Long-term exposure to black carbon and mortality in the Danish Nurse Cohort

<bold>Background:</bold> Black carbon (BC) is a particularly toxic component of particulate matter (PM), but current evidence on its health effects remains limited. <bold>Aim:</bold> To address this gap, we examined the association of long-term exposure to black carbon and other air pollutants with all-cause and cause-specific mortality in the Danish Nurse Cohort. <bold>Methods:</bold> We followed 25,966 women from the Danish Nurse Cohort (>44 years), recruited in 1993/1999, until their death or 31 December 2019. We estimated residential annual mean concentrations of BC, PM <2.5 µm (PM2.5), and nitrogen dioxide (NO2) since 1990 using the Danish DEHM/UBM/AirGIS dispersion model. We applied time-varying Cox regression models to estimate the association of three-year running means of air pollutants with all-cause and cause-specific mortality, adjusting for potential individual and area-level confounders. <bold>Results:</bold> Over a mean follow-up of 23 years, 7,242 nurses died in total, with 681 due to respiratory diseases. In fully adjusted models, we did not observe an association between all-cause mortality and BC (hazard ratio [HR]: 1.00 [95% confidence interval, 0.97, 1.02] per interquartile range increase of 0.35 μg/m³), NO2 (HR: 0.98 [0.95, 1.02] per 8.0 μg/m³), or PM2.5 (HR: 0.98 [0.92, 1.05] per 2.5 μg/m³). Associations with respiratory mortality were 1.06 (0.97, 1.15) for BC, 1.05 (0.94, 1.16) for NO2, and 1.13 (0.96, 1.46) for PM2.5. <bold>Conclusions:</bold> We found no association between air pollution and all-cause mortality in nurses in Denmark. However, our findings suggest that long-term exposure to BC, NO2 and PM2.5 may increase the risk of respiratory mortality.