Different exposure metrics of rotating night shift work and hyperhomocysteinaemia among Chinese steelworkers: a cross-sectional study

OBJECTIVE: To examine the associations of rotating night shift work with hyperhomocysteinaemia (HHcy) odds by different exposure metrics. DESIGN: Cross-sectional study. SETTING: Occupational physical examination centre for steel production workers, Tangshan, China. PARTICIPANTS: A total of 6846 steelworkers, aged 22–60 years, from the baseline survey of a Chinese occupational cohort. PRIMARY AND SECONDARY OUTCOME MEASURES: Different exposure metrics of night shift work, including current shift status, duration of night shifts (years), cumulative number of night shifts (nights), cumulative length of night shifts (hours), average frequency of night shifts (nights/month), average length of night shifts (hours/night) and percentage of hours on night shifts, were used to examine the effects of past and current night shift work on HHcy odds. The total homocysteine concentration in the plasma above 15 µmol/L was defined as HHcy. RESULTS: Compared with those who never worked night shifts, current night shift workers had elevated odds of HHcy (OR 1.23, 95% CI 1.06 to 1.44). Considering a person’s lifetime work schedule and compared with individuals who never worked night shifts, duration of night shifts >28 years (OR 1.35, 95% CI 1.12 to 1.61), average frequency of night shifts >7 nights/month (OR 1.25, 95% CI 1.07 to 1.47) and percentage of hours on night shifts >30% (OR 1.23, 95% CI 1.05 to 1.43) were associated with higher HHcy odds. The duration of night shifts >20 years and the average frequency of night shifts >7 nights/month could significantly increase the odds of HHcy regardless of whether the average length of night shifts was greater than 8 hours/night. After stratification by sex, no significant association was found in female workers between different exposure metrics of night shift work and HHcy. CONCLUSIONS: Long duration and high frequency of night shift work are associated with higher HHcy odds among male steelworkers.