Dose response to vitamin D supplementation among postmenopausal African American women

Abstract

Background: Reports on the dose response to vitamin D are conflicting, and most data were derived from white men and women.

Objective: The objective was to determine the response of serum 25-hydroxyvitamin D [25(OH)D] to oral vitamin D(3) supplementation in an African American population.

Design: Healthy black postmenopausal women (n = 208) participated in a vitamin D(3) supplementation trial for a period of 3 y. Analyses were done in the vitamin D supplementation arm (n = 104) to quantify the response in serum 25-hydroxyvitamin D concentrations at a steady state vitamin D input. The participants received 20 microg/d (800 IU) oral vitamin D(3) for the initial 2 y and 50 microg/d (2000 IU) for the third year.

Results: Supplementation with 20 microg/d (800 IU/d) vitamin D(3) raised the mean serum 25(OH)D concentration from a baseline of 46.9 +/- 20.6 nmol/L to 71.4 +/- 21.5 nmol/L at 3 mo. The mean (+/-SD) concentration of serum 25(OH)D was 87.3 +/- 27.0 nmol/L 3 mo after supplementation increased to 50 microg/d (2000 IU/d). All participants achieved a serum 25(OH)D concentration >35 nmol/L, 95% achieved a concentration >50 nmol/L, but only 60% achieved a concentration >75 nmol/L. All patients had concentrations <153 nmol/L. On the basis of our findings, an algorithm for prescribing vitamin D so that patients reach optimal serum concentrations was developed. The algorithm suggests a dose of 70 microg (2800 IU/d) for those with a concentration >45 nmol/L and a dose of 100 microg (4000 IU/d) for those with a concentration <45 nmol/L.

Conclusions: Supplementation with 50 microg/d (2000 IU/d) oral vitamin D(3) is sufficient to raise serum 25-hydroxyvitamin D concentrations to >50 nmol/L in almost all postmenopausal African American women. However, higher doses were needed to achieve concentrations >75 nmol/L in many women in this population.

FIGURE 1

Mean (± SD) changes from baseline in 25-hydroxyvitamin D [25(OH)D] concentrations in the vitamin D (solid line) group and the placebo group (dashed line) throughout the 36-mo study period. A significant group-by-time interaction was observed (P < 0.0001).

FIGURE 2

Mean (± SD) urinary calcium excretion by weight in the vitamin D group (solid line) and the placebo group (dashed line) throughout the 36-mo study period. Calcium excretion remained stable throughout the study. No significant group-by-time interaction was observed.