A randomized controlled trial of vitamin D3 supplementation in African American women.

BACKGROUND: We conducted a randomized, placebo-controlled, double-blind trial to test the hypothesis that vitamin D(3) supplementation would prevent bone loss in calcium-replete, African American postmenopausal women.

METHODS: Two hundred eight healthy black postmenopausal women, 50 to 75 years of age, were assigned to receive either placebo or 20 microg/d (800 IU) of vitamin D(3). Calcium supplements were provided to ensure a total calcium intake of 1200 to 1500 mg/d. After 2 years, the vitamin D(3) dose was increased to 50 microg/d (2000 IU) in the active group, and the study continued for an additional year. Bone mineral density (BMD) was measured every 6 months. Markers of bone turnover, vitamin D metabolites, and parathyroid hormone (PTH) levels were measured in serum.

RESULTS: There were no significant differences in BMD between the active and control groups throughout the study. There was also no relationship between serum 25-hydroxyvitamin D levels attained and rates of bone loss. There was an increase in BMD of the total body, hip, and radius at 1 year in both groups. Over the 3 years, BMD declined at these sites by 0.26% to 0.55% per year. The BMD of the lumbar spine increased slightly in the placebo and active groups. There were no persistent changes in serum PTH levels or the markers of bone turnover, although there was a transient decline in PTH in both groups at 3 months. No significant adverse events were attributed to vitamin D supplementation.

CONCLUSIONS: There was no observed effect of vitamin D(3) supplementation on bone loss or bone turnover markers in calcium-replete, postmenopausal African American women. Further studies are needed to determine if these findings are applicable to women of other ethnic groups.