This is a randomized double-blind controlled trial on the effect of vitamin D supplementation to assess the ovulation rate of women with polycystic ovary syndrome (PCOS) and other reproductive, endocrine and metabolic outcomes after one year of treatment.

The hypothesis is that vitamin D supplementation results in significant improvement in the ovulation rate of women with PCOS either spontaneously or with oral ovulation induction agent.

Anovulatory women with PCOS diagnosed by the Rotterdam criteria will be recruited.

Participants will be randomized to the (1) vitamin D group or (2) placebo group. Those in the vitamin D group will take vitamin D 50,000 IU/ week for 4 weeks, followed by 50,000IU once every 2 weeks for 52 weeks, whereas those in the placebo group will take placebo tablets with the same external appearance. Those who remain anovulatory after 6 months will be treated with a 6-month course of letrozole (2.5mg to 7.5mg for 5 days per cycle titrated according to response) for ovulation induction.

The primary outcome is the ovulation rate and will be compared between the 2 groups.

Inclusion Criteria:

• Premenopausal
• Aged 18-40 years
• Irregular long menstrual cycles (>35 days)
• PCOS according to the Rotterdam criteria
• Agree for transvaginal ultrasound

Exclusion Criteria:

• Use of hormonal medication (including contraception) within 3 months prior to study inclusion, except the use of a progestogen to induce withdrawal bleeding every 3 months
• History of any medical condition or medications that may predispose to vitamin D sensitivity, altered vitamin D metabolism and/ or hypercalcemia, including active tuberculosis or current therapy for tuberculosis, sarcoidosis, history of renal/ ureteral stones, parathyroid disease, renal or liver failure or current use of anti-convulsants
• Use of insulin-sensitizing drugs, lipid lowering drugs or anti-hypertensive
• Anticipated to use the above medications in the coming one year
• Known type 2 diabetes mellitus
• Refusal to join the study
• Abnormal blood calcium level

For those on supplements, we asked them to stop their own supplements.

all IPD that underlie results in a publication

starting 6 months after publication

review by investigators