Is long-term silica dust exposure linked to heart disease deaths as well as lung disease deaths?

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People commonly encounter silica dust in both working and living environments, but its potential long-term health effects across different exposure situations have not been well established.

This observational cohort study followed 74,040 workers who had worked for at least 1 year at 29 metal mines and pottery factories in China between January 1, 1960, and December 31, 1974. Follow-up continued until December 31, 2003, with a median follow-up of 33 years.

The researchers estimated each worker’s cumulative silica dust exposure (CDE) by linking work history to a job-exposure matrix. They calculated standardized mortality ratios for underlying causes of death using Chinese national mortality rates. They used the Cox proportional hazards model to estimate hazard ratios (HRs) for selected causes of death associated with CDE. Population attributable risks were estimated from the prevalence of silica dust exposure among workers and the HRs. The researchers then used the population attributable risk and the national mortality rate to calculate the number of deaths attributable to silica dust exposure among Chinese workers.

During 2,306,428 person-years of follow-up, 19,516 deaths occurred. All-cause mortality was higher among workers exposed to silica dust than among non-exposed workers: 993 versus 551 deaths per 100,000 person-years.

CDE was measured in milligrams/cubic meter-years: the sum of silica dust concentrations multiplied by the years of silica exposure. The researchers found significant positive exposure-response relationships between CDE and mortality from all causes (HR 1.026, 95% confidence interval 1.023–1.029), respiratory diseases (HR 1.069, 95% confidence interval 1.064–1.074), respiratory tuberculosis (HR 1.065, 95% confidence interval 1.059–1.071), and cardiovascular disease (HR 1.031, 95% confidence interval 1.025–1.036).

Even among workers exposed to respirable silica concentrations at or below 0.1 mg/m³, standardized mortality ratios were significantly elevated relative to Chinese national mortality rates: 1.06 for all causes (95% confidence interval 1.01–1.11), 1.65 for ischemic heart disease (1.35–1.99), and 11.01 for pneumoconiosis (7.67–14.95).

After adjustment for potential confounders, including smoking, the researchers estimated that silica dust exposure accounted for 15.2% of all deaths in this study. They also estimated that 4.2% of deaths among Chinese workers, or 231,104 deaths, were attributable to silica dust exposure.

The stated limitations were missing data on dietary patterns and leisure-time physical activity, possible underestimation of silica dust exposure for people who worked at the mines or factories before 1950, and reliance on relatives’ oral reports to establish the cause of death for a small proportion of deaths (4.3%).

The authors concluded that long-term silica dust exposure was associated with substantially increased mortality among Chinese workers. Increased risk was observed not only for deaths from respiratory diseases and lung cancer, but also for deaths from cardiovascular disease.

The abstract also directs readers to an Editors’ Summary later in the article.