Long-term exposure to black carbon and mortality: A 28-year follow-up of the GAZEL cohort.

Background: The current evidence on health effects of long-term exposure to outdoor airborne black carbon (BC) exposure remains scarce.
Objectives: To examine the association between long-term exposure to BC and mortality in a large population-based French cohort, with 28 years of follow-up.
Methods: Data from the GAZEL cohort were collected between 1989 and 2017. Land use regression model with temporal extrapolation wa used to estimate yearly BC and PM _2.5 exposure at the residential addresses from 1989 until censoring for 19,906 participants. Time-varying Cox models with attained age as time-scale was used to estimate the associations between BC and all-cause and cardiovascular mortality, after adjusting for individual and area-level covariates. To handle confounding by PM _2.5 , we used the residual of BC regressed on PM _2.5 as an alternate exposure variable. For all-cause mortality, we also examined effect modification by sex, smoking status, BMI and fruit/vegetable intake.
Results: The median of 20-year moving average of BC exposure was 2.02 10 ^-5 /m in study population. We found significant associations between BC exposure and all-cause mortality (n = 2357) using both 20-year moving average of BC and residual of BC, with corresponding hazard ratios (HR) of 1.14 (95 %CI: 1.07-1.22) and 1.17 (95 %CI: 1.10-1.24) for an inter-quartile range (IQR) increase (0.86 10 ^-5 /m for BC and 0.57 10 ^-5 /m for residual of BC). We found a similar association between BC and cardiovascular mortality (n = 277) with a HR of 1.15 (95 %CI: 0.95-1.38). The dose-response relationship between BC and all-cause mortality was monotonic but nonlinear with a steeper slope at high BC levels. In addition, the effect of BC was higher among never-smokers and among those having fruit/vegetables less than twice a week.
Conclusions: There was a positive association between long-term exposure to BC and increased mortality risk, reinforcing the emerging evidence that BC is a harmful component of PM _2.5 .
(Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)