Inclusion Criteria

DISEASE CHARACTERISTICS:

- Women with breast density ≥ 25% (correlating with the BIRAD-2 category of "scattered
fibroglandular densities" or greater)

- Hormone receptor status not specified

PATIENT CHARACTERISTICS:

- Premenopausal defined as meeting at least one of the following criteria:

- Have regular menstrual cycles

- Have had at least four cycles in the last six months

- Have had a hysterectomy with ovaries intact and FSH level < 20 IU/L

- Calcium < 10.5 mg/dL

- Not pregnant

- Fertile patients must use effective contraception

- Patients with a history of breast cancer (including DCIS) or ovarian cancer are not
eligible

- Patients with two or more bone fractures in the past five years are not eligible

- Patients with a diagnosis of osteoporosis with physician recommendation for treatment
of low bone mass are not eligible

- Patients known to have hyperparathyroid disease or other serious disturbances of
calcium metabolism requiring intervention in the past 5 years are not eligible

- Patients with a history of kidney stones (unless documented not to have been a
calcium stone) are not eligible

PRIOR CONCURRENT THERAPY:

- 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 is allowed

- Patients who are currently using hormonal contraception, should be taking it for at
least 4 months prior to study entry

- 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

- 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

- Patients participating in a concurrent breast cancer chemoprevention trial are not
eligible

- No history of breast implants or breast reduction