Association between exposure to ambient air pollution and semen quality in adults: a meta-analysis

Air pollution has become a global concern and may be hazardous to human reproductive capacity, but the impact of exposure to air pollutants on semen quality remains controversial. We performed the meta-analysis to examine the association between air pollution exposure and semen quality. We searched PubMed, Web of Science Core Collection, and Cochrane Library databases (before December 2019). We selected original epidemiological studies on humans, written and published in English, that provided quantitative information to determine the associations between air pollution and sperm parameters. A random-effects model was used when the pooled effect estimates were found to be heterogeneous (I-2 > 50% or P < 0.05), otherwise, a fixed-effects model was applied. Publication bias was not evaluated for less than 10 included articles. Our meta-analysis showed that the standardised mean differences (SMDs) (95% confidence interval, 95% CI) of sperm concentration, sperm count, and sperm total motility were -0.17 (-0.20, -0.13), -0.05 (-0.08, -0.02), and -0.33 (-0.54, -0.11), respectively. However, exposure to air pollution was not related to sperm progressive motility (SMD = 0.00, 95% CI: -0.13, 0.12). The results indicated that exposure to air pollutants at a higher level was associated with impaired semen quality, including declined sperm concentration, reduced sperm count, and declined total motility. The results suggested that high level of air pollution exposure had a negative effect on semen quality. Improvement of air quality is important for enhancing semen quality.