Search

ObjectivesTo examine the association of shift work with and without night work with breast cancer among women in the public sector.MethodsUsing the Finnish Public Sector cohort study (N=33 359, mean age of 40.6 years at baseline), we investigated the associations of shift work and potential confounders with incident breast cancer. Exposure to permanent day work or shift work was defined from first two consecutive surveys from 2000, 2004, 2008 or 2012 and past information on exposure in a subcohort (n=20 786). Incident cases of breast cancer (n=1129) were retrieved from the National Cancer Register and the cohort members were followed to the end of 2016. HR and 95% CI from Cox proportional hazard regression models were calculated.ResultsShift work with and without night shifts was not overall associated with breast cancer. When stratified according to age, both shift work without nights (HR 2.01, 95% CI 1.12 to 3.60) and shift work with nights (OR 2.05, 95% CI 1.04 to 4.01) were associated with an increased risk after a period of 10 years or more follow-up among women aged 50 years or older, when adjusted for age, socioeconomic status, children, smoking, alcohol and body mass index. In a subgroup with past information on exposure to shift work, the increased risk by longer exposure to shift work was not significant.ConclusionsThis study provides support for an increased risk of breast cancer among elderly shift workers. However, insufficient information on exposure and intensity of night work may attenuate the risk estimates.

Objective: We performed a systematic review to assess potential consequences of extended working hours on accidents, near-accidents, safety incidents and injuries (incidents) by considering the overall certainty of evidence. Methods: We searched five databases systematically (Medline, Embase, PsycINFO, Web of Science, and Proquest Health and safety Science Abstract) and identified 10072 studies published until December 2020. Twenty-two studies met the inclusion criteria. We followed a systematic approach to evaluate risk of bias and synthesize results in a meta-analysis. The certainty of evidence was determined by a modified version of The Grading of Recommendations Assessment, Development and Evaluation (GRADE). Results: Our analyses indicated an association between working >12 hours/day (RR: 1.24, 95%CI: 1.11, 1.40), or working >55 hours/week (RR: 1.24, 95%CI: 0.98, 1.57), and elevated risk of incidents. The certainty of evidence evaluated as low. Weak or no associations were observed for other exposure contrasts: working >8 hours/day (RR: 0.93, 95%CI: 0.72, 1.19), or working overtime (RR: 1.08, 95%CI: 0.75, 1.55), working 41-48 hours/week (RR: 1.02, 95%CI: 0.92, 1.13) or 49-54 hours/week (RR: 1.02, 95%CI: 0.97, 1.07). The certainty of evidence was evaluated as low (very low for 41-48 hours/week). Conclusions: Daily working hours >12 hours and weekly working hours exceeding 55 hours was associated and increased risk of incidents. The level of evidence was low. Hence, further high-quality research is warranted to elucidate these associations.

BACKGROUND: Airline crew are being exposed to extended workdays and compressed work periods, with quick returns between duties, implying a heightened physiological and psychological strain that may lead to sleep deprivation and fatigue. The aim of the study was assessment of the effect of an extended day of flight duty and a compressed work week with regard to recovery, cumulative fatigue, and neurobehavioral performance.METHODS: We followed 18 pilots and 41 cabin crewmembers during four consecutive days of flight duty, comprising a total of ≥ 39 h, where the first day was ≥ 10 h. Information on demographics, work characteristics, health status, and physical activity was collected at baseline. Subjects completed logs for the first and fourth workday, including the Samn-Perelli Fatigue Checklist at three time points during these workdays. Two computer-based neurobehavioral tests were completed the evening prior to the first shift, and after the first and the fourth day of the work period.RESULTS: Number of flight sectors during the work period was 10-20. Self-reported fatigue levels increased during the workdays. Neurobehavioral test-scores did not deteriorate. The effects of each additional flight sector during the work period was elevated reaction times (RT) both among cabin crewmembers (B = 5.05 ms, 95% CI 0.6, 9.5) and pilots (B = 4.95 ms, 95% CI 0.4, 9.5). Precision was unaffected.DISCUSSION: Airline pilots and cabin crewmembers seem to obtain satisfactory sleep before and during the period of 4 consecutive days. The association between multiple flight sectors and increased fatigue supports previous findings.Goffeng EM, Wagstaff A, Nordby K-C, Meland A, Goffeng LO, Skare O, Lilja D, Lie J-AS. Risk of fatigue among airline crew during 4 consecutive days of flight duty. Aerosp Med Hum Perform. 2019; 90(5):466-474.

