Academic journal article Scandinavian Journal of Work, Environment & Health

The Relationship between Current and Former Shift Work and the Metabolic Syndrome

Academic journal article Scandinavian Journal of Work, Environment & Health

The Relationship between Current and Former Shift Work and the Metabolic Syndrome

Article excerpt

Objective The occurrence of possible health hazards among former shift workers is not well-known. We studied associations of former and current shift work with the metabolic syndrome (MetS).

Methods Participants were 1811 full-time employees of a large airline company (1009 men). Working times were categorized into five groups: day worker [N=297 (the reference group)], former shift worker (N=341), 2-shift worker (N=41 8), night-shift worker (N=283), and in-flight worker (N=472). MetS was measured by the International Diabetes Federation (IDF) criteria and the National Institute of Health Adult Treatment Panel III (NCEP) guideline. The prevalence of the syndrome in the study population was 28.5% and 20.8%, respectively.

Results Among male former shift workers, MetS was more prevalent compared to male day workers [IDF: age-adjusted odds ratio (OR) 2.13, 95% confidence interval (95% CI) 1.35-3.37; NCEP: OR 1.83, 95% CI 1.13-2.96]. Associations did not change after additional adjustments for education, smoking, physical activity, alcohol consumption, and insomnia symptoms (IDF: OR 2.00, 95% CI 1.26-3.19; NCEP: OR 1.67, 95% CI 1.02-2.72). Male 2-shift workers also had an elevated risk of IDF-defined MetS (OR 1.64, 95% CI 1.06-2.55) but the association weakened in the fully adjusted analyses (OR 1 .48, 95% CI 0.93-2.24). Prevalence of the MetS was marginally significantly higher among night-shift work (IDF: OR 1.51, 95% CI 0.95-2.34) and was attenuated further with additional adjustments (OR 1 .37, 95% CI 0.84-2.22). Among women, no significant differences in prevalence of the MetS between day and shift work were observed.

Conclusion Findings of the cross-sectional study suggest that MetS diagnosed by standardized criteria is more prevalent among former male shift workers than current day workers who have never worked in shifts.

Key terms cardiovascular risk factor; epidemiology.

Shift work has become common in our 24/7 society and around 20% of the European employees work in shifts, the corresponding number being, for example in China, as high as 36% (1). Epidemiological studies have repeatedly pointed to an increased risk of major diseases including cardiovascular diseases (CVD) in shift work (2). However, the pathways of the association and the specific groups of workers at risk are not fully understood. Shift work disturbs sleep and our natural biological body rhythms, and it may increase psychosocial stress and predispose to physiological disturbances related to metabolic syndrome (MetS) and CVD (3).

MetS is a clustering of risk factors for CVD such as insulin resistance, hypertension, lipid abnormalities, and central obesity (4). Karlsson and co-workers (5) found that several risk factors of MetS - including obesity, elevated triglycérides, and low levels of high-density lipoprotein (HDL) cholesterol - clustered together more often among shift than day workers. Other studies suggest that the occurrence of MetS as defined by the International National Cholesterol Education Program-Adult Treatment Panel III (NCEP) criteria is higher in rotating shift work (6, 7). However, in the study by Sookoian et al (7), shift work was unrelated to the International Diabetes Federation (IDF)-defined MetS. Recent followup studies have added to our knowledge by showing that rotating shift workers have an elevated risk for developing MetS when IDF or NECP MetS criteria is used as the outcome measure (8-10).

Despite previous reports suggesting that former shift workers and 2-shift workers may have an increased CVD risk (11, 12), previous MetS studies have concentrated on rotating shift work and therefore there is need to assess the risk in diverse shift schedules. In the present study, we separated former shift workers from current day workers and designated in-flight workers, whose work schedules are highly irregular, as a separate study group. Our aims were to study whether (i) the risk of MetS is increased among ex-shift workers, (ii) the previously reported relation between night-shift work and MetS can be repeated among employees of a large airline company (ie, Finnair), (iii) the occurrence of MetS is increased in types of shift work other than night shift, and (iv) there are gender differences in relation between working hours and MetS. …

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