Estimation of the benchmark duration of alternating shift work associated with increased total cholesterol levels among male Japanese workers.

Abstract

The aim of this study was to estimate the benchmark doses (BMD) and their 95% lower confidence limits (BMDL) for the threshold number of years of alternating shift work associated with a relative increase in serum total cholesterol level (T-Cho), as an index of lipid metabolism. We conducted a 14-year prospective cohort study among male workers (N=6886) at a Japanese steel company who had received annual health check-ups between 1991 and 2005. The endpoints were either a 20, 25, 30, 35, 40 or 45% increase in T-Cho levels during the observation period, compared to T-Cho at baseline. We investigated the associations between the years of alternating shift work and the relative increases in T-Cho using pooled logistic regression, adjusted for other potential covariates. We estimated the BMDL and BMD for years of alternating shift work among 40-, 50-, or >50-year old subjects using benchmark responses (BMR) of 5 or 10% and parameters for the duration of alternating shift work and other covariates. Assuming a mean age of 44 years among workers in their 40s, the BMDL/BMD for years of alternating shift work with a BMR of 5% were 21.0/28.0 (> or =20%), 21.3/26.1 (> or =25%), 24.1/28.8 (> or =30%), 25.6/29.8 (> or =35%), 27.1/31.5 (> or =40%), and 27.7/32.1 (> or =45%). The threshold number of years of alternating shift work that caused a 5% increase in T-Cho was shown to be > or =21 years among middle-aged workers. Special attention should be paid to influence the process at an earlier stage and not when the risk has already materialized.