Shift Work Exposure Research Articles

Shiftwork and Metabolic Dysfunction

Many of the health problems that are more prevalent among shiftworkers are thought to be linked to their heightened susceptibility to metabolic syndrome, i.e., the association of even moderate degrees of visceral obesity, dyslipidemia, abnormal blood pressure, and serum glucose levels in the same individual. Although previous studies have identified associations between shiftwork and metabolic syndrome, there is relatively little evidence to date of how the risk of developing it varies as a function of exposure to shiftwork. The current study seeks to confirm earlier findings of an association between shiftwork exposure and metabolic dysfunction, and to examine the impact of exposure duration, while adjusting for a number of covariates in the analyses. The analyses were based on data from VISAT, a study involving the measurement of physiological, behavioral, and subjective outcomes from 1757 participants, 989 being current or former shiftworkers. The sample comprised employed and retired wage earners, male and female, who were 32, 42, 52, and 62 yrs old. The first analysis sought to confirm previous findings of an association between exposure to shiftwork and the risk of developing metabolic syndrome. It indicated that participants who were or who had previously been shiftworkers (i.e., working schedules that involved rotating shifts; not being able to go to bed before midnight; having to get up before 05:00 h; or being prevented from sleeping during the night) were more likely to exhibit symptoms of metabolic syndrome, after adjusting for age, sex, socioeconomic status, smoking, alcohol intake, perceived stress, and sleep difficulty (odds ratio [OR] 1.78; 95% confidence interval [CI] 1.03–3.08). The results suggest the association between shiftwork and metabolic syndrome cannot be fully accounted for by either higher levels of strain or increased sleep difficulty among shiftworkers, although it remains a possibility that either one or both of these factors may have played a contributing role. The second analysis addressed the issue of duration of exposure to shiftwork. Participants with >10 yrs' experience of working rotating shifts were more likely to exhibit symptoms of metabolic syndrome than participants without exposure to shiftwork, i.e., dayworkers, even after adjusting for age and sex (OR 1.96; 95% CI 1.03–3.75). Thus, the current study confirms the association between shiftwork exposure and metabolic syndrome. It also provides new information regarding the time course of the development of the illness as function of exposure duration, although this was only examined in relation to rotating shiftwork. It is concluded that those responsible for monitoring workers' health should pay particular attention to indices of metabolic dysfunction in workers who have been exposed to shiftwork for >10 yrs. (Author correspondence: p.t.tucker@swansea.ac.uk)

Abstract 2611: Role of circadian genes in breast cancer: Analysis of the CECILE study, a population-based case-control study conducted in France

Abstract Breast cancer risk has been associated with shift work and light exposure at night. It has been suggested that disruption of circadian rhythms induced by these exposure may play a role in tumorigenesis. Circadian rhythms regulate diverse physiologic processes, including regulation of sex hormone levels, and genes controlling the circadian rhythm were found to regulate cell proliferation, cell cycle regulation and apoptosis. However, only few studies have investigated the role of these genes in breast cancer. The purpose of this study was to analyze the association between polymorphisms in circadian genes and breast cancer risk. The CECILE study is a population-based case-control study on environmental and genetic factors. A total of 1135 incident cases and 1167 controls provided DNA samples. We genotyped 570 tagging and functional SNPs from the 22 genes in the circadian rhythm pathway defined by KEGG. Preliminary results based on a SNP by SNP analysis using unconditional logistic regression highlighted 36 SNPs with p-value<0.05 in RORA, CUL1, NPAS2, CRY1, CRY2 and CLOCK genes. Of these, 3 SNPs in RORA were significantly associated with breast cancer after Bonferroni correction for multiple testing (p<0.0001). In ongoing analyses, we use the Multilevel Inference for SNP Association (MISA) method, which is a more powerful method that allows estimating associations at the SNP, gene and pathway level. These analyses will be presented. Our results suggest a role of the circadian gene in breast cancer risk. Further analysis on possible interaction between shift work and genetic variants highlighted in this study in relation to breast cancer risk will be conducted in the CECILE study. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2611. doi:1538-7445.AM2012-2611

Outbreak of Sudden Cardiac Deaths in a Tire Manufacturing Facility: Can It Be Caused by Nanoparticles?

