Effect of vitamin D deficiency on metabolic syndrome among Korean shift workers

Abstract

OBJECTIVE: This study aimed to investigate the effect of vitamin D deficiency on metabolic syndrome among shift workers. METHODS: This study included 207 756 workers who underwent a comprehensive health examination at a large South Korean university hospital between 2012 and 2018. We performed multivariate-adjusted logistic regression analysis and analyzed mediation and exposure-mediator interaction. RESULTS: Overall, 5.5% of the participants had metabolic syndrome. Compared to day work, the odds ratios (OR) of metabolic syndrome and vitamin D deficiency (<12 ng/mL) for shift work were 1.14 [95% confidence interval (CI) 1.06–1.22] and 1.63 (95% CI 1.57–1.70), respectively. Among shift workers, the OR of metabolic syndrome for vitamin D levels of 12–20 and <12 ng/mL, compared with a level of ≥20 ng/mL, were 1.36 (95% CI 1.15–1.61) and 1.51 (95% CI 1.26–1.81), respectively. Shift work and vitamin D deficiency showed an additive interaction; the relative excess risks due to interaction, attributable proportion, and synergy index were 0.26 (95% CI 0.08–0.44), 0.17 (95% CI 0.07–0.28), and 2.09 (95% CI 1.23–3.55), respectively. When vitamin D deficiency was treated as a mediator, the direct and total effects of shift work on metabolic syndrome were 1.12 (95% CI 1.04–1.22) and 1.15 (95% CI 1.07–1.25), respectively. The indirect effect was 1.03 (95% CI 1.02–1.04) and accounted for 18% of the total effect. CONCLUSION: Vitamin D is a potential mediator of the impact of shift work on metabolic risk factors.

Keywords

• shift work
• circadian rhythm
• work schedule
• shift worker
• metabolic cardiovascular disease risk
• korea
• metabolic syndrome
• vitamin d
• nutritional deficiency