Zinc levels in seminal plasma and their correlation with male infertility: A systematic review and meta-analysis

Zinc is an essential trace mineral for the normal functioning of the male reproductive system. Current studies have investigated the relationship between seminal plasma zinc and male infertility but have shown inconsistent results. Hence, we systematically searched PubMed, EMBASE, Science Direct/Elsevier, CNKI and the Cochrane Library for studies that examined the relationship between seminal plasma zinc and male infertility, as well as the effects of zinc supplementation on sperm parameters. Twenty studies were identified, including 2,600 cases and 867 controls. Our meta-analysis results indicated that the seminal plasma zinc concentrations from infertile males were significantly lower than those from normal controls (SMD (standard mean differences) [95% CI] -0.64 [-1.01, -0.28]). Zinc supplementation was found to significantly increase the semen volume, sperm motility and the percentage of normal sperm morphology (SMD [95% CI]: -0.99 [-1.60, -0.38], -1.82 [-2.63, -1.01], and -0.75 [-1.37, -0.14], respectively). The present study showed that the zinc level in the seminal plasma of infertile males was significantly lower than that of normal males. Zinc supplementation could significantly increase the sperm quality of infertile males. However, further studies are needed to better elucidate the correlation between seminal plasma zinc and male infertility.