheimer’s disease (AD). Mounting evidence suggests the emerging important role of circadian rhythms in many diseases. Circadian rhythm disruption is considered to contribute to both T2DM and AD. Here, we review the relationship among circadian rhythm disruption, T2DM and AD, and suggest that the occurrence and progression of T2DM and AD may in part be associated with circadian disruption. Then, we summarize the promising therapeutic strategies targeting circadian dysfunction for T2DM and AD, including pharmacological treatment such as melatonin, orexin, and circadian molecules, as well as non-pharmacological treatments like light therapy, feeding behavior, and exercise.

Do sex hormones confound or mediate the effect of chronotype on breast and prostate cancer? A Mendelian randomization study

Morning-preference chronotype has been found to be protective against breast and prostate cancer. Sex hormones have been implicated in relation to chronotype and the development of both cancers. This study aimed to assess whether sex hormones confound or mediate the effect of chronotype on breast and prostate cancer using a Mendelian Randomization (MR) framework. Genetic variants associated with chronotype and sex hormones (total testosterone, bioavailable testosterone, sex hormone binding globulin, and oestradiol) (p<5×10-8) were obtained from published genome-wide association studies (n≤244,207 females and n≤205,527 males). These variants were used to investigate causal relationships with breast (nCases/nControls = 133,384/113,789) and prostate (nCases/nControls = 79,148/61,106) cancer using univariable, bidirectional and multivariable MR. In females, we found evidence for: I) Reduced risk of breast cancer per category increase in morning-preference (OR = 0.93, 95% CI:0. 88, 1.00); II) Increased risk of breast cancer per SD increase in bioavailable testosterone (OR = 1.10, 95% CI: 1.01, 1.19) and total testosterone (OR = 1.15, 95% CI:1.07, 1.23); III) Bidirectional effects between morning-preference and both bioavailable and total testosterone (e.g. mean SD difference in bioavailable testosterone = -0.08, 95% CI:-0.12, -0.05 per category increase in morning-preference vs difference in morning-preference category = -0.04, 95% CI: -0.08, 0.00 per SD increase in bioavailable testosterone). In males, we found evidence for: I) Reduced risk of prostate cancer per category increase in morning-preference (OR = 0.90, 95% CI: 0.83, 0.97) and II) Increased risk of prostate cancer per SD increase in bioavailable testosterone (OR = 1.22, 95% CI: 1.08, 1.37). No bidirectional effects were found between morning-preference and testosterone in males. While testosterone levels were causally implicated with both chronotype and cancer, there was inconsistent evidence for testosterone as a mediator of the relationship. The protective effect of morning-preference on both breast and prostate cancer is clinically interesting, although it may be difficult to effectively modify chronotype. Further studies are needed to investigate other potentially modifiable intermediates.

Modification Effect of Job Demand and Contingent Work Schedule on Overweight and Obesity Among Civil Servants in Taiwan

OBJECTIVE

Evidence indicated that shift work is a contributing factor to risk of obesity and leads to cardiovascular diseases (CVDs), but few researches have examined the moderating effects of job demand and contingent work schedule on overweight and obesity. Thus, we assessed the modification effect of contingent work schedules and job demand on overweight and obesity among Taiwan's civil servants.

METHODS

Multistage stratified random cluster sampling was used based on a proportional probabilistic sampling (PPS) in a national survey for civil servants. A total of 20,046 participants from 647 registered governmental institutions were enrolled and anonymously and voluntarily filled out web-based questionnaires.

RESULTS

Compared to fixed work schedule, odd ratios (ORs) of obesity and overweight were 1.63 and 1.78 times in contingent work schedule, respectively. In addition, the modification effects of contingent work schedule and high job demand on overweight and obesity with Rothman's synergy index were 2.43 and 2.56, respectively. Using a hierarchical regression model adjusted for covariates, both high job demand and contingent work schedule were interactively associated with overweight and obesity compared to low job demand and fixed work schedule.

CONCLUSION

Since precarious schedules affect employee's obesity through work-related stress and unhealthy behaviors, further research is needed to determine whether interventions aimed at modification of work schedule may be useful in combating obesity.

