A cross-sectional study on the shift work and metabolic syndrome in Japanese male workers

Introduction. Shift work has been reported to be associated with an increase in the metabolic syndrome (MetS). To clarify the association between the type of shift work and the risk of MetS, a cross-sectional field survey was conducted after adjusting for age and lifestyle factors. Methods. The subjects were 3007 Japanese males, aged 34-64 years old, who were employees (1700 day and 1307 shift workers) of a car-manufacturing company. The standard Japanese criteria for the diagnosis of MetS was used. Age, smoking habit, drinking habit, sleeping habit and exercise habit were used as the independent variables. Results. The prevalence of MetS in the day workers, two-shift workers, and three-shift workers were 13.8% (234/1700), 10.7% (120/1125) and 17.6% (32/182), respectively. There was a significant difference in the prevalence between the two-shift workers and the day workers. Estimation of the odds ratios (95% confidence intervals) of age, two-shift work and habitual exercise for MetS were 1.03 (1.01-1.04), 0.77 (0.61-0.98) and 0.64 (0.51-0.81), respectively. Conclusion. Two-shift work was associated with lower risk of MetS, which is not in accordance with past reports. This finding should therefore be re-analysed, including investigation of the job content in each group.