Role of Zinc (Zn) in Human Reproduction: A Journey from Initial Spermatogenesis to Childbirth

Abstract

Zinc (Zn), the second-most necessary trace element, is abundant in the human body. The human body lacks the capacity to store Zn; hence, the dietary intake of Zn is essential for various functions and metabolism. The uptake of Zn during its transport through the body is important for proper development of the three major accessory sex glands: the testis, epididymis, and prostate. It plays key roles in the initial stages of germ cell development and spermatogenesis, sperm cell development and maturation, ejaculation, liquefaction, the binding of spermatozoa and prostasomes, capacitation, and fertilization. The prostate releases more Zn into the seminal plasma during ejaculation, and it plays a significant role in sperm release and motility. During the maternal, labor, perinatal, and neonatal periods, the part of Zn is vital. The average dietary intake of Zn is in the range of 8-12 mg/day in developing countries during the maternal period. Globally, the dietary intake of Zn varies for pregnant and lactating mothers, but the average Zn intake is in the range of 9.6-11.2 mg/day. The absence of Zn and the consequences of this have been discussed using critical evidence. The events and functions of Zn related to successful fertilization have been summarized in detail. Briefly, our current review emphasizes the role of Zn at each stage of human reproduction, from the spermatogenesis process to childbirth. The role of Zn and its supplementation in in vitro fertilization (IVF) opens opportunities for future studies on reproductive biology.

Keywords: cellular metabolism; human reproduction; male infertility; seminal plasma; zinc.

Figure 1

ZIPs (the zinc-regulated transporters, iron-regulated transporter-like proteins). The role of zinc (Zn) during spermatogenesis at the molecular level. The figure depicts how Zn initiates the transcription of kinase, Zn finger proteins as transcription factors, and the Zn uptake process during spermatogenesis.

Figure 2

Different roles of Zn ions during sperm–ova interactions. Zona pellucida (ZP) hardening occurs through membrane protein changes when the ZP protein acts using the Zn-binding protease. The major functions of zinc in the prevention of polyspermy are depicted in the figure. 1—Zn dependent metalloprotease on zona pellucida for sperm recognition; 2—how Zn efflux results in polyspermy.