Shift Work And Hypertension In Steel Workers: A Retrospective Cohort Study

Objectives The retrospective cohort study was conducted in steel workers to estimate the association of shift work and hypertension. Restricted cubic spline was used to estimate the dose-response relation of the beginning age of shift work and duration of shift work and hypertension. We conducted this study to put forward some effective suggestions for the establishment of working hours system in the steel enterprises.Methods The retrospective cohort study was conducted in steel workers who attended annual health examinations in a physical examination center from August 2014 to November 2015. The observation time was from the first worker into the factory in March 1971 to November 2015. The subjects were divided into the shift workers and day workers according to shift work or not when they entered the factory. The baseline information about sociodemographic characteristics, living habits, history of hypertension of personal and family, shift work status and occupational factors exposure were obtained by trained interviewers through face to face survey and extracting the occupational health record, as well as the measurement of blood pressure. Epidata3.1 was employed to built databank and SPSS19.0, SAS9.1.3 were used for statistical analysis.Chi-square test was applied to compare the constitution of age, sex, nation, and other factors between two groups. The relationship between shift work, types of shift work and hypertension was analyzed by chi-square test. The propensity score stratification and multivariable Cox proportion model was applied to analyse the relationship between shift work and hypertension. Cox regression was used to analyze the relationship between hypertension and the combined effect of shift work, high temperature and noise and effect on hypertension after leaving shift work. Restricted cubic spline was employed to estimate the dose response relation between the age of beginning to shift work, shift work duration and hypertension.Results 1 A total of 7314 questionnaires was collected and unqualified 303 questionnaires was deleted, and 7011 workers entered the cohort finally. In total of105269.4 person-years in this study, and the average following-up time was 15.0 personyears. The age was 16 to 42 years old when these workers entered the cohort, and the average age was(22.1±4.0) years old. The length of the time employed was 1 to 43 years,and average length of the time employed was(15.0±9.6) years. The incidence density of hypertension was 16.61‰ among the steel workers. The difference in age, sex, smoking,drinking, family history of hypertension, high temperature and noise exposure status were statistically significant(P<0.05), and there was no significant difference in educational level, nation, marital status, high-salt intake and exercise between two groups.2 The incidence density of hypertension in shift workers was 1.540(95%CI: 1.381-1.719)times that of in day workers. The attributable risk(AR) was 5.43 ‰, attributable risk percent(AR%) was 35.06%, the population attributable risk(PAR) was 3.57‰, the population attributable risk percentage(PAR%) was 21.49%. 3 The risk of hypertension in 4-team /3-shift was 1.601 times(95%CI: 1.433-1.790) that of the day workers. 4Compared with day work, shift work, shift work and high temperature, shift work and noise the risk of hypertension was 1.599(1.309-1.958), 1.922(1.567-2.357) and1.602(1.429-1.831) respectively,(P<0.05). The risk of hypertension in high temperature and noise workers was 1.087(0.853-1.386) and 1.112(0.863-1.432) times that of day workers, however there was no significance difference(P>0.05). 5 A non-linear dose response relation was found between the beginning age of shift work and hypertension(?2=12.30, P < 0.05). 6 A non-linear dose response relation was found between the duration of shift work and hypertension(?2=8.15, P < 0.05), the difference was statistically significant in 15 years. 7 With the extension of the years after leaving shifts the relative risk for hypertension decreased when the duration of shift work was 1 to 10 years, and the same result was found when duration was over 10 years.Conclusions 1 Shift work was an independent risk factor for hypertension. 2 About35.06% of hypertension can attribute to shift work in shift workers. About 21.49% of hypertension can attribute to shift work in steel workers. 3 Less than 15 years shift work duration can reduce the risk of hypertension. 4 With the extension of time leaving shifts,the risk of hypertension decreased.