الفهرس 
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Abstract
Obesity is a worldwide epidemic that is not restricted to adults. Unfortunately, child and adolescent obesity has become a major public health problem (Jia et al., 2021). It is a complex interaction between biological, developmental, behavioral, genetic, and environmental factors (Biener et al., 2020). The main factors causing child obesity are unhealthy eating habits, physical inactivity and over exposure to aggressive marketing from the catering corporate making energy dense foods and drinks more tempting, affordable and readily available (Smith et al., 2020). Obesity is strongly associated with multiple co-morbidities as insulin resistance (IR), dyslipidemia, cardiovascular disease, diabetes mellitus, hypertension, osteoarthritis, sleep apnea, and stroke (Viitasalo et al., 2019). It is known that people who are overweight or obese commonly experience poorer antioxidant protection, and oxidative stress levels are elevated in obesity (Furukawa et al., 2017). Selenium is an essential trace element which possesses the symbol (Se), it was discovered by Swedish chemist Jons Jacob Berzelius in the year 1817 (Minich, 2022). It has antioxidant properties and protective role against oxidative damages (Zhong et al., 2018). Physiological functions of Se are mainly mediated through Se-containing proteins, selenoproteins containing Se in the form of selenocysteine. Selenoproteins, such as glutathione peroxidases and selenoprotein-p, were initially recognized as antioxidants that catalyzes the degradation of organic hydroperoxides (Hariharan & Dharmaraj, 2020). Dietary Se intake is considered as the key determinant of selenium status. However, certain internal factors may also affect dietary Se intake by limiting its bioavailability. Particularly, gut microbiota may mediate the effects of dietary Se on Se status of the host through modulation of selenoprotein metabolism (Rayman, 2020). Selenoprotien p1 (SEPP1) is considered as one of the most sensitive functional markers of Se status. SEPP1 functions as a Se transporter to maintain antioxidative seleno-enzymes in several tissue, and it