Abstract
The joint association of long-term silica dust exposure and cigarette smoking with mortality has not been well established. To evaluate the joint association of silica dust exposure and cigarette smoking with mortality in a large cohort of workers at mines and factories in China. This cohort study included 44 708 adults who were employed in 20 metal mines and 9 pottery factories in central and southern China for at least 1 year between January 1, 1960, and December 31, 1974. Participants were retrospectively followed up to January 1, 1960, and prospectively followed up to December 31, 2003. Data analysis was conducted from April 5, 2019, to October 26, 2019. Cumulative respirable silica dust exposure was estimated by linking a job-exposure matrix to participants' personal work histories. Cigarette smoking data were collected through participant questionnaires. The main outcome was mortality, with codes from the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) used to categorize diseases associated with mortality. Among 44 708 participants, 38 221 (85.49%) were men, with a mean (SD) age at cohort entrance of 26.9 (8.1) years. A total of 13 700 deaths were observed during 1 534 005 person-years of follow-up, with a median follow-up period of 34.9 years (range, 4.8-43.9 years). Silica exposure was associated with a higher risk of mortality among individuals with all diseases, lung cancer, respiratory tuberculosis, cardiovascular diseases, and diseases of the respiratory system; cigarette smoking was associated with an increased risk of mortality among individuals with all diseases, lung cancer, respiratory tuberculosis, cerebrovascular diseases, and diseases of the respiratory tract. The hazard ratios for the joint association of silica dust exposure and cigarette smoking with mortality were 4.51 (95% CI, 3.23-6.29) for lung cancer, 3.21 (95% CI, 2.53-4.08) for certain infectious and parasitic diseases, 3.93 (95% CI, 2.99-5.15) for respiratory tuberculosis, 6.27 (95% CI, 4.83-8.15) for diseases of the respiratory system, and 12.52 (95% CI, 7.92-19.80) for pneumoconiosis, with a significant additive interaction (P < .001). The proportions of the joint association for the additive interaction of silica dust exposure and cigarette smoking were 21.63% for lung cancer, 42.12% for certain infectious and parasitic diseases, 42.25% for respiratory tuberculosis, 29.55% for diseases of the respiratory system, and 36.46% for pneumoconiosis. These findings suggest that cigarette smoking is associated with an increased risk of mortality in individuals exposed to silica dust. Smoking cessation and the control of silica dust concentrations may be important for reducing the risk of mortality among individuals exposed to silica.
Highlights
Crystalline silica is one of the most common minerals on earth, and exposure to this mineral widely occurs among individuals in a variety of industrial occupations, such as mining, pottery making, sandblasting, rock drilling, tunneling operations, construction, and metal casting.[1]
Silica exposure was associated with a higher risk of mortality among individuals with all diseases, lung cancer, respiratory tuberculosis, cardiovascular diseases, and diseases of the respiratory system; cigarette smoking was associated with an increased risk of mortality among individuals with all diseases, lung cancer, respiratory tuberculosis, cerebrovascular diseases, and diseases of the respiratory tract
The hazard ratios for the joint association of silica dust exposure and cigarette smoking with mortality were 4.51 for lung cancer, 3.21 for certain infectious and parasitic diseases, 3.93 for respiratory tuberculosis, 6.27 for diseases of the respiratory system, and 12.52 for pneumoconiosis, with a significant additive interaction (P < .001)
Summary
Crystalline silica is one of the most common minerals on earth, and exposure to this mineral widely occurs among individuals in a variety of industrial occupations, such as mining, pottery making, sandblasting, rock drilling, tunneling operations, construction, and metal casting.[1]. According to the World Health Organization, approximately 320 million people in China smoke cigarettes, which represents one-third of the total number of individuals who smoke worldwide.[9] Data have indicated that cigarette smoking is associated with mortality in patients with lung cancer,[10] chronic obstructive pulmonary disease,[11] and cardiovascular disease.[12] published studies have reported that the rate of smoking among individuals employed in industrial settings is high compared with that of the general population.[13] A previous study indicated that approximately 62% of individuals who worked in metal mines and pottery factories had a history of smoking.[14] the joint association of silica exposure and cigarette smoking with mortality has not been well assessed to date. We conducted a large cohort study of adults who worked in metal mines and pottery factories to evaluate the independent and joint associations of silica dust exposure and cigarette smoking with mortality
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