{"paper_id":"936f34a5-6a66-4251-9c5a-6f737e3b5ab1","body_text":"Vitamin D and aspects of female fertility\nNick Voulgaris,1 Labrini Papanastasiou,1 George Piaditis,1 Anna Angelousi,2  \nGregory Kaltsas,2 George Mastorakos,3 Eva Kassi4\n1Department of Endocrinology and Diabetes Center, “G. Gennimatas”, General Hospital of Athens, Athens Greece; \n2Endocrine Unit, Department of Pathophysiology, National and Kapodistrian University of Athens, “Laiko” University \nHospital, Athens, Greece; 3Endocrine Unit, 2nd Department of Obstetrics and Gynecology, National and Kapodistrian \nUniversity of Athens, “Aretaieion” University Hospital, Athens, Greece; 4Department of Biological Chemistry, Medical \nSchool, National and Kapodistrian University of Athens, Athens, Greece \nABSTRACT\nThe role of vitamin D in female reproduction has been intensively examined over the last few \ndecades. A large body of evidence suggests that vitamin D might have beneficial effects on \nmetabolic/hormonal parameters of PCOS and endometriosis, while it appears to be associated \nwith IVF outcomes. However, due to the heterogeneity among observational and interventional \nstudies, no cause-effect relationship has yet been established. The aim of this review is to analyze \nrecent in vitro animal and human studies which examined the association of vitamin D with \ndisease entities affecting female fertility potential. Recent research data strongly imply that \nvitamin D is implicated in female reproduction and might represent a beneficial and inexpensive \ntherapeutic approach, in combination with first-line medical treatments, to female infertility.\nKey words: Endometriosis, Female fertility, IVF, PCOS, Vitamin D\nReview\nHORMONES 2017, 16(1):5-21\nAddress for correspondence:\nEva Kassi, MD, Department of Biological Chemistry, Medical \nScholl, National and Kapodistrian University of Athens,  \n75 Mikras Asias Str., P.C. 11527, Goudi, Athens, Greece; \nE-mail: ekassi@med.uoa.gr\nReceived: 07-11-2016, Accepted: 28-02-2017\nINTRODUCTION\nVitamin D is a secosteroid hormone mainly pro-\nduced in the skin after sunlight exposure and is primar-\nily known for its role in bone health and mineraliza-\ntion.1 In the last few years, the extraskeletal actions \nof vitamin D have emerged as a significant area of \nintensive scientific interest. The understanding that \nvitamin D receptor (VDR) and the enzymes required \nfor the production of the active form of vitamin D are \nexpressed in almost all human cells and tissues has \nlinked vitamin D insufficiency/deficiency to many \nchronic diseases such as cancer, autoimmune and \ninfectious diseases as well as cardiovascular diseases \nand diabetes mellitus type 2.1,2 Vitamin D deficiency, \ndefined as serum 25-hydroxyvitamin D levels of \n<20 ng/ml, is estimated to affect about 50% of the \npopulation worldwide.1\nInfertility is a hot topic in the field of public health, \naffecting about 48.5 million couples worldwide3 with \nsignificant psychological, medical and economic \nconsequences. PCOS and endometriosis comprise the \nmain causes of female infertility, with in vitro fertili-\nzation (IVF) offering a solution to this problem. Data \naccruing from studies undertaken either in animals \n\n6 N. VOULGARIS ET AL\nor humans point to a potential role of vitamin D in \nfemale fertility.4 In this context, epidemiological data \nhave demonstrated a seasonality in human reproduc-\ntive capacity, which could be partially explained by \nseasonal variation of vitamin D levels. 5\nThe aim of this review is to critically assess current \nliterature data regarding the role of vitamin D in IVF \nand its association with PCOS and endometriosis.\nMeTHODOlOgy\nWe searched Pubmed for English language pub-\nlications up to February 2017 under the following \nterms: “Vitamin D and female infertility” and “Vi-\ntamin D and female reproduction” and “Vitamin D \nand PCOS” and “Vitamin D and endometriosis”, \n“Vitamin D and granulose cells” and “Vitamin D \nand IVF”. We also used the terms 25-hydroxyvitamin \nD or 25(OH)vitamin D or 1,25-dihydroxyvitaminD \nor 1,25(OH)\n2D3 instead of Vitamin D, and the term \nassisted reproduction technologies (ART) instead of \nIVF. Additionally, we included references on relevant \ntopics from the reviewed articles in order to widen \nour search. Because a comprehensive background \nis a prerequisite for further discussions on vitamin \nD-induced effects, we provide a brief description \nof vitamin D metabolism and mechanism of action.\nVITAMIN D MeTAbOlISM AND MeCHANISM \nOF ACTION\nVitamin D is a steroid hormone well known for \nits role in calcium homeostasis and bone mineraliza-\ntion. It is mainly produced in the skin after sunlight \nexposure. Diet and dietary supplements constitute \nalternative sources of vitamin D for humans. 1 There \nare two distinct forms of vitamin D, that of D2 or ergo-\ncalciferol and D3 or cholecalciferol. Cholecalciferol is \nformed in the human skin from 7-dehydrocholesterol \n(7-DHC), a cholesterol precursor, in the presence of \nultraviolet B radiation (UVB). UVB converts 7-DHC \nto previtamin D 3, which is rapidly isomerized to \nvitamin D3. Ergocalciferol derives from several nu-\ntritional sources including green plants, mushrooms, \nfish fat and cod liver oil. Another source of vitamin D \nis commercially available vitamin D supplements.6,7 \nVitamin D, supplied either by UV irradiation of \nthe skin or from the diet, is biologically inactive and \nrequires two successive hydroxylations in the liver \nand in the kidneys by 25-hydroxylase (CYP27A1) \nand 1a-hydroxylase (CYP27B1) to produce its bio-\nlogically active form, 1,25-dihydroxy-vitamin-D \n[1,25(OH)2D3] or calcitriol, respectively. 1 It should \nbe noted that the vitamin D status of the human body \nis best indicated by the circulating levels of 25(OH)\nVitD due to its longer half-life and higher serum con-\ncentration compared to 1,25(OH)2D3.1 Calcitriol acts \nthrough binding to specific nuclear receptor, VDR, \nwhich upon activation initiates multiple genomic ef-\nfects. Calcitriol may also bind to a plasma membrane \nreceptor mediating several non-genomic effects. 8 \nVDR acts in concert with the retinoid X receptor \n(RXR), forming a heterodimer, as well as with other \ncofactors (repressors or activators) which regulate \nits function. 9 The VDR-RXR heterodimer binds to \nvitamin D responsive elements (VDREs) located in \nthe promoter region of target genes, thus regulating \ntheir transcription.\n8 \nThe main action of vitamin D is the absorption of \ncalcium and phosphate from the gut, this required for \nbone mineralization.1 However, the wide distribution \nof VDR in almost all human tissues and the fact that \n3% of the human genome is regulated by the vitamin \nD endocrine system point to a potential extra-skeletal \nrole of vitamin D in various systems and organs, \namong them reproduction.1,10\nIn vitro studies \nIn animal cells\nVDR is expressed in the reproductive tissues (en-\ndometrium, ovaries and fallopian tubes) of cycling \nmice, especially during the estrous cycle,11 as well as \nin placenta, decidua and the ovaries of pregnant mice.12\nAnimal models have shown that vitamin D induces \novarian steroidogenesis. Vitamin D increased dehy-\ndroepiandrosterone sulfotranserase (SULT2A1) tran-\nscription, an enzyme that mediates sulfo-conjugation \nof endogenous hydroxysteroids.13 Moreover, calcitriol \nsignificantly decreased the expression of the anti-\nMullerian hormone messenger RNA (AMH-mRNA) \nin hen granulosa cell cultures, whereas it increased \nthe FSH receptor gene, indicating a positive role of \nvitamin D in follicular development and selection. 14\n\nVitamin D and female fertility 7   \nIn human cells\nVDR is expressed in human ovarian tissue and \nplacenta.15,16 In terms of ovarian steroidogenesis, hu-\nman ovarian cells stimulated progesterone, estradiol \nand estrone production in the presence of calcitriol.16 \nFurthermore, human granulosa cells cultured with \nvitamin D 3 increased 3β-HSD messenger (mRNA) \nlevels and progesterone release. 17 In line with ani -\nmal models, in vitro experiments in human models \nshowed that vitamin D induces dehydroepiandrosterone \nsulfotranserase (SULT2A1).13 Vitamin D is also as-\nsociated with markers of ovarian reserve, especially \nwith AMH.18 Interestingly, a subsequent study dem-\nonstrated that the human AMH promoter contains a \nfunctional VDRE.\n19 Finally, human granulosa cells \ntreatment with vitamin D 3 resulted in a significant \ndecrease in AMHR-II and FSH receptor mRNA. 17 \nGiven the inhibitory effects of AMH on the develop-\nment of human granulosa cells, the decrease of AMH \nexpression after vitamin D treatment may reflect a \nbeneficial effect of vitamin D in the differentiation \nof these cells.\nIn vitro studies on endometriosis have yielded \nlimited data. One of them showed that treatment of hu-\nman endometriotic stromal cells (ESCs) with calcitriol \nsignificantly suppresses the interleukin(IL)-1β and \ntumor necrosis factor-alpha (TNF-α) induced inflam-\nmatory responses, mainly via reducing IL-8 mRNA \nexpression and prostaglandin activity; viable ESCs \nnumbers were also reduced. These results illustrate \na potential immunomodulatory role of vitamin D in \nthe inflammatory process of endometriosis. 20\nWith regard to IVF, an in vitro study21 investigated \nthe immunomodulatory effect of vitamin D treatment \non cytokine production [IL-6, IL-8, IL-10, transform-\ning growth factor-β (TGF-β)] by endometrial cells \nof women with repeated implantation failure (RIF), \nthe latter defined as three or more unsuccessful ART \ncycles after embryo transfer. 