Differential effects of neighborhood ambient PM2.5 exposure and social vulnerability on cancer-related systemic inflammation by race in a large health care system population from 2000 to 2020

Background: The environment can impact cancer risk both directly, such as through the air we breathe, and indirectly, through the neighborhoods we live in. These risk factors often work in concert but can have disparate effects. Methods: To understand how air pollution, as measured by ambient particulate matter 2.5 (PM2.5) levels and neighborhood disadvantage based on a geographically assigned social vulnerability index (SVI), may act together to impact cancer risk, we used 2000–2020 statewide cohort data from a large health system based in metropolitan Detroit, MI, USA (n = 245,438). Systemic inflammation was used as a surrogate indicator of cancer risk among study participants and was measured via the white blood cell count ratios of the neutrophil-to-lymphocyte ratio (NLR) and the neutrophil-to-monocyte ratio (NMR). Results: After adjusting for these and other confounding variables, PM2.5 concentration had a greater positive association with the NMR than with the NLR (Z score = 37.7 vs. 21.8). According to the race-stratified multivariable models, PM2.5 had a greater association with both inflammatory indices in White participants. PM2.5 levels had the strongest positive linear relationship with both the Charlson comorbidity index and the SVI among Black participants. A PM2.5 × SVI interaction term was found to be statistically significant only for White participants, suggesting that these two variables act synergistically to increase systemic inflammation in White participants, whereas in Black participants, there was evidence that the SVI may mediate the effects of PM2.5 exposure on both inflammatory indices. Conclusion: At the population level, neighborhood environmental factors linked with both air pollution and neighborhood disadvantage appear to have an impact on systemic inflammation; however, these factors may act in a disparate fashion according to race.