Hindawi Publishing Corporation BioMed Research International Volume 2013, Article ID 921348, 6 pages http://dx.doi.org/10.1155/2013/921348 Research Article Possible Role of Hyperinsulinemia and Insulin Resistance in Lower Vitamin D Levels in Overweight and Obese Patients Giovanni De Pergola, 1 Alessandro Nitti, 1 Nicola Bartolomeo, 2 Antonella Gesuita, 1 Vito Angelo Giagulli, 3 Vincenzo Triggiani, 4 Edoardo Guastamacchia, 4 and Franco Silvestris 1 1 Clinical Nutrition Unit, Department of Biomedical Sciences and Human Oncology, Section of Clinical Oncology, School of Medicine, University of Bari, Policlinico, Piazza Giulio Cesare 11, 70124 Bari, Italy 2 Department of Biomedical Sciences and Human Oncology, School of Medicine, University of Bari, Policlinico, Piazza Giulio Cesare, 70124 Bari, Italy 3 Outpatient Clinic for Metabolic Diseases and Endocrinology, Conversano Hospital, ASL Bari, 70014 Conversano, Italy 4 Section of Endocrinology and Metabolic Diseases, Department of Emergency and Organ Transplantation, School of Medicine, University of Bari, Policlinico, Piazza Giulio Cesare, 70124 Bari, Italy Correspondence should be addressed to Giovanni De Pergola; gdepergola@libero.it Received 5 August 2012; Revised 6 December 2012; Accepted 8 December 2012 Academic Editor: Joseph Fomusi Ndisang Copyright © 2013 Giovanni De Pergola et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A cohort of 66 healthy overweight and obese patients, 53 women and 13 men were examined. Waist circumference and fasting 25(OH)D, insulin, glucose, lipid (cholesterol, HDL cholesterol, and triglyceride), C-reactive protein (CRP), and complement 3 (C 3 ), and 4 (C 4 ) serum concentrations were measured. Insulin resistance was assessed by the homeostasis model assessment (HOMA IR ). Results. 25(OH)D levels showed a signi�cant negative correlation with BMI (  ), waist circumference (  ), fasting insulin (  ), HOMA IR (  ), triglycerides (  ), CRP (  ), C 3 (  ), and C 4 (  ). Multiple regression analyses were performed with 25(OH)D as the dependent variable and BMI (or waist circumferences), fasting insulin (or HOMA IR ), triglycerides, and CRP (or C 3 or C 4 ) as independent variables. Only insulin or HOMA IR maintained a signi�cant independent association with 25(OH)D levels, whereas vitamin D did not maintain a signi�cant independent association with CRP or C 3 or C 4 concentrations. Conclusions. e present study, performed in overweight and obese subjects, shows that 25(OH)D levels are negatively associated with in�ammatory parameters such as CRP and C 3 and C 4 levels, but not independently of BMI, body fat distribution, insulin levels, or insulin resistance. Our results suggest that hyperinsulinemia and/or insulin resistance are directly responsible for decrease of 25(OH)D levels in obesity. 1. Introduction Vitamin D is well known to be involved in the calcium and bone metabolism, and most observational and random- ized placebo-controlled trials concerning this vitamin have focused on the skeletal effects and have linked low vitamin D levels to fractures [1–3]. However, interest is growing in the nonskeletal effects of vitamin D [4] and in the relationship between vitamin D de�ciency and diseases such as obesity, diabetes mellitus, and metabolic syndrome. Serum 25-hydroxyvitamin D3 (25(OH)D) level re�ects total vitamin D from dietary intake and sunlight exposure, as well as the conversion of vitamin D from adipose stores in the liver. erefore, it is the best indicator of overall vitamin D status [5]. Several studies have demonstrated that serum 25(OH)D concentrations are inversely correlated with measures of obesity such as body mass index (BMI), waist circumference, and subcutaneous and visceral fat [6–10]. Insulin resistance and hyperinsulinemia are typical fea- tures of abdominal obesity, and, interestingly, inverse asso- ciations between 25(OH)D levels and fasting insulin concen- trations [11–13] or insulin resistance (measured by HOMA IR index) [11–13] or insulin sensitivity index [14, 15] have been