Investigation of B12 vitamin deficiency with the serum metylmalonic acid and homocysteine levels in obese adolescents and comparison with normal weight adolescents

Introduction and Aim: Obesity is defined as abnormal or excessive fat accumulation that presents a risk to health by World Health Organization. Obesity was a high priority health problem for adults for last century, now it has become threatening for children and adolescents by increasing prevalence three times in last 20 years. Parents who have obese child might be mistaken for assuming that their child has no lack of nutrients due to their excessive food consumption. However, especially in puberty children start to eat independently from their parents, thus, consumption of carbohydrates and fat can increase and it can lead lack of nutrients. Besides eating protein-poor food, non-alcoholic fatty liver disease (NAFLD) which has big incidence to occur in obese people, lead B12 vitamin deficiency. In clinic laboratories, serum B12 vitamin level is measured to determine B12 level in the body. However, due to limitations of this method, level of B12 vitamin inside the cell cannot be detected. Recently, methylmelanoic acid (MMA) and homocysthein (Hcy), which are specific and functional biomarkers of B12 vitamin, have been measured to detect B12 level inside the cells. Aim of this study is to compare B12 vitamin levels between obese and normal weighted adolescences and analyse functional markers of B12 in diagnosis of B12 vitamin deficiency. Methods and Materials: 12-18 age ranged 58 obese adolescents and 30 normal weighted adolescents participated to this study. Serum B12 vitamin, ferritin and folic acid levels were measured with automated photometric technique. Hcy level was measured with automated chemiluminescence method. Plasma MMA was measured with liquid chromatography-tandem mass spectrometry technique. In order to determine analytic performance of MMA measurement, optimization of quantitation limits, determination limits and accuracy between days and intradays were done. Data were statistically analysed using SPSS 21.0 program. Statistical significance was taken as p≤0.05. Results: Accuracy of MMA technique was %100 ± 4 (0,1-2,5 µmol/L ranged calibration standards were used). Incline was linear. CV% of intraday and between days was less than 4. Determination and quantitation limits were 0,03 μmol/L and 0,06 μmol/L, respectively. When we compared Obese and normal weight groups based on MMA levels, there was a significant difference between the groups. However, homocysteine and B12 vitamin levels were similar within the groups. Obese adolescents have 12% probability to have B12 vitamin deficiency if we based on only serum B12 vitamin level, however, if we consider MMA levels, the B12 deficiency is nearly %65, if we consider Hcy level, the deficiency probability is 22,5%. Combine B12 were significantly different between obese and normal weight adolescents. After performing ROC analysis, the area under the slope calculated as 0,897 for Hcy, 0,857 for MMA and 0,148 for serum B12. Conclusion: Our study showed that despite non-obese and obese adolescents have normal serum B12 vitamin level, levels of MMA and Hcy, which are markers of functional B12 vitamin, were not in the normal range, obese group had more tendency to have functional B12 deficiency compared to the non-obese group. Key words: Obesity, adolescent, B12 vitamin, functional B12 vitamin deficiency, homocysteine, methylmalonic acid, non-alcoholic fatty liver disease, LC MS/MS, cobalamin, deficiency, combine B12, ROC curve