Seminal plasma selenium concentrations, sperm mtDNAcn, and semen quality: association and mediation analyses among healthy Chinese men

Objective: To investigate the associations of seminal plasma selenium (Se) concentrations with semen quality and to explore the mediating role of sperm mitochondrial DNA copy number (mtDNAcn). Design: Cross-sectional study with repeated measurements. Setting: Hubei Province Human Sperm Bank of China. Population: A total of 1159 healthy men who repeatedly provided 5617 semen samples were included. Main Outcome Measures: Seminal plasma Se concentration and sperm mtDNAcn of healthy men screened as potential sperm donors were determined using inductively coupled plasma mass spectrometry (ICP-MS) and real-time fluorescent quantitative PCR (RT-qPCR), respectively. Methods: Linear mixed-effects models and mediation analyses were performed. Result(s): After adjusting for potential confounders, we observed positive associations of seminal plasma Se concentrations with sperm concentration and total count (both p-Values for trend < 0.001). Volunteers in the highest vs. lowest quartiles of seminal plasma Se concentrations had 70.1% (95% CI: 53.3%, 88.9%) and 59.1% (95% CI: 40.5%, 80.2%) higher sperm concentration and total count, respectively. We also found inverse associations between within-subject pooled seminal plasma Se concentrations and sperm mtDNAcn, and between sperm mtDNAcn and sperm concentration, total count, total motility, and progressive motility (all p-Values for trend < 0.05). Mediation analyses showed that sperm mtDNAcn mediated 19.7% (95% CI: 15.9%, 25.3%) and 23.1% (95% CI: 17.4%, 33.4%) of the associations between within-subject average seminal plasma Se concentrations and sperm concentration and total count, respectively. Conclusions: Seminal plasma Se concentrations were positively associated with sperm concentration and total count, which was partly mediated by sperm mtDNAcn.