22 Whole endometrial \ncells (WECs) and endometrial stromal cells (ESCs), \nobtained from RIF and normal fertile women, were \ntreated with calcitriol. Endometrial cells from both \nthe RIF group and the fertile group were capable of \nreducing cytokine production after calcitriol treatment, \nparticularly IL-6 which facilitates the implantation \nprocess. On the other hand, WECs from both groups \nand ESCs only from the RIF group increased IL-8 \nand TGF-β production, respectively, which could \nbe beneficial for RIF women. Moreover, calcitriol \ndownregulated the increased amounts of interferon γ \n(IFN-γ) produced by unexplained recurrent spontaneous \nabortion (URSA) women, albeit increasing the secre-\ntion of TGF-β.23 Interestingly, in both studies whole \nand stromal endometrial cells were able to produce \nthe active form of vitamin D, since they express 1a-\nhydroxylase. On the basis of these inconclusive data, \nthe authors could not determine any clear effect of \ncalcitriol on implantation, either positive or not, and \nhighlighted the need for further research.\n21 \nIt has also been shown that in the fetoplacental \nunit, calcitriol affects human chorionic gonadotropin \n(hCG) production by human synctiotrophoblasts24 and \nstimulates estradiol and progesterone synthesis by \nhuman placental cells. 25 Meanwhile, the expression \nof human placental lactogen (hPL) was also reported \nto be regulated by calcitriol. 26 In addition, human \nterm placental trophoblasts were found to express \ncalbindin-D28k (CaBP28k), which belongs to a large \nclass of calcium binding proteins and might be as-\nsociated with calcium transfer or cell development in \nhuman trophoblast.27 Moreover, a recent study showed \na direct and beneficial effect of vitamin D on human \nextravillous trophoblast (EVT) invasion. Given that \nvitamin D deficiency is likely to increase the risk of \npre-eclampsia and fetal growth restriction through \ninadequate EVT invasion, optimal vitamin D status \ncould prevent these complications.28 Finally, human \nendometrial stromal cells cultured with calcitriol \nincreased HOXA10 gene expression, which is crucial \nfor the embryo implantation process. 29\nRecent evidence from in vitro studies conducted in \nhuman and animal cells points to the functional role \nof the vitamin D endocrine system in the physiology \nof female reproduction. However, there are divergent \nresults, possibly attributable to its two forms and \nseveral metabolites, the different concentrations of \nvitamin D used and to species-specific variations. \nMoreover, since various cell types are involved in the \nreproductive machinery and a local system mainly \ndriven by 1a-hydroxylase activity is present in almost \nall of these cells responsible for the concentrations of \nthe active metabolite at the tissue level, any relevant \nexperimental data extracted from in vitro experiments \nmust be interpreted with caution.\n\n8 N. VOULGARIS ET AL\nAnimal studies \nData from animal studies also provide evidence of \na clear role of vitamin D, either direct or indirect, in \nfemale reproductive functions. Diet-induced vitamin \nD deficient female rats demonstrated a reduction in \noverall fertility by 75% compared to vitamin D replete \nones. Vitamin D deficient rat litters had small size \nand impaired neonatal growth. The impaired fertility \nrates were attributed to decreased impregnation and \nto increased number of pregnancy complications. 30\nVDR knockout mice (VDR-/-) \nVDR knockout mice manifested, apart from im-\npaired bone formation and growth retardation, uterine \nhypoplasia and impaired folliculogenesis. Impressively, \nestrogen administration increased uterine weight of \nthe VDR mutant mice, indicating a potential role of \nVDR in estrogen signaling. 31\nMoreover, aromatase activity (the key enzyme in \nestrogen biosynthesis) and CYP19 gene (which encodes \naromatase) expression were decreased in the ovaries \nof VDR null mutant mice (VDR -/-). Biochemically, \nthe VDR-/- mice were hypocalcemic with elevated \nlevels of FSH and LH indicative of hypergonadotropic \nhypogonadism. Calcium supplementation increased \naromatase activity and CYP19 gene expression in the \novary but failed to correct the elevated gonadotropins. \nDespite the above endocrinological abnormalities \nsome VDR-/- mice with normocalcemia were fertile. \nThe authors concluded that vitamin D has a potential \nrole in estrogen biosynthesis through maintenance of \nnormocalcemia and a direct effect on the expression \nof the aromatase gene.32 Interestingly, a study showed \nthat VDR-/- mice fed a high or medium calcium diet \nmaintain 100% fertility.33 \n1-a hydroxylase knockout mice [1a(OH)ase-/-]\n1-a hydroxylase knockout [1α(OH)ase -/-] female \nmice develop infertility with decreased estrogen and \nprogesterone levels, elevated gonadotropins (FSH \nand LH), impaired follicular development, defective \ncorpus luteum formation and uterine hypoplasia.34,35 \nMoreover, similarly to VDR -/- mice, a high calcium \ndiet given to 1α(OH)ase-/- mice improved their fertil-\nity.34 These results indicate that infertility is a second-\nary result of hypocalcemia and not a direct effect of \nvitamin D due to the absence of VDR. However, an \nolder study reported reduced reproductive capacity of \nvitamin D deficient female rats regardless of serum \ncalcium concentration. Vitamin D or calcitriol sup-\nplementation restored fertility, suggesting a direct \nrole of vitamin D on female infertility. 36\nAs concerns endometriosis and animal studies, \nvitamin D treatment of surgically induced endo-\nmetriosis in rat models resulted in regression of the \nendometrial implants.37,38 Moreover, the VDR agonist \nelocalcitrol inhibited the development of endometriosis \nin a mouse model.39\nInteresting results emerged from a recent study on \npregnant vitamin D deficient mice. According to their \nfindings, maternal vitamin D deficiency is highly likely \nto contribute to the exposure of the developing fetus \nto higher glucocorticoid levels; this occurs through a \nreduction of placental 11β-HSD2 (11β-Hydroxysteroid \ndehydrogenase type 2) gene expression coding for the \nenzyme responsible for glucocorticoid inactivation \nwhile inducing the expression of the fetal head gene \nGILZ (glucocorticoid-induced leucine zipper) mainly \nregulated by glucocorticoids. Of note, a high exposure \nto glucocorticoids during this crucial period might be \nassociated with adverse longterm health outcomes \n(mainly cardiometabolic and psychiatric disorders).40\nVitamin D and polycystic ovary syndrome \n(PCOS)\nPolycystic ovary syndrome (PCOS) is the most \ncommon endrocrinopathy and the leading cause of \ninfertility among women of reproductive age.41,42 It is \na syndrome with clinical and biochemical heterogene-\nity which affects about 6-10% of women worldwide. \n(a) Vitamin D and insulin resistance\nAccumulating evidence suggests that vitamin D is \nassociated with various metabolic and reproductive \nfeatures of PCOS and thus may be involved in the \npathogenesis of the syndrome. It is noteworthy that \nhyperinsulinemia and IR have a central role in the \npathogenesis of PCOS, affecting the severity of clini-\ncal features independently of the presence of obesity. \nThe following potential mechanisms linking vitamin \nD with IR have been proposed: (i) vitamin D improves \ninsulin action by upregulating the expression of the \ninsulin receptor and enhancing insulin responsiveness \nfor glucose transport;43 (ii) 1,25(OH)2D3 activates the \n\nVitamin D and female fertility 9   \ntranscription of the VDRE of the human insulin gene \nwhich it has in its promoter;45 (iii) vitamin D regulates \nintracellular and extracellular calcium, which is crucial \nfor insulin-mediated actions in insulin-responsive \ntissues;43 (iv) vitamin D exerts anti-inflammatory \nactions.2,9 However, most PCOS women are either \noverweight or obese. Obesity is associated with lower \n25(OH)VitD levels, mainly due to the sequestration \nof the lipophilic vitamin in adipose tissue as well as \ndue to lower sunlight exposure of obese subjects. \nThese data raise the crucial question: Is vitamin D \ndeficiency an additional risk factor aggravating IR in \nPCOS irrespectively of obesity? The following data \nattempt to address this issue.\n(b) VDR gene polymorphisms and PCOS\nThe role of VDR in the regulation of the human \ngenome has motivated researchers to examine the \ncontribution of the VDR gene polymorphisms in \nmetabolic and endocrine disturbances of PCOS. The \nresults reflect an influence of VDR gene variants in \nPCOS features; however, because they are as yet \ncontroversial, it is difficult to establish a clear as-\nsociation of VDR polymorphisms with the develop-\nment of PCOS.\nVDR ApaI46,47 and BsmI gene47 polymorphisms \nwere associated with an increased risk of PCOS, \nafter adjustment of results for age and body mass \nindex (BMI). By contrast, other studies failed to \nfind any association of these variants with PCOS \nsusceptibility. In a recent case-control study, VDR  \ngene polymorphisms (TaqI, ApaI, BsmI, FokI) were \nnot associated with the classic PCOS phenotype in \nSilesian women.48 An Indian case-control study also \nfailed to show any significant association between \nVDR gene variants and PCOS. However, Cdx2 and \nFokI variants were associated with testosterone levels \nand infertility, respectively.49 The association between \nthe VDR gene rs757343 polymorphism and PCOS \nrisk was examined in two studies, but both failed to \nobserve any link.50,51 \nOne study reported an association of the VDR ApaI \ngene polymorphism with testosterone levels in PCOS \nwomen, whereas VDR Cdx2 variants were associated \nwith insulin sensitivity.52 VDR BsmI and VDR TaqI \ngene polymorphisms were also associated with low \nSHBG levels and elevated LH levels, respectively.