Large Doses of Vitamin D Fail to Increase 25-Hydroxyvitamin D Levels or to Alter Cardiovascular Risk Factors in Obese Adolescents: A Pilot Study.

Vitamin D deficiency and cardiometabolic risk factors are common in obese adolescents. Observational studies demonstrate an inverse relationship among serum 25-hydroxyvitamin D (25OHD) and obesity, insulin resistance, and inflammatory cytokines. This pilot study explores if vitamin D supplementation could reduce serum concentrations of inflammatory cytokines (interleukin [IL] 6, IL-10, tumor necrosis factor α), adiponectin, lipids, hemoglobin A1C, and high-sensitivity C-reactive protein (hs-CRP). A secondary aim was to determine the associations between baseline serum 25OHD concentrations and body mass index (BMI), hs-CRP, inflammatory cytokines, and lipids. Overweight and obese adolescents enrolled in this 24-week, randomized, double-blind study were given 150,000 IU ergocalciferol or placebo at baseline and 12 weeks. Outcome measurements included serum 25OHD, inflammatory cytokines, adiponectin, hs-CRP, lipids, hemoglobin A1C, and BMI at baseline, 12, and 24 weeks. Of 40 participants, 31 (78%) completed the study. Mean ± standard error 25OHD levels were similar in vitamin D and placebo groups at baseline (19.6 ± 5.3 vs. 25.8 ± 10.8 ng/mL) and 24 weeks (20.1 ± 3.4 vs. 24.6 ± 8.4 ng/mL). Inflammatory and cardiovascular markers were not significantly different between groups at 24 weeks. Serum 25OHD at baseline was associated with BMI (r = -.44 [95% confidence interval, -.66 to -.15]) but not with other outcome measures. Supplementation with vitamin D at 150,000 IU every 3 months failed to increase serum 25OHD or alter inflammatory markers and lipids in overweight and obese youth. Further studies are needed to establish the dose of vitamin D required to increase 25OHD and determine potential effects on metabolic risk factors in obese teens.