ObjectivesThe purpose of this study was to review clinical characteristics and working environments of sudden cardiac death (SCD) cases associated with a tire manufacturer in Korea, and review possible occupational risk factors for cardiovascular disease including nanoparticles (ultrafine particles, UFPs).MethodsWe reviewed (i) the clinical course of SCD cases and (ii) occupational and non-occupational risk factors including chemicals, the physical work environment, and job characteristics.ResultsPossible occupational factors were chemicals, UFPs of rubber fume, a hot environment, shift work, overworking, and noise exposure. The mean diameter of rubber fume (63-73 nm) was (larger than diesel exhaust [12 nm] and outdoor dust [50 nm]). The concentration of carbon disulfide, carbon monoxide and styrene were lower than the limit of detection. Five SCD cases were exposed to shift work and overworking. Most of the cases had several non-occupational factors such as hypertension, overweight and smoking.ConclusionThe diameter of rubber fume was larger than outdoor and the diesel exhaust, the most well known particulate having a causal relationship with cardiovascular disease. The possibility of a causal relation between UFPs of rubber fume and SCD was not supported in this study. However, it is necessary to continue studying the relationship between large sized UFPs and SCD.

Work-related cardiovascular disease risk factors using a socioecological approach: implications for practice and research

Cardiovascular disease (CVD) is a leading cause of mortality. Numerous investigations have linked occupational factors and CVD. Occupational factors such as overtime work have an enormous effect on the CVD risk of industrial workers. However, risk factors for CVD are not systematically reviewed in the workplace. The purpose of the paper is to review work-related risk factors for CVD. A systematic review of work-related CVD risk factors was performed, yielding 180 articles. All articles were assessed in relation to inclusion and exclusion criteria, resulting in 44 articles being reviewed. The sole inclusion criteria was work-related environmental factors and intra/inter-personal factors (psychosocial factors), which is based on the socioecological perspective. The articles were also assessed regarding the quality of each study using the scoring methods developed by Cesario et al. and Brown et al. The literature review demonstrated that work environment factors such as shift work, overtime work, and noise and chemical exposures; and psychosocial factors such as job stress, social support, and socioeconomic status cannot be explained or intervened by one single risk factor. Furthermore, certain occupational factors were shown to aggravate or attenuate other risk factors. The implication of these findings is to incorporate work-related environmental and psychosocial factors into assessment of the patient's CVD risks and intervention plan. Future research should also incorporate a well-defined conceptual framework to address the effects of work-related environmental and psychosocial factors on CVD among CVD patients.

P-1391 - Elaborating the ideological and structural content of women's work in a globalized economy

Women's employment in the global market now has been increasing as a result of globalization and internationalization of labour. This study has two main objectives in its attempt to analyze the relations of gender. The global market, and health in the workplace. First, the article tries to elucidate the structural content of work as seen in the work organization; and second, to elaborate the ideological content of work as defined by ideologies of the organization, of the state and of the market production system. The study used quantitative methodology through surveys of 630 women workers in 23 establishments, as well as qualitative methodology using 10 interviews and focus group discussions. The study showed that assembly line work was also reported to be boring , fast-paced and requires upskilling regularly. Most of the respondents (76.3%) did overtime work. Quantitative overload was significantly related to a number of symptoms of psychological health issues such as poor work motivation, low self-esteem, absenteeism, and tardiness. The study showed that ill health under a global economy results from the impact of measures designed to enhance the profitability of capital- from shiftwork, overtime, apprenticeship, homeworking, subcontracting, teleworking, part-time work, and piece-rate work exposure to dangerous chemicals, industrial injuries, stress, or a damaged and polluted environment. This study tried to develop additional theorizing on the relations of women, global market and health using health sociology and medical anthropology.

The influence of shift work and light at night exposure on melatonin levels and breast cancer risk

ObjectivesWork at night has been identified as a risk factor for several cancer sites, and melatonin, a hormone that follows a circadian rhythm, has been proposed as an intermediate in...

