Korean J Pediatr 2012;55(6):206-211 • http://dx.doi.org/10.3345/kjp.2012.55.6.206 207 VDD and nutritional rickets in children and adolescents from the United States5-10) and other countries11-14). There are several risk factors for VDD in infants and children, including limited sun exposure because of residence in northern latitudes, dark skin, excessive use of sun block, and reliance on breastfeeding without adequate supplementation5,6,15-19). In particular, a previous study reported that exclusive breastfeeding is a risk factor for iron deficiency anemia (IDA) in infants, that the risk of IDA at 9 months was higher in exclusively breastfed infants, and that infants given iron supplements had better visual acuity and higher psychomotor and developmental scores at 13 months than infants not given iron supplemen20). In recent years, breast feeding has become more common in Korea and other countries, prompting concern that IDA and VDD may also be increasing in infants and children21,22). Children in Korea may be vulnerable to IDA and VDD because of Korea’s relatively northern latitude, skin pigmentation, and the increasing prevalence of breastfeeding. In the present study, we evaluated the prevalence of VDD in Korean children with IDA and assessed the risk factors of VDD. Materials and methods 1. Subjects and data collection Seventy-nine children, 4 months to 13 years in age, who were diagnosed with IDA at our institution (latitude 37.4° N) between April 2010 and March 2011 were prospectively enrolled. Data on demographics, birth history, feeding practices, micronutrient supplements, immunization status, and medical history were collect- ed by questionnaire. The parent study also evaluated anemia and dietary supplementation. Feeding patterns were grouped into three categories with regard to use of breast milk, cow's milk, and formula. All subjects were examined by a pediatrician for evidence of illness. This examination included a full blood panel, and measurement of serum levels of reticulocytes, ferritin, iron, total iron-binding capacity (TIBC), 25-hydroxyvitamin D (25OHD), alkaline phosphatase (ALP), phosphate, and calcium. Wrist radiographs were performed to assess bone status. 2. Definitions of anemia and VDD IDA was defined as hemoglobin (Hb) less than 11 g/dL and serum ferritin less than 12 ng/mL for both males and females23). Serum ferritin is an acute-phase reactant, so concentrations may be elevated in the presence of chronic inflammation, infection, or liver disease, and simultaneous measurement of C-reactive protein (CRP) is required to rule out inflammation. In this study, if serum ferritin was greater than 12 ng/mL, we considered the clinical symptoms and measured CRP and diagnosed for IDA if the mean corpuscular volume (MCV) was below than 70 fL, red blood cell distribution width (RDW) was elevated, and transferrin saturation was below 15%. There is no consensus on the measurement and definition of VDD and its functional outcomes in children24,25). In this study, VDD was defined as serum 25OHD less than 20 ng/mL8,10,26,27); vitamin D insufficiency (VDI) was defined as serum 25OHD between 20 and 30 ng/mL25,27); and vitamin D sufficiency was defined as 25OHD greater than 30 ng/mL. Serum 25OHD levels were measured by a radioimmunoassay kit from DiaSorin (Stillwater, MN, USA). Radiologic evidence of rickets was defined as the presence of fraying of the epiphyseal edges, cupping of the epiphyses, widening of the wrist, or angulation of the distal forearm bones. All radiographs were reviewed by a single radiologist who was blinded to serum vitamin D levels. 3. Statistical analysis Data are expressed as means±SDs. Statistical analysis was performed with the SPSS ver. 17.0 (SPSS Inc., Chicago, IL, USA). The quantitative parameters of the groups were compared by t-tests. The chi-square and Fisher's exact tests were used to compare categorical variables. Multivariable logistic regression was used to examine the simultaneous influence of several variables on the risk for VDD. Significance was evaluated using a two-sided P value of less than 0.05 with a confidence interval (CI) of 95%. Results Table 1 shows the demographic and clinical characteristics of the 79 IDA children who were eligible for enrollment. The mean age at enrollment was 21.7±35.4 months and the mean body mass index Table 1. Clinical Characteristics of Children with Iron Deficiency Anemia Characteristics n=79 Female sex 24 (30) Age (mo) 21.7±35.4 Body mass index (kg/m2) 17.3±1.8 Preterm delivery 21 (27) Breastfeeding 70 (89) Vitamin-mineral supplement 15 (19) History of admission* 43 (54) History of maternal anemia 19 (24) Values are presented as number (%) or mean±SD. *Bronchiolitis, pneumonia, gastroenteritis, urinary tract infection or otitis media.