The Impact of E-Cigarette Use on Male Reproductive Health: A Systematic Review and Meta-Analysis

Abstract

Background: E-cigarette use is increasing worldwide, raising concerns about its potential effects on male reproductive health. However, evidence regarding its association with semen parameters and reproductive hormones remains fragmented across human observational studies and animal experiments. This systematic review aimed to synthesize evidence on the effects of e-cigarette aerosol exposure on male reproductive outcomes. Methods: A systematic review and meta-analysis was conducted using PubMed and Scopus, following the PRISMA reporting guideline. Eligible studies investigated exclusive e-cigarette aerosol exposure in adult men or male animal models and reported objective semen parameters or reproductive outcomes, with appropriate control groups. Six studies met the inclusion criteria, comprising two human observational studies and four in vivo animal experiments. Random-effects meta-analysis was performed using standardized mean differences (SMDs) and 95% confidence intervals (CIs), with statistical heterogeneity assessed using the I² statistic. Narrative synthesis was used when quantitative pooling was not feasible. Results: In animal studies, e-cigarette exposure was associated with increased sperm morphological abnormalities (SMD = 3.99, 95% CI 0.38–7.59; p = 0.03; I² = 86%). Sensitivity analysis excluding one study reduced heterogeneity to 12% and yielded a larger pooled effect (SMD = 5.41, 95% CI 3.22–7.60; p < 0.001). In human studies, e-cigarette users had lower total sperm counts than controls (SMD = −0.33, 95% CI −0.49 to −0.17; p < 0.001; I² = 0%). No statistically significant difference in sperm motility was identified in the available human or animal data. Evidence concerning reproductive hormones and testicular histopathology was limited and heterogeneous. Conclusion: The available evidence suggests an association between e-cigarette exposure and adverse male reproductive outcomes, particularly lower total sperm counts in humans and increased sperm morphological abnormalities in animal models. However, the small number of eligible studies, substantial heterogeneity in the initial animal meta-analysis, and limitations of the human observational evidence preclude definitive causal conclusions. Further well-designed longitudinal human studies and standardized animal experiments are needed to clarify the reproductive effects of e-cigarette exposure.