Effect of rotating shift work on childbearing and birth weight: a study of women working in a semiconductor manufacturing factory

Stable circadian rhythm is important for both maternal and fetal health. This retrospective analysis of women in a semiconductor factory evaluated the effect of shift work exposure on childbearing and birth weight. Records of 440 female employees (initial mean age: 28.4 years) including 111 mothers who had 158 live births during the period of observation (1997-2007) were reviewed. The data analyzed included maternal age, general health condition, highest educational level, life-style and occupational factors, as well as newborn gender, birth weight, birth order and gestational age. The childbearing rates of female workers on three different work schedules (consistent daytime work (CDW), intermittent (i-) or persistent (p-) rotating shift works (RSW)) were 32.1%, 20.0% and 25.4%, respectively (P=0.047). After controlling for potential confounding factors, childbearing rates among women with CDW exceeded those of shift workers (odds ratio (OR), 1.7; 95% confidence interval (CI), 1.0-3.0). The birth weights of newborns from mothers on the three work schedules (CDW, i-RSW and p-RSW) were significantly different (3271.7±395.4, 3251.3±460.9, and 2998.5±381.2 g, respectively (P<0.01). Newborns within the lightest birth weight quintile were significantly more likely to be born to mothers with exposure to p-RSW (OR, 4.3; 95% CI, 1.1-16.8). Rotating shift work exposure was significantly associated with decreased childbearing and lighter birth weight in women working in this semiconductor manufacturing factory. Work schedules should be carefully planned for female employees who are pregnant or preparing for pregnancy. Prenatal evaluations for mothers with persistent day-night rotating shift work exposures are especially necessary.

Shiftwork Duration and the Awakening Cortisol Response Among Police Officers

Police officers are required to work irregular hours, which induces stress, fatigue, and sleep disruption, and they have higher rates of chronic disease and mortality. Cortisol is a well-known “stress hormone” produced via activation of the hypothalamic-pituitary-adrenal axis. An abnormal secretion pattern has been associated with immune system dysregulation and may serve as an early indicator of disease risk. This study examined the effects of long- and short-term shiftwork on the cortisol awakening response among officers (n = 68) in the Buffalo Cardio-Metabolic Occupational Police Stress (BCOPS) pilot study (2001–2003). The time each officer spent on day (start time: 04:00–11:59 h), afternoon (12:00–19:59 h), or night (20:00–03:59 h) shifts was summarized from 1994 to examination date to characterize long-term (mean: 14 ± 9 yrs) and short-term (3, 5, 7, or 14 days prior to participation) shiftwork exposures. The cortisol awakening response was characterized by summarizing the area under the curve (AUC) for samples collected on first awakening, and at 15-, 30-, and 45-min intervals after waking. Data were collected on a scheduled training or off day. The cortisol AUC with respect to ground (AUCG) summarized total cortisol output after waking, and the cortisol AUC with respect to increase (AUCI) characterized the waking cortisol response. Officers also completed the Center for Epidemiologic Studies Depression scale. Waking cortisol AUC values were lower among officers working short-term night or afternoon shifts than day shifts, with maximal differences occurring after 5 days of shiftwork. The duration of long-term shiftwork was not associated with the cortisol awakening response, although values were attenuated among officers with more career shift changes. (Author correspondence: burch@mailbox.sc.edu)

Chronic Phase Shifts of the Photoperiod throughout Pregnancy Programs Glucose Intolerance and Insulin Resistance in the Rat

Shift work during pregnancy is associated with an increased risk for preterm birth and low birth weight. However, the impact upon the long term health of the children is currently unknown. In this study, we used an animal model to determine the consequences of maternal shift work exposure on the health of the adult offspring. Pregnant rats were exposed to chronic phase shifts (CPS) in their photoperiod every 3–4 days throughout gestation and the first week after birth. Adult offspring were assessed for a range of metabolic, endocrine, circadian and neurobehavioural parameters. At 3 months of age, male pups exposed to the CPS schedule in utero had increased adiposity (+29%) and hyperleptinaemia (+99% at 0700h). By 12 months of age, both male and female rats displayed hyperleptinaemia (+26% and +41% respectively) and hyperinsulinaemia (+110% and +83% respectively). 12 month old female CPS rats displayed poor glucose tolerance (+18%) and increased insulin secretion (+29%) in response to an intraperitoneal glucose tolerance test. In CPS males the glucose response was unaltered, but the insulin response was reduced by 35%. The glucose response to an insulin tolerance test was decreased by 21% in CPS females but unaltered in males. Disruption of circadian rhythmicity during gestation resulted in gender dependent metabolic consequences for the adult offspring. These results highlight the need for a thorough analysis of shift work exposure in utero on the health of the adult offspring in humans.

