Long-Term Exposure to Silica Dust and Risk of Total and Cause-Specific Mortality in Chinese Workers: A Cohort Study

A retro-prospective cohort study by Weihong Chen and colleagues provides new estimates for the risk of total and cause-specific mortality due to long-term silica dust exposure among Chinese workers

Estimated SMRs for underlying cause of death of silica-dust-exposed workers in the cohort (<i>n</i> = 72,248), 1970–2003.

<p>SMRs were estimated based on Chinese national mortality rates (not available before 1970).</p

Annual silica dust concentrations, average of all job titles in different mines/factories in China, 1950–2003.

<p>Annual silica dust concentrations, average of all job titles in different mines/factories in China, 1950–2003.</p

Characteristics of the cohort (<i>n</i> = 74,040) based on CDE, 1960–2003.

<p>Values expressed as mean ± standard deviation, unless otherwise indicated. Percentages may not total 100 due to rounding.</p>a<p>Levels are tertiles of CDE of all the workers with exposure to silica dust: low, 0.01–1.23 mg/m³-y; medium, 1.24–4.46 mg/m³-y; and high, >4.46 mg/m³-y.</p>b<p>Data were available for the sub-cohorts that had been followed through the end of 2003. Smokers were defined as those who had smoked regularly for over 1 y. Smokers who stopped smoking within 1 y before the end of follow-up were defined as current smokers.</p>c<p>These characteristics were calculated among workers exposed to silica dust. Mean silica dust concentration was calculated as CDE divided by duration of silica dust exposure.</p>d<p>These characteristics were calculated among workers diagnosed with pneumoconiosis. Latency of pneumoconiosis was defined as the period between the year of first exposure to dust and the year of first diagnosis of pneumoconiosis.</p><p>NA, not applicable.</p

Estimated HRs for total and cause-specific mortality associated with CDE in the cohort (<i>n</i> = 74,040), 1960–2003.

<p>All Cox proportional hazards models included age as the time variable. Categorical analyses were based on levels of CDE, including unexposed, low, medium, and high; the unexposed level was used as the reference category (low level for pneumoconiosis). In all models, the HRs associated with CDE were adjusted for gender, year of hire (five categories: 1955 or earlier, 1956–1960, 1961–1965, 1966–1970, and 1970 or later), age at hire (continuous), and type of mine/factory (four categories: tungsten, iron/copper, tin, and pottery).</p>a<p>Levels were tertiles of CDE of all the workers with exposure to silica dust: low, 0.01–1.23 mg/m³-y; medium, 1.24–4.46 mg/m³-y; and high, >4.46 mg/m³-y.</p>b<p>Assessed by including the median values of exposure within each category as a continuous variable in the model, including the reference category.</p

Estimated HRs for total and cause-specific mortality associated with a continuous CDE variable in nested case–control samples from workers with detailed data on historical silica exposure and smoking, 1960–2003.

<p>HRs and 95% CIs were derived from penalized spline regression models to examine the nonlinear relation of CDE to mortality. The vertical solid line in each panel represents the 95th percentile of CDE. Dashed lines represent the point estimate of the HR adjusted for duration of follow-up (time-dependent, continuous) and calendar time (time-dependent, continuous); solid lines represent HR further adjusted for smoking (never smoked/ever smoked), with dotted lines indicating the 95% CI; the rug plots along the horizontal axes give the distribution of CDE values. For simplicity of presentation, the reference value of CDE was set to 0 mg/m³-y (0.01 mg/m³-y for pneumoconiosis).</p

Description of the cohort (<i>n</i> = 74,040) based on different types of mine/factory, 1960–2003.

<p>Description of the cohort (<i>n</i> = 74,040) based on different types of mine/factory, 1960–2003.</p