Vitamin D and Reproductive health: a critical link of vitamin D deficiency with subfertility

Subfertility is one of the most critical health concerns affecting people and couples globally, with devastating emotional, psychological, and social implications. Emerging research now indicates that vitamin D plays a critical role in reproductive health and affects the gonadal function, fertility, and hormonal level through its regulation of calcium homeostasis, the activity of aromatase, and the control of reproductive hormones. Studies on animal models have shown that vitamin D deficiency causes gonadal insufficiencies, such as low sperm quality, poor folliculogenesis, and hypogonadotropic hypogonadism. Vitamin D supplementation has also been used to improve reproductive outcomes in conditions such as PCOS and endometriosis. In PCOS, vitamin D helps regulate insulin resistance, ovarian function, and inflammation, while in endometriosis, it modulates immune responses and reduces chronic inflammation. This chapter entails a comprehensive discussion about subfertility, the role of vitamin D in female reproduction, and the consequences of deficiency leading to subfertility.