The effects of shift work on body weight change − a systematic review of longitudinal studies

This systematic review aims to summarize the available evidence to elucidate the effects of shift work, which includes night work, on body weight change. A systematic search strategy using longitudinal studies was performed. Articles were included based on strict inclusion criteria; methodological quality was assessed by a standardized quality checklist. The results were summarized using a levels of evidence synthesis. The search strategy resulted in eight articles that met the inclusion criteria. Five of them were considered to be high- and three of them low-quality studies. Seven studies presented crude results for an association between shift work exposure and change in body weight: five high- and two low-quality studies. There was strong evidence for a crude relationship between shift work and body weight increase. Five studies presented weight-related outcomes adjusted for potentially relevant confounders (age, gender, bodyweight at baseline, and physical activity). Two studies found a significant difference between groups in the same direction. Consequently, the evidence for a confounders-adjusted relationship between shift work exposure and body weight was considered to be insufficient. Strong evidence for a crude association between shift work exposure and body weight increase was found. In order to further clarify the underlying mechanisms, more and better high quality studies about this subject are necessary.

Association between night shift work, melatonin and estradiol in nurses

Synthesis of melatonin is regulated through visible light exposure, with peak production during the night. Melatonin regulates various physiological processes including secretion of other hormones, and has anticarcinogenic properties as demonstrated in animal and in vitro experiments. It has been suggested that night shift work (exposure to light at night) may disrupt circadian rhythm, and melatonin synthesis leading to other hormonal alterations including increase in estradiol. Few epidemiological studies have investigated an association between night shift work, melatonin secretion and estradiol and their results are inconsistent, with support only from The Nurses Health Study in the US. In order to clarify the associations between night shift work, melatonin and estradiol we performed analyses of the data collected in the cross-sectional study of 360 nurses working currently on rotating night-shifts and 365 nurses who work currently only during the day. Information on occupational history, use of hormones, menopausal status and breast cancer risk factors was collected in personal interviews. Morning and evening urinary 6-sulfatoxymelatonin (MT6), and estradiol levels in blood were determined. Preliminary analyses showed no significant associations between current night shift work, melatonin and estradiol in pre-menopausal women. However, significant positive associations were found between total night shift work duration and estradiol in postmenopausal nurses. Our findings in post-menopausal women support the thesis on alterations in estradiol as a result of prolonged exposure to rotating night shift work in nurses.

EPIGENETIC EFFECTS OF SHIFTWORK ON BLOOD DNA METHYLATION

In the present study, the authors investigated the effects of shiftwork exposure on DNA methylation using peripheral blood DNA from subjects working in two chemical plants in Northern Italy. The investigation was designed to evaluate (a) DNA methylation changes in Alu and long interspersed nuclear element-1 (LINE-1) repetitive elements as a surrogate of global methylation and (b) promoter methylation of glucocorticoid receptor (GCR), tumor necrosis factor alpha (TNF-α), and interferon-gamma (IFN-γ). One hundred and fifty white male workers (mean ± SD: 41.0 ± 9 yrs of age) were examined: 100 3 × 8 rotating shiftworkers (40.4 ± 8.7 yrs of age) and 50 day workers (42.2 ± 9.4 yrs of age). The authors used bisulfite-pyrosequencing to estimate repetitive elements and gene-specific methylation. Multiple regression analysis, adjusted for age, body mass index (BMI), and job seniority, did not show any significant association between the five DNA methylation markers and shiftwork. However, job seniority, in all subjects, was significantly associated with Alu (β = −0.019, p = .033) and IFN-γ (β = −0.224, p < .001) methylation, whereas TNF-α methylation was inversely correlated with age (β = −0.093, p < .001). Considering only shiftworkers, multiple regression analysis, adjusted for age, BMI, and job seniority, showed a significant difference between morning and evening types in TNF-α methylation (mean morning type [MT] 11.425 %5mC versus evening type [ET] 12.975 %5mC; β = 1.33, p = .022). No difference was observed between good and poor tolerance to shiftwork. Increasing job seniority (<5, 5–15, >15 yrs) was associated with significantly lower Alu (β = −0.86, p = .006) and IFN-γ methylation (β = −6.50, p = .007) after adjustment for age, BMI, and morningness/eveningness. In addition, GCR significantly increased with length of shiftwork (β = 3.33, p = .05). The data showed alterations in blood DNA methylation in a group of shiftworkers, including changes in Alu repetitive elements methylation and gene-specific methylation of IFN-γ and TNF-α promoters. Further studies are required to determine the role of such alterations in mediating the effects of shiftwork on human health. (Author correspondence: giovanni.costa@unimi.it)

