Vitamin D in follicular development and oocyte maturation

Abstract

Vitamin D (VD) is a secosteroid hormone synthesized predominantly in the skin upon ultraviolet light exposure, which can also be obtained from dietary sources. In target cells, the bioactive VD binds to specific VD receptor to regulate downstream transcription of genes that are involved in a wide range of cellular processes. There is increasing recognition that the proper physiological levels of VD are critical for optimizing reproductive potential in women. The direct VD action in the ovary was first suggested in the 1980s. Since then, research has attempted to determine the role of VD in follicular development and oocyte maturation in animal models and clinical settings. However, data published to date are inconclusive due to the complexity in VD metabolism and the fact that VD actions are pervasive in regulating physiological functions in various systems, including the reproductive, endocrine and nervous systems that control reproduction. This review summaries in vitro, in vivo, and clinical evidence regarding VD metabolism and signaling in the ovary, as well as VD-regulated or VD-associated ovarian follicular development, steroidogenic function, and oocyte maturation. It is suggested that adequate animal models are needed for well-controlled studies to unravel molecular mechanisms of VD action in the ovary. For clinical studies, follicular development and function may be evaluated more effectively in a relatively homogeneous patient population under a well-controlled experimental design. A comprehensive understanding of VD-regulated folliculogenesis and oogenesis will provide critical insight into the impact of VD in female reproductive health.

Correlation between 25-hydroxy vitamin D levels in women and in vitro fertilization outcomes: A cross-sectional study

“…The female may feel disappointed when only one or two follicles are obtained, but here, more is not necessarily better, because every single mature follicle can release one egg, which in turn can be fertilized later [ 33 , 34 ]. Some studies [ 35 , 36 ] have concluded that the sufficiency of vitamin D is important for follicular development with improved steroidogenic function and egg maturation. However, it is difficult to study the direct effect of vitamin D on the ovary since the functions and actions of vitamin D as an endocrine and paracrine factor are highly context-dependent, as types and developmental stages of follicles as well as vitamin D metabolite forms and doses must be carefully considered during experimental design.…”

“…Regarding the effect of vitamin D on the eggs number and their MR, it must be mentioned that all clinical research aimed at evaluating the effect of vitamin D on the ovaries was conducted on females suffering from fertility problems, and most of these researches were in the context of PCOs [ 35 , 37 ]. As for our study, it aimed to select reproductively healthy females.…”

“…Also, one should not forget that vitamin D is transported to the target cells via binding to a high-affinity carrier protein (VBP), which has heterogeneous polymorphisms between humans with different races, which in turn affects vitamin D binding. Another study [ 35 ] showed that the correlation between vitamin D deficiency and a decrease in the development of follicles, in addition to a decrease in the number of eggs produced, expression of E 2 , and weight of the ovaries. This could explain the increase in the total eggs number in group A of our study, in comparison to group B.…”

Age-related changes in Folliculogenesis and potential modifiers to improve fertility outcomes - A narrative review

“…In target cells, VD binds to specific VD receptors (VDR) to regulate transcription of genes involved in diverse cellular processes, including pro-differentiation, anti-proliferation, pro-apoptosis, immunosuppression, and anti-inflammation roles [ 277 ]. Along with its essential role in bone physiology and health, there is an increasing recognition that VD is critical for normal folliculogenesis and optimizing reproductive potential in women [ 277 , 278 ].…”

Vitamin D Effects on Folliculogenesis via Ovarian Paracrine Factors

“…Finally, it is converted to biologically active 1,25dihydroxy VitD in the kidney. The VitD receptor binds to VitD response element regions in DNA and regulates the transcription of many genes [2]. VitD regulates cellular functions through VitD receptor.…”