the aim of this randomised clinical trial study is to evaluate whether supplementation with vitamin D could inhibit the growth of uterine fibroids in reproductive stage women.

180 patients with vitamin D deficiency (12 ng/ml ≤ serum 25-hydroxyvitamin D3 < 20 ng/ml) and uterine fibroids will be randomly assigned in a ratio of 1:1 to two groups: intervention group A and control group B. 180 patients with vitamin D insufficiency (20 ng/ml ≤ serum 25-hydroxyvitamin D3 < 30 ng/ml) and uterine fibroids will be also randomly assigned in a ratio of 1:1 to two groups: intervention group C and control group D. The intervention group A will receive 1600 IU/d of vitamin D3; The intervention group C will receive 800 IU/d of vitamin D3; the control group B and the control group D will receive regular follow-up. Patients will be followed up at the same time points for 24 months. The outcome measure is the growth of uterine fibroids in different groups.

Inclusion Criteria:

• 1. Patients are willing to cooperate with the follow-up and sign informed consent;
• 2. Females aged 35-50 who are diagnosed as having uterine fibroids by transvaginal or abdominal ultrasonography;
• 3. The maximum average diameter of intramural myoma is ≤ 4cm，≥ 1cm; The amount of myoma is less than 4;
• 4. Serum 25-hydroxyvitamin D3 < 30 ng/ml, ≥ 12 ng/ml.

Exclusion Criteria:

• 1. Patients with heavy menstrual bleeding (>80.0 mL), menstrual disorders, pelvic discomfort, infertility, or other indications for operation;
• 2. Patients complicated with myoma degeneration and adenomyosis that were suspected or diagnosed by ultrasound or gynecologic examination;
• 3. Allergic to vitamin D3;
• 4. Use of sexual hormone, mifepristone, gonadotropin-releasing hormone agonist (GnRHa), or other medication which is likely to interfere with uterine fibroids within 3 months;
• 5. Pregnancy, lactation, postmenopause, or planned pregnancy within two years;
• 6. Suspected or identified as other tumors of genital tract;
• 7. History of osteoporosis or vitamin D deficiency taking vitamin D supplements within previous one month;
• 8. History of autoimmune diseases, infectious diseases (tuberculosis, AIDS), autoimmune diseases, digestive system diseases (malabsorption, crohn disease, and dysentery);
• 9. Alanine aminotransferase (ALT) or aspartate transaminase(AST) more than 3 times of the normal upper limit, total bilirubin (TBIL) more than 2 times of the normal upper limit;
• 10. Creatinine levels≥1.4 mg/dL (123μmol/L) or creatinine clearance ≤ 50 mL/min;
• 11. History of malignant tumors;
• 12. Simultaneous participation in another clinical study with investigational medicinal product(s) or researcher thinks the subjects are not suitable for this trial.