Association of sitting time with cardiovascular events among manual and non-manual workers: a prospective cohort study (PURE-China)

Background Prolonged sitting time is associated with an increased risk of cardiovascular disease (CVD) in the general population. However, it is unclear how these risks differ across occupational groups. This study aimed to investigate the association between sitting time and CVD in manual and non-manual workers among Chinese adults. Methods This population-based cohort study recruited 47,931 participants aged 35 to 70 years from 115 communities across 12 provinces in China between 2005 and 2009. Daily sitting time was measured using the International Physical Activity Questionnaire (IPAQ). The main outcome was a major CVD event (defined as cardiovascular death, myocardial infarction, stroke, or heart failure). Information on each participant's occupation was collected using standardized questionnaires and categorized into manual and non-manual occupations according to the Italian National Institute of Statistics 2001 (ISTAT-2001) occupational classification standard. Cox frailty models were used to examine the associations. Results Of 43,256 in the final sample (excluding those with CVD at baseline and missing data), 25,252 (58.4%) were women, and the mean (+/- SD, Standard Deviation) age was 50.6 +/- 9.5 years. During a median follow-up of 11.9 (IQR, Interquartile Range: 9.5-12.6) years, 3,408 major CVD events (899 myocardial infarctions, 2,400 strokes, 240 incident heart failure, and 764 cardiovascular deaths) were documented. Compared with the reference group (< 4 h per day of sitting), the risk of major CVD events was positively associated with increasing sitting time among manual workers (HR, 1.20; 95% CI, 1.05-1.37 for 6-8 h per day; HR, 1.43; 95% CI, 1.12-1.82 for >= 8 h per day), while the risk among non-manual workers was greater for those reporting daily sitting times of more than 8 h (HR, 1.86; 95% CI, 1.18-2.95). Similar trends were observed when CVD mortality and incidence were analysed separately. Conclusions Longer daily sitting time was associated with an increased risk of major CVD in both manual and non-manual occupational groups, and the risk was especially high among non-manual workers. Our findings highlight the importance of including measures to reduce sedentary behaviour within a comprehensive strategy to reduce the burden of cardiovascular disease in China.