Impact of vitamin D treatment on 25 hydroxy vitamin D levels and insulin homeostasis in obese African American adolescents in a randomized trial

BACKGROUND: Obesity is affecting children in epidemic proportions in the United States with nearly 25% of children being obese. Consequences of obesity including dyslipidemia, type 2 diabetes and cardiovascular disease are leading to morbidity at younger ages. Parallel to the obesity and diabetes epidemics, the prevalence of vitamin D deficiency has reached very high levels and has been associated with insulin resistance and dyslipidemia. Studies exploring the impact of vitamin D repletion on insulin sensitivity and dyslipidemia in children are sparse. The aim of this study was to determine the impact of treatment with vitamin D (ergocalciferol) in obese African American (AA) children on vitamin D levels and insulin secretion and sensitivity. METHODS: This pilot study was conducted in a tertiary care Pediatric Emergency Department (ED). African American obese children (n = 29; 22 female) 13–17 y, with 25-hydroxy vitamin D level [25(OH)D] <20 ng/ml, were randomized to receive either 50,000 IU vitamin D(2)/week or a placebo for 12 weeks. Pre- and post- oral glucose tolerance testing with glucose and insulin levels drawn at 0, 30, 60, 90 and 120 min were performed. Pre/post intervention lipid profiles and calcium levels were also evaluated. RESULTS: There was no difference in serum 25(OH)D between groups at baseline. Follow-up 25(OH)D level was greater in the treatment vs. placebo group, and significantly increased from baseline in the treatment group only. However, there was no difference between groups in baseline vs. follow-up insulin- or lipid-related parameters. Follow-up serum 25(OH)D was positively correlated with fasting insulin and high-density lipoprotein (HDL) level in the vitamin D treated group only. CONCLUSION: While serum 25(OH)D levels in obese AA teens increased adequately with vitamin treatment for 12 weeks and correlated with fasting insulin, it did not significantly impact insulin secretion or sensitivity. Larger studies are required over a longer period of time to confirm and explore the reasons for this finding.