Sex/gender in the association between ambient air pollution and cardiovascular mortality: Systematic review and meta-analysis

When assessing the association between air pollution and cardiovascular mortality, it remains unclear whether females or males are more susceptible and whether and to what extent the pre-existing studies have accounted for different sex/gender dimensions. We searched three databases to identify short-term and long-term studies on the association between air pollution and cardiovascular mortality published 2000-2023 to assess their integration of sex/gender. We further evaluated whether sex/gender was a source of heterogeneity within these through a moderator analysis using random effects models. We examined sex/gender differences through random effects pooling of the female-to-male-ratio (FMR) of each study. We identified 106 studies, all of which operationalised sex/gender in binary terms and lacked a sex/gender-theoretical concept. However, the biological and social dimensions of sex/gender were indirectly included in the discussions. Meta-analyses did not identify sex/gender as a source of heterogeneity (e.g. short-term particulate matter with a diameter <10 mu m (PM10): p-value of moderator test= 0.85; long-term: 0.34). The pooled FMR showed no sex/gender differences for short-term associations (1.0[CI: 0.0;0.0] for each air pollutant) and a trend towards higher effect estimates for males than females in long-term studies with a pooled FMR ranging from 0.93 to 0.99. Binary categorisation without conceptualisation does not appear to be sufficient to identify vulnerable sex/gender groups, if any, in the association between air pollution and cardiovascular mortality. Considering the multiple biological and sociocultural dimensions of sex/gender from the very beginning of study planning will help to move beyond speculative discussions and derive meaningful action for prevention and health care.