Personalized Vitamin D Supplementation in European and African Americans

Potential volunteers will be screened by telephone. Those meeting all inclusion and no
exclusion criteria will be invited to a screening study visit. At screening, informed consent
will be obtained. The study team will then collect the following to determine study
eligibility: basic demographic information (age, ancestry, and education); medical history;
medication and supplement use; and blood for screening 25(OH)D and calcium tests. At
baseline, participants will be randomly assigned to the control or dosing algorithm group.
Both participants and study staff who have contact with the participants will be blinded to
group assignment. Follow-up visits will occur at three and six months. At baseline and
follow-up visits, height and weight will be measured and blood will be drawn for the vitamin
D panel, calcium, and PTH. Blood for DNA and body composition will only be obtained at the
baseline visit. Participants will be asked to return all unused study supplements and
compliance will be assessed at each follow-up visit by pill count. The control group will
receive 2500 IU of vitamin D3 daily while the dosing algorithm group will initially receive
1000, 2500, or 4000 IU daily, with the initial dosing based on the 25(OH)D at baseline, and
the dosing may be adjusted at the 3-month visit.

Inclusion Criteria:

- Healthy, community-dwelling postmenopausal woman of self-reported European (Madison
site) or African (Milwaukee site) descent

- Able and willing to sign informed consent

- Baseline serum 25(OH)D concentration of 10.0-29.9 ng/mL

- Willing to not alter the amount of their baseline vitamin D supplementation during the
course of this study

- Willing to use sunscreen (SPF ≥15) when sun exposure of >15 minutes is expected during
the months of May through September

Exclusion Criteria:

- Diagnosis of kidney or liver disease (organs that metabolize vitamin D)

- Current hypercalcemia (serum calcium ≥ 10.5 mg/dL) or other disorders that may affect
vitamin D metabolism and predispose to hypercalcemia, i.e., sarcoidosis, active
tuberculosis or other granulomatous disease.

- Other chronic diseases or conditions potentially affecting vitamin D metabolism or
absorption (inflammatory bowel disease, cystic fibrosis, ulcerative colitis, and
malabsorptive surgery)

- History of nephrolithiasis

- Current use of medications that affect vitamin D metabolism (glucocorticoids,
anticonvulsants, antifungals, and HIV/AIDS medications)

- History of any form of cancer within the past two years with the exception of basal or
squamous cell skin lesions, in situ tumors or thyroid cancer

- Terminal illness/on hospice

- Severe end-organ disease (e.g., cardiovascular, pulmonary, etc.), which may limit the
ability to complete the study

- Treatment with high dose vitamin D (≥50,000 IU weekly) or any active metabolites of
vitamin D, e.g., calcitriol, within six months of screening; current use of multiple
vitamins and other vitamin D supplements will be allowed.

- Use of tanning beds or salons or unwillingness to utilize sunscreen during periods of
sun exposure of 15 minutes or longer from May through September

- Planned trips/vacations likely to be associated with substantial amounts of sun
exposure during the course of the study (i.e., more than 500 miles south of
Madison/Milwaukee)