Occupational exposure to respirable crystalline quartz and the risk of incident acute myocardial infarction

We aimed to investigate the association between occupational exposure to respirable crystalline quartz (RCQ) and acute myocardial infarction (AMI) in a Danish register-based cohort (DOC*X Dust, n = 903,415). Through 1976-2017, information on occupation was linked to quantitative exposure estimates of RCQ, obtained from the job-exposure matrix of SYN-JEM. The follow-up period (1996-2018) counted 19,357,326 person-years, where 35,511 first-time AMIs occurred, according to register-based hospital contacts. Incidence rate ratios (IRRs) for AMI based on cumulative, recent, and maximum exposure were computed using Poisson regression adjusted for socio-economic factors, comorbidities, air pollution, and other occupational exposures such as noise, physically demanding work, exposure to diesel exhaust, and job strain. For cumulative exposure, the IRR for AMI in the unadjusted model was highest in the two lowest exposed quartiles (IRR for Q1 = 1.19 (95%CI: 1.13-1.25), IRR for Q2 = 1.12 (95%CI: 1.06, 1.17)). However, in the fully adjusted model, these associations were no longer significant and even inverse for exposed above 25th percentile. The lowest IRR was observed in the highest RCQ exposure quartile (IRR = 0.87, (95%CI: 0.83-0.92)). In general, the RCQ exposure levels in the DOC*X Dust cohort were presumed to be lower than in countries that - contrary to Denmark - have an active mining industry. In conclusion, no increased risk of AMI due to RCQ exposure was observed, but cautious interpretation is warranted because of potential bias from the healthy worker survivor effect.