INTRODUCTION: It is hypothesized that air pollutants could be associated with semen parameters. This systematic review and meta-analysis of observational studies was conducted to reach a firm conclusion regarding the possible association between outdoor air pollution and semen parameters among the adult population. METHODS: PubMed, Scopus, and ISI Web of Science were systematically searched using the text keywords and MeSH terms, including "air pollution" and "semen parameters,". The population, Intervention, Comparison, and Outcome (PICO) framework was used as follows: P (Adult men), I (Individuals with the highest exposure to the air pollutants), C (Individuals with the lowest exposure to the air pollutants), O [Semen parameters, including semen volume, total sperm count, sperm concentration, total motility, progressive motility, normal morphology rate, and DNA fragmentation index (DFI)]. The overall effect was presented as a weighted mean difference (WMD) and 95% confidence interval (CI) analyzed via a fixed (inverse-variance) or random (DerSimonian-Laird) weighted model. Low, moderate, and high heterogeneity were defined as I RESULTS: Seventeen studies covering 24,065 participants were enrolled in this systematic review and meta-analysis. Higher exposure to outdoor air pollution was associated with significant decreases in semen volume (WMD: -0.13 mL
95% CI, -0.21 to -0.05
P = 0.001
I CONCLUSION: Based on the results, it can be stated that air pollution can impair sperm parameters. Further prospective cohort studies are needed to illuminate this issue and clarify the underlying mechanisms.