The Effect of Vitamin D in Female Infertility

Vitamin D is a group of fat-soluble steroids responsible for en-hancing intestinal absorption of calcium and phosphate, which is directly related to the maintenance of the normal structure and function of the skeletal system. Observational studies have described associations between low circulating levels of vita-min D and a large number of diseases, including cardiovascular diseases, malignancies, diabetes, obesity, and infections, neu-ropsychiatric and autoimmune diseases.Accumulating evidence from animal and human studies sug-gests that vitamin D is involved in many functions of the repro-ductive system in both genders.Vitamin D has a biologically plausible role in female reproduc-tion; it has been associated with features of polycystic ovary syndrome (PCOS), endometriosis and in vitro fertilization (IVF) outcome.Increasing evidence suggests that vitamin D might have a regulatory role in PCOS-related symptoms, including ovula-tory dysfunction, insulin resistance and hyperandrogenism. Although several data converge towards a beneficial effect of vitamin D supplementation in metabolic disturbances in women with PCOS, a significant knowledge gap precludes the estab-lishment of a clear cause-effect relationship.Vitamin D deficiency also has been reported to contribute to the pathogenesis of endometriosis due to its immunomodulatory and anti-inflammatory properties. Although most of the stud-ies supported a role of vitamin D in the onset of these diseases, randomized controlled trials to assess the efficacy of vitamin D supplementation have never been performed.Studies investigating the association of vitamin D status with IVF outcome revealed inconsistent results. Some studies report positive effect; however other found that vitamin D deficiency did not play an important role in the outcome of assisted repro-ductive technology (ART). Given such contradictory results, there is a need for further researches with better design.