\n53 \n(c) Observational studies\nNumerous observational studies investigated the \nassociation of 25(OH)VitD status with metabolic and \nendocrine parameters of PCOS (Table 1). In general, \nPCOS women had lower 25(OH)VitD levels compared \nto healthy controls. Among the PCOS population, \nobese women exhibited lower 25(OH)VitD levels \nthan overweight or lean subjects. \ni) 25(OH)VitD status and metabolic markers\nThe potential effects of PCOS and obesity on PTH, \nvitamin D metabolites and metabolic aspects of the \nsyndrome were investigated in a study of 291 PCOS \nwomen and 109 controls. Serum 25(OH)VitD levels \nwere lower in controls compared to PCOS women, \nwhile increased body weight had a negative effect \non vitamin D status. Moreover, 25(OH)VitD serum \nlevels were inversely correlated with body mass \nindex (BMI), PTH, insulin levels and the homeo-\nstasis model assessment of insulin resistance index \n(HOMA-IR), although these differences were BMI \ndependent.54 Additionally, another study reported that \nPCOS women had higher levels of 25(OH)VitD than \ncontrols, although after adjustment for age and BMI \nthe significance was almost abolished.\n55 In line with \nthe previous results, 25(OH)VitD levels were found \nto be higher in PCOS women than in controls. In the \nlatter study, the quantitative insulin sensitivity check \nindex (QUICKI) was used as a surrogate index of \nIR. Interestingly, PCOS subjects had lower QUICKI \nthan controls at any concentration of 25(OH)VitD.56 \nIn contrast with the aforementioned findings, one \nstudy failed to confirm any difference in 25(OH)VitD \nlevels between PCOS patients (n=37) and the control \n(n=70) group. However, the investigated population \nwere adolescent females and only 13% of them were \nvitamin D sufficient (>30 ng/ml), which could have \nbiased the results.\n57\nOn the other hand, a recent study conducted in \nAustralia showed that vitamin D levels were lower in \noverweight PCOS women than in overweight controls \n(31.6±11.3 versus 46.1±20.0 nmol/L), and this differ-\nence remained significant after adjustment for BMI \nand abdominal visceral fat. The hyperinsulinemic \neuglycemic clamp (HEC), the gold standard for the \nevaluation of insulin sensitivity, was used to evaluate \n\n10 N. VOULGARIS ET AL\nTAble 1. Vitamin D and Polycystic Ovary Syndrome (PCOS) - Observational Studies  \nAuthor Number of \nParticipants\nCountry Main Results 25(OH)VitD Measurement Reference\nPanidis et al 291 PCOS\n109 Controls\nGreece Lower 25(OH)VitD levels in controls\n25(OH)VitD levels inversely correlated with BMI, PTH, insulin levels and HOMA-IR\nRadioimmunoassay 54\nMahmoudi \net al\n85 PCOS\n115 Controls\nIran Higher 25(OH)VitD levels in PCOS \nPositive effect of PCOS on PTH, insulin levels and HOMA-IR\nRadioimmunoassay 55\nNgo et al 27 PCOS\n20 Controls\nAustralia Higher 25(OH)VitD levels in PCOS \nLower QUICKI in PCOS\nRadioimmunoassay 56\nSadhir et al 37 PCOS\n70 Controls\nUSA No significant association between 25(OH)VitD levels between PCOS and control group Liquid chromatography-\ntandem mass spectometry\n57\nJoham et al 42 PCOS\n34 Controls\nAustralia Lower 25(OH)VitD levels in overweight PCOS \nVitamin D and IR association in PCOS women\nChemiluminescence\nImmunoassay \n58\nMuscogiuri \net al\n38 PCOS Italy 25(OH)VitD levels inversely correlated with BMI, WHR and total fat mass. \nLow vitamin D status in PCOS determined by the degree of adiposity. \n25(OH)VitD levels positively correlated with glucose uptake during HEC and with SHBG\nChemiluminescence\nImmunoassay \nRadioimmunoassay\n59\nHahn et al 120 PCOS Germany\n25(OH)VitD levels negatively correlated with BMI, body fat, HOMA-IR, Insulin levels and FAI\n25(OH)VitD levels positively correlated with HDL, SHBG\nRadioimmunoassay 60\nSahin et al 50 PCOS\n40 Controls\nTurkey 25(OH)VitD levels not associated with HOMA-IR in PCOS Chemiflex Immunoassay 61\nGanie et al 122 PCOS\n46 Controls\nIndia No significant association between 25(OH)VitD levels and plasma insulin, HOMA-IR, \nQUICKI in normal BMI PCOS women\nRadioimmunoassay 62\nYildizhan \net al\n100 PCOS Turkey 25(OH)VitD levels inversely correlated with BMI, WHR, HOMA-IR, TG, total testosterone \nand DHEA-S in obese PCOS\nHigh -performance Liquid \nChromatography (HPLC)\n63\nWehr et al 206 PCOS Austria 25(OH)VitD levels positively associated with QUICKI , HDL and SHBG; \n25(OH)VitD levels negatively associated with BMI, WHR, waist circumference, systolic and \ndiastolic blood pressure, fasting and stimulated glucose, fasting insulin, HOMA-IR and TG\nELISA 64\nLi et al 25 PCOS\n27 Controls\nUnited\nKingdom\n25(OH)VitD levels in PCOS negatively correlated with BMI, FAI \n25(OH)VitD levels in PCOS positively correlated with QUICKI, HDL-C, SHBG\nLiquid chromatography-\ntandem mass spectometry \n65\nPatra et al 60 PCOS India 25(OH)VitD levels inversely correlated with HOMA-IR and fasting plasma glucose levels ELISA 66\nMishra et al 44PCOS\n45 Controls\nIndia 25(OH)VitD levels inversely associated with HOMA-IR in PCOS. No significant \nassociation with testosterone, LH/FSH levels\nElectrochemiluminescence \nImmunoassay\n67\nSavastano \net al\n90 PCOS\n40 Controls\nItaly 25(OH)VitD levels inverse associated with BMI, PED/PEA-15, insulin, HOMA-IR, FAI and \nL/A ratio in PCOS\nChemiluminescence\nImmunoassay\n68\nPal et al 540 PCOS USA Vitamin D sufficiency associated with successful ovulation (OV)\nHigher 25(OH)VitD status in women with live-birth following ovulation induction\nRadioimmunoassay 69\nOtt et al 91 PCOS Austria Vitamin D deficiency significant predictive parameter for follicle development and \npregnancy in PCOS women undergoing CC stimulation\nNot determined 70\n25(OH)VitD: 25-hydroxy Vitamin D; CC: clomiphene citrate; FAI: free androgen index; FG: Ferriman-Gallwey; ΗDL: high-density lipoprotein; HEC: hyperinsulinemic–euglycemic clamp; \nHOMA-IR: homeostasis model assessment–insulin resistance; L/A ratio: leptin/adiponectin ratio; PED/PEA15: phosphoprotein enriched in diabetes gene product; QUICKI: quantitative \ninsulin-sensitivity check index; SHBG: sex hormone-binding globulin, TG: triglycerides; WHR: waist to hip ratio.\n\nVitamin D and female fertility 11   \nInterestingly, low 25(OH)VitD levels in PCOS \nwomen was associated with higher levels of an antia-\npoptotic protein, phosphoprotein enriched in diabetes \ngene product (PED/PEA-15).68 This inverse association \ncould account for the dysregulated ovarian apoptosis \nseen in PCOS women. \nA recent retrospective cohort study reported that \nPCOS infertile women with adequate 25(OH)VitD \nlevels (>30 ng/ml) were more likely to achieve ovula-\ntion compared to those with 25(OH)VitD levels <20 \nng/ml. Moreover, women achieving live births had \nhigher 25(OH)VitD levels compared to those failing \nto carry out a live birth. Thus, an adequate 25(OH)\nVitD status could be a determining factor for a suc-\ncessful ovulation and pregnancy outcome for infertile \nPCOS women.69\nFinally, a prospective cohort study assessed repro-\nductive parameters of PCOS and found that 25(OH)\nVitD\n deficiency (<25 nmol/L) was a significant pre-\ndictive parameter for both follicle development and \npregnancy in anovulatory infertile PCOS women who \nunderwent clomiphene citrate (CC) stimulation. 70\nThe heterogeneity of the studies could be explained \nby the variety of methodologies used for the assess-\nment of VitD, the heterogeneity of study populations \n(small study samples, absence of control group) and \nthe lack of adjustement for confounders, such as \nseasonality of 25(OH)VitD.\nIt could be concluded that the existing data converge \ntowards a high prevalence of vitamin D deficiency \namong PCOS women and an inverse association with \ninsulin sensitivity markers. However, the exact inter-\nrelationship between vitamin D status, obesity, IR and \nhyperandrogenism in PCOS still remains unclear and \nwarrants further research. \n(d) Interventional studies and PCOS\nA notable number of interventional studies (Table \n2) explored the therapeutic implications of vitamin D \nin the metabolic and reproductive aspects of PCOS.71-84 \nMeanwhile, recent meta-analyses of supplementa-\ntion studies could not support a therapeutic effect \nof vitamin D treatment on metabolic disorders of \nthe syndrome, 85-87 apart from its positive effect on \nthe reduction of serum triglycerides. 88 In terms of \nhyperandrogenism markers, one meta-analysis con-\nIR. Vitamin D was correlated with IR only in women \nwith PCOS, but not in the non-PCOS group. 58\nThe gold standard technique of HEC was also \nused in a study of 38 PCOS women, 37% of whom \nwere reported to be vitamin D deficient (25(OH)VitD \nlevels <50nmol/L). In this study, 25(OH)VitD levels \nwere inversely correlated with BMI, waist to hip ratio \nand total fat mass but were positively correlated with \nglucose uptake during HEC. Moreover, total fat mass \nof these PCOS subjects, estimated by dual-energy \nX-ray absorptiometry (DEXA), was an independent \npredictor of 25(OH)VitD levels, indicating that low \nvitamin D status in PCOS is determined by the degree \nof adiposity and is unrelated to PCOS. However, the \nabsence of a control group in this study limits its \npotential.59 A high prevalence (67.5%) of vitamin D \ndeficiency [25(OH)VitD <20 ng/ml] was observed \namong 120 PCOS women (lean=32, overweight=18, \nobese=70). Furthermore, vitamin D levels were (i) \nnegatively correlated with BMI, body fat, HOMA-\nIR and insulin levels, and (ii) positively correlated \nwith HDL. In agreement with the previous study, the \ninverse relationship between 25(OH)VitD levels and \nobesity was irrelevant to PCOS.60 Likewise, vitamin \nD status was not correlated with HOMA-IR in normal \nBMI (<25 kg/m2) PCOS women.61,62 Several studies \ndemonstrated an inverse correlation of BMI, body fat \nand HOMA-IR with serum 25(OH)VitD levels. 