Relationship Between Shift Work and Clustering of the Metabolic Syndrome Diagnostic Components

Aim: To examine the relationship between the type of work and the number of metabolic syndrome diagnostic components (MetS-DC), as well as the risk of MetS, with adjustment for lifestyle habits in Japanese workers. Methods: We examined the baseline data from 4,427 participants (81.4% male) aged 19 to 69 years old. The physical activity of each participant was classified according to the International Physical Activity Questionnaire (IPAQ). We defined the four MetS-DC in this study as follows: 1) high blood pressure (BP): systolic BP >= 130 mmHg, or diastolic BP >= 85 mmHg, or the use of antihypertensive drugs; 2) dyslipidemia: high-density lipoprotein-cholesterol concentration < 40 mg/dl or triglyceride concentration >= 150 mg/dl, or on medication for dyslipidemia; 3) dysglycemia: fasting blood sugar level >= 110 mg/dl, or if less than eight hours after meals >= 140 mg/dl, or on medication for diabetes mellitus; 4) overweight: a body mass index >= 25 kg/m(2). We defined MetS as overweight plus two or more of the MetS-DC. Results: There were 3,094 subjects in the daytime work group, 73 in the fixed nighttime work group, 1,017 in the shift work group and 243 in the day-to-night work group. The Poisson regression analysis revealed that fixed nighttime (regression coefficient [b] = -0.233, P=0.028) and shift work (b=0.098, P=0.034) independently contributed to the number of MetS-DC, compared to daytime work. The multivariate logistic analysis not including sleep hours in the model showed that shift work was positively related to MetS (odd ratio = 1.47, P<0.01). Conclusion: Shift work were significantly associated with the number of MetS-DC, and was related to risk of MetS compared to daytime work.