Case fatality of myocardial infarction among shift workers.

PURPOSE: Shift work has been associated with an excess risk of cardiovascular disease (CVD) and more specifically myocardial infarction (MI). The majority of the studies that found a positive association between shift work and CVD have been based on incidence data. The results from studies on cardiovascular-related mortality among shift workers have shown little or no elevated mortality associated with shift work. None of the previous studies have analysed short-term mortality (case fatality) after MI. Therefore, we investigated whether shift work is associated with increased case fatality after MI compared with day workers. METHODS: Data on incident cases with first MI were obtained from case-control study conducted in two geographical sites in Sweden (Stockholm Heart Epidemiology Program and Västernorrland Heart Epidemiology Program), including 1,542 cases (1,147 men and 395 women) of MI with complete working time information and 65 years or younger. Case fatality was defined as death within 28 days of onset of MI. Risk estimates were calculated using logistic regression. RESULTS: The crude odds ratios for case fatality among male shift workers were 1.63 [95 % confidence interval (CI) 1.12, 2.38] and 0.56 (95 % CI 0.26, 1.18) for female shift workers compared with day workers. Adjustments for established cardiovascular risk factors such as diabetes type II and socio-economic status did not alter the results. CONCLUSION: Shift work was associated with increased risk of case fatality among male shift workers after the first MI.

Incidence of chronic bronchitis in a cohort of pulp mill workers with repeated gassings to sulphur dioxide and other irritant gases.

BACKGROUND: Occupational exposure to irritants is associated with chronic bronchitis. The aim of this study was to elucidate whether repeated peak exposures with respiratory symptoms, gassings, to sulphur dioxide (SO2) and other irritant gases could increase the risk of chronic bronchitis. METHODS: The study population comprised 3,060 Swedish pulp mill workers (84% males) from a cohort study, who completed a comprehensive questionnaire with items on chronic bronchitis symptoms, smoking habit, occupational history, and specific exposures, including gassings. 2,037 have worked in sulphite mills. Incidence rates and hazard ratios (HRs) for the observation period, 1970-2000, in relation to exposure and the frequency of repeated gassings to SO2 and other irritant gases were calculated. RESULTS: The incidence rate for chronic bronchitis among workers with repeated gassings was 3.5/1,000 person-years compared with 1.5/1,000 person-years among unexposed workers (HR 2.1, 95% confidence interval (CI) 1.4-3.1). The risk was even higher in the subgroup with frequent gassings (HR 3.2, 95% CI 2.0-5.2), particularly among never-smokers (HR 8.7, 95% CI 3.5-22). CONCLUSIONS: Repeated gassings to irritant gases increased the incidence of chronic bronchitis in our study population during and after work in pulp mills, supporting the hypothesis that occupational exposures to irritants negatively affect the airways. These results underscore the importance of preventive actions in this work environment.

Metabolic syndrome - a risk factor for all-cause disability pension: a prospective study based on the Swedish WOLF cohort.

Objective The aim was to study the impact of metabolic syndrome on the risk for disability pension among Swedish employees. Methods A working population-based prospective cohort [Work, Lipids and Fibrinogen (WOLF) cohort, N=10 803], was linked to national registry records of all-cause disability pension for the period 1992-2013. Occupational health service data included 1992-2009 anthropometric measurements, blood samples, and questionnaires. Metabolic syndrome was defined according to International Diabetes Federation criteria, and risk for any all-cause disability pension was analyzed using Cox proportional hazard regression as hazard ratios (HR) with 95% confidence intervals (CI) adjusted for age, sex and other covariates. Results Of the employees, 17.9% (men 21.5%, women 9.7%) met the criteria for metabolic syndrome. The prevalence of all-cause disability pension was 15.2% in men with metabolic syndrome and 7.5% in men without metabolic syndrome; for women, the corresponding results were 23.2% and 12.7%. After adjustment for socio-demographic factors, health behaviors, work-related factors, diabetes, and obesity, the risk for all-cause disability pension among subjects with metabolic syndrome displayed an HR of 1.37 (95% CI 1.18-1.60). Results were similar for men and women. In a subgroup, further adjustment for chronic diseases resulted in an HR of 1.32 (95% CI 1.04-1.68). Conclusion This study demonstrates an increased risk for all-cause disability pension, even after adjustment for other risk factors, among Swedish employees with metabolic syndrome compared to those without at baseline.

