Shift work outside of normal daytime hours increases risk fo
Adults employed in shift work outside of a normal daytime schedule have a greater risk for metabolic syndrome, according to findings published in Nutrition, Metabolism and Cardiovascular Diseases.

Researchers conducted a systematic review and meta-analysis of studies evaluating the association between shift work and metabolic syndrome in the PubMed, Embase and Web of Science electronic databases published up until Dec. 16, 2020. Studies were included if they provided a diagnostic criteria of metabolic syndrome, evaluated the association between shift work and metabolic syndrome, were observational studies, and reported RRs, HRs or ORs with 95% CI or provided sufficient data to calculate them. Shift work was defined as employment in any work schedule that is not a regular daytime schedule. Night shift was defined as working between 9 p.m. and 8 a.m., two-shift work was defined as jobs where shifts took place from 6 to 8 a.m. and 2 to 4 p.m., and three-shift work was defined as work time from 6 to 8 a.m., 2 to 4 p.m. and 9 to 11 p.m.

There were 38 studies included in the review, with 13,542 cases of metabolic syndrome among 112,757 participants (mean age, 43.53 years). There were 20 studies conducted in Asia, 13 in Europe and five in America. Fourteen studies did not distinguish between sexes, whereas 15 analyzed men and nine analyzed women.

In a random-effects model, adults employed in shift work had an increased risk for metabolic syndrome compared with non-shift workers. After adjusting for publication bias, adults in shift work still had an increased risk for metabolic syndrome.

The risk for metabolic syndrome was higher for people employed in two-shift work and three-shift work compared with non-shift work. No publication bias was found for either category. Only one study reported an increased risk for metabolic syndrome with one-shift work.

“Explanations for the connection between shift work and metabolic syndrome include circadian disruption, differences in eating habits and sleep duration and quality, among other factors,” the researchers wrote.

As association between shift work and an increased risk for metabolic syndrome was found for men and women, although heterogeneity was lower for both. A similar pattern was observed in Asian studies and non-Asian studies.

“The present evidence suggests that shift work is significantly associated with metabolic syndrome risk when compared with non-shift work,” the researchers wrote. “Given that metabolic syndrome is a common health problem, and that the practice of shift work is increasing, a new shift work target relating to public health prevention may achieve large benefits at a population level.”