Shift work, particularly, night work has been classified as a probable carcinogen to humans based on the increased risk observed in epidemiological studies for some cancer types, including female breast cancer. The underlying molecular mechanisms are not well established, but may involve aberrant epigenetic modifications. Here, effects of changes in methylation status of 5-methyl cytosine in melatonin and female hormone receptor genes were investigated as possible mechanisms for increased breast cancer risk in female night shift workers. Methylation in promoter regions of the MTNR1A, MTNR1B, PGR, ESR1 and ESR2 genes was analyzed by pyrosequencing in a nested case-control study of female nurses, including 354 breast cancer cases and 356 healthy controls. The effects of methylation as well as the combined effects of methylation and shift work on breast cancer risk were assessed. We demonstrate that increased methylation of the MTNR1A promoter is associated with increased risk of breast cancer (OR=1.13, 95% CI: 1.02 -1.24, P=0.019). No association between promoter methylation levels and breast cancer risk was observed for the other receptor genes investigated. Furthermore, MTNR1A methylation levels were not affected by shift work. Altogether, our data suggest that epigenetic regulation of MTNR1A may contribute to breast cancer.

Sleep problems are commonly associated with chronic pain. It is not known whether pain is more related to a particular type of sleep problem or to more composite measures of sleep disturbance. The aim of the study was to investigate cross-sectionally the association between three commonly used sleep problem scales and musculoskeletal pain, when controlling for age, lifestyle and work factors. A total of 1032 nurses answered the Epworth Sleepiness Scale, Bergen Insomnia Scale, Pittsburg Sleep Quality Index and questionnaires regarding work, personality and lifestyle factors. Data collection started in October 2014 and ended in November 2015. Data were analyzed with hierarchical multiple regressions. Musculoskeletal pain was associated with Epworth Sleepiness Scale and Bergen Insomnia Scale, with Bergen Insomnia Scale showing the strongest association. Post hoc analyses of the most frequently reported pain locations, back pain headache and neck pain, confirmed that Bergen Insomnia Scale showed the strongest association. Insomnia seems to be more strongly associated with musculoskeletal pain than subjective sleepiness, thus the measures used to explore this association should be carefully selected when studying the relation between disturbed sleep and pain.

The aim of this study was to investigate fluctuations in heart rate variability (HRV), which reflect autonomic nervous system (ANS) function and potential psychological and physical strain, among 24 health care workers during work and sleep during four consecutive extended work shifts. Data included 24/36/12 h of HRV measurements, two logbooks, and a questionnaire. A cross-shift/cross-week design was applied. HRV was measured during work, leisure time, and sleep. The HRV data included time-domain [mean RR, SD of normal to normal R-R intervals (SDNN), and root mean square of the successive differences (RMSSD)] and frequency-domain [low frequency (LF)/high frequency (HF) ratio] parameters. HRV parameters revealed significant differences among work, leisure time, and sleep. Mean RR, RMSSD, and SDNN values were lower and the LF/HF ratio was higher on the first versus last day of the work period; however, the differences were most prominent in the morning hours. The results indicate higher levels of cardiovascular stress on the first versus fourth day of the working period, and measurements at night indicate a satisfactory recovery from the extended shifts.

Occupational factors such as shiftwork and especially night work that involves disruption of the circadian rhythm may contribute to increased breast cancer risk. Circadian disruption may also affect telomere length (TL). While short TL generally is associated with increased cancer risk, its association with breast cancer risk is inconclusive. We suggest that working schedules might be an important factor in assessment of effects of TL on breast cancer risk. Moreover, telomere shortening might be a potential mechanism for night work‐related breast cancer. In this study, effects of shift work on TL and its association with breast cancer risk were investigated in a nested breast cancer case–control study of Norwegian nurses. TL was assessed by qPCR in DNA from 563 breast cancer patients and 619 controls. Here, we demonstrate that TL is affected by intensive night work schedules, as work with six consecutive night for a period of more than 5 years was associated with decreased telomere lengths (−3.18, 95% CI: −6.46 to −0.58, P = 0.016). Furthermore, telomere shortening is associated with increased breast cancer risk in workers with long periods of consecutive night shifts. Thus, nurses with longer telomere lengths had a lower risk for breast cancer if they had worked more than four (OR: 0.37, 95% CI: 0.16–0.79, P = 0.014) or five (OR: 0.31, 95% CI: 0.10–0.83, P = 0.029) consecutive night shifts for a period of 5 years or more. These data suggest that telomere shortening is associated with the duration and intensity of night work and may be a contributing factor for breast cancer risk among female shift workers.

