Korean J Pediatr 2012;55(6):206-211 • http://dx.doi.org/10.3345/kjp.2012.55.6.206 209 Fig. 1. Changes in vitamin D status (bars, left axis) and mean vi­ tamin D level (line, right axis) throughout the year. Vitamin D insu­ fficiency+deficiency was 76% in spring (March to May), 67% in winter (December to February), 33% in summer (June to August), and 22% in autumn (September to November) (P <0.001). The mean level of serum 25­ hydroxyvitamin D (25OHD) was significantly lower in spring/winter than in summer/autumn (24±20 vs. 47±26 ng/mL, P <0.001). Table 4. Odds Ratio for Vitamin D Deficiency in Iron Deficiency Anemia Patients Variable Odds ratio 95% CI Age (<24 mo) 5.19 0.55-49.36 Female sex 0.86 0.27-2.71 Breastfeeding 1.88 0.65-6.06 Serum Hb level 0.95 0.65-1.39 Vitamin D tested in winter/spring 5.66* 1.66-19.31 Hb, hemoglobin; CI, confidence interval. *P <0.05 currently or had recently been breastfed, and 97% of the subjects who were VDD had been breastfed. However, subjects with VDD or VDI did not have lower serum Hb, ferritin, or iron than those with sufficient levels of 25OHD. Children with VDD tended to be younger than 2 years old, to have been breastfed, and to have been tested in winter or spring. In our study, seasonal variation in vitamin D production was the greatest risk factor for VDD. Among children who were vitamin D deficient, only 6% had radiographic evidence of rachitic changes and only 1 child had had clinical signs of hypocalcemia. There is currently no consensus on the prevalence of rickets and VDD in young children in Korea, so we compared our data with that of several other countries, although their definitions of VDD or VDI were somewhat different. VDD defined as serum 25OHD less than 20 ng/mL (50 nmol/L) was present in 12% of children aged between 8 to 24 months in Boston (latitude 42° N)8). VDD defined as serum 25OHD less than 25 ng/mL was present in 8.1% of children in California (latitude 38.5° N) and 31% of children in Alaska (over 58° N)5,7). Low level of 25OHD defined as less than 20 ng/mL was present in 87% of children in Australia (latitude 37.4° S)11). Relative to our results, the prevalence of VDD was lower in three of these studies and higher in one study. The populations of three studies are healthy children and the Australian study enrolled East African immigrant children with significant skin pigmentation, decreased daylight exposure and low socioeconomic status, so those results may not be comparable to ours because of differences of populations. However, anemia itself may predispose patients to VDD, because anemic patients are often fatigued and may be less likely to go outside to obtain adequate sun exposure for vitamin D synthesis28). And several observations suggested the role of vitamin D in erythropoiesis29-31) and the correlation of VDD and a greater risk of anemia28). Thus, although there was no significant association between the severity of anemia and low serum level of 25OHD in our study, anemia may be related to vitamin D production and further investigation needs to be conducted in healthy children. Our univariate analysis indicated that the breastfeeding is one of the risk factors for VDD. Previous studies have also reported that breastfeeding without supplementation was a risk factor for VDD5,6,9,19,32). Human breast milk has low levels of vitamin D; hence, the American Academy of Pediatrics recommended that all breastfeeding infants, regardless of whether they are given formula supplements, should be given 400 IU of vitamin D per day33). But in multivariate logistic analysis, we did not find that the breastfeeding is an independent risk factor for VDD in children with IDA. In addition, we also found a positive correlation between younger age and VDD. This correlation may be because of decreased vitamin D stores in this age group, prolonged breastfeeding, increased vitamin D requirements due to skeletal growth and/or insufficient sun exposure. However, these explanations are speculative, and were not formally assessed by this study. Thus we compared the prevalence of VDD or VDI according to age, in spite of the asymmetrical distribution of age in our patients. The prevalence of VDD was greater in children younger than 2 years than in children older than 2 years (P<0.05). All children with radiologic evidence of rickets were younger than 2 years. Interestingly almost all subjects who had VDD received breastfeeding and the prevalence of breast feeding was 93% in children younger than 2 years. Although we did not fully assess the reason of significant correlation between the younger age and VDD, higher prevalence of breastfeeding may affect the higher prevalence of VDD in children younger than 2 years. In addition prevalence of VDD is decreased in children over 2 year but, 36% still had VDI. Another study suggested that age younger than 5 years was a risk