The Relationship Between Shift Work and Metabolic Risk Factors: A Systematic Review of Longitudinal Studies
Section snippets
Context
Shift work has become an inevitable part of society. It has been estimated that about one in five workers in Europe perform shift work involving night work.1 There is growing concern that shift work involving chronic disruption of circadian rhythms contributes to the development of negative health effects, including cardiovascular disease (CVD), metabolic disorders, and cancer.2 In recent decades, the association between shift work on health has been extensively studied, with most consistent
Literature Search and Selection
A literature search was performed in 2015 with the help of an experienced librarian. The electronic search was performed in MEDLINE, followed by other electronic databases, including Embase, BIOSIS Previews, and SciSearch. In the search strategy, a frequently applied time frame of the past 20 years was used (1995 through March 2015). The full search strategy used for MEDLINE can be found in the Appendix (available online). In addition to the electronic search, key publications (eight reviews)
Study Selection
Figure 1 shows the flow diagram of the literature search. The electronic search resulted in 367 hits. Of these, the large majority (n=318) was excluded based on reading titles and abstracts, leaving 49 articles describing potentially relevant studies. After a check in key publications, one reference was added. Thus, 50 full-text articles were retrieved and further checked for eligibility. One extra publication was added manually afterwards, resulting in 39 publications describing 22 studies
Discussion
Based on the best-evidence system applied in this review, there was strong evidence for an effect of shift work on body weight gain, the risk of overweight, and impaired glucose tolerance. However, insufficient evidence was found for a relationship between shift work and other metabolic outcomes, including lipid metabolism and blood pressure.
The insufficient evidence was also apparent in previous reviews on this topic. For example, Esquirol and colleagues9 observed mixed results between studies
Conclusions
Shift work seems a risk factor for some, but not all, metabolic risk factors. Overall, a lack of high-quality studies with a longitudinal design and the inconsistency in study findings led to insufficient evidence with respect to the relation between shift work and blood lipids and blood pressure. To strengthen the evidence, more studies of high methodologic quality and a longitudinal nature are needed that provide detailed information on the exposure to shift work.
Acknowledgments
This study was supported by funds of the Ministry of Social Affairs and Employment. The Ministry of Social Affairs and Employment had no role in study design; election, synthesis, and interpretation of data; writing of the report; or the decision to submit the manuscript for publication. The authors report no conflicts of interest.
No financial disclosures were reported by the authors of this paper.
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