Effect of vitamin D3 supplementation on vascular and metabolic health of vitamin D-deficient overweight and obese children: a randomized clinical trial.

Randomized clinical trial in vitamin D-deficient overweight or obese children and adolescents aged 10-18 years, predominantly Black. The study assessed vascular and metabolic outcomes over 6 months.

Oral vitamin D3 tablets (Douglas Laboratories) were given daily for 6 months in two active doses: 1000 IU/day or 2000 IU/day. Both active doses were compared with 600 IU/day.

Vitamin D3 at 1000 or 2000 IU/day increased vitamin D status but did not improve arterial endothelial function or arterial stiffness versus 600 IU/day. The clearest benefits were metabolic and blood-pressure related, especially in the 1000 IU/day group: central systolic BP was lower by -2.66 (95% CI -5.27, -0.046), central diastolic BP by -3.57 (95% CI -5.97, -1.17), systemic diastolic BP by -3.28 (95% CI -5.55, -1.00), and fasting glucose by -2.67 (95% CI -4.88, -0.46) versus 600 IU/day. Insulin also improved at 3 and 6 months (0.014; 95% CI 0.0015, 0.026 and 0.015; 95% CI 0.0019, 0.027), and the 2000 IU/day group showed a modest BMI reduction versus 600 IU/day (-0.59; 95% CI -1.12, -0.062). Lipids and other secondary outcomes were not significantly different, and the authors concluded that vitamin D optimization may support cardiovascular health in this population despite no observed vascular-function benefit.

Follow-up was only 6 months, and the trial did not show benefit on the main vascular endpoints. The sample was from a single center and predominantly Black, which limits generalizability. Per-arm dietary and physical activity data were limited, and several outcomes showed no significant group-by-time interaction, including lipids and other secondary measures.