Ischemic stroke and shift work.

OBJECTIVES: This study analyzed the potential association between shift work and ischemic stroke. METHODS: The analysis was carried out using a nested case-control study consisting of 138 shift workers and 469 day workers from the register of the Northern Sweden Monitoring of Trends and Determinants in Cardiovascular Diseases (MONICA) study and the Västerbotten Intervention Programme. Logistic regression analysis was used to analyze the risk estimate for day workers in a comparison with shift workers and the risk of ischemic stroke. RESULTS: The crude odds ratio for shift workers' risk of experiencing an ischemic stroke was 1.0 (95% confidence interval 0.6-1.8) for both the men and the women. The risk estimates were consistent despite the introduction of several recognized risk factors for ischemic stroke in the logistic regression models. CONCLUSIONS: In the present study, none of the findings indicated a higher risk of shift workers undergoing an ischemic stroke than day workers.

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

OBJECTIVES: 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). RESULTS: 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). CONCLUSIONS: 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.

Sickness absence and early retirement at two workplaces--effects of organisational intervention in Sweden.

This study sought to compare sickness absence and early retirement at two workplaces in Sweden before and after they had received financial support from the Working Life Fund and implemented vocational rehabilitation activities. Two paper and pulp manufacturing plants were compared and a cohort study was set up. The cohort included everyone born in 1934 or later who was employed in December 1988 (918 employees at Plant A and 1543 at Plant B). For 10 years (1989-98), sick leave and disability pensions were monitored. The periods before and after the intervention (1989-93 and 1994-98, respectively) were compared. Cumulative incidence was calculated for short-, long-term and very long-term sick leave, company pension and early retirement. There was no difference between the plants in terms of the three different outcomes when sick leave was measured before and after the intervention. Sick leave in Period 1 was strongly correlated with an elevated risk of sick leave in Period 2. The cumulative incidence of short-term sick leave decreased from 0.92 (95% CI, 0.91-0.93) in Period 1 to 0.79 (95% CI, 0.77-0.80) in Period 2. For employees in the upper age groups, relative risk for long-term and very long-term sick leave was elevated in both periods. The incidence of early retirement and company pension differed between the companies. We conclude that the size of financial investments in rehabilitation programmes has no significant impact on sickness absence or disability pension, based on a comparison between two paper and pulp manufacturing plants in Sweden during the early 1990s.

Shift workers' mortality scrutinized.

The objective of this article is to reappraise previous published data on the mortality of male shift workers from Taylor and Pocock (1972). Mortality rate ratios were calculated for shift workers, ex-shift workers, and for shift workers plus ex-shift workers, respectively, compared to day workers using the Mantel-Haenszel method. The overall risk for current and former shift workers was 1.05 (95% Confidence Interval: 0.95-1.16). For ex-shift workers the mortality was increased compared to day workers (1.24, 95% Confidence Interval: 1.03-1.51). In the age specific analyses increased mortality was observed in shift workers compared with day workers in the age group of 45-54 yrs (Relative Risk: 1.47, 95% Confidence Interval: 1.12-1.93). We suggest that shift work is associated with increased mortality risk.

Respiratory health among bleachery workers exposed to ozone and chlorine dioxide.

OBJECTIVES: This study investigated the possibility of occupational exposure to ozone increasing the risk of obstructive airway disease among bleachery workers. : Bleachery workers (N = 129) from two Swedish pulp mills using ozone for bleaching were studied together with referents (N = 80) from adjacent paper mills. The pulp mills had previously used chlorine dioxide as the bleaching agent. Testings included spirometry, methacholine challenge testing, and questionnaires. Area samplings showed sporadic ozone levels exceeding 0.9 ppm. RESULTS: There was a greater prevalence of wheezing (25%) among the bleachery workers with a history of gassings (from ozone, chlorine, or sulfur dioxide) than among those without gassings (18%) and among the referents (13%). Among the current smokers the fraction with a slightly increased bronchial responsiveness to methacholine was greater among the bleachery workers reporting gassings than among those that had not been gassed. For the period from 1992 to 1996, when the mills were using ozone, there was an increased incidence rate of wheezing among the workers in the bleachery (incidence rate ratio 2.3, 95% confidence interval 1.6-5.8). CONCLUSIONS: Repeated exposure to irritants increases the risk of asthma-like symptoms. This finding reinforces the view that repeated peak exposures to irritants must be prevented in pulp mills.