63-66 \nRecently, a study found an inverse association of \n25(OH)VitD levels with HOMA-IR but not with BMI, \nwhile PCOS subjects exhibited marked dyslipidemia.67\nii) 25(OH)VitD status and hyperandrogenism \nmarkers\nIn a study of 120 PCOS women (median age 28 \nyears), 25(OH)VitD levels were significantly corre-\nlated with free androgen index (FAI) and SHBG but \nnot with testosterone, DHEA-S, androstendione and \nLH/FSH ratio.\n60 In subsequent studies 25(OH)VitD \nlevels were positively associated with SHBG64,65 and \nnegatively associated with FAI.65\nOn the other hand, a study of 100 PCOS women \ndemonstrated that 25(OH)VitD levels were negatively \ncorrelated with testosterone and DHEA-S levels in \nobese PCOS subjects. 63 However, a recent study \nfailed to observe any association between 25(OH)\nVitD levels and hyperandrogenism markers. 67\n\n12 N. VOULGARIS ET AL\ncluded that vitamin D treatment could improve fol-\nlicle development and menstrual cyclicity, especially \nin combination with metformin, 87 whereas the other \nfound no beneficial effect.85\nInterestingly, recent studies indicate new potential \npathways via which vitamin D could be implicated in \nthe pathogenesis of PCOS. More specifically, advanced \nglycation end-products (AGEs) are involved in the \npathological process of PCOS. 89,90 The interaction \nof AGEs with their receptor (AGE-RAGE) induces \npro-inflammatory gene activation resulting in cellular \ndamage.91 These adverse effects are counteracted by \nan extracellular form of RAGE, the soluble receptor \nfor AGEs (sRAGE), which binds to circulating AGEs, \nthereby inhibiting AGE-RAGE interaction. Based on \nthe above data, 16 PCOS women and 35 controls were \ntreated with vitamin D3 for 8 weeks. The improvement \nin vitamin D status of PCOS women was associated \nwith a significant increase in sRAGE, indicating that \nvitamin D could exert anti-inflammatory actions by \nincreasing sRAGE levels. 92 Moreover, serum AMH \nlevels in PCOS patients were reduced, thus vitamin \nD3 supplementation might improve ovary dysfunction \nand folliculogenesis in these women via normaliza-\ntion of AMH levels.\n92\nApart from AGEs, TGF-β dysregulation may pos-\nsibly be im plicated in the pathophysiology of PCOS, \ngiven its role in angiogenesis, fibroblast activation and \ntissue fibrosis, which could explain morphological and \nvascular alterations of PCOS ovaries.93 PCOS women \ndisplay an abnormal increase in TGF-β1 bioavailability, \nwhich is mainly attributed to the decreased levels of \nsoluble endoglin (sENG), a circulating receptor that \nbinds TGF-β1.94,95\nRecently, a study examined possible effects of \nvitamin D administration on TGF-β1 bioavailability \nin vitamin D deficient PCOS women. Vitamin D sup-\nplementation significantly increased serum sENG and \ndecreased TGF-β1 bioavailability (TGF-β1/sENG). \nMoreover, vitamin D replacement decreased serum \ntriglycerides, the Ferriman-Gallwey score and the \nmenstrual interval. Further, the decrease in TGF-β1 \nbioavailability (Δ TGF-β1/sENG ratio) was associ-\nated with an improvement in lipid profile. These \nfindings suggest that vitamin D induced decrease in \nTGF-β1 bioavailability in PCOS subjects might be \na novel mechanism through which vitamin D exerts \nits beneficial effects on certain aspects of PCOS.\n93\nIn conclusion, despite the abundance of existing \nliterature data regarding supplementation studies, their \nresults are inconsistent and no clear conclusion can \nbe drawn about the effect of vitamin D administration \non metabolic and reproductive parameters of PCOS. \nThe aforementioned intervention studies are subject to \nseveral limitations, which partially explain the lack of \napparent concordance. Firstly, some of them include \na small sample size and/or lack randomization and \nallocation concealment, hence increasing the risk of \nselection bias. There is substantial heterogeneity with \nrespect to 25(OH)VitD status of patients at baseline, \nthe methodology used for 25(OH)VitD assessment, \ndosing regimen and intervention formulations, dura-\ntion, use of concomitant therapies, all of which could \ncontribute to the discrepancy of the observed results. \nFurthermore, these studies were conducted in different \ncountries and at different seasons, factors which could \nalso influence the results. In fact, lack of adjustment \nfor confounders such as the seasonality of 25(OH)\nVitD or even the existence of residual confounders \nare significant shortcomings in the studies conducted. \nThe use of a single baseline vitamin D measurement \nwhich may not reflect longterm vitamin D status could \nalso affect the validity of the interventional studies.96 \nMoreover, the ultrasound criteria of diagnosis of \nPCOS and of the definition of ovulatory cycles varies \namong studies this also conducing to the low quality \nof many of them.\nVitamin D and endometriosis\nEndometriosis is a common benign inflammatory \ndisorder that affects 5 to 10% of women of reproduc-\ntive age, the main clinical features including pelvic \npain, dysmenorrhea, dyspareunia and infertility. 97 \nThe pathogenesis of endometriosis has not been well \nestablished, but it seems that an altered immune and \ninflammatory response enables the survival of endo-\nmetrial implants.97\nThe association between vitamin D and endome-\ntriosis is based on the following findings: 1) the human \nendometrium expresses VDR and 1a-hydroxylase, \nthus it could be a possible site of extrarenal syn-\nthesis and action of vitamin D; 98 2) vitamin D has \nimmunomodulatory effects; macrophages, dendritic \n\nVitamin D and female fertility 13   \nTAble 2. Vitamin D and PCOS – Interventional Studies.\nAuthor Study \nDesign\nParticipants Country Intervention Duration Main Results 25(OH)D \nMeasurement\nReference\nThys-Jacobs \net al\nSingle \nArm\n13 PCOS USA 1500mg calcium carbonate \ndaily and 50.000 IU Vitamin D\n2 \n(ergocalciferol) weekly or biweekly\n6 months Restoration of menstrual cycles (7/13), \nimprovement of acne (3/13) and \npregnancy outcome (2/13)\nRadioligand-binding \nassay\n71\nRashidi et al RCT 60 PCOS\n3 groups\n(n=20)\nIran group 1: 1000mg calcium and 400 \nIU Vitamin D per day\ngroup 2: 1000mg calcium and \n400 IU Vitamin D and 1500mg \nmetformin per day\ngroup 3: 1500mg metformin per \nday\n3 months \ntreatment  \nand  \n3 months  \nfollow up\nImprovement of folliculogenesis  \nand menstrual regularity in Group 2\nNot provided 72\nFirouzabadi \net al\nRCT 100 PCOS \n2 groups\n(n=50)\nIran group 1: 1500mg metformin per \nday\ngroup 2: 1500mg metformin/\nday plus 1000mg calcium/day plus \n100.000 IU Vitamin D\n3/month\n6 months Improvement of menstrual \nabnormalities, follicle development and \ninfertility in Group 2 (non-statistically \nsignificant)\nRIA 73\nAsadi et al RCT 110 PCOS \n2 groups\n(n=55)\nIran group 1: 300.000 IU \ncholecalciferol once\ngroup 2: Placebo\n2 months\nEndometrial thickness (thicker) in Group 1\nNo significant difference in pregnancy \noutcome between the two groups\nNot provided 74\nWehr et al Single \narm\n46 PCOS Austria 20.000 IU cholecalciferol per week 24 weeks\nDecrease of fasting and stimulated glucose, \nC-peptide levels, TG, estradiol levels\nImprovement of menstrual frequency \n(50%)\nIncrease of total clolesterol and LDL\nEnzyme \nimmunoassay\n75\nSelimoglu \net al \nSingle \narm\n11 PCOS Turkey 300.000 IU Vitamin D\n3 orally, \nsingle dose\n3 weeks Decrease in HOMA-IR\nNo significant change in DHEAS, total \nand free testosterone, androstendione\nRIA 76\nPal et al Single \narm\n12 PCOS USA Vitamin D\n3 2000 IU daily and \nVitamin D2 50.000 IU monthly \n(modified to 50.000 IU weekly) \nand calcium 530mg/day\n3 months Reduction in total testosterone and \nandrostendione levels\nReduction in BP\nNo change in IR parameters \nRIA 77\nRazavi et al RCT 60 PCOS\n2 groups\n(n=30)\nIran group 1: Vitamin D 200 IU, \nVitamin K 90 μg, Calcium 500mg \ntwice a day\ngroup 2: Placebo\n8 weeks Reduction in serum free testosterone, \nDHEAS in Group 1\nELISA 78\nKotsa et al Single \narm\n15 PCOS Greece 1 μg alphacalcidol/day 3 months Increase in first phase insulin secretion\nIncrease in HDL and decrease in TG\nRIA 79\nAMH: anti-Mullerian hormone; APO-A1: apolipoprotein A1; BP: blood pressure; DHEAS: dehydroepiandrosterone sulfate; FG: Ferriman-Gallwey score; HDL: high-density \nlipoprotein; HOMA-IR: homeostasis model assessment–insulin resistance; IR: insulin resistance; LDL: low-density lipoprotein; PCOS: polycystic ovary syndrome; PTH: para-\nthyroid hormone; QUICKI: quantitative insulin-sensitivity check index; RCT: randomized control trial; RIA: radioimmunoassay; sENG: soluble endoglin; sRAGE: soluble form \nof receptor for advanced glycation end-products; TG: triglycerides; TGF-β1: transforming growth factor beta 1; VLDL; very low-density lipoprotein.