Vitamin D and Breast Cancer Biomarkers in Female Patients

Inclusion criteria

1. Premenopausal women 55 years of age or younger with regular menstrual cycles (at least four cycles in the last six months). Women with fewer than 4 menses in the last 6 months or who have had a hysterectomy with ovaries intact will be considered premenopausal if FSH level \< 20. 2. Women with breast density ≥ 25% (scattered fibroglandular densities or greater) are eligible. 3. Prior Treatment 1. Patients who are currently receiving hormone replacement therapy (estrogen or progesterone); or are taking tamoxifen or raloxifene are not eligible. Women who have taken these medications must have stopped for at least 4 months prior to study entry. Topical estrogen (eg, transdermal patches and vaginal estrogens) is allowed. 2. Patients who are currently using hormonal contraception, should be taking it for at least 4 months prior to study entry. 4. Vitamin D Use 1. Patients who are taking regular vitamin D supplementation (above 400 IUs daily) and refuse or are unable to stop use are not eligible. Women who agree to stop will need to do so for at least 6 months prior to registration. 2. Patients may not start vitamin D supplementation after registration (regardless of results of vitamin D testing) but they may continue vitamin D if they are already taking 400 IUs daily or less and have been taking vitamin D for at least 6 months prior to baseline mammogram. 5. Patients with a history of breast cancer (including DCIS) or ovarian cancer are not eligible. 6. Patients with a history of breast implants or breast reduction are not eligible. 7. Patients with two or more bone fractures in the past five years are not eligible. 8. Patients with a diagnosis of osteoporosis with physician recommendation for treatment of low bone mass are not eligible. 9. Patients known to have hyperparathyroid disease or other serious disturbances of calcium metabolism requiring intervention in the past 5 years are not eligible. 10. Patients with a history of kidney stones (unless documented not to have been a calcium stone) are not eligible. 11. Patients participating in a concurrent breast cancer chemoprevention trial are not eligible. 12. Required initial laboratory values - Calcium \< 10.5 mg/dL