Sex differences in the association between air pollution and obesity: a systematic review and meta-analysis.

Background: Obesity contributes to non-communicable disease burden, and air pollution may promote adiposity, but sex differences are unclear.

Objectives: To quantify sex-specific associations between air pollution and obesity in adults, and to assess modification by sex.

Methods: Following a registered protocol (PROSPERO CRD420251065352), we searched Embase and MEDLINE to 20 June 2025 for observational studies in adults (≥18 years) reporting sex-specific or sex-stratified estimates for ambient pollutants and obesity (BMI, WC, general or abdominal obesity). Risk of bias was assessed using Joanna Briggs Institute (JBI) tools. Effect estimates were standardised to a 10 μg/m3 increment and pooled using random-effects models. Sex differences were summarised as ratio of odds ratios (ROR,OR_female/OR_male) for categorical outcomes and Δβ for continuous outcomes.

Results: We included 28 studies (≈800,000 adults). Sixteen contributed to the meta-analysis, 10 of which were conducted in China. Air pollution was associated with higher odds of general and abdominal obesity in both females and males. For general obesity, pooled associations were slightly stronger in females for O3 (ROR 1.06, 95% CI 1.02 to 1.11) and NO2 (ROR 1.03, 95% CI 1.01 to 1.06). Sex differences for abdominal obesity and continuous outcomes were generally small and imprecise.

Conclusions:
Air pollution was associated with higher adiposity, with broadly similar effects in females and males and modest pollutant- and phenotype-specific differences. For general obesity, females appeared more susceptible to O3 and NO2 exposure than males. Evidence was dominated by studies from China and some pollutant-outcome combinations were based on few studies, underscoring the need for adequately powered sex-stratified analyses and improved exposure and outcome harmonisation.