J Pediatr Endocr Met 2012;25(1-2):83–87 © 2012 by Walter de Gruyter • Berlin • Boston. DOI 10.1515/jpem-2011-0426 *Corresponding author: Samim Ozen, Mersin Children’s Hospital, Department of Pediatric Endocrinology, 33240 Guneykent, Toroslar, Mersin, Turkey Phone: +90 324 223 07 01, Fax: +90 324 223 07 22, E-mail: samimozen@gmail.com Received October 5, 2011; accepted December 10, 2011; previously published online January 17, 2012 The relation of vitamin D deficiency with puberty and insulin resistance in obese children and adolescents Muammer Buyukinan 1 , Samim Ozen 2, *, Serap Kokkun 3 and Eylem Ulas Saz 4 1 Department of Pediatric Endocrinology, Dr. Behcet Uz Children’s Training and Research Hospital, 35020 Izmir, Turkey 2 Department of Pediatric Endocrinology, Mersin Children’s Hospital, 33240 Toroslar, Mersin, Turkey 3 Department of Pediatrics, Dr. Behcet Uz Children’s Training and Research Hospital, 35020 Izmir, Turkey 4 Department of Pediatrics, School of Medicine, Ege University, 35100 Bornova, Izmir, Turkey Abstract The prevalence of obesity among children and adolescents has been rapidly increasing in recent years. Obese individuals are at risk for vitamin D deficiency. The aim of this study was to investigate the relation of vitamin D deficiency with puberty and insulin resistance in obese children and adolescents. A total of 106 children and adolescents (48 prepubertal and 58 pubertal) between 8 and 16 years of age were included in the study. Fasting blood glucose, insulin, lipid profile, calcium, phosphorus, alkaline phosphatase, parathyroid hormone, 25-hydroxyvitamin D [25(OH)D] levels, as well as blood glucose and insulin concentrations at 120 min of oral glucose tolerance test were measured. Insulin resistance was calcu- lated using the homeostasis model assessment. Daily vitamin D intake was questioned. Serum 25(OH)D level was normal in only 3.8%, insufficient in 34.0%, and deficient in 62.2% of the subjects. There was a statistically significant rate of 25(OH)D deficiency in the pubertal group compared with that in the prepubertal group. Those subjects with 25(OH)D defi- ciency were found to have greater insulin resistance. Vitamin D deficiency is common among obese children and adoles- cents. Low vitamin D levels in obese individuals may acceler- ate the development of metabolic syndrome, type 2 diabetes mellitus, and cardiovascular disease by further increasing insulin resistance. Keywords: insulin resistance; obesity; puberty; vitamin D. Introduction Obesity is a major public health problem worldwide due to its constantly increasing prevalence. Its prevalence in child- hood is also progressively increasing due to reduction in physical activity and changes in nutritional habits. Obesity in children is defined as a body mass index (BMI) ≥ 95th percentile. Obesity is considered a significant health problem in children as it leads to insulin resistance, type 2 diabetes mellitus (DM), hypertension, dyslipidemia, atherosclero- sis, and coronary heart diseases in the future (1–3). Obese individuals are at high risk for vitamin D deficiency. Recent studies have shown that vitamin D deficiency is positively correlated with BMI in obese subjects (3–5). Pancreatic islet cells contain vitamin D receptors (VDR), and these receptors are controlled by 1,25-dihydroxyvitamin D [1,25(OH)2D]. Therefore, increasing insulin secretion and sensitivity is one of the well-known endocrine functions of vitamin D (6). Vitamin D deficiency has been found to be associated with insulin resistance, impaired glucose tolerance, and type 2 DM in adult studies (7–12). Vitamin D requirement is especially increased during puberty due to the dramatic increase in bone turnover and growth (1, 2). Measurement of serum 25-hydroxyvitamin D [25(OH)D] levels is considered the best indicator of vitamin D status because 25(OH)D is the major metabolite and represents the stored form of vitamin D. Serum 25(OH)D levels of ≥ 75 nmol/L (30 ng/mL) are defined as normal, 50–75 nmol/L (20–30 ng/mL) as insufficiency, and < 50 nmol/L (20 ng/mL) as deficiency (4–6). Parathyroid hormone (PTH), which is closely associated with vitamin D levels, is another hormone with significant effects on calcium (Ca) metabolism. In the presence of vitamin D deficiency, serum Ca homeostasis is preserved by an increase in PTH, while excessive PTH syn- thesis is inhibited by 1,25(OH)2D (1, 2). Few studies have investigated the relation between insu- lin and carbohydrate metabolism, and vitamin D deficiency, which is rather common during childhood due to continuous growth and development. The aim of this study was to inves- tigate the relation of vitamin D deficiency with puberty, insu- lin resistance, and metabolic syndrome in obese children and adolescents. Patients and methods A total of 106 Turkish children and adolescents (52 boys and 54 girls) between the ages of 8 and 16 years and with BMI ≥ 95th per- centile, admitted to the outpatient clinic of Pediatric Endocrinology between November 2009 and February 2010, were included in the study. Patients with obesity due to syndromic or endocrine causes; Brought to you by | University of California - San Francisco Authenticated Download Date | 2/18/15 6:09 PM