An intersectional approach to understanding systolic blood pressure distribution in a large French study: a MAIHDA analysis

Inequities in systolic blood pressure (SBP), a widely used biomarker, have been shown to be patterned by age, sex, and socioeconomic position, but few studies have investigated how they combine to result in differential SBP risk. This study brings new insights by simultaneously considering sex, age, education, as well as race/ethnicity - a dimension seldom investigated in French health studies- in an intersectional perspective. Using data from the CONSTANCES cohort (2012-2021) in the French general population, we applied intersectionality theory and multilevel analysis of individual heterogeneity and discriminatory accuracy (MAIHDA) to examine SBP levels among 150,739 adults, not under BP lowering treatment, nested within 126 intersectional strata. Our models revealed substantial heterogeneity in SBP across strata, mainly driven by age and sex additive main effects. Older age, male sex, lower education, and Subsaharan African (SSA) and Overseas France (DROMs) groups were associated with increased SBP. SSA and DROMs individuals with fewer years of formal education consistently exhibited among the highest SBP values within each sex-age combination. Although age explained most of the between-strata variance, 25-39-year-old SSA and DROMs with fewer years of formal education displayed higher SBP levels than some 40-59-year-old individuals from other ethnoracial backgrounds, suggesting a premature increase of SBP levels for these strata. Our results show that SBP varies according to socially structured experiences, to the disadvantage of marginalized social groups. They emphasize the need for more intersectionality-grounded research on a wider range of biomarkers, and advocate for a more systematic inclusion of racism as a major axis of oppression in health inequities studies.