Clock Genes and Cancer

Period genes ( Per2, Per1) are essential circadian clock genes. They also function as negative growth regulators. Per2 mutant mice show de novo and radiation-induced epithelial hyperplasia, tumors, and an abnormal DNA damage response. Human tumors show Period gene mutations or decreased expression. Other murine clock gene mutations are not associated with a tumor prone phenotype. Shift work and nocturnal light exposure are associated with circadian clock disruption and with increased cancer risk. The mechanisms responsible for the connection between the circadian clock and cancer are not well defined. We propose that circadian disruption per se is not uniformly tumor promoting and the mechanisms for tumor promotion by specific circadian clock disturbances will differ dependent upon the genes and pathways involved. We propose that Period clock gene mutations promote tumorigenesis by unique molecular pathways. Per2 and Per1 modulate beta-catenin and cell proliferation in colon and non-colon cancer cells. Per2 mutation increases intestinal beta-catenin levels and colon polyp formation. Per2 mutation also increases Apc(Min/+)-mediated intestinal and colonic polyp formation. Intestinal tumorigenesis per se may also alter clock function as a result of increased beta-catenin destabilizing PER2 protein. Levels and circadian rhythm of PER2 in Apc(Min/+) mouse intestine are markedly decreased, and selective abnormalities in intestinal clock gene and clock-controlled gene expression are seen. We propose that tumor promotion by loss of PERIOD clock proteins is unique to these clock genes as a result of altered beta-catenin signaling and DNA damage response. PERIOD proteins may offer new targets for cancer prevention and control.

Commentary: Metabolic syndrome as a result of shift work exposure?

In this new article from Belgium, ‘Rotating shift work and the metabolic syndrome: a prospective study’ by De Bacquer et al., 2 a successfully designed follow-up study (46 years), with reasonable confounding control, has been conducted. The results show adverse patterns of high-density lipoprotein cholesterol, triglycerides, blood pressure and anthropometrical data in subjects engaged in shift work compared with day workers. The authors show adverse outcomes both for combinations of metabolic data, using standard definitions of the metabolic syndrome, and for several isolated metabolic variables. Additionally, an anticipated dose–response effect is observed and discussed, although admittedly the exposure categories for shift workers are rather crude, or include only a few participants. The limitations of the study that might limit interpretation are well discussed and do not compromise the main findings. However, a difficulty arises with inclusion of the persons already affected by disease in the cohort as the direction of causality, and mechanisms underlying disease cannot be determined. Why has it been, and why is it still, difficult to explore metabolic syndrome data similar to those found in the De Bacquer study among shift workers? First, there are circadian variations in lipid and lipoprotein profiles, not only within but also between individuals, 3 that have to be estimated and considered. Secondly, evidence of elevated blood pressure in shift workers compared with day workers has not been convincingly demonstrated. However, a few cohort studies, notably from Japan, have confirmed a greater impact on hypertension progression in shift workers. 4 Ambulatory blood pressure monitoring provides more complete information on blood pressure itself and its variation over a 24-h period when an individual is engaged in routine activities. Future studies may wish to employ this technique to provide a better assessment of the impact of shift work on blood pressure. Importantly, loss of nocturnal dipping of blood pressure has adverse consequences in terms of cardiovascular risk, and may not be evident from daytime measurements alone, therefore assessment of nocturnal blood pressure may be particularly important in this regard. 5

