Objectives: The aim of this cohort study was to investigate the effects of shift work on changes in parameters related to metabolic disturbances.
Methods: The study population included 1529 male blue-collar workers, aged 19-49 years at baseline, working in a sash and zipper factory in Japan. The participants were divided into four groups according to the work schedule at baseline, the end point being workers doing fixed daytime work in both years (day-day), workers who changed from shift work to fixed daytime work (shift-day), workers who changed from fixed daytime work to shift work (day-shift), and workers doing shift work in both years (shift-shift). The changes in body mass index (BMI), blood pressure, serum cholesterol, and glycosylated hemoglobin A1c over a period of 10 years were compared among the groups by work schedule.
Results: The age-adjusted mean increase in BMI was 1.03 kg/m(2) for the day-shift workers, and it was significantly larger than that of the day-day workers and shift-day workers. The shift-shift workers showed a significantly larger increase in BMI than the day-day workers. These tendencies remained after adjustment for age and all other confounding factors, such as BMI, smoking, drinking, and leisure-time physical activity at baseline. The increase in total cholesterol tended to be higher among the shift-shift workers and the day-shift workers, but there were no significant differences. Blood pressure and hemoglobin A1c did not differ among the four groups.
Conclusions: Shift work is considered to be a risk factor for excess weight. However, no significant difference in the biomarkers was found between daytime workers and shift workers.