Does vitamin D increase the effectiveness of clomiphene citrate for women with PCOS?

This study looked at adding vitamin D for women with polycystic ovarian syndrome (PCOS) who were overweight and being treated with clomiphene citrate (Clomid). It found that vitamin D increased ovulation and pregnancy rates for these patients.

Polycystic ovarian syndrome (PCOS) is a common condition of women of reproductive age. PCOS involves infrequent ovulation and hormonal changes and is linked to obesity. Over 90% of women whose infertility is caused by a lack of ovulation have PCOS. 

Vitamin D deficiency is common, with 20-48% of adults having low vitamin D. However it is more common in women with PCOS. Vitamin D has many roles in the body, including allowing calcium to be absorbed from food. The ovaries are sensitive to calcium, and the mineral may play a role in how a follicle is selected. The follicle is where the egg develops prior to ovulation.

Clomiphene citrate is a treatment for infertility which causes the body to release more estrogen than it otherwise would. This can promote ovulation. It is unclear whether vitamin D can improve ovulation rates during treatment with clomiphene citrate.

This study included 186 women with PCOS and infertility. The patients had body mass indexes (a measurement of weight in relation to height) between 25 and 30 kg/m², which indicates being overweight. All of the women were treated with clomiphene citrate and a calcium supplement. Half of the women were randomly assigned to also take a high-dose vitamin D supplement (10000 UI twice weekly), and the other half took a placebo (inactive pill). Calcium and vitamin D or placebo were started one month before the first clomiphene citrate cycle. The patients were followed for three cycles.

Within the first three treatment cycles, significantly more patients in the vitamin D group ovulated (92.5% vs. 78.5%). Also, the dominant follicle was significantly larger for women in the vitamin D group (18.07 vs. 16.79 mm), which may indicate better development of the egg.

More patients taking vitamin D had a positive pregnancy test (61.3% vs. 49.5%) and a pregnancy visible on ultrasound (50.5% vs. 39.8%). Among pregnant patients, fewer of those taking vitamin D had a miscarriage during the study (29.8% vs. 45.9%).

This study found that adding vitamin D to clomiphene citrate treatment increased ovulation and pregnancy rates in patients with PCOS.

This study did not test vitamin D levels before treatment due to ethical considerations, so it was not able to show that patients had low vitamin D before treatment. Also, this study had a small number of patients.