Objective It has been hypothesized that the underlying mechanism of elevated breast cancer risk among long-term, night-working women involves circadian genes expression alteration caused by exposure to light at night and/or irregular work hours. The aim of the present study was to determine the effect of rotating night shift work on expression of selected core circadian genes. Methods The cross-sectional study was conducted on 184 matched nurses and midwives, who currently work either day or rotating night shifts, to determine the effect of irregular work at night on circadian gene expression in peripheral blood leukocytes. Transcript levels of BMAL1, CLOCK, CRY1, CRY2, PER1, PER2, and PER3 were determined by means of quantitative real-time polymerase chain reaction (PCR). Results After adjusting for hour of blood collection, there were no statistically significant changes of investigated circadian genes among nurses and midwives currently working rotating night shifts compared to nurses working day shifts. The highest expression of PER1 messanger ribonucleic acid (mRNA) was observed for women currently working shifts who had worked >15 years in rotating night shift work. PER1 gene expression was associated with the lifetime duration of rotating night shift work among women currently working night shifts (P=0.04). PER1 and PER3 transcript levels in blood leukocytes were significantly down-regulated in the later versus early hours of the morning between 06.00–10.00 hours (β-coefficient -0.226, P=0.001 and β-coefficient -0.181, P

Purpose Light-at-night exposure can disrupt the human circadian rhythm via clock gene expressions. The circadian rhythm influences antioxidant enzymes’ activity and cellular mRNA levels of these enzymes. The employees working based on a shift system adjust to the changes occurring both on the cell level and on the level of the whole organism. Therefore, a question should be answered whether shift work disturbs oxidant–antioxidant balance and/or generates oxidative stress. Methods A cross-sectional study was conducted among nurses selected from the Local Registry of the Chamber of Nurses and Midwives in Lodz: 359 nurses worked daily only and 349 working rotating night shifts. These two groups differed significantly in respect of age (p

Objectives Synthesis of melatonin follows a circadian cycle, with high melatonin levels during the night and low levels during the day. Light exposure at night has been hypothesised as one of potential mechanisms of breast carcinogenesis in the night shift workers through inhibition of melatonin synthesis. The aim of the study was to examine a number of determinants for night shift work in relation to 6-sulfatoxymelatonin (MT6s), primary melatonin metabolite. Methods The cross-sectional study included 354 nurses and midwives (aged 40–60 years) currently working on rotating night shifts and 370 working days only. Data from questionnaires and 1-week diaries were used to characterise current job and total occupational history. Associations between rotating night shift work characteristics and MT6s (creatinine adjusted) in spot morning urine were tested in multiple linear regression models. Results No significant differences were found for MT6s concentrations between women currently working on rotating night shifts and those working only day shifts (means 47.2 vs 45.7 ng/mg Cr, respectively). The adjusted means among rotating night shift nurses and midwives varied depending on the department of employment, from 35.1 ng/mg Cr in neonatology to 68.2 ng/mg Cr in the orthopaedics department. Women working eight or more night shifts per month had significantly lower MT6s levels than those having fewer night shifts per month (37.9 vs 47.4 ng/mg Cr, respectively). Total night shift work history was not associated with MT6s. Conclusions The results of this study indicate that working eight or more night shifts per month may disrupt the synthesis of melatonin.

