The relationship between vitamin D₃ and insulin in polycystic ovary syndrome - a critical review

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder affecting women of reproductive age. It is characterized by hormonal, reproductive and metabolic disturbances, including hyperandrogenism, altered gonadotropin level, ovarian cysts and ovulatory dysfunction as well as insulin resistance, hyperinsulinemia and dyslipidemia. It was shown that increased insulin concentration is a plausible factor in the pathogenesis of PCOS. Insulin leads to overstimulation of ovarian theca cells to androgen biosynthesis and contributes to insulin resistance in tissues such as muscle, liver, adipose tissue and ovary of PCOS patients. Noteworthy, recent studies suggested that supplementation with vitamin D₃ may be an alternative therapy increasing insulin sensitivity and thereby improving reproductive parameters in PCOS women. Indeed, various action of vitamin D₃ on the ovarian, hormonal and metabolic features observed in PCOS were presented. Many studies reported therapeutic effects of vitamin D₃, but some research found a lack of influence or contradicted these findings. Therefore, the aim of this review was to summarize the available evidence about vitamin D₃ and insulin interaction in PCOS, and discusses the potential usefulness of VD₃ in PCOS treatment.