Effects of shift work and intermittent noise exposure on hearing: Mechanisms and prophylactic potential

It is well established that intermittent noise exposure characteristically produces less hearing loss than equal energy/intensity continuous noise in animal models. Ongoing different shift work regimes open for direct studies on hearing effects of intermittent noise exposure in man without ethical concern. Amazingly, few such studies are reported. In one recent study in the present volume, noise-exposed employees working 12 hours a day for two consecutive days followed by two days off, the cycle then repeated, had significantly lower permanent hearing loss than employees working nine-hour shifts from 8 am to 5 pm Monday to Friday. This commentary refers to the few studies reported, gives a short overview of the mechanisms behind noise-induced hearing loss and the protective effect of intermittent exposure, and concludes that direct studies in man on the effects of different shift work regimes on occupational hearing loss under specified noise conditions represent a prophylactic potential that calls for increased research activity. Such studies might pave the way for direct use of more optimal intermittent noise exposure regimes in future design of the noise exposure workday/-week and make future hearing conservation programs more effective.

Persistent Rotating Shift-Work Exposure Accelerates Development of Metabolic Syndrome among Middle-Aged Female Employees: A Five-Year Follow-Up

Limited follow-up studies are available as to whether special job-types, such as day-night rotating shift work, contribute to the progression of metabolic syndrome among female industrial employees. A retrospective cohort study on the development of metabolic syndrome was conducted by utilizing health examination records for a five-year interval. The records of 387 female employees without metabolic syndrome at baseline were used for the analysis. Data analyzed included age, metabolic syndrome components, insulin resistance status, lifestyle factors, and job-types. The initial mean age of subjects was 32.8 yrs. Abnormal rates at baseline, including metabolic syndrome components and insulin resistance, were all significantly higher among the 34 female workers with metabolic syndrome outcome. Also, the persistent rotating shift-work exposure rates and five-year change of metabolic syndrome component measurements were significantly unfavorable for subjects with metabolic syndrome outcome. After controlling for the potential confounders, significant raised risks were found in the female worker with persistent rotating shift-work exposure (odds ratio [OR], 3.5; 95% confidence interval [CI], 1.3–9.0 vs. day workers) and in smokers (OR, 5.4; 95% CI, 1.1–25.8 vs. non-smokers). At the same time, the female workers initially with one or two metabolic syndrome components had a 4.6-fold (95% CI, 1.3–17.0) and 12.7-fold (95% CI, 3.2–50.1), respectively, increased risk of progressing to metabolic syndrome within five years. In conclusion, persistent day-night rotating shift work, smoking, and baseline metabolic syndrome components associate with the progression toward metabolic syndrome for middle-aged female workers. (Author correspondence: pchen@ntu.edu.tw, gphinx@gmail.com).

Internal locus of control and choice in health service shift workers

This study examined the relationship between shift work-specific locus of control (SH-LOC), active choice of work schedule and health outcomes, personal initiatives and coping behaviours in 1611 Danish Health Service shift workers. The 20-item SH-LOC scale was administered as part of a battery of measures. Multivariate analysis of covariance (controlling for age, workplace experience and weekly work hours) tested for differential responses to shift working and coping strategies. Interactive effects of internality and type of work rota were examined. Higher internality was linked to better tolerance to shift work. This did not appear to be a result of greater personal action in higher internals. The importance of control as a potential moderating factor to shift work exposure and the possible use of this measure in the process of shift worker monitoring is highlighted.