\n\n14 N. VOULGARIS ET AL\nArdabili et al RCT 50 PCOS \n2 groups\n(n1=24, n2=26)\nIran group 1: 50.000 IU Vitamin D 3/20 \ndays\ngroup 2: Placebo orally \n2 months Reduction in TG, total cholesterol, \nVLDL, PTH in Group 1\nNo change in HOMA-IR, QUICKI, \ninsulin levels\nNo change in HDL-C, LDL-C, Apo-A1\nChemoluminescence \nImmunoassay\n80\n82\nRaja-Khan \net al\nRCT 28PCOS\n(n\n1=13, n2=15)\nUSA group1: 12.000 Vitamin D3/day\ngroup2: \n12 weeks No change in HOMA-IR, QUICKI, \ninsulin levels\nRIA 81\nAsemi et al RCT 104 PCOS\n4 groups \n(n=26)\nIran group 1: 1000 mg/day calcium \nplus Vitamin D placebo\ngroup 2: 50.00 IU/week Vitamin \nD plus calcium placebo\ngroup 3: 1000mg calcium/d plus \n50.000 IU/week Vitamin D\ngroup 4: calcium placebo plus \nVitamin D placebo\n8 weeks Decrease in insulin levels, HOMA-IR, \nTG, VLDL and increase in QUICKI in \nGroup 3\nELISA 83\nGarg et al RCT 32 PCOS\n2 groups \n(n\n1=15, n2=17)\nIndia group 1: Metformin (500mg ×2 \nfor weeks and 500mg ×3 for 6 \nweeks) plus Vitamin D\n3 (120.000 \nIU once monthly)\ngroup 2: Metformin (500mg ×2 \nfor weeks and 500mg ×3 for 6 \nweeks) plus placebo\n6 months No significant difference in HOMA-IR \nand insulin secretion\nChemiluminescence\nImmunoassay\n84\nIrani et al RCT 16 PCOS\n35 Controls \nUSA 50.000 IU of Vitamin D\n3 orally \nonce weekly\n8 weeks Increase in serum sRAGE levels and \ndecrease in serum AMH levels in PCOS\nImmunoassay 92\nIrani et al RCT 68 PCOS 2 \ngroups\n(n1=45, n2=23)\nUSA group 1: 50.000 IU Vitamin D 3 \norally once weekly\ngroup 2: Placebo\n8 weeks Increase in serum sENG and decrease in \nTGF-β1 bioavailability (TGF-β1/sENG \nratio) in Group 1\nDecrease in FG score, TG, menstrual \ninterval in Group1\nImmunoassay 93\nAMH: anti-Mullerian hormone; APO-A1: apolipoprotein A1; BP: blood pressure; DHEAS: dehydroepiandrosterone sulfate; FG: Ferriman-Gallwey score; HDL: high-density \nlipoprotein; HOMA-IR: homeostasis model assessment–insulin resistance; IR: insulin resistance; LDL: low-density lipoprotein; PCOS: polycystic ovary syndrome; PTH: para-\nthyroid hormone; QUICKI: quantitative insulin-sensitivity check index; RCT: randomized control trial; RIA: radioimmunoassay; sENG: soluble endoglin; sRAGE: soluble form \nof receptor for advanced glycation end-products; TG: triglycerides; TGF-β1: transforming growth factor beta 1; VLDL; very low-density lipoprotein.\nTAble 2. Vitamin D and PCOS – INTERVENTIONAL STUDIES.\nAuthor Study \nDesign\nParticipants Country Intervention Duration Main Results 25(OH)D \nMeasurement\nReference\n\nVitamin D and female fertility 15   \ncells and lymphocytes express the VDR, while the \nactive metabolite of vitamin D, 1,25(OH) 2D3 acting \nthrough the VDR was found to induce the destruction \nof microbial agents and to inhibit antigen presentation \nand maturation of dendritic cells. Moreover, vitamin \nD exerts antiproliferative effects on lymphocytes, \nespecially on Th1 cells, promoting a shift from Th1 \nto Th2 phenotype.\n1,2,9\nData linking vitamin D and endometriosis emerge \nmainly from observational studies and show conflicting \nresults. Several studies failed to note any difference \nbetween serum 25(OH)VitD levels in patients with \nendometriosis and healthy subjects. 99,100 However, \nVDR and 1a-hydroxylase expression was higher in \nthe endometrium and ovaries of women with endo-\nmetriosis compared to healthy subjects, although \nthis difference was statistically significant only for \n1a-hydroxylase, implying a higher local production \nof the active metabolite calcitriol and/or an increased \naction of vitamin D.100\nOn the other hand, recently published data show \nan inverse relationship between vitamin D level and \nendometriosis, as women with greater 25(OH)VitD \nlevel had a 24% lower risk of developing endometrio-\nsis than women with lower levels. 101 What is more, \nin this large prospective cohort study the researchers \nfound that higher consumption of dairy foods was \nassociated with a lower risk of endometriosis. Simi-\nlarly, a Japanese study reported lower 25(OH)VitD \nlevels in women with severe endometriosis compared \nto controls and women with mild endometriosis. 20 \nRecently, an observational study found a high rate \nof hypovitaminosis D [25(OH)VitD serum level <30 \nng/ml] in a cohort of 49 women with a single ovarian \nendometrioma.102\nIn contrast, significantly higher levels of 25(OH)\nVitD were observed in the serum of women with endo-\nmetriosis compared to healthy individuals (24.9±14.8 \nng/ml vs 20.4±11.8 ng/ml).103\nAdditionally, VDBP in serum, peritoneal fluid (PF) \nand urine was examined as a possible biomarker of \nendometriosis. A study using proteomic technologies \nfor VDBP analysis demonstrated its presence in the PF \nof women with endometriosis, whereas one vitamin D \nbinding protein (DBP) isoform (DBPE) was expressed \nto a lower degree in the PF of women with untreated \nendometriosis compared to the control group. 104 \nHowever, another study found no difference be-\ntween serum and peritoneal fluid levels of VDBP of \nwomen with endometriosis compared to the control \ngroup.105 VDBP levels were also evaluated in urine \nsamples of women with endometriosis and found to \nbe significantly higher in women with endometriosis, \nalbeit the sensitivity (58%) and specificity (76%) of \nthis method limits its diagnostic value.106 Moreover, it \nhas been shown that VDBP expression is significantly \nhigher in ectopic endometrial tissue in comparison \nwith the normal endometrium, suggesting a plausible \nlocal role of VDBP in the progression of the disease.107\nFinally, in a cross-sectional study, VDBP was \nincreased in all samples of women suffering from \nendometriosis compared to the control group.108 Inter-\nestingly, a subsequent analysis of the samples identi-\nfied a specific allele of VDBP (GC*2) to be about \n3-fold higher in all endometriosis groups than in the \ncontrol group. This specific VDBP polymorphism \n(high expression of GC*2) could be responsible for \nan insufficient activation of macrophages leading \nto an altered immune response, which enables the \ndevelopment of endometriosis. 108 The role of VDR \ngene polymorphisms (ApaI, TaqI, FokI, BmsI) in the \npathogenesis of endometriosis and infertility associated \nwith the disease has been studied but no association \nhas been identified.\n109\nTaken together, these data may indicate a plausible \nimplication of vitamin D in the pathogenesis of en-\ndometriosis through exerting an autocrine/paracrine \nrole in the endometrial microenvironment; however, \nfurther research is needed to determine whether vitamin \nD supplementation could have a role as an adjuvant \ntherapy in the treatment of endometriosis or is merely \na confounding factor.\nVitamin D and in vitro fertilization (IVF) \nThe implication of Vitamin D in the outcome of \nART (clinical pregnancy and live birth) has been \nexamined in numerous studies. Nevertheless, the data \nare inconsistent and a clear role of vitamin D in the \nsuccess of IVF outcome remains elusive.\nIn the first experimental attempt to link vitamin D \nstatus with IVF outcome, vitamin D sufficient women \nundergoing IVF had higher pregnancy and implan-\n\n16 N. VOULGARIS ET AL\ntation rates compared with the vitamin D deficient \nwomen.110 The beneficial impact of high vitamin D \nstatus on IVF outcome could be attributed to the ef-\nfects of vitamin D on the endometrium, since vitamin \nD status was not significantly associated with ovarian \nresponse parameters. \nIn line with the previous study, a retrospective-\ncohort study found a positive relationship between \nvitamin D status and IVF success only in non-Hispanic \nwhites compared to Asians, indicating that the role of \nvitamin D in IVF should be evaluated in relation to \nethnic origin. Furthermore, it was also hypothesized \nthat the positive effects of vitamin D on ART outcome \nmay be mediated through endometrial pathways. 111\nIn order to test this hypothesis, a subsequent study \ninvestigated the influences of vitamin D status on ART \noutcomes in donor-recipient cycles.112 Egg-donation \nrecipients with non-replete vitamin D status [25(OH)\nVitD <30 ng/ml] had reduced clinical pregnancy and \nlive birth rates. Moreover, no correlation between \nrecipient vitamin D status and ovarian stimulation \nparameters, fertilization rates, embryo quality or the \nnumber of embryos transferred was noted, suggesting \nthat vitamin D appears to exert its effects on fertility \nvia the endometrium. However, donor characteristics \nwere not included in the latter study, which could \nconfound these results. \nThe majority of the following studies demonstrated \na positive relationship between higher vitamin D status \nand IVF outcome.113-115 Recent data imply that vitamin \nD deficiency (<20 ng/ml) compromises pregnancy \nachievement in women undergoing Day 5 (blastocyst \nstage) single embryo transfer (SET). The lower clinical \npregnancy rates were attributed to a harmful effect of \nvitamin D deficiency on endometrial receptivity. 116 \nConversely, a prospective observational study found \nthat elevated follicular fluid (FF) 25(OH)VitD levels \nin combination with decreased FF glucose levels were \nassociated with poorer embryo quality and negative \nIVF outcome, indicating a potential negative role of \nvitamin D at the oocyte level.\n117 However, the above \nobservation is in contrast to the detrimental effects of \nvitamin D deficiency on the endometrium reported \nin previous studies.110-112,116 Additionally, two Iranian \nstudies118,119 failed to demonstrate any significant as-\nsociation between serum or FF vitamin D levels and \nimplantation or pregnancy rates. However, the high \nprevalence of vitamin D deficiency in the examined \npopulation limits the strength of their research. \nFurthermore, vitamin D status was not associated \nwith clinical pregnancy rates of women undergoing \neuploid embryo transfer, 120 frozen-thawed embryo \ntransfer121 and clinical pregnancy rates among oocyte \nrecipients.122 An interventional trial examined poten-\ntial effects of vitamin D insufficiency treatment on \nfertility outcomes regarding frozen-thawed embryo \ntransfer cycles but did not show any association.