Background: The association between crystalline silica exposure and risk of heart disease mortality remains less clear.
Methods: We investigated a cohort of 42,572 Chinese workers who were potentially exposed to crystalline silica and followed from 1960 to 2003. Cumulative silica exposure was estimated by linking a job-exposure matrix to each person’s work history. Low-level silica exposure was defined as never having held a job with an exposure higher than 0.1 mg/m3. We estimated hazard ratios (HRs) in exposure–response analyses using Cox proportional hazards model.
Results: We identified 2846 deaths from heart disease during an average of 35 years follow-up. Positive exposure–response trends were observed for cumulative silica exposure associated with mortality from total heart disease (HRs for increasing quartiles of cumulative silica exposure compared with the unexposed group = 0.89, 1.09, 1.32, 2.10; P for linear trend < 0.001) and pulmonary heart disease (0.92, 1.39, 2.47, 5.46; P for linear trend < 0.001). These positive trends remained among workers with both high- and low-level silica exposure. There was also a positive trend for ischemic heart disease among workers with low-level exposure, with quartile HRs of 1.04, 1.13, 1.52, and 1.60 (P for linear trend < 0.001).
Conclusion: Low-level crystalline silica exposure was associated with increased mortality from heart disease, including pulmonary heart disease and ischemic heart disease, whereas high-level exposure mainly increased mortality from pulmonary heart disease. Current permissible exposure limits for crystalline silica in many countries may be insufficient to protect people from deaths due to heart disease.
From the aKey Laboratory of Environment and Health, Ministry of Education & Ministry of Environmental Protection, and State Key Laboratory of Environmental Health (Incubating), Department of Occupational and Environmental Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei,China; bInstitute of Health Surveillance, Analysis and Protection, Hubei Center for Disease Control and Prevention, Wuhan, Hubei, China; cDepartment of Epidemiology and Environmental Health, Rollins School of Public Health, Emory University, Atlanta, GA; and dDepartment of Epidemiology, Harvard School of Public Health, Boston, MA.
Submitted 22 September 2013; accepted 14 February 2014.
Supported by the National Basic Research Program of China (grant number 2011CB503804).
Correspondence: Weihong Chen, 13 Hangkong Road, Wuhan, Hubei 430030, China. E-mail: firstname.lastname@example.org.