Aims/hypothesis: Low 25-hydroxyvitamin D levels predict future cardiovascular events and are common in patients with type 2 diabetes. We compared the effect of 100,000 and 200,000 IU doses of vitamin D(3) on endothelial function, blood pressure and markers of glycaemic control in patients with type 2 diabetes.
Methods: This was a randomised, parallel group, placebo-controlled trial. Patients with type 2 diabetes and baseline 25-hydroxyvitamin D levels <100 nmol/l were enrolled from community and hospital-based diabetes clinics. Participants were assessed in a university department of clinical pharmacology and received a single oral dose of placebo or vitamin D(3) (100,000 IU or 200,000 IU) at baseline, randomly allocated via numbered bottles prepared offsite; participants and investigators were both blinded to treatment allocation. Endothelial function, office blood pressure, B-type natriuretic peptide, insulin resistance and glycosylated haemoglobin were measured at baseline, and at 8 and 16 weeks.
Results: We randomised 61 participants to the three groups (placebo 22, 100,000 IU vitamin D(3) 19, 200,000 IU vitamin D(3) 20). There was no significant difference in the primary outcome of endothelial function at 8 weeks (placebo 5.2%, n = 22; 100,000 IU 4.3%, n = 19; 200,000 IU 4.9%, n = 17) or at 16 weeks. Insulin resistance and glycosylated haemoglobin did not improve with either dose of vitamin D(3). On covariate analysis, systolic blood pressure was significantly lower in both treatment arms than in the placebo group at 8 weeks (placebo 146.4 mmHg, 100,000 IU 141.4 mmHg [p = 0.04 vs placebo], 200,000 IU 136.8 mmHg [p = 0.03 vs placebo]). B-type natriuretic peptide levels were significantly lower in the 200,000 IU group by 16 weeks (placebo 34 pg/ml, 200,000 IU 21 pg/ml, p = 0.02). No significant excess of adverse effects was noted in the treatment arms.
Conclusions/interpretation: High-dose vitamin D(3) improved systolic blood pressure and B-type natriuretic peptide levels, but not endothelial function, insulin resistance or glycosylated haemoglobin in patients with type 2 diabetes.