Serotonin and Serotonin Transporter Gene Variant in Rotating Shift Workers

Because serotonin (5-HT) is a neurotransmitter associated with circadian rhythm regulation, we explored a possible relation among 5-HT, serotonin metabolite, 5-hydroxyindolacetic acid (5HIAA), and the functional polymorphism of the serotonin transporter gene (SLC6A4) promoter with rotating shift work. 683 men were included in this study: 437 day workers were compared with 246 rotating shift workers. Platelet 5-HT content differed significantly (P = 0.002) between day workers (41.28+/-1.99 pg/mg) and rotating shift workers (37.91+/-4.16 pg/mg); 5-HIAA content was also significantly (P = 0.00004) higher in day workers (11.40+/-0.82 pg/mg) than in rotating shift workers (9.33+/-1.02 pg/ mg). We looked for further differences in SLC6A4 promoter (5-HTTLPR, 44 bp insertion: long (L)/deletion: short (S) alleles). We found a significant (P = 0.016) difference in genotype distribution between day workers LL: 126 (28.8%), LS: 202 (46.2%), and SS: 109 (24.9%), and rotating shift workers LL: 47 (19.1%), LS: 124 (50.4%), and SS: 75 (30.5%). When we divided the subjects between workers with less and more than 60 month rotating shift-work exposure, the difference in SLC6A4 genotypes frequency was only significant in the group with > or =60 months (P = 0.011). In addition, there was a significantly lower content of platelet 5-HIAA in S allele carriers in comparison with the other genotypes (SS: 9.2+/-1.0 pg/mg vs. SL/LL: 11.0+/-0.8 pg/mg, P <0.02). Platelet 5-HT and 5-HIAA contents were significantly lower in rotating shift workers than day workers, and there was a significant association between the S variant of SLC6A4 promoter and shift work. These findings may be important for targeting effective therapeutic strategies to ameliorate the associated comorbidities and behavioral problems in rotating shift workers.

Prevalence and determinants of excessive daytime sleepiness in an Asian multi-ethnic population

Background and purpose To investigate the prevalence and determinants of daytime sleepiness in an Asian multi-ethnic population. Cross-sectional survey based on a questionnaire in multi-ethnic Asian adult population of Singapore (2.4 million). Patients and methods Measured frequency of excessive daytime sleepiness (EDS), socio-demographic status, sleep duration, perceived sleep insufficiency, frequent awakenings, difficulty falling asleep, snoring, breathing pauses, GHQ-12, shift work, solvent exposure at work, substance use, medications, and chronic diseases in random sample of 2298 adults, aged 20–74 years, representing Chinese, Malays and Indians. Results Among the respondents, 10.8% reported usually feeling sleepy in the daytime, and 9.0% were classified as having EDS. Marked ethnic difference was observed, with higher rates of EDS in Malays and Chinese, compared to Indians. Increased risk of EDS was associated with perceived sleep insufficiency; snoring and breathing pauses; shift work and solvent exposure at work; psychiatric morbidity and chronic diseases, particularly chronic rhinitis; and medications with sedating effects. Conclusions Daytime sleepiness is associated with a multiplicity of highly prevalent risk factors in the community, including sleep behavior, breathing-, work- and medically related factors. Significant ethnic differences, which were not explained by these factors, were observed between Chinese, Malays and Indians.

Total mortality and cause-specific mortality of Swedish shift- and dayworkers in the pulp and paper industry in 1952-2001

The study investigated the relationship between shiftwork and mortality, both total mortality and cause-specific mortality from coronary heart disease (CHD), stroke, and diabetes. Methods The cohort consisted of 2354 shiftworkers and 3088 dayworkers in two pulp and paper manufacturing plants. The mortality of the cohort was monitored from 1 January 1952 to 31 December 2001 by linkage to the national Cause of Death Register. Groups of workers defined by different durations of shiftwork exposure were compared with dayworkers by calculating standardized relative rates (SRR). Death due to any cause (total mortality) was not higher among the shiftworkers than among the dayworkers [SRR 1.02, 95% confidence interval (95% CI) 0.93-1.11]. A longer duration of shiftwork was associated with an increased risk of CHD, and shiftworkers with >30 years of shiftwork had the highest risk of CHD (SRR 1.24, 95% CI 1.04-1.49) Diabetes was more common as the number of shift years of exposure increased [b(linear coefficient) = 4.14 x 10(-5), 95% CI 2.46 x 10(-5) -5.81 x 10(-5)]. Compared with dayworkers, shiftworkers had a greater risk of death due to stroke (SRR 1.56, 95% CI 0.98-2.51). In the present study, no general increase in mortality was observed among shiftworkers when they were compared with dayworkers. However, the results demonstrate an increased mortality from CHD among shiftworkers with a long duration of shiftwork exposure. Mortality due to diabetes also increased as the number of shift years and mortality due to ischemic stroke in shiftworkers increased.