Socioeconomic Inequalities in the External Exposome in European Cohorts: The EXPANSE Project

Abstract

Socioeconomic inequalities in the exposome have been found to be complex and highly context-specific, but studies have not been conducted in large population-wide cohorts from multiple countries. This study aims to examine the external exposome, encompassing individual and environmental factors influencing health over the life course, and to perform dimension reduction to derive interpretable characterization of the external exposome for multicountry epidemiological studies. Analyzing data from over 25 million individuals across seven European countries including 12 administrative and traditional cohorts, we utilized domain-specific principal component analysis (PCA) to define the external exposome, focusing on air pollution, the built environment, and air temperature. We conducted linear regression to estimate the association between individual- and area-level socioeconomic position and each domain of the external exposome. Consistent exposure patterns were observed within countries, indicating the representativeness of traditional cohorts for air pollution and the built environment. However, cohorts with limited geographical coverage and Southern European countries displayed lower temperature variability, especially in the cold season, compared to Northern European countries and cohorts including a wide range of urban and rural areas. The individual- and area-level socioeconomic determinants (i.e., education, income, and unemployment rate) of the urban exposome exhibited significant variability across the European region, with area-level indicators showing stronger associations than individual variables. While the PCA approach facilitated common interpretations of the external exposome for air pollution and the built environment, it was less effective for air temperature. The diverse socioeconomic determinants suggest regional variations in environmental health inequities, emphasizing the need for targeted interventions across European countries.

Keywords: European cohorts; environmental health equity; external exposome; socioeconomic determinants.

Figure 1

Geographical distribution of the included cohorts.

Figure 2

Exposure distribution by country and exposome domain. Cohorts are ordered from North (top) to South (bottom).

Figure 3

Distribution of PCA loadings by cohort and the external exposome domain. The symbol size is proportional to PC contribution of the exposure variables.

Figure 4

Association between the first PC of each domain of the external exposome and individual- and area-level SEP, by cohort type: administrative cohorts (top panel), adult cohorts (middle panel), and birth cohorts (bottom panel). Coefficient estimates are reported with 95% confidence intervals from the multivariable linear models adjusting for age (except birth cohorts). Estimates on the right side of the vertical dotted line represent a positive association between SEP and the first PC of each external exposome domain (e.g., higher levels of traffic-related pollution, built-up land use, and warm season mean temperature associated with higher SEP).