Vitamin D3 supplementation for 16 weeks improves flow-mediated dilation in overweight African-American adults.

BACKGROUND: A growing body of evidence has linked vitamin D deficiency to increased risk of cardiovascular disease. Vitamin D deficiency is also more common in African Americans for whom an increased cardiovascular disease risk exists. This study sought to test the hypothesis that 16 weeks of 60,000 IU monthly supplementation of oral vitamin D(3) would improve flow-mediated dilation (FMD) in African Americans, whereas no change would be observed in the placebo group. METHODS: A randomized, double-blind, placebo-controlled clinical trial was conducted. Fifty-seven African-American adults were randomly assigned to either the placebo group or vitamin D group. RESULTS: Following 16 weeks of placebo (n = 23; mean age 31 ± 2 years) or 60,000 IU monthly oral vitamin D(3) (n = 22; mean age 29 ± 2 years), serum concentrations of 25-hydroxyvitamin D (25(OH)D) increased from 38.2 ± 3.0 to 48.7 ± 3.2 nmol/l and 34.3 ± 2.2 to 100.9 ± 6.6 nmol/l, respectively. No changes in serum parathyroid hormone (PTH), serum calcium, or urine calcium/creatinine were observed following either treatment. Following 16 weeks of treatment, significant improvements in FMD were only observed in the vitamin D group (1.8 ± 1.3%), whereas the placebo group had no change (-1.3 ± 0.6%). Similarly, the vitamin D group exhibited an increase in absolute change in diameter (0.005 ± 0.004 cm) and FMD/shear (0.08 ± 0.04 %/s(-1), area under the curve (AUC) × 10(3)) following treatment, whereas no change (-0.005 ± 0.002 cm and -0.02 ± 0.02 %/s(-1), AUC, respectively) was observed following placebo. CONCLUSION: Supplementation of 60,000 IU monthly oral vitamin D(3) (~2,000 IU/day) for 16 weeks is effective at improving vascular endothelial function in African-American adults.

A 16-week randomized clinical trial of 2000 international units daily vitamin D3 supplementation in black youth: 25-hydroxyvitamin D, adiposity, and arterial stiffness.

CONTEXT: Vitamin D insufficiency/deficiency is commonly observed in black youth. OBJECTIVE: The aim was to determine 25-hydroxyvitamin D [25(OH)D] in response to 2000 IU vitamin D supplementation over time; to evaluate the relation between 25(OH)D concentrations and total body fat mass by dual-energy x-ray absorptiometry; and to determine whether vitamin D supplementation improves arterial stiffness measured by pulse wave velocity (PWV). DESIGN: We conducted a randomized, blinded, controlled clinical trial. SETTING AND PARTICIPANTS: Forty-nine normotensive black boys and girls, aged 16.3 ± 1.4 yr, were randomly assigned to either the control group (400 IU/d; n = 24) or the experimental group (2000 IU/d; n = 25). RESULTS: Plasma 25(OH)D values at baseline and at 4, 8, and 16 wk were 34.0 ± 10.6, 44.9 ± 9.4, 51.2 ± 11.1, and 59.8 ± 18.2 nmol/liter, respectively, for the control group; and 33.1 ± 8.7, 55.0 ± 11.8, 70.9 ± 22.0, and 85.7 ± 30.1 nmol/liter, respectively, for the experimental group. The experimental group vs. the control group reached significantly higher 25(OH)D concentrations at 8 and 16 wk, respectively. Partial correlation analyses indicated that total body fat mass at baseline was significantly and inversely associated with 25(OH)D concentrations in response to the 2000-IU supplement across time. Furthermore, carotid-femoral PWV increased from baseline (5.38 ± 0.53 m/sec) to posttest (5.71 ± 0.75 m/sec) in the control group (P = 0.016), whereas in the experimental group carotid-femoral PWV decreased from baseline (5.41 ± 0.73 m/sec) to posttest (5.33 ± 0.79 m/sec) (P = 0.031). CONCLUSION: Daily 2000 IU vitamin D supplementation may be effective in optimizing vitamin D status and counteracting the progression of aortic stiffness in black youth. Plasma 25(OH)D concentrations in response to the 2000 IU/d supplementation are negatively modulated by adiposity.