Disturbance of the Circadian System in Shift Work and Its Health Impact

The various non-standard schedules required of shift workers force abrupt changes in the timing of sleep and light-dark exposure. These changes result in disturbances of the endogenous circadian system and its misalignment with the environment. Simulated night-shift experiments and field-based studies with shift workers both indicate that the circadian system is resistant to adaptation from a day- to a night-oriented schedule, as determined by a lack of substantial phase shifts over multiple days in centrally controlled rhythms, such as those of melatonin and cortisol. There is evidence that disruption of the circadian system caused by night-shift work results not only in a misalignment between the circadian system and the external light-dark cycle, but also in a state of internal desynchronization between various levels of the circadian system. This is the case between rhythms controlled by the central circadian pacemaker and clock genes expression in tissues such as peripheral blood mononuclear cells, hair follicle cells, and oral mucosa cells. The disruptive effects of atypical work schedules extend beyond the expression profile of canonical circadian clock genes and affects other transcripts of the human genome. In general, after several days of living at night, most rhythmic transcripts in the human genome remain adjusted to a day-oriented schedule, with dampened group amplitudes. In contrast to circadian clock genes and rhythmic transcripts, metabolomics studies revealed that most metabolites shift by several hours when working nights, thus leading to their misalignment with the circadian system. Altogether, these circadian and sleep-wake disturbances emphasize the all-encompassing impact of night-shift work, and can contribute to the increased risk of various medical conditions. Here, we review the latest scientific evidence regarding the effects of atypical work schedules on the circadian system, sleep and alertness of shift-working populations, and discuss their potential clinical impacts.

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.

Night shift work and breast cancer risk: a meta-analysis of observational epidemiological studies

Previous observational epidemiological studies have reported inconsistently the association between night shift work (NSW) and the risk of breast cancer (BC). This study aimed to investigate those associations by using a meta-analysis of observational epidemiological studies. We searched PubMed and EMBASE using keywords related to this topic from inception till November 2020. The pooled effect sizes such as odds ratio (OR), hazard ratio (HR) or relative risk (RR) with 95% confidence interval (CI) were calculated using a random-effects model. In the meta-analysis of a total of 32 observational studies including 13 case-control studies, 4 nested case-control studies and 15 cohort studies, NSW significantly increased the risk of BC (OR/RR/HR, 1.11; 95% CI, 1.04-1.20; I2 = 72.4%). In the subgroup meta-analysis by type of study, NSW was also associated with the increased risk of BC in case-control studies (OR, 1.34; 95% CI, 1.17-1.53; I2 = 63.8%). However, no significant association was found in both nested case-control studies (OR, 1.14; 95% CI, 0.89-1.46; I2 = 65.8%) and cohort studies (RR/HR, 0.98; 95% CI, 0.93-1.03; I2 = 25.3%). Besides, there was no significant association between NSW for over 20 years and the risk of BC (OR/RR/HR, 1.03; 95% CI, 0.95-1.11; I2 = 36.6%, n = 14). Given that cohort studies provide higher evidence than case-control studies, there is no association between NSW and the risk of BC.

Circadian Rhythm Dysregulation and Restoration: The Role of Melatonin

Sleep is an essential component of overall human health but is so tightly regulated that when disrupted can cause or worsen certain ailments. An important part of this process is the presence of the well-known hormone, melatonin. This compound assists in the governing of sleep and circadian rhythms. Previous studies have postulated that dysregulation of melatonin rhythms is the driving force behind sleep and circadian disorders. A computer-aided search spanning the years of 2015–2020 using the search terms melatonin, circadian rhythm, disorder yielded 52 full text articles that were analyzed. We explored the mechanisms behind melatonin dysregulation and how it affects various disorders. Additionally, we examined associated therapeutic treatments including bright light therapy (BLT) and exogenous forms of melatonin. We found that over the past 5 years, melatonin has not been widely investigated in clinical studies thus there remains large gaps in its potential utilization as a therapy.

