Table 2.

Polycystic ovary syndrome and vitamin D deficiency.

Study	Article Type	Study Group	Summary
Tavakoli et al. [48]	Cell line (human)	Endometrial samples (from women with recurrent spontaneous abortion and healthy controls)	Vitamin D supplementation may have a beneficial effect in case of recurrent miscarriages. As a result of vitamin D supplementation, Th2 cytokine dominance was observed with decreased proliferation of inflammatory cytokines.
Diaz et al. [49]	Cell line (human)	Term placentae samples (37–41 weeks of gestation, from uncomplicated pregnancies)	Calcitriol supplementation prevents the production of TNF alpha, IL-6 and IFN gamma—this is likely mediated by VDR.
Liu et al. [50]	Cell line (human)	Human trophoblastic cell lines from American Type Tissue Culture Collection	In human trophoblast cells, Vitamin D metabolites significantly enhance antibacterial responses.
Kuyucu et al. [34]	Animal study	Prepubertal female rats, control group (n = 8), PCOS group (n = 8) and PCOS + D3 group (n = 8)	Vitamin D treatment significantly reduced endometrial, epithelial and stromal thickness in PCOS patients, as well as pathological proliferation and apoptosis. AMH was also decreased as a result of vitamin D supplementation (this however did not reach the level of significance).
Guo et al. [36]	Case control study	Endometrial samples from women who underwent standardized IVF treatment (n = 16)	VDR plays role in the development of endometrial susceptibility: increased VDR expression in the endometrium (especially in the implantation window of the menstrual cycle) is significantly more likely to lead to pregnancy.
Zadeh-Vakili et al. [32]	Case control study	PCOS women (n = 260) and women with physiological cycles (n = 221)	The genetic variant of VDR is associated with the severity of the clinical features of PCOS, but not with the risk of the disease itself.
Aghadavod et al. [38]	Case control study	Control group (n = 20 normal weights and n = 20 over-weights); PCOS group (n = 20 normal weight and n = 20 over-weight)	Vitamin D levels in follicular fluid are significantly lower in PCOS and overweight patients. Vitamin D levels in follicular fluid strongly correlate with BMI. VDR expression in granulosa cells is significantly lower in PCOS/overweight patients than in non PCOS or normal weight individuals.
Zhao et al. [39]	Case control study	In total, 305 women were divided into 4 groups based on serum vitamin D levels.	Optimal vitamin D levels improve embryo quality and lead to significantly higher clinical pregnancy rates.
March et al. [27]	Retrospective birth cohort study	In total, 728 women born between 1973–1975 in a single maternity hospital were traced and interviewed in adulthood (age = 27–34 year; n = 728).	Prevalence estimates for Rotterdam and AES may be up two twice of that for NIH criteria A significant proportion of women with PCOS are not diagnosed or are diagnosed late.
Pal et al. [28]	Retrospective cohort study (Secondary analysis of randomized controlled trial data)	Participants in the Pregnancy in PCOS I randomized controlled trial (n = 540) who met the National Institutes of Health diagnostic criteria for PCOS.	In women with PCOS, serum vitamin D level is an independent predictor of reproductive success rates following induction of ovulation. Probability of ovulation correlates with vitamin D levels in PCOS. The reproductive threshold for serum vitamin D is higher in than that recommended for the non-pregnant population.
Hahn et al. [45]	Prospective cohort study	PCOS women (n = 120)	In PCOS, insulin resistance correlates negatively with vitamin D levels.
Pittas et al. [46]	Randomized controlled trial	Caucasian adults (n = 314)	In older healthy adults with impaired fasting glucose (IFG), calcium and vitamin D supplementation may reduce the further development of insulin resistance.