Improvement of Apolipoprotein B in Argentine Indigenous School Children after Vitamin D Supplementation V. Hirschler, G. Maccallini, M. Hidalgo, M. Sanchez, C. Molinari, C. Gonzalez Buenos Aires, Argentina. orresponding author: vhirschler@intramed.net Background: Concentration of Apo B provides a direct measure of the number of circulating atherogenic lipoprotein particles. Previous studies showed an association between low vitamin D and Apo B levels in indigenous children. Objective: To determine whether vitamin D supplementation improves non-traditional cardiovascular disease (CVD) risk factors such as Apo B levels among indigenous children. Study Design: A prospective two-year study evaluated a treated cohort of 190 children (104 males) aged 9.4± 2.2 years from a low socio-economic level. Anthropometric measures and serum levels of glucose, lipids, Apo B, and vitamin D were measured. All children received vitamin D supplementation of 100,000 u/year in 2013 or 2014 and were divided into two groups: group A had never been treated with vitamin D and received vitamin D in 2014 (n=104; 54.7%); while group B received vitamin D in 2013 but not in 2014 (n=86; 45.3%). Results: The prevalence of OW/OB per CDC was 12.7% (24). Several multiple regression linear analyses showed that changes in vitamin D were significantly associated with lower LDL-C levels (Beta-0.41, p< 0.01; R2 0.07); and with lower Apo B levels (Beta-0.37, p< 0.01; R2 0.17). Boxplot. Median levels and interquartile range for Apo B and LDL-C Comparison of Clinical Characteristics between Groups (Change= 2014-2013) Median change in Apo B and LDL-C concentration and interquartile range according to Groups A and B. Conclusions: These results suggest that vitamin D supplementation among indigenous children improved LDL-C and Apo B levels. Further studies are needed to determine the potential benefits of vitamin D supplementation.