\n123 \nFinally, a recent meta-analysis failed to document \nany correlation between vitamin D deficiency and \npregnancy rates in women undergoing IVF. 124 The \nheterogeneity among the aforementioned studies \nand their contradictory results highlight the need for \nfurther research so as to clarify the exact association \nof vitamin D status and IVF success.\nVitamin D status and female fertility\nEndocrine Task Force guidelines define vitamin \nD deficiency as a 25(OH)VitD level of <20 ng/ml, \nvitamin D insufficiency as a 25(OH)VitD level of \n21-29 ng/ml and vitamin D sufficiency as a 25(OH)\nVitD level of ≥30 ng/ml.125 The Institute of Medicine \nCommittee defines vitamin D deficiency at a level \nbelow 20 ng/ml. 126 These definitions however are \nrelated only to skeletal health and an optimal level \nof vitamin D levels for its non-skeletal actions has \nnot been established. Of interest, according to the \nEndocrine Society Task Force, vitamin D2 or vitamin \nD3 are the suggested treatment options for vitamin D \ndeficiency. On the other hand, literature data indicate \nthat vitamin D3 is more effective in increasing 25(OH)\nVitD levels than vitamin D2.127-130 Clearly, the optimal \nlevel of vitamin D in female fertility and the type of \nsupplements required for the treatment of vitamin \nD deficiency are two significant issues which merit \nfurther research and need to be addressed.\nCONClUSION\nThere are a large number of in vitro,  animal as \nwell as human observational studies which strongly \npoint towards an association between vitamin D and \nfemale fertility. Research data indicate that vitamin \nD might be implicated in the pathogenesis and pre-\nvention of endometriosis, while vitamin D status has \n\nVitamin D and female fertility 17   \nbeen linked to IVF outcome. Furthermore, vitamin \nD supplementation in PCOS women ameliorated \nsome of the metabolic and, mainly, the reproductive \ndisorders. Although promising, these data are not \nsufficient to establish a cause-effect relationship be-\ntween vitamin D status and fertility issues. Moreover, \nthere is still no general consensus as to the minimum \nlevel of vitamin D optimal for female reproductive \nhealth and fertility, while the screening of vitamin \nD status in women undergoing IVF is still under \ndebate. Vitamin D administration is a well-tolerated \nand inexpensive treatment. However, whether vitamin \nD supplementation could be a novel adjunct agent \nin the treatment of metabolic/hormonal aspects of \nPCOS and endometriosis is a question still awaiting \nan answer. Large-scale, high quality dose-response \nRCTs with longer follow-up are needed 1) to determine \nthe exact role of vitamin D in female IVF outcome, \nevaluated by indices such as the number of oocytes \nretrieved, the number and the quality of the embryo \nformed, the clinical pregnancy rates as well as the \nlive birth rates and 2) to identify threshold effects of \nvitamin D supplementation on hormonal, metabolic \nand reproductive outcomes in PCOS.\nReFeReNCeS\n 1. Holick MF, 2007 Vitamin D deficiency. N Engl J Med \n357: 266-281.\n 2. Kassi E, Adamopoulos C, Basdra EK, Papavassiliou AG, \n2013 Role of vitamin D in atherosclerosis. Circulation \n128: 2517-2531.\n 3. Mascarenhas MN, Flaxman SR, Boerma T, Vanderpoel \nS, Stevens GA, 2012 National, regional, and global \ntrends in infertility prevalence since 1990: a systematic \nanalysis of 277 health surveys. PLoS Med 9: e1001356.\n 4. Anagnostis P, Karras S, Goulis DG, 2013 Vitamin D \nin human reproduction: a narrative review. Int J Clin \nPract 67: 225-235.\n 5. Rojansky N, Brzezinski A, Schenker JG, 1992 Season-\nality in human reproduction: an update. Hum Reprod \n7: 735-745.\n 6. Holick MF, Chen TC, 2008 Vitamin D deficiency: a \nworldwide problem with health consequences. Am J \nClin Nutr 87:1080s-1086s.\n 7. Holick MF, 2008 The vitamin D deficiency pandemic \nand consequences for nonskeletal health: mechanisms \nof action. Mol Aspects Med 29: 361-368.\n 8. Haussler MR, Jurutka PW, Mizwicki M, Norman AW, \n2011 Vitamin D receptor (VDR)-mediated actions of \n1alpha,25(OH)(2)vitamin D(3): genomic and non-\ngenomic mechanisms. Best Pract & Res Clin Endocrinol \nMetab 25: 543-559.\n 9. Rosen CJ, Adams JS, Bikle DD, et al, 2012 The non-\nskeletal effects of vitamin D: an Endocrine Society \nscientific statement. Endocr Rev 33: 456-492.\n 10. Bouillon R, Carmeliet G, Verlinden L, et al, 2008 \nVitamin D and human health: lessons from vitamin D \nreceptor null mice. Endocr Rev 29: 726-776.\n 11. Zarnani AH, Shahbazi M, Salek-Moghaddam A, et al, \n2010 Vitamin D3 receptor is expressed in the endo-\nmetrium of cycling mice throughout the estrous cycle. \nFertil Steril 93: 2738-2743.\n 12. Shahbazi M, Jeddi-Tehrani M, Zareie M, et al, 2011 \nExpression profiling of vitamin D receptor in placenta, \ndecidua and ovary of pregnant mice. Placenta 32: 657-\n664.\n 13. Echchgadda I, Song CS, Roy AK, Chatterjee B, 2004 \nDehydroepiandrosterone sulfotransferase is a target \nfor transcriptional induction by the vitamin D receptor. \nMol Pharmacol 65: 720-729.\n 14. Wojtusik J, Johnson PA, 2012 Vitamin D regulates \nanti-Mullerian hormone expression in granulosa cells \nof the hen. Biol Reprod 86: 91.\n 15. Avila E, Diaz L, Halhali A, Larrea F, 2004 Regula-\ntion of 25-hydroxyvitamin D3 1alpha-hydroxylase, \n1,25-dihydroxyvitamin D3 24-hydroxylase and vitamin \nD receptor gene expression by 8-bromo cyclic AMP \nin cultured human syncytiotrophoblast cells. J Steroid \nBiochem Mol Biol 89-90: 115-119.\n 16. Parikh G, Varadinova M, Suwandhi P, Araki T, Ros-\nenwaks Z, Seto-Young D, 2010 Vitamin D regulates \nsteroidogenesis and insulin-like growth factor binding \nprotein-1 (IGFBP-1) production in human ovarian cells. \nHorm Metab Res 42: 754-757.\n 17. Merhi Z, Doswell A, Krebs K, Cipolla M, 2014 Vitamin \nD alters genes involved in follicular development and \nsteroidogenesis in human cumulus granulosa cells. J \nClin Endocrinol Metab 99: E1137-1145.\n 18. Broekmans FJ, Visser JA, Laven JS, Broer SL, Them-\nmen AP, Fauser BC, 2008 Anti-Mullerian hormone \nand ovarian dysfunction. Trends Endocrinol Metab \n19: 340-347\n 19. Malloy PJ, Peng L, Wang J, Feldman D, 2009 Interaction \nof the vitamin D receptor with a vitamin D response \nelement in the Mullerian-inhibiting substance (MIS) \npromoter: regulation of MIS expression by calcitriol in \nprostate cancer cells. Endocrinology 150: 1580-1587.\n 20. Miyashita M, Koga K, Izumi G, et al, 2016 Effects of \n1,25-Dihydroxy Vitamin D3 on Endometriosis. J Clin \nEndocrinol Metab 101: 2371-2379.\n 21. Rajaei S, Mirahmadian M, Jeddi-Tehrani M, et al, 2012 \nEffect of 1,25(OH)2 vitamin D3 on cytokine production \nby endometrial cells of women with repeated implanta-\ntion failure. Gynecol Endocrinol 28: 906-911.\n 22. Levi Setti PE, Colombo GV , Savasi V , Bulletti C, \nAlbani E, Ferrazzi E, 2004 Implantation failure in as-\nsisted reproduction technology and a critical approach \n\n18 N. VOULGARIS ET AL\nto treatment. Ann N Y Acad Sci 1034: 184-199.\n 23. Tavakoli M, Jeddi-Tehrani M, Salek-Moghaddam A, et \nal, 2011 Effects of 1,25(OH)2 vitamin D3 on cytokine \nproduction by endometrial cells of women with recur-\nrent spontaneous abortion. Fertil Steril 96: 751-757.\n 24. Barrera D, Avila E, Hernandez G, et al, 2008 Calcitriol \naffects hCG gene transcription in cultured human syn-\ncytiotrophoblasts. Reprod Biol Endocrinol 6: 3.\n 25. Barrera D, Avila E, Hernandez G, et al, 2007 Estra-\ndiol and progesterone synthesis in human placenta is \nstimulated by calcitriol. J Steroid Biochem Mol Biol \n103: 529-532.\n 26. Tuan RS, Moore CJ, Brittingham JW, Kirwin JJ, Akins \nRE, Wong M, 1991 In vitro study of placental trophoblast \ncalcium uptake using JEG-3 human choriocarcinoma \ncells. J Cell Sci 98: 333-342.\n 27. Belkacemi L, Gariepy G, Mounier C, Simoneau L, La-\nfond J, 2003 Expression of calbindin-D28k (CaBP28k) \nin trophoblasts from human term placenta. Biol Reprod \n68: 1943-1950.\n 28. Chan SY , Susarla R, Canovas D, et al, 2015 Vitamin \nD promotes human extravillous trophoblast invasion \nin vitro. Placenta 36: 403-409.\n 29. Du H, Daftary GS, Lalwani SI, Taylor HS, 2005 Direct \nregulation of HOXA10 by 1,25-(OH)2D3 in human \nmyelomonocytic cells and human endometrial stromal \ncells. Mol Endocrinol 19: 2222-2233.\n 30. Halloran BP, DeLuca HF, 1980 Effect of vitamin D \ndeficiency on fertility and reproductive capacity in the \nfemale rat. J Nutr 110: 1573-1580.\n 31. Yoshizawa T, Handa Y , Uematsu Y , et al, 1997 Mice \nlacking the vitamin D receptor exhibit impaired bone \nformation, uterine hypoplasia and growth retardation \nafter weaning. Nat Genet 16: 391-396.\n 32. Kinuta K, Tanaka H, Moriwake T, Aya K, Kato S, Seino \nY , 2000 Vitamin D is an important factor in estrogen \nbiosynthesis of both female and male gonads. Endo-\ncrinology 141: 1317-1324.\n 33. Johnson LE, DeLuca HF, 2001 Vitamin D receptor null \nmutant mice fed high levels of calcium are fertile. J \nNutr 131: 1787-1791. \n 34. Sun W, Xie H, Ji J, Zhou X, Goltzman D, Miao D, 2010 \nDefective female reproductive function in 1,25(OH)2D-\ndeficient mice results from indirect effect mediated by \nextracellular calcium and/or phosphorus. Am J Physiol \nEndocrinol Metab 299: E928-935.