Berndt Karlsson

Is there an association between shift work and having a metabolic syndrome? Results from a population based study of 27 485 people

OBJECTIVES To explore how metabolic risk factors for cardiovascular disease (CVD) differ between shift workers and day workers in a defined population. Shift work has been associated with an increased risk of CVD. Risk factors and causal pathways for this association are only partly known. METHODS A working population of 27 485 people from the Västerbotten intervention program (VIP) has been analysed. Cross sectional data, including blood sampling and questionnaires were collected in a health survey. RESULTS Obesity was more prevalent among shift workers in all age strata of women, but only in two out of four age groups in men. Increased triglycerides (>1.7 mmol/l) were more common among two age groups of shift working women but not among men. Low concentrations of high density lipoprotein (HDL) cholesterol (men<0.9 and women<1.0 mmol/l) were present in the youngest age group of shift workers in both men and women. Impaired glucose tolerance was more often found among 60 year old women shift workers. Obesity and high triglycerides persisted as risk factors in shift working men and women after adjusting for age and socioeconomic factors, with an OR of 1.4 for obesity and 1.1 for high triglyceride concentrations. The relative risks for women working shifts versus days with one, two, and three metabolic variables were 1.06, 1.20, and 1.71, respectively. The corresponding relative risks for men were 0.99, 1.30, and 1.63, respectively. CONCLUSIONS In this study, obesity, high triglycerides, and low concentrations of HDL cholesterol seem to cluster together more often in shift workers than in day workers, which might indicate an association between shift work and the metabolic syndrome.

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.

Incidence of asthma among workers exposed to sulphur dioxide and other irritant gases

The aim of the present study was to investigate whether repeated peak exposure (gassings) to sulphur dioxide (SO2) and other irritant gases increases the risk of new-onset asthma. A questionnaire was sent to 4,112 sulphite workers, of whom 1,919 completed the questionnaire and 396 completed the short-form questionnaire, which was sent out as a last reminder. A sample of 130 nonrespondents completed a telephone interview using the short-form questionnaire. The incidence of adult-onset, physician-diagnosed asthma during employment duration was analysed in relation to exposure to SO2 and gassings giving rise to respiratory symptoms. Incidence rates, as well as incidence rate ratios with 95% confidence interval (CI), were calculated. Further Cox regression models were used allowing assessment of hazard ratios (HR) stratified for sex and adjusted for atopy, smoking habits and age. The incidence rate for asthma among sulphite mill workers reporting gassings of SO2 was 6.2 out of 1,000 person-yrs, compared with 1.9 out of 1,000 person-yrs among subjects unexposed to SO2 and any gassings (HR (95% CI) 4.0 (2.1–7.7)). Among males reporting gassings to SO2, the HR (95% CI) for asthma was 5.8 (2.6–13) compared with unexposed males. In conclusion, repeated peak exposure to sulphur dioxide increased the incidence of asthma during work in sulphite pulp mills, which supports the hypothesis of irritant-induced asthma.

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 (). 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.

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.

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/1860 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.

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

BackgroundOccupational 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.MethodsThe 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.ResultsThe 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).ConclusionsRepeated 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.

Shift work, parental cardiovascular disease and myocardial infarction in males

Background Shift work has been associated with an increased risk of cardiovascular disease (CVD). However, there is a need for more studies to determine whether there is an interaction between shift work and other risk factors of CVD, thereby increasing the risk of CVD in shift workers. Aims To discern whether shift work and parental mortality from myocardial infarction (MI) or sudden cardiac death (SCD) interact to increase the risk of MI in men. Methods A case-control dataset was used to assess interaction between shift work and parental history of CVD, using death from MI or SCD, or death before age 65, on an additive scale. Results were reported as relative excess risk due to interaction, attributable proportion due to interaction (AP) and synergy index (SI). Results There was an interaction between shift work and paternal mortality from MI or SCD, when both factors were present [SI = 2.39; 95% confidence interval (CI) 1.02‒5.6 and AP = 0.4; 95% CI 0.08‒0.73]. Conclusions Paternal mortality from MI or SCD interacts with shift work to increase the risk of MI in men.