Shift Work is Associated with an Elevated White Blood Cell Count: A Systematic Review and Meta-Analysis.

The white blood cell (WBC) count increases significantly in reaction to infections and certain chronic diseases. Shift employment increases the risk for chronic low-grade inflammation and the progression of several chronic diseases. The objective of this study was to systematically evaluate the evidence from studies on total and differential WBC counts in shift employees. A literature search was performed in PubMed^®, Web of Science, and Scopus databases using keywords for research published before March 1, 2022. A meta-analysis was conducted for total and differential WBC counts using a random-effects approach. A total of 25 studies covering a sample of 37,708 day and shift employees were included in this review. The studies represented America, Europe, East Asia, and Middle East. A significant increase in the total counts (×10⁹/L) of WBC [mean difference (MD) = 0.43; 95% confidence interval (CI): 0.34-0.52; P < 0.001], lymphocytes (MD = 0.16; 95% CI: 0.02-0.30; P = 0.02), monocytes (MD = 0.04; 95% CI: 0-0.07; P = 0.03), and eosinophils (MD = 0.01; 95% CI: 0-0.01; P = 0.03) was observed in shift workers compared to the day counterparts. However, neutrophils and basophils were not significantly different between the groups. Shift work significantly increases the total and differential blood counts in peripheral circulation. Therefore, total and differential WBC counts represent a relatively inexpensive biomarker for diagnostics and prognostics of diseases in shift workers.