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Metabolic disturbances in shift workers
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational Medicine.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

An increased risk for coronary heart disease among shift workers is earlier shown in the epidemiological literature. The aim of this thesis has been to penetrate metabolic disturbances and obesity among shift workers compared to day workers, and to compare if there are differences in total mortality or cause specific mortality of coronary heart disease (CHD), diabetes or ischaemic stroke in between the two groups.

In an intervention study on female nurses (N=11), on night schedules in Umeå hospital, the highest peak value of glucose and insulin after meal ingestion was seen in the late evening (23:30). The post-prandial area under curve (AUC) of glucose and insulin was correspondingly largest after meal ingestion the same clock hour compared to meal ingestion other clock times.

In two different cross-sectional studies Västerbotten Inventory Study (VIP) (N= 27,485) and in a subset of Work, Lipids and Fibrinogen Study (WOLF) (N= 1,324) metabolic differences in between shift and day workers has been evaluated. In both studies have obesity, high triglycerides and low HDL-cholesterol been more prevalent among the shift-working group compared to the day-working group. After adjustments for age and socio-economic factors in the VIP-study obesity and high triglycerides remained as risk factors in shift workers in both men and women. After directly age standardisation, a clustering effect, simultaneously, of two or more metabolic risk factors (obesity, hypertension, and high triglycerides) was seen in both genders among the shift workers compared to the day workers. Correspondingly, in the Wolf study low HDL-cholesterol and high triglycerides remained as significant risk factors after adjustments of confounders as age, socio-economic group, physical activity, current smoking, low social support and high job strain.

In a cohort study from one company (MoDo) with two plants in the pulp and paper industry 2,354 male shift workers and 3,088 male day workers were followed from January 1, 1952 to December 31, 2001 regarding total and cause specific mortality due to CHD, diabetes and ischaemic stroke. Groups of workers defined by different duration of shift exposure were compared with day workers by calculating standardised relative rates (SRR). No increased risk of total mortality was seen among shift workers compared to day workers. Higher duration of shift work was associated with increased risk for CHD, and shift workers with 30 years or more had the highest risk. Diabetes was more common with increasing number of shift year exposure. Compared to day workers shift workers had also an increased risk to die because of ischaemic stroke, with the highest relative difference in the least shift exposed group (< 5 years).

Place, publisher, year, edition, pages
2004. , 55 p.
Series
Umeå University medical dissertations, ISSN 0346-6612
Keyword [en]
shift work, epidemiology, mortality, diabetes, stroke, coronary heart disease, obesity, triglycerides, HDL-cholesterol, insulin, glucose
Research subject
Occupational and Environmental Medicine
Identifiers
URN: urn:nbn:se:umu:diva-242ISBN: 91-7305-643-X (print)OAI: oai:DiVA.org:umu-242DiVA: diva2:142784
Public defence
2004-05-14, Sal B, 9 tr, Tandläkarhögskolan i Umeå, Norrlands Universitetssjukhus, 09:00
Opponent
Available from: 2004-04-20 Created: 2004-04-20 Last updated: 2010-08-02Bibliographically approved
List of papers
1. Postprandial responses of glucose, insulin and triglycerides: influence of the timing of meal intake during night work
Open this publication in new window or tab >>Postprandial responses of glucose, insulin and triglycerides: influence of the timing of meal intake during night work
Show others...
2002 (English)In: Nutrition and health, ISSN 0260-1060, Vol. 16, no 2, 133-141 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:umu:diva-3884 (URN)12102366 (PubMedID)
Available from: 2004-04-20 Created: 2004-04-20 Last updated: 2010-08-02Bibliographically approved
2. Is there an association between shift work and having a metabolic syndrome?: results from a population based study of 27,485 people
Open this publication in new window or tab >>Is there an association between shift work and having a metabolic syndrome?: results from a population based study of 27,485 people
2001 (English)In: Occupational and Environmental Medicine, ISSN 1351-0711, E-ISSN 1470-7926, Vol. 58, no 11, 747-752 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-3885 (URN)10.1136/oem.58.11.747 (DOI)
Available from: 2004-04-20 Created: 2004-04-20 Last updated: 2013-04-02Bibliographically approved
3. Metabolic disturbances in male workers with rotating three-shift work: results of the WOLF study
Open this publication in new window or tab >>Metabolic disturbances in male workers with rotating three-shift work: results of the WOLF study
2003 (English)In: International Archives of Occupational and Environmental Health, ISSN 0340-0131, E-ISSN 1432-1246, Vol. 76, no 6, 424-430 p.Article in journal (Refereed) Published
Abstract [en]

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 (‡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 HDLcholesterol 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 ‡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.

Keyword
shift work, metabolic factors, abdominal, obesity, job strain
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-3886 (URN)10.1007/s00420-003-0440-y (DOI)
Available from: 2004-04-20 Created: 2004-04-20 Last updated: 2013-04-02Bibliographically approved
4. Total mortality and cause-specific mortality of Swedish shift- and dayworkers in the pulp and paper industry in 1952-2001.
Open this publication in new window or tab >>Total mortality and cause-specific mortality of Swedish shift- and dayworkers in the pulp and paper industry in 1952-2001.
Show others...
2005 (English)In: Scandinavian Journal of Work, Environment and Health, ISSN 0355-3140, Vol. 31, no 1, 30-35 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Adolescent, Adult, Age Distribution, Cerebrovascular Accident/*mortality, Child, Cohort Studies, Coronary Disease/*mortality, Diabetes Mellitus/*mortality, Humans, Male, Middle Aged, Occupational Health, Paper, Sweden/epidemiology, Work Schedule Tolerance
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:umu:diva-18085 (URN)15751616 (PubMedID)
Available from: 2007-12-06 Created: 2007-12-06 Last updated: 2010-08-02Bibliographically approved

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