Effect of vitamin D₃ treatment on endothelial function in obese adolescents

Background: Obesity in children is associated with vitamin D deficiency and endothelial dysfunction. It is not known if treatment with vitamin D improves endothelial function in obese adolescents. Objective: This study aimed to determine whether treatment with vitamin D₃ improves endothelial function in obese adolescents. Methods: Nineteen obese adolescents, 13–18 years of age, with 25-hydroxy vitamin D (25[OH]D) levels <75 nmol L⁻¹ were treated with 100 000 IU vitamin D₃ orally once a month for 3 months in an open-label, single-centre prospective trial. Endothelial function was assessed by flow-mediated dilatation (FMD) of the brachial artery at study entry and 1 month after the third dose of vitamin D₃. Biochemical parameters, including calcium, fasting lipids, glucose, insulin and high-sensitivity C-reactive protein, were also obtained. Results: Mean 25(OH)D levels increased from 55.9 ± 12.2 to 86.9 ± 16.7 nmol L⁻¹ (P < 0.01). There was no correlation between 25(OH)D levels and brachial artery FMD. The brachial artery FMD (%) did not change significantly following vitamin D₃ treatment (9.5 ± 3.53 vs. 10.3 ± 3.83, P = 0.83). Serum parathyroid hormone declined from 3.8 ± 1.5 to 3.1 ± 1 pmol L⁻¹ (P = 0.01). The remainder of biochemical measurements did not show a significant change. Conclusions: Treatment with vitamin D₃, 100 000 IU once a month for 3 months was effective in increasing 25(OH)D levels in obese adolescents but did not impact endothelial function.