Circadian rhythm disruption with high-fat diet impairs glycemic control and bone quality

Biological functions, including glycemic control and bone metabolism, are highly influenced by the body's internal clock. Circadian rhythms are biological rhythms that run with a period close to 24 hours and receive input from environmental stimuli, such as the light/dark cycle. We investigated the effects of circadian rhythm disruption (CRD), through alteration of the light/dark schedule, on glycemic control and bone quality of mice. Ten-week-old male mice (C57/BL6, n = 48) were given a low-fat diet (LFD) or a high-fat diet (HFD) and kept on a dayshift or altered schedule (RSS3) for 22 weeks. Mice were divided into four experimental groups (n = 12/group): Dayshift/LFD, Dayshift/HFD, RSS3/LFD, and RSS3/HFD. CRD in growing mice fed a HFD resulted in a diabetic state, with a 36.2% increase in fasting glucose levels compared to the Dayshift/LFD group. Micro-CT scans of femora revealed a reduction in inner and outer surface expansion for mice on a HFD and altered light schedule. Cancellous bone demonstrated deterioration of bone quality as trabecular number and thickness decreased while trabecular separation increased. While HFD increased cortical bone mineral density, its combination with CRD reduced this phenomenon. The growth of mineral crystals, determined by small angle X-ray scattering, showed HFD led to smaller crystals. Considering modifications of the organic matrix, regardless of diet, CRD exacerbated the accumulation of fluorescent advanced glycation end-products (fAGEs) in collagen. Strength testing of tibiae showed that CRD mitigated the higher strength in the HFD group and increased brittleness indicated by lower post-yield deflection and work-to-fracture. Consistent with accumulation of fAGEs, various measures of toughness were lowered with CRD, but combination of CRD with HFD protected against this decrease. Differences between strength and toughness results represent different contributions of structural and material properties of bone to energy dissipation. Collectively, these results demonstrate that combination of CRD with HFD impairs glycemic control and have complex effects on bone quality.

Potential role of melatonin in prevention and treatment of leukaemia

Leukaemia is a haematological malignancy originated from the bone marrow. Studies have shown that shift work could disrupt the melatonin secretion and eventually increase leukaemia incidence risk. Melatonin, a pineal hormone, has shown promising oncostatic properties on a wide range of cancers, including leukaemia. We first reviewed the relationship between shift work and the incidence rate of leukaemia and then discussed the role of melatonin receptors (MT1 and MT2) and their functions in leukaemia. Moreover, the connection between inflammation and leukaemia, and melatonin-induced anti-leukaemia mechanisms including anti-proliferation, apoptosis induction and immunomodulation are comprehensively discussed. Apart from that, the synergistic effects of melatonin with other anticancer compounds are also included. In short, this review article has compiled the evidence of anti-leukaemia properties displayed by melatonin and discuss its potential to act as adjunct for anti-leukaemia treatment. This review may serve as a reference for future studies or experimental research to explore the possibility of melatonin serving as a novel therapeutic agent for leukaemia.

Chronotype and risk of post-menopausal endometrial cancer in the California Teachers Study

Working at night causes circadian disruption and it has been classified as a probable carcinogen. An evening chronotype, or preference for late day activity, has been shown to increase risk for several adverse health effects, such as metabolic disorders and recently, breast cancer. To further explore this emerging area of interest, we examined the association between endometrial cancer (EC) risk, another common cancer in women, and chronotype. The women in this study were members of the California Teachers Study cohort, which was established in 1995. Chronotype was reported on a subsequent questionnaire (Q5), administered in 2012-2013. The women included in this analysis were under age 90 years, were post-menopausal at Q5, and had no hysterectomy. The cancer cases, identified through linkages to the California Cancer Registry, were diagnosed between 1996 and 2014. We used unconditional logistic regression models to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) of the associations between chronotype and EC diagnosis. There were 437 EC cases and 26,753 cancer-free controls included in this analysis. Controls were more likely to classify themselves as current morning chronotypes than were cases (39% and 34%, respectively). Compared to morning types, women who were definite evening types had a statistically significantly elevated OR of 1.44 (95% CI 1.09-1.91). This association was more pronounced among obese women as compared to non-obese women. For evening type compared to morning type, the OR among obese women was 2.01 (95% CI 1.23, 3.29) while the OR for non-obese women was 1.12 (95% CI 0.77, 1.63). To our knowledge, the association between EC risk and evening chronotype has not been previously reported, but is consistent with the small body of literature which suggests increased breast cancer risks among evening chronotypes. Because this study was based on a retrospective analysis in a cohort of mostly white female teachers in California, further analysis of chronotype as a potential EC risk factor should be considered in other cohorts and in prospective analyses in order to further explore this relationship.