OBJECTIVE: In order to devise effective preventive strategies, it is important to study workplace stressors that might increase the risk of workplace accidents - both affecting workers themselves as well as causing harm to third-parties. The aim of this report is to provide a systematic, updated overview and scientific review of empirical research regarding accidents in relation to long work hours and shift work, primarily based on epidemiological studies. METHODS: The search for articles was part of a large review study on the effects of work hours on various health outcomes, safety, and performance. The search strategy included 5 international scientific databases, and nearly 7000 articles were initially identified using our search string. Following the application of inclusion and exclusion criteria, 443 publications were found and evaluated using a pre-defined scoring system. Of these, 43 concerned safety and accidents but only 14 were considered to be of high quality (total score 2 or 3 on a scale from 0-3) and therefore used for this study. RESULTS: Both shift work and long working hours present a substantial and well-documented detrimental effect on safety - all the studies that are included in this review have one or more significant findings in this respect. The trends are quite coherent although the increases in accident rates are mostly from 50% to 100%. In epidemiological terms, this may be seen as rather small differences. The use of such data is therefore only of importance if the accident incidence is high or if accidents may have large effects. CONCLUSIONS: The findings are most relevant to safety-critical activities such as the transport and health sectors. Work periods >8 hours carry an increased risk of accidents that cumulates, so that the increased risk of accidents at around 12 hours is twice the risk at 8 hours. Shift work including nights carries a substantial increased risk of accidents, whereas "pure" night work may bring some protection against this effect due to resynchronization. The evaluated studies give no clear indications of any age or gender being specifically susceptible or protected against the effects of work times scheduling on accident risk. Language: en

Some studies have demonstrated increased risk of different cancers among female nurses. A review of relevant papers was made to assess whether the increase is caused by occupational exposures or other factors. A computerized literature search on combinations of the keywords 'nurses', 'occupation', 'hazards', 'cancer' and 'mortality' and related articles was performed. A total of 30 reports were identified from 19 independent studies conducted between 1983 and 2001. The majority of the studies were registry studies, with limited data on employment history and confounding factors. In conclusion, knowledge about exposures and observed excesses of cancer risk give reason to suspect an occupational influence on breast cancer and leukaemia. The grouping together of nurses from different workplaces may camouflage real differences in risk. Future studies should collect information at the individual level about work history and personal risk factors.

Introduction Some studies have suggested that night work may be associated with an increased risk of breast cancer in nurses. We aimed to explore the role of circadian gene polymorphisms in the susceptibility to night work-related breast cancer risk. Methods We conducted a nested case-control study of Norwegian nurses comprising 563 breast cancer cases and 619 controls within a cohort of 49,402 Norwegian nurses ages 35 to 74 years. We studied 60 single-nucleotide polymorphisms (SNPs) in 17 genes involved in the regulation of the circadian rhythm in cases and controls. The data were analyzed in relation to the two exposure variables "maximum number of consecutive night shifts ever worked" and "maximum number of consecutive night shifts worked for at least 5 years." The odds of breast cancer associated with each SNP was calculated in the main effects analysis and in relation to night shift work. The statistically significant odds ratios were tested for noteworthiness using two Bayesian tests: false positive report probability (FPRP) and Bayesian false discovery probability (BFDP). Results In the main effects analysis, CC carriers of rs4238989 and GG carriers of rs3760138 in the AANAT gene had increased risk of breast cancer, whereas TT carriers of BMAL1 rs2278749 and TT carriers of CLOCK rs3749474 had reduced risk. The associations were found to be noteworthy using both the FPRP and BFDP tests. With regard to the effect of polymorphisms and night work, several significant associations were observed. After applying FPRP and BFDP in women with at least four night shifts, an increased risk of breast cancer was associated with variant alleles of SNPs in the genes AANAT (rs3760138, rs4238989), BMAL1 (rs2290035, rs2278749, rs969485) and ROR-b (rs3750420). In women with three consecutive night shifts, a reduced risk of breast cancer was associated with carriage of variant alleles of SNPs in CLOCK (rs3749474), BMAL1 (rs2278749), BMAL2 (rs2306074), CSNK1E (rs5757037), NPAS2 (rs17024926), ROR-b (rs3903529, rs3750420), MTNR1A (rs131113549) and PER3 (rs1012477). Conclusions Significant and noteworthy associations between several polymorphisms in circadian genes, night work and breast cancer risk were found among nurses who had worked at least three consecutive night shifts.