\n 35. Panda DK, Miao D, Bolivar I, et al, 2004 Inactivation \nof the 25-hydroxyvitamin D 1alpha-hydroxylase and \nvitamin D receptor demonstrates independent and \ninterdependent effects of calcium and vitamin D on \nskeletal and mineral homeostasis. J Biol Chem 279: \n16754-16766.\n 36. Kwiecinksi GG, Petrie GI, DeLuca HF, 1989 1,25-Dihy-\ndroxyvitamin D3 restores fertility of vitamin D-deficient \nfemale rats. Am J Physiol 256: E483-487.\n 37. Abbas MA, Taha MO, Disi AM, Shomaf M, 2013 Re-\ngression of endometrial implants treated with vitamin \nD3 in a rat model of endometriosis. Eur J Pharmacol \n715: 72-75\n 38. Yildirim B, Guler T, Akbulut M, Oztekin O, Sariiz \nG, 2014 1-alpha,25-dihydroxyvitamin D3 regresses \nendometriotic implants in rats by inhibiting neovas -\ncularization and altering regulation of matrix metal-\nloproteinase. Postgrad Med 126: 104-110.\n 39. Mariani M, Vigano P, Gentilini D, et al, 2012 The \nselective vitamin D receptor agonist, elocalcitol, re-\nduces endometriosis development in a mouse model \nby inhibiting peritoneal inflammation. Hum Reprod \n27: 2010-2019\n 40. Tesic D, Hawes JE, Zosky GR, Wyrwoll CS, 2015 \nVitamin D Deficiency in BALB/c Mouse Pregnancy \nIncreases Placental Transfer of Glucocorticoids. En-\ndocrinology 156: 3673-3679.\n 41. Azziz R, Woods KS, Reyna R, Key TJ, Knochenhauer \nES, Yildiz BO, 2004 The prevalence and features of the \npolycystic ovary syndrome in an unselected population. \nJ Clin Endocrinol Metab 89: 2745-2749.\n 42. Goodarzi MO, Dumesic DA, Chazenbalk G, Azziz R, \n2011 Polycystic ovary syndrome: etiology, pathogenesis \nand diagnosis. Nat Rev Endocrinol 7: 219-231.\n 43. Pittas AG, Lau J, Hu FB, Dawson-Hughes B, 2007 The \nrole of vitamin D and calcium in type 2 diabetes. A \nsystematic review and meta-analysis. J Clin Endocrinol \nMetab 92: 2017-2029.\n 44. Maestro B, Davila N, Carranza MC, Calle C, 2003 \nIdentification of a Vitamin D response element in \nthe human insulin receptor gene promoter. J Steroid \nBiochem Mol Biol 84: 223-230.\n 45. Maestro B, Molero S, Bajo S, Davila N, Calle C, 2002 \nTranscriptional activation of the human insulin receptor \ngene by 1,25-dihydroxyvitamin D(3). Cell Biochem \nFunct 20: 227-232.\n 46. Mahmoudi T, 2009 Genetic variation in the vitamin \nD receptor and polycystic ovary syndrome risk. Fertil \nSteril 92: 1381-1383.\n 47. Mahmoudi T, Majidzadeh AK, Farahani H, et al, 2015 \nAssociation of vitamin D receptor gene variants with \npolycystic ovary syndrome: A case control study. Int \nJ Reprod Biomed (Yazd) 13: 793-800.\n 48. Jedrzejuk D, Laczmanski L, Milewicz A, et al, 2015 \nClassic PCOS phenotype is not associated with de-\nficiency of endogenous vitamin D and VDR gene \npolymorphisms rs731236 (TaqI), rs7975232 (ApaI), \nrs1544410 (BsmI), rs10735810 (FokI): a case-control \nstudy of lower Silesian women. Gynecol Endocrinol \n31: 976-979.\n 49. Dasgupta S, Dutta J, Annamaneni S, Kudugunti N, \nBattini MR, 2015 Association of vitamin D receptor \ngene polymorphisms with polycystic ovary syndrome \namong Indian women. Indian J Med Res 142: 276-285.\n 50. Ranjzad F, Mahmoudi T, Irani Shemirani A, et al, 2012 A \ncommon variant in the adiponectin gene and polycystic \n\nVitamin D and female fertility 19   \novary syndrome risk. Mol Biol Rep 39: 2313-2319.\n 51. Zadeh-Vakili A, Ramezani Tehrani F, Daneshpour MS, \nZarkesh M, Saadat N, Azizi F, 2013 Genetic polymor-\nphism of vitamin D receptor gene affects the phenotype \nof PCOS. Gene 515: 193-196.\n 52. Wehr E, Trummer O, Giuliani A, Gruber HJ, Pieber \nTR, Obermayer-Pietsch B, 2011 Vitamin D-associated \npolymorphisms are related to insulin resistance and \nvitamin D deficiency in polycystic ovary syndrome. \nEur J Endocrinol 164: 741-749.\n 53. Ranjzad F, Mahban A, Shemirani AI, et al, 2011 Influ-\nence of gene variants related to calcium homeostasis \non biochemical parameters of women with polycystic \novary syndrome. J Assist Reprod Genet 28: 225-232.\n 54. Panidis D, Balaris C, Farmakiotis D, et al, 2005 Serum \nparathyroid hormone concentrations are increased in \nwomen with polycystic ovary syndrome. Clin Chem \n51: 1691-1697.\n 55. Mahmoudi T, Gourabi H, Ashrafi M, Yazdi RS, Ezabadi \nZ, 2010 Calciotropic hormones, insulin resistance, and \nthe polycystic ovary syndrome. Fertil Steril 93: 1208-\n1214.\n 56. Ngo DT, Chan WP, Rajendran S, et al, 2011 Deter -\nminants of insulin responsiveness in young women: \nImpact of polycystic ovarian syndrome, nitric oxide, \nand vitamin D. Nitric oxide 25: 326-330.\n 57. Sadhir M, Kansra AR, Menon S, 2015 Vitamin D De-\nficiency among Adolescent Females with Polycystic \nOvary Syndrome. J Pediatr Adolesc Gynecol 28: 378-\n381.\n 58. Joham AE, Teede HJ, Cassar S, et al, 2015 Vitamin D \nin polycystic ovary syndrome: Relationship to obesity \nand insulin resistance. Mol Nutr Food Res 60: 110-118.\n 59. Muscogiuri G, Policola C, Prioletta A, et al, 2012 Low \nlevels of 25(OH)D and insulin-resistance: 2 unrelated \nfeatures or a cause-effect in PCOS? Clinl Nutr 31: \n476-480.\n 60. Hahn S, Haselhorst U, Tan S, et al, 2006 Low serum \n25-hydroxyvitamin D concentrations are associated with \ninsulin resistance and obesity in women with polycystic \novary syndrome. Exp Clin Endocrinol Diabetes 114: \n577-583.\n 61. Sahin S, Eroglu M, Selcuk S, et al, 2014 Intrinsic \nfactors rather than vitamin D deficiency are related to \ninsulin resistance in lean women with polycystic ovary \nsyndrome. Eur Rev Med Pharmacol Sci 18: 2851-2856.\n 62. Ganie MA, Marwaha RK, Nisar S, et al, 2016 Impact \nof hypovitaminosis D on clinical, hormonal and insu-\nlin sensitivity parameters in normal body mass index \npolycystic ovary syndrome women. J Obstet Gynaecol \n36: 508-512.\n 63. Yildizhan R, Kurdoglu M, Adali E, et al, 2009 Serum \n25-hydroxyvitamin D concentrations in obese and \nnon-obese women with polycystic ovary syndrome. \nArch Gynecol Obstet 280: 559-563.\n 64. Wehr E, Pilz S, Schweighofer N, et al, 2009 Associa-\ntion of hypovitaminosis D with metabolic disturbances \nin polycystic ovary syndrome. Eur J Endocrinol 161: \n575-582.\n 65. Li HW, Brereton RE, Anderson RA, Wallace AM, \nHo CK, 2011 Vitamin D deficiency is common and \nassociated with metabolic risk factors in patients with \npolycystic ovary syndrome. Metabolism 60: 1475-1481.\n 66. Patra SK, Nasrat H, Goswami B, Jain A, 2012 Vitamin \nD as a predictor of insulin resistance in polycystic \novarian syndrome. Diabetes Metab Syndr 6: 146-149.\n 67. Mishra S, Das AK, Das S, 2016 Hypovitaminosis D \nand Associated Cardiometabolic Risk in Women with \nPCOS. J Clin Diagn Res 10: Bc01-4.\n 68. Savastano S, Valentino R, Di Somma C, et al, 2011 \nSerum 25-Hydroxyvitamin D Levels, phosphoprotein \nenriched in diabetes gene product (PED/PEA-15) and \nleptin-to-adiponectin ratio in women with PCOS. Nutr \nMetab (Lond) 8: 84.\n 69. Pal L, Zhang H, Williams J, et al, 2016 Vitamin D \nStatus Relates to Reproductive Outcome in Women \nWith Polycystic Ovary Syndrome: Secondary Analysis \nof a Multicenter Randomized Controlled Trial. J Clin \nEndocrinol Metab 101: 3027-3035.\n 70. Ott J, Wattar L, Kurz C, et al, 2012 Parameters for \ncalcium metabolism in women with polycystic ovary \nsyndrome who undergo clomiphene citrate stimulation: \na prospective cohort study. Eur J Endocrinol 166: 897-\n902.\n 71. Thys-Jacobs S, Donovan D, Papadopoulos A, Sarrel P, \nBilezikian JP, 1999 Vitamin D and calcium dysregula-\ntion in the polycystic ovarian syndrome. Steroids 64: \n430-435.\n 72. Rashidi B, Haghollahi F, Shariat M, Zayerii F, 2009 \nThe effects of calcium-vitamin D and metformin on \npolycystic ovary syndrome: a pilot study. Taiwan J \nObstet Gynecol 48: 142-147.\n 73. Firouzabadi R, Aflatoonian A, Modarresi S, Sekhavat \nL, MohammadTaheri S, 2012 Therapeutic effects of \ncalcium & vitamin D supplementation in women with \nPCOS. Complement Ther Clin Pract 18: 85-88.\n 74. Asadi M, Matin N, Frootan M, Mohamadpour J, Qorbani \nM, Tanha FD, 2014 Vitamin D improves endometrial \nthickness in PCOS women who need intrauterine insemi-\nnation: a randomized double-blind placebo-controlled \ntrial. Arch Gynecol Obstet 289: 865-870.\n 75. Wehr E, Pieber TR, Obermayer-Pietsch B, 2011 Effect \nof vitamin D3 treatment on glucose metabolism and \nmenstrual frequency in polycystic ovary syndrome \nwomen: a pilot study. J Endocrinol Invest 34: 757-763.\n 76. Selimoglu H, Duran C, Kiyici S, et al, 2010 The effect \nof vitamin D replacement therapy on insulin resistance \nand androgen levels in women with polycystic ovary \nsyndrome. J Endocrinol Invest 33: 234-238.\n 77. Pal L, Berry A, Coraluzzi L, et al, 2012 Therapeutic \nimplications of vitamin D and calcium in overweight \nwomen with polycystic ovary syndrome. Gynecol \n\n20 N. VOULGARIS ET AL\nEndocrinol 28: 965-968.\n 78. Razavi M, Jamilian M, Karamali M, Bahmani F, Agha-\ndavod E, Asemi Z, 2016 The Effects of Vitamin D-K-\nCalcium Co-Supplementation on Endocrine, Inflam-\nmation, and Oxidative Stress Biomarkers in Vitamin \nD-Deficient Women with Polycystic Ovary Syndrome: \nA Randomized, Double-Blind, Placebo-Controlled \nTrial. Horm Metab Res 48: 446-451.\n 79. Kotsa K, Yavropoulou MP, Anastasiou O, Yovos JG, \n2009 Role of vitamin D treatment in glucose metabo-\nlism in polycystic ovary syndrome. Fertil Steril 92: \n1053-1058.\n 80. Rahimi-Ardabili H, Pourghassem Gargari B, Farzadi \nL, 2013 Effects of vitamin D on cardiovascular disease \nrisk factors in polycystic ovary syndrome women with \nvitamin D deficiency. J Endocrinol Invest 36: 28-32.\n 81. Raja-Khan N, Shah J, Stetter CM, et al, 2014 High-dose \nvitamin D supplementation and measures of insulin \nsensitivity in polycystic ovary syndrome: a randomized, \ncontrolled pilot trial. Fertil Steril 101: 1740-1746.