Effect of short-term vitamin D supplementation on markers of vascular health in South Asian women living in the UK - A randomised controlled trial

Objective: Low vitamin D levels and risk factors for vascular disease are both common in South Asian women. This trial evaluated whether vitamin D supplementation could improve markers of vascular health in South Asian women with low 25-hydroxyvitamin D levels. Methods: Parallel-group, double-blind, randomised placebo-controlled trial. Healthy South Asian women with baseline serum 25-hydroxyvitamin D levels of <75 nmol/L were randomised to receive a single dose of 100,000 units oral vitamin D3 or matching placebo. Outcomes were measured at baseline, 4 and 8 weeks. The primary outcome was change in endothelial function measured using brachial artery flow-mediated dilatation. Secondary outcomes included blood pressure, arterial stiffness, microvascular function measured using laser Doppler iontophoresis, insulin resistance, serum lipids, circulating markers of inflammation, thrombosis and adipokines. Results: 50 women were randomised, 25 to each group. Mean age was 41 years; mean baseline 25-hydroxyvitamin D level was 27 nmol/L. 25-Hydroxyvitamin D levels rose in the vitamin D group relative to the placebo group by 4 weeks (16 nmol/L, 95% CI 11 to 21, p < 0.001). There was no improvement in flow-mediated dilatation in the vitamin D group relative to placebo at 4 weeks (0.1%, 95% CI -0.9 to 1.1, p = 0.84) or 8 weeks (0.0%, 95% CI -1.4 to 1.4, p = 0.98). There was no improvement in cholesterol, insulin resistance or markers of inflammation. Both platelet activation inhibitor-1 and tissue plasminogen activator levels fell significantly in the vitamin D group relative to placebo at 8 weeks. Conclusion: A single large dose of vitamin D3 did not improve blood pressure or endothelial function in South Asian women with low baseline 25-hydroxyvitamin D levels. Trial registration: ISRCTN75081811. (C) 2013 Elsevier Ireland Ltd. All rights reserved.