Environmental exposures are increasingly recognized as critical determinants of health, contributing significantly to premature mortality. The adverse health effects of air pollutants, including fine particulate matter (PM) and nitrogen dioxide (NO₂), are well-documented. Additionally, populations with lower socio-economic status face higher mortality rates. This analysis aimed to assess whether social deprivation modify the association between environmental exposures and overall and premature mortality at the national level, potentially exacerbating health inequalities.

We performed a cross-sectional ecological analysis at the municipal level across metropolitan France. Using generalized negative binomial linear models, we evaluated the associations between average concentrations of three air pollutants (NO₂, PM₁₀, PM₂.₅) from 2009 to 2019 and mortality rates for 2018-2019, focusing on overall and premature deaths (<75 and <65 years). The three models incorporated the French Deprivation Index (2015) and included interaction terms between each environmental exposure and social deprivation to assess potential effect modification. Spatial autocorrelation was accounted for with an interaction term between longitude and latitude. Strength of associations are reported as Relative Rates (RR) of one additional standard deviation along with their 95% Confidence Intervals (lower to higher value). All data were sourced from open-access repositories (INERIS, INSEE, CépiDc).

The analysis included 1,044,055 deaths (322,588 before 75 years and 163,773 before 65 years) across 34,172 municipalities. Higher exposure to all three air pollutants (NO₂, PM₁₀, and PM₂.₅) was associated with elevated risk of premature mortality (before 75 years respectively RR = 1.010 (1.006 to 1.015), RR  = 1.019 (1.013 to 1.024), RR = 1.007 (1.001 to 1.013) and before 65 years respectively RR = 1.012 (1.006 to 1.018), RR = 1.020 (1.013 to 1.027), RR = 1.008 (1.000 to 1.016). Associations with overall mortality were observed for NO₂ and PM₁₀ (respectively, RR = 1.012 (1.002 to 1.018), RR = 1.012 (1.008 to 1.016). Higher levels of social deprivation were independently associated to higher mortality, with RR ranging from 1.059 (1.059 to 1.063) for PM2.5 and overall mortality model to 1.167 (1.160 to 1.174) for NO2 and premature mortality (<65 years). Analyses of interactions showed that social deprivation amplified the effects of NO₂ and PM₁₀ on overall mortality and PM₂.₅ on premature mortality (<75 years). No significant interactions were observed for mortality <65 years.

This is the first analysis to assess the interplay between environmental exposures and social deprivation on recent overall and premature mortality in metropolitan France. Our findings confirm established links between air pollution, social deprivation, and mortality while highlighting the modifying effects of social vulnerability on . These results underscore the importance of tailoring interventions to reduce air pollution in socially disadvantaged areas to effectively mitigate health inequalities.