Unrestrained eating behavior and risk of digestive system cancers: a prospective cohort study

BACKGROUND

Unrestrained eating behavior, as a potential proxy for diet frequency, timing, and caloric intake, has been questioned as a plausible risk factor for digestive system cancers, but epidemiological evidence remains sparse.

OBJECTIVES

We investigated prospectively the associations between unrestrained eating behavior and digestive system cancer risk.

METHODS

Participants in the Nurses' Health Study who were free of cancer and reported dietary information in 1994 were followed for ≤18 y. Cox models were used to estimate HRs and 95% CIs for unrestrained eating (eating anything at any time, no concern with figure change, or both) and risk of digestive system cancers.

RESULTS

During follow-up, 2064 digestive system cancer cases were documented among 70,450 eligible participants in analyses of eating anything at any time, In total, 2081 digestive system cancer cases were documented among 72,468 eligible participants in analyses of no concern with figure change. In fully adjusted analyses, women with the behavior of eating anything at any time had a higher risk of overall digestive system cancer (HR: 1.22; 95% CI: 1.10, 1.35), overall gastrointestinal tract cancer ((HR: 1.33; 95% CI: 1.18, 1.50), buccal cavity and pharynx cancer (HR: 1.50; 95% CI: 1.02, 2.21), esophageal cancer (HR: 1.62; 95% CI: 1.01, 2.62), small intestine cancer (HR: 1.92; 95% CI: 1.02,3. 59), and colorectal cancer (HR: 1.20; 95% CI: 1.04, 1.38), and a non-statistically significant increased risk of stomach cancer (HR: 1.54; 95% CI: 0.96,2.48), compared with women without this behavior. No statistically significant association was observed for pancreatic cancer and liver and gallbladder cancer. The combined effect of eating anything at any time and having no concern with figure change was associated with a significantly increased risk of overall digestive system cancer (HR: 1.27; 95% CI: 1.10, 1.46), overall gastrointestinal tract cancer (HR: 1.45; 95% CI: 1.23, 1.71), and colorectal cancer (HR: 1.34; 95% CI: 1.11, 1.63), compared with women exhibiting the opposite.

CONCLUSIONS

Unrestrained eating behavior was independently associated with increased risk of gastrointestinal tract cancers. The potential importance of unrestrained eating behavior modification in preventing gastrointestinal tract cancers should be noted.

A Longitudinal Study of the Relationship between Shift Work and Prostate-Specific Antigen in Healthy Male Workers

As shift work has become prevalent globally, it is important to evaluate the health effects of shift work on employees. Several studies have demonstrated a positive association between shift work and prostate cancer. Therefore, we aimed to further examine the relationship between shift work and elevated prostate-specific antigen (PSA). Our study collected data from 66,817 male participants at baseline and followed up for about 6 years. We categorized shift worker status and shift schedule types. To evaluate the risk of elevated PSA on shift workers, we estimated hazard ratios using the Cox proportional hazards regression analyses. During a median follow-up of 4.1 years, 1030 participants developed elevated PSA. The multivariable-adjusted hazard ratio (HR) of elevated PSA for shift workers compared with daytime workers was 1.37 (1.04-1.80). Among shift workers, rotating shift workers (HR = 1.47, 95% CI 1.06-2.03) showed a significantly increased risk of elevated PSA compared with daytime workers. Our longitudinal study provides evidence for an association between shift work, especially rotating shift work, and elevations of PSA.