Postprandial responses of glucose, insulin and triglycerides: influence of the timing of meal intake during night work.

The objective was to study the postprandial responses of glucose, insulin and triglycerides to meal intake at different clock times during night work. Eleven night shift working nurses participated. Identical test meals were ingested at 19:30, 23:30 and 03:30, and contained 440 kcal/1,860 kJ of energy (33 E% fat, 51 E% carbohydrate, 16 E% protein). The food intake was standardized three days before the first test meal. Blood samples were drawn just before the test meals were ingested and thereafter at 30, 60, 90, 120, 180 and 240 minutes. The postprandial responses were estimated as the total area under the curve (AUC) and significance testing was done using repeated measures ANOVA. The highest insulin level was found after meal intake at 23:30, and the lowest after meal intake 03:30. The glucose response showed the same pattern. The insulin response to food intake in night working nurses is more pronounced in the night compared with morning and evening. The results would have implications for metabolic and cardiovascular disorders in night workers.

Breast cancer among shift workers: results of the WOLF longitudinal cohort study.

OBJECTIVE: The aim of this study was to investigate whether shift work (with or without night work) is associated with increased risk of breast cancer. METHODS: The population consisted of 4036 women. Data were obtained from WOLF (Work, Lipids, and Fibrinogen), a longitudinal cohort study. Information about baseline characteristics was based on questionnaire responses and medical examination. Cancer incidence from baseline to follow-up was obtained from the national cancer registry. Two exposure groups were identified: shift work with and without night work. The group with day work only was used as the reference group in the analysis. Cox regression analysis was used to calculate relative risk. RESULTS: In total, 94 women developed breast cancer during follow-up. The average follow-up time was 12.4 years. The hazard ratio for breast cancer was 1.23 [95% confidence interval (95% CI) 0.70-2.17] for shifts without night work and 2.02 (95% CI 1.03-3.95) for shifts with night work. When including only women <60 years of age, the risk estimates were 1.18 (95% CI 0.67-2.07) for shifts without night work, and 2.15 (95% CI 1.10-4.21) for shifts with night work. CONCLUSIONS: Our results indicate an increased risk for breast cancer among women who work shifts that includes night work.

Metabolic disturbances in male workers with rotating three-shift work. Results of the WOLF study.

OBJECTIVES: The aim of the present study was to investigate the relationship between important metabolic risk factors for coronary heart disease (CHD) and type 2 diabetes in shift workers and day workers. METHODS: Cross-sectional data from a sub-population in the WOLF study consisting of 665 day workers and 659 three-shift workers in two plants were analysed. RESULTS: A higher proportion of shift workers than day workers had high triglyceride levels (> or =1.7 mmol/l), low levels of HDL-cholesterol (<0.9 mmol/l) and abdominal obesity (waist/hip ratio>0.9). The risk of low HDL-cholesterol was doubled in shift workers, (odds ratio (OR): 2.02, 95% confidence interval (95% CI): 1.24-3.28) after being adjusted for age, socio-economic factors, physical activity, current smoking, social support and job strain. High levels of triglycerides were also significantly associated with shift work (OR: 1.40, 95% CI: 1.08-1.83). The OR for abdominal obesity was 1.19, (95% CI: 0.92-1.56). The prevalence of hyperglycaemia (serum glucose > or =7.0 mmol/l) was similar in day and shift workers. No significant interaction was seen between shift work and abdominal obesity with regard to the associations with triglycerides and HDL-cholesterol. CONCLUSIONS: We found a significant association between shift work and lipid disturbances (i.e. low HDL-cholesterol and high triglyceride levels). We did not find any association with hyperglycaemia.