Abstract: Objective To investigate the effects of exposure to shift work and long working hours on the risk of Metabolic Syndrome (MS) among medical personnel and to explore the interaction between these two occupational factors. Methods Taking medical personnel from a comprehensive tertiary hospital for a study involving questionnaires, physical examinations, and biochemical analyses. Restricted Cubic Spline (RCS) models were utilized to analyze the dose-response relationships between the duration of shift work (in years), weekly working hours, and MS. Multivariable logistic regression models were applied to assess the association of shift work and long working hours with MS. Furthermore, both multiplicative and additive models were established to evaluate the interaction effect between shift work and long working hours on MS. Results A total of 689 medical personnel participated, with a mean age of (34.7±8.7) years and a median work tenure of 10.0 (5.0, 17.0) years; 509 (73.90%) participants were female. Among the participants, 509 (73.9%) engaged in shift work, 535 (77.6%) worked long hours, and 400 (58.1%) were exposed to both conditions. MS was detected in 132 participants, yielding a prevalence rate of 19.2%. The RCS models indicated significant non-linear relationships between both the duration of shift work and weekly working hours and the risk of MS after adjusting for covariates (both P<0.05). The risk of MS was positively associated with the duration of shift work up to 12.5 years, after which the association became negative. The risk of MS increased significantly for weekly work durations of 41-54 hours, with the rate of increase slowing after 55 hours. Binary logistic regression results showed a significantly elevated risk of MS in the groups with 0.1-<12.0 years (OR=5.263, 95% CI: 2.458-11.268) and ≥12.0 years of shift work (OR=3.515, 95% CI: 1.796-6.879). Similarly, an increased risk was observed for those working 41-54 hours/week (OR=2.014, 95% CI: 1.057-3.837) and ≥55 hours/week (OR=4.634, 95% CI: 2.360-9.098). In the interaction models, both a significant multiplicative interaction (OR=1.885, 95% CI: 1.387-2.561) and a significant additive interaction (OR=1.316, 95%CI: 1.158-1.496) were observed between shift work and long working hours on the risk of MS. Conclusion Both shift work and long working hours are associated with an increased risk of Metabolic Syndrome in medical personnel. Moreover, a significant interaction effect exists between these two occupational exposures on the risk of developing MS.

Key words: Metabolic syndrome, Shift work, Long working hours, Restricted cubic spline, Interaction effect