THE ASSOCIATIONS BETWEEN PREVIOUS SHIFT WORK AND THE INCIDENCE OF HYPERTENSION AMONG WORKING ADULTS

Abstract

Evidence suggests that individuals employed in shift work are at increased risk for developing chronic diseases. However, relatively few studies have explored the relationship between shift work and the incidence of hypertension. The purpose of this study was to determine the association between previous shift work duration and incidence of hypertension in a population-based cohort of working adults in Ontario. We used cohort data from the Ontario respondents of the Canadian Community Health Survey (CCHS) for 2001 and 2005. Respondents were included if they were between 35– 65 years, in an employee position, and with no diagnosis of hypertension at cohort inception. Shift work was defined as regular nights or rotational shifts that included night work. Cohort data were linked with the Ontario Health Insurance Plan (OHIP) and the Canadian Institute for Health Information Discharge Abstract (DAD) databases at the Institute of Clinical Evaluative Sciences (ICES) to determine the incidence of hypertension defined as one hospital admission with a hypertension diagnosis, or two physician claims with a hypertension diagnosis within a two-year window. This algorithm has 73% sensitivity and 95% specifity compared to physician recorded diagnoses. The follow-up period was 11 years. The cohort consisted of 15062 adults with 2,377 (19%) classified as shift workers. The incidence of hypertension was 28% (n = 5303). Shift workers compared to non-shift workers were more likely to be male (59% vs 47%) and younger (age < 45 years, 53% vs. 48%). In Cox proportional hazard regression models, adjusting for personal and demographic characteristics, shift work was associated with incident hypertension (HR = 1.1, 95% CI 1.0-1.3). In an age- and sex-stratified analyses, among men < 45 years of age, shift work was associated with incident hypertension (HR = 1.3, 95% CI 1.0-2.0). Among women of any age or men 45 years or older, there was no association between shift work and incident hypertension. Previous shift work duration is associated with the development of hypertension. Age and sex differences in these associations require further exploration. The relationship between shift work and hypertension was most pronounced among men who were less than 45 years of age.