Abstract

Objectives: The widespread adoption of 24 h continuous operations in a number of industries has resulted in an increase in shift work, which may influence lipid metabolism because of disturbed circadian rhythms, broken sleep and lifestyle problems. The objective of the present study was to assess the effect of shift work on serum total cholesterol as an index of lipid metabolism.

Methods: A 14-year prospective cohort study was conducted in day workers (n = 4079) and alternating shift workers (n = 2807) who received annual health check-ups between 1991 and 2005 in a Japanese steel company. The end-points were either a 20%, 25%, 30%, 35%, 40% or 45% increase in serum total cholesterol during the period of observation, compared with serum total cholesterol at entry to the study. The association between the job schedule type and increase in serum total cholesterol was investigated using multivariate pooled logistic regression analyses. The odds ratios for the effect of shift work were obtained after adjustment for a number of potential confounders.

Results: The significant odds ratios of alternating shift work (and 95% confidence intervals) were: ⩾20%, 1.16 (1.07 to 1.26); ⩾25%, 1.16 (1.05 to 1.28); ⩾35%, 1.23 (1.05 to 1.43); ⩾40%, 1.30 (1.07 to 1.58); and ⩾45%, 1.28 (1.01 to 1.63) for serum total cholesterol.

Conclusion: Generally the odds ratios of alternating shift work tended to be higher for stricter cut-points of relative increase in serum total cholesterol level. Our study in male Japanese workers revealed that alternating shift work adversely affected lipid metabolism.