People living in industrialized societies have developed specific working schedules during the day and at night, including permanent night shifts and rotating night shifts. The aim of this study was to examine the association between circadian polymorphisms and rotating night shift work. This cross-sectional study comprised 709 nurses and midwives (348 current rotating and 361 current day workers). Genetic polymorphism of selected clock genes BMAL1 (rs2279287), CLOCK (rs1801260), PER1 (rs2735611), PER2 (rs2304672), PER3 (rs10462020), CRY1 (rs8192440), CRY2 (rs10838527, rs10838527) was determined using real-time polymerase chain reaction (PCR) assays. There were no differences in BMAL1, CLOCK, CRY2, PER1, PER2, and PER3 genotypes among nurses and midwives working rotating night and day shifts. The frequency of women with rare CRY1 TT genotype was higher in the group of rotating night shift than day workers (17.0% versus 13.9%, P=0.06). Moreover, CRY1 TT genotype was associated with the total rotating shift-work duration, compared to women rarely working night shifts. These results suggest that CRY1 (rs8192440) polymorphism may influence the adaptation to the rotating night shift work among nurses and midwives. This project was supported by a grant from the Polish- Norwegian Research Fund (PNRF 243-AI-1/07) and ECNIS2 (7PR/2011/266198). The authors declare no actual or potential competing financial interests.

Record linkage studies have been used for decades to study occupational diseases and mortality. While low response rates represent an increasing problem in connection with sample surveys, response rates at censuses in the Nordic countries are close to 100%. The linking of census data with data about mortality, emigration and cancer by the unique personal identification numbers, ensures complete information on relevant events. Results from a large census-based Nordic study on cancer incidence by occupation are presented, and advantages and problems related to such type of studies are discussed. In record linkage studies occupational group, socio-economic status or any other characteristic may be used as the exposure indicator. The results of such studies usually must be interpreted in light of established etiologic associations. The two main purposes with record linkage studies are that they may be used as reference material in the general description of cancer incidence and distribution in a population, and that they serve as a basis for generation of hypotheses to be tested in analytical studies with more detailed information.

Objectives To examine the relationship of shift work and breast cancer risk by different exposure metrics of night shift work. Methods A nested case-control study was performed among Norwegian nurses who graduated before 1985. Cases of breast cancer were identified by linking the Norwegian Cancer Registry to the Norwegian Board of Health9s registry of nurses. A total of 699 (74%) of the live cases (diagnosed 1990–2007) and 895 (65%) of the frequency-matched controls, cancer-free at the time of sampling, were interviewed about known and suspected risk factors, including a detailed occupational history. ORs for risk of breast cancer in relation to new and previously used exposure metrics were estimated by multivariate unconditional logistic regression models. Results No increase of risk was found after long duration with ≥ 3 night shifts per month. Non-significantly increased risks were observed for ≥30 years in hospitals or other institutions (OR= 1.1), ≥ 12 years in schedules including night work (OR=1.3), ≥ 1007 night shifts during lifetime (OR= 1.2), lifetime average number of night shifts per month ≥ 4 (OR=1.2), and ≥ 5 years with ≥ 4 and ≥ 5 consecutive night shifts (OR = 1.4 to 1.6). Significantly increased risk was found for ≥ 5 years with ≥ 6 consecutive night shifts (OR=1.8, 95% CI 1.1 to 2.8). Conclusions Breast cancer risk may be related to number of consecutive night shifts.

Objectives 6-sulfatoxymelatonin (MT6s) in the morning urine is a valid biomarker of melatonin synthesis at night. Controlled experimental studies have shown decrease in melatonin synthesis after light exposure at night, however, only few epidemiological studies examined morning MT6s in nurses working rotating night shifts. The aim of our study was to investigate which characteristics of rotating night shift work influence melatonin synthesis. Methods The cross-sectional study included 355 nurses and midwives (aged 40–60) currently working on rotating night shifts. Data on the current job (hospital department, frequency of night shifts, activities, napping) and potential confounders were collected through a personal interview. MT6s concentrations were determined in the morning urine samples after night shift (ELISA assay, adjusted for creatinine). Associations between rotating night shift work characteristics and MT6s were tested in multiple linear regression models. Results The adjusted geometric means (GM) in the rotating night shift nurses and midwives varied depending on the department of employment from GM=32 ng/mg Cr at the neonatology department to GM=72 ng/mg Cr) at the orthopaedics department. Women working 8 or more night shifts per month had significantly lower MT6s than those having on average less night shifts per month (35 ng/mg Cr vs 43 ng/mg Cr respectively). MT6s concentrations were significantly lower in women working for more than 10 h when compared to those working fewer hours (p=0.025). Conclusions Preliminary results of our study indicate that the frequency of night shifts and number of working hours may influence MT6s levels.