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J Clin Endocrinol Metab. 2013 Mar;98(3):1137-46. doi: 10.1210/jc.2012-3106. Epub 2013 Feb 5.

Effects of vitamin D supplementation in older African American women.

Author information

  • 1Bone Metabolism Unit, Creighton University School of Medicine, 601 North 30th Street, Suite 6718, Omaha, Nebraska 68131, USA. jcg@creighton.edu

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.

PMID:
23386641
[PubMed - indexed for MEDLINE]
PMCID:
PMC3590472
Free PMC Article

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