Ozone exposure associates with sperm quality indicators: Sperm telomere length as a potential mediating factor.

Evidence linking O exposure and human semen quality is limited and conflicting and the mechanism underlying the association remains unclear. Therefore, we investigated the associations between ambient O exposure and sperm quality parameters and explored the mediating role of sperm mitochondrial DNA copy number (mtDNAcn) and sperm telomere length (STL) among 1068 potential sperm donors who provided 5002 repeated semen samples over approximately 90 days. We found that every 10 μg/m increase in O exposure was associated with a decrease in STL, sperm concentration, total count, total motile sperm number, and semen volume. However, O exposure was associated with increased total motility and progressive motility. The association for sperm quality parameters was stronger when exposure was measured at spermatogenesis stages I and II. For STL, the strongest association was observed when exposure was measured at spermatogenesis stage II. Additionally, we found that approximately 9% and 8% of the association between O exposure and sperm concentration and count was mediated by STL, respectively. In summary, our findings suggest that O pollution may affect sperm telomere length, eventually leading to reduced semen quality.