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  • Title: Effects of vitamin D supplementation in older African American women.
    Author: Gallagher JC, Peacock M, Yalamanchili V, Smith LM.
    Journal: J Clin Endocrinol Metab; 2013 Mar; 98(3):1137-46. PubMed ID: 23386641.
    Abstract:
    CONTEXT: Serum 25-hydroxyvitamin D (25OHD) is lower in women with darker skin color. Is it due to lower skin production, lower absorption, or different metabolism of vitamin D? OBJECTIVES: The objective of the study was to measure the effect of vitamin D3 on serum 25OHD and serum PTH in older African American women with vitamin D insufficiency and the serum 25OHD 20 ng/mL or less (<50 nmol/L). The results can be used to estimate the Recommended Dietary Allowance (RDA). DESIGN AND SETTING: This was a randomized, double-blind placebo trial at Creighton University Medical Center and Indiana University Medical Center. PARTICIPANTS: Participants were 110 healthy older African American women. INTERVENTIONS: The intervention consisted of participants randomly assigned to placebo, vitamin D3 400, 800, 1600, 2400, 3200, 4000, or 4800 IU daily; calcium supplements were given to maintain total calcium intake of 1200-1400 mg/d. MAIN OUTCOME MEASUREMENTS: Change in serum 25OHD and serum PTH levels at 12 months was measured. RESULTS: Mean baseline serum 25OHD was 13 ng/mL (33 nmol/L). On 4800 IU, serum 25OHD averaged 50 ng/mL (125 nmol/L) compared with 47 ng/mL (117 nmol/L) in Caucasian women. Serum PTH at 12 months decreased significantly (P = .008) when related to serum 25OHD but not dose. Hypercalcemia occurred in 7% and hypercalciuria in 15%. Events were unrelated to vitamin D dose. CONCLUSION: Vitamin D3 800 IU increased serum 25OHD greater than 20 ng/mL (>50 nmol/L) in 97.5% of the African American women just as it did in the Caucasian women, and therefore, the RDA is the same for both groups. Because absorption and metabolism of oral vitamin D absorption is similar in both groups, lower levels of serum 25OHD in African Americans must be due to lower production of vitamin D in skin.
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