The Relationship Between Shift Work and Metabolic Risk Factors: A Systematic Review of Longitudinal Studies

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Context

Although the metabolic health effects of shift work have been extensively studied, a systematic synthesis of the available research is lacking. This review aimed to systematically summarize the available evidence of longitudinal studies linking shift work with metabolic risk factors.

Evidence acquisition

A systematic literature search was performed in 2015. Studies were included if (1) they had a longitudinal design; (2) shift work was studied as the exposure; and (3) the outcome involved a metabolic risk factor, including anthropometric, blood glucose, blood lipid, or blood pressure measures.

Evidence synthesis

Eligible studies were assessed for their methodologic quality in 2015. A best-evidence synthesis was used to draw conclusions per outcome. Thirty-nine articles describing 22 studies were included. Strong evidence was found for a relation between shift work and increased body weight/BMI, risk for overweight, and impaired glucose tolerance. For the remaining outcomes, there was insufficient evidence.

Conclusions

Shift work seems to be associated with body weight gain, risk for overweight, and impaired glucose tolerance. Overall, lack of high–methodologic quality studies and inconsistency in findings led to insufficient evidence in assessing the relation between shift work and other metabolic risk factors. To strengthen the evidence, more high-quality longitudinal studies that provide more information on the shift work schedule (e.g., frequency of night shifts, duration in years) are needed. Further, research to the (mediating) role of lifestyle behaviors in the health effects of shift work is recommended, as this may offer potential for preventive strategies.

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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