\n 82. Ardabili HR, Gargari BP, Farzadi L, 2012 Vitamin D \nsupplementation has no effect on insulin resistance \nassessment in women with polycystic ovary syndrome \nand vitamin D deficiency. Nutr Res 32: 195-201.\n 83. Asemi Z, Foroozanfard F, Hashemi T, Bahmani F, Ja-\nmilian M, Esmaillzadeh A, 2015 Calcium plus vitamin \nD supplementation affects glucose metabolism and \nlipid concentrations in overweight and obese vitamin \nD deficient women with polycystic ovary syndrome. \nClin Nutr 34: 586-592.\n 84. Garg G, Kachhawa G, Ramot R, et al, 2015 Effect of \nvitamin D supplementation on insulin kinetics and \ncardiovascular risk factors in polycystic ovarian syn-\ndrome: a pilot study. Endocr Connect 4: 108-116.\n 85. He C, Lin Z, Robb SW, Ezeamama AE, 2015 Serum \nVitamin D Levels and Polycystic Ovary syndrome: A \nSystematic Review and Meta-Analysis. Nutrients 7: \n4555-4577.\n 86. Jia XZ, Wang YM, Zhang N, et al, 2015 Effect of \nvitamin D on clinical and biochemical parameters in \npolycystic ovary syndrome women: A meta-analysis. \nJ Obstet Gynaecol Res 41: 1791-1802.\n 87. Fang F, Ni K, Cai Y , Shang J, Zhang X, Xiong C, 2017 \nEffect of vitamin D supplementation on polycystic ovary \nsyndrome: A systematic review and meta-analysis of \nrandomized controlled trials. Complement Ther Clin \nPract 26: 53-60.\n 88. Xue Y , Xu P, Xue K, et al, 2017 Effect of vitamin D on \nbiochemical parameters in polycystic ovary syndrome \nwomen: a meta-analysis. Arch Gynecol Obstet 295: \n487-496.\n 89. Diamanti-Kandarakis E, Katsikis I, Piperi C, et al, 2008 \nIncreased serum advanced glycation end-products is a \ndistinct finding in lean women with polycystic ovary \nsyndrome (PCOS). Clin Endocrinol (Oxf) 69: 634-641.\n 90. Merhi Z, 2014 Advanced glycation end products and \ntheir relevance in female reproduction. Hum Reprod \n29: 135-145\n 91. Kalea AZ, Schmidt AM, Hudson BI, 2009 RAGE: \na novel biological and genetic marker for vascular \ndisease. Clin Sci (Lond) 116: 621-637.\n 92. Irani M, Minkoff H, Seifer DB, Merhi Z, 2014 Vita-\nmin D increases serum levels of the soluble receptor \nfor advanced glycation end products in women with \nPCOS. J Clin Endocrinol Metab 99: E886-890.\n 93. Irani M, Seifer DB, Grazi RV , et al, 2015 Vitamin D \nSupplementation decreases TGF-beta1 bioavailability \nin PCOS: A randomized placebo-controlled trial. J \nClin Endocrinol Metab 100: 4307-4314.\n 94. Raja-Khan N, Kunselman AR, Demers LM, Ewens \nKG, Spielman RS, Legro RS, 2010 A variant in the \nfibrillin-3 gene is associated with TGF-beta and inhibin \nB levels in women with polycystic ovary syndrome. \nFertil Steril 94: 2916-2919.\n 95. Tal R, Seifer DB, Shohat-Tal A, Grazi RV , Malter HE, \n2013 Transforming growth factor-beta1 and its recep-\ntor soluble endoglin are altered in polycystic ovary \nsyndrome during controlled ovarian stimulation. Fertil \nSteril 100: 538-543.\n 96. Karras SN, Anagnostis P, Naughton D, Annweiler C, \nPetroczi A, Goulis DG, 2015 Vitamin D during preg-\nnancy: why observational studies suggest deficiency \nand interventional studies show no improvement in \nclinical outcomes? A narrative review. J Endocrinol \nInvest 38: 1265-1275.\n 97. Bulun SE, 2009 Endometriosis. N Engl J Med 360: \n268-279.\n 98. Vigano P, Lattuada D, Mangioni S, et al, 2006 Cycling \nand early pregnant endometrium as a site of regulated \nexpression of the vitamin D system. J Mol Endocrinol \n36: 415-424.\n 99. Hartwell D, Rodbro P, Jensen SB, Thomsen K, Chris-\ntiansen C, 1990 Vitamin D metabolites--relation to \nage, menopause and endometriosis. Scand J Clin Lab \nInvest 50: 115-121.\n 100. Agic A, Xu H, Altgassen C, et al, 2007 Relative expres-\nsion of 1,25-dihydroxyvitamin D3 receptor, vitamin \nD 1 alpha-hydroxylase, vitamin D 24-hydroxylase, \nand vitamin D 25-hydroxylase in endometriosis and \ngynecologic cancers. Repr Sci 14: 486-497.\n 101. Harris HR, Chavarro JE, Malspeis S, Willett WC, \nMissmer SA, 2013 Dairy-food, calcium, magnesium, \nand vitamin D intake and endometriosis: a prospective \ncohort study. Am J Epidemiol 177: 420-430.\n 102. Ciavattini A, Serri M, Delli Carpini G, Morini S, \nClemente N, 2017 Ovarian endometriosis and vitamin \nD serum levels. Gynecol Endocrinol 33: 164-167.\n 103. Somigliana E, Panina-Bordignon P, Murone S, Di Lucia \nP, Vercellini P, Vigano P, 2007 Vitamin D reserve is \nhigher in women with endometriosis. Hum Reprod \n22: 2273-2278.\n 104. Ferrero S, Gillott DJ, Anserini P, et al, 2005 Vitamin \n\nVitamin D and female fertility 21   \nD binding protein in endometriosis. J Soc Gynecol \nInvestig 12: 272-277.\n 105. Borkowski J, Gmyrek GB, Madej JP, et al, 2008 Se-\nrum and peritoneal evaluation of vitamin D-binding \nprotein in women with endometriosis. Postepy Hig \nMed Dosw (Online) 62: 103-109.\n 106. Cho S, Choi YS, Yim SY , et al, 2012 Urinary vitamin \nD-binding protein is elevated in patients with endo-\nmetriosis. Hum Reprod 27: 515-522.\n 107. Hwang JH, Wang T, Lee KS, Joo JK, Lee HG, 2013 \nVitamin D binding protein plays an important role in \nthe progression of endometriosis. Int J Mol Med 32: \n1394-1400.\n 108. Faserl K, Golderer G, Kremser L, et al, 2011 Poly-\nmorphism in vitamin D-binding protein as a genetic \nrisk factor in the pathogenesis of endometriosis. J Clin \nEndocrinol Metab 96: E233-241\n 109. Vilarino FL, Bianco B, Lerner TG, et al, 2011 Analysis \nof vitamin D receptor gene polymorphisms in women \nwith and without endometriosis. Hum Immunol 72: \n359-363.\n 110. Ozkan S, Jindal S, Greenseid K, Shu J, Zeitlian G, \nHickmon C, et al, 2010 Replete vitamin D stores predict \nreproductive success following in vitro fertilization. \nFertil Steril 94: 1314-1319.\n 111. Rudick B, Ingles S, Chung K, Stanczyk F, Paulson R, \nBendikson K, 2012 Characterizing the influence of \nvitamin D levels on IVF outcomes. Hum Reprod 27: \n3321-3327.\n 112. Rudick BJ, Ingles SA, Chung K, Stanczyk FZ, Paulson \nRJ, Bendikson KA, 2014 Influence of vitamin D levels \non in vitro fertilization outcomes in donor-recipient \ncycles. Fertil Steril 101: 447-452.\n 113. Garbedian K, Boggild M, Moody J, Liu KE, 2013 \nEffect of vitamin D status on clinical pregnancy rates \nfollowing in vitro fertilization. CMAJ open 1: E77-82.\n 114. Paffoni A, Ferrari S, Vigano P, et al, 2014 Vitamin D \ndeficiency and infertility: insights from in vitro fertiliza-\ntion cycles. J Clin Endocrinol Metab 99: E2372-2376.\n 115. Farzadi L, Khayatzadeh Bidgoli H, Chojazadeh et \nal, 2015 Correlation between follicular fluid 25-OH \nvitamin D and assisted reproductive outcomes. Iran \nJ Reprod Med 13: 361-366.\n 116. Polyzos NP, Anckaert E, Guzman L, et al, 2014 Vi-\ntamin D deficiency and pregnancy rates in women \nundergoing single embryo, blastocyst stage, transfer \n(SET) for IVF/ICSI. Hum Reprod 29: 2032-2040.\n 117. Anifandis GM, Dafopoulos K, Messini CI, et al, 2010 \nPrognostic value of follicular fluid 25-OH vitamin D \nand glucose levels in the IVF outcome. Reprod Biol \nEndocrinol 8: 91.\n 118. Aleyasin A, Hosseini MA, Mahdavi A, et al, 2011 \nPredictive value of the level of vitamin D in follicular \nfluid on the outcome of assisted reproductive technol-\nogy. Eur J Obstet Gynecol Reprod Biol 159: 132-137.\n 119. Firouzabadi RD, Rahmani E, Rahsepar M, Firouz -\nabadi MM, 2014 Value of follicular fluid vitamin D \nin predicting the pregnancy rate in an IVF program. \nArch Gynecol Obstet 289: 201-206.\n 120. Franasiak JM, Molinaro TA, Dubell EK, et al, 2015 \nVitamin D levels do not affect IVF outcomes follow-\ning the transfer of euploid blastocysts. Am J Obstet \nGynecol 212: 315.e1-6.\n 121. van de Vijver A, Drakopoulos P, Van Landuyt L, et al, \n2016 Vitamin D deficiency and pregnancy rates fol-\nlowing frozen-thawed embryo transfer: a prospective \ncohort study. Hum Reprod 31: 1749-1754.\n 122. Fabris A, Pacheco A, Cruz M, Puente JM, Fatemi \nH, Garcia-Velasco JA, 2014 Impact of circulating \nlevels of total and bioavailable serum vitamin D on \npregnancy rate in egg donation recipients. Fertil Steril \n102: 1608-1612.\n 123. Aflatoonian A, Arabjahvani F, Eftekhar M, Sayadi M, \n2014 Effect of vitamin D insufficiency treatment on \nfertility outcomes in frozen-thawed embryo transfer \ncycles: A randomized clinical trial. Iran J Reprod Med \n12: 595-600.\n 124. Lv SS, Wang JY , Wang XQ, Wang Y , Xu Y , 2016 Serum \nvitamin D status and in vitro fertilization outcomes: a \nsystematic review and meta-analysis. Arch Gynecol \nObstet 293: 1339-1345.\n 125. Holick MF, Binkley NC, Bischoff-Ferrari HA, et al, \n2011 Evaluation, treatment, and prevention of vitamin \nD deficiency: an Endocrine Society clinical practice \nguideline. J Clin Endocrinol Metab 96: 1911-1930.\n 126. Rosen CJ, Abrams SA, Aloia JF, et al, 2012 IOM com-\nmittee members respond to Endocrine Society vitamin \nD guideline. J Clin Endocrinol Metab 97: 1146-1152.\n 127. Heaney RP, Recker RR, Grote J, Horst RL, Armas LA, \n2011 Vitamin D(3) is more potent than vitamin D(2) \nin humans. J Clin Endocrinol Metab 96: E447-452.\n 128. Trang HM, Cole DE, Rubin LA, Pierratos A, Siu S, \nVieth R, 1998 Evidence that vitamin D3 increases \nserum 25-hydroxyvitamin D more efficiently than \ndoes vitamin D2. Am J Clin Nutr 68: 854-858.\n 129. Armas LA, Hollis BW, Heaney RP, 2004 Vitamin D2 \nis much less effective than vitamin D3 in humans. J \nClin Endocrinol Metab 89: 5387-5391.\n 130. Binkley N, Gemar D, Engelke J, et al, 2011 Evalua-\ntion of ergocalciferol or cholecalciferol dosing, 1,600 \nIU daily or 50,000 IU monthly in older adults. J Clin \nEndocrinol Metab 96: 981-988.","source_license":"CC0","license_restricted":false}