In this study, we will test the central hypothesis that enhancement of vitamin D status in obese and overweight children will improve their vascular health and their cardiovascular disease (CVD) and metabolic syndrome risk profile.

Our primary objective is to determine, in obese and overweight children aged 10 to 18 years with vitamin D deficiency (defined as serum 25-hydroxyvitamin D <20 ng/mL), the efficacy of enhanced vitamin D3 supplementation in improving vascular endothelial function, arterial stiffness, insulin sensitivity, and metabolic syndrome risk status; and to assess whether these effects are dose-dependent. As a secondary objective, we will examine the vitamin D supplementation-induced effect on adipokines and inflammatory markers relevant to CVD risk. In a double-masked, controlled trial, we will randomize 252 eligible children to receive either 600 IU (conventional supplementation), or 1000 IU or 2000 IU (enhanced supplementation) of vitamin D3 daily for 6 months.

In terms of reporting of results, the following pre-specified outcomes are included in the primary manuscript (PubMed PMID:31950134 -- see Reference section for citation details)

1. Waist Circumference
2. Serum High Density Lipoprotein (HDL) Cholesterol
3. Serum Triglycerides
4. Inflammatory markers (Plasma TNF-alpha, high-sensitivity C-reactive protein, and IL-6)
5. Adiopkines (Plasma Leptin and Adiponectin)

Plasma nitric oxide metabolites were not measured.

Inclusion Criteria:

• Eligible subjects will be 10 to 18 years of age;
• obese or overweight (BMI ≥85th %tile);
• otherwise healthy, and
• have a serum 25(OH)D concentration <20 ng/mL

Children taking multivitamins should be able to hold off their multivitamins during the course of the study.

Exclusion Criteria:

Children will be excluded if they

• (a) have hepatic or renal disease, metabolic rickets, malabsorptive disorders, primary hyperparathyroidism, hyperthyroidism, or other chronic disorders that could affect vitamin D metabolism;
• (b) are receiving treatment with anticonvulsants, systemic glucocorticoids, pharmacologic doses of vitamin D (≥1000 IU of vitamin D2 or D3 daily), antihypertensives, vasoactive drugs, antilipidemics, metformin, antipsychotics, or other oral insulin regulators;
• (c) have cholelithiasis or urolithiasis;
• (d) have type 1 or type 2 diabetes; or
• (e) have a condition or underlying abnormality that could compromise the safety of the subject.

Post-menarchial girls with a positive pregnancy test at randomization, or subjects found during the screening phase to have hypercalcemia (serum calcium >10.8 mg/dL) or significant fasting hyperglycemia (fasting blood glucose ≥ 125 mg/dL) will also be excluded.

6 months

Our findings of reductions in central-systolic BP and fasting glucose concentrations and improvement in insulin sensitivity lack adjustment for multiplicity and therefore should be considered as hypothesis-generating and interpreted with caution.