Abstract:
In the last decades, the scientific interest in vitamin D has grown since many studies indicated that besides its well-established role in bone metabolism, it could have other important roles in the body, including its effects on immunity, endocrine, cardiovascular, and reproductive function.
The association between vitamin D and reproductive health is quite complex, and includes multiple pathways. Vitamin D affects calcium metabolism and availability of calcium, and its known that calcium promotes steroidogenesis, and development and function of gametes. Vitamin D receptors and enzymes involved in metabolism of vitamin D are distributed through all parts of endocrine system involved in reproduction, including: hypothalamus (which secrets GnRH and CRH, hormones which stimulate pituitary gland); pituitary gland (which secretes LH and FSH, hormones which stimulate gonads, and ACTH, hormone which stimulates adrenals), testes and ovaries (which secret sex hormones and produce gametes); adrenals (which also secret sex hormones, and other steroid hormones which interact with sex hormones); bones (which secret osteocalcin, a hormone which affects production and metabolism of sex hormones); fat tissue, prostate, breasts, placenta and skin (which are involved in metabolism of steroid hormones, particularly sex hormones); liver (which is also involved in metabolism of steroid hormones, but also secrets SHBG, a protein which binds sex hormones and influences their bioavailability to other tissues). Furthermore, vitamin D receptors and metabolizing enzymes are distributed in seminal vesicles and epididymis, prostate, fallopian tubes, uterus (endometrium, myometrium), and trophoblast. In addition, vitamin D influences immune system (has anti-inflammatory effect), has anti-oxidative effect (decreases production of reactive oxygen spices), and decreases insulin resistance, and all those factors (insulin resistance, inflammation and oxidative stress) can negatively influence reproductive function both in men and women.
Numerous studies have shown that defects in levels and metabolism of vitamin D can adversely affect reproductive function. In both men and women with vitamin D insufficiency or deficiency, higher rates of reproductive abnormalities were shown, including infertility, hypogonadism in men, and syndrome of polycystic ovaries (PCOS) in women, lower pregnancy rates, higher pregnancy complications rates (pre-eclampsia, gestational diabetes mellitus, spontaneous pregnancy losses, preterm birth, fetal growth retardation), and worse neonatal development and increased post-partum and post-natal morbidity. Vice versa, data show that correction of vitamin D deficiency by supplementation in such subjects positively affected their reproductive health, leading to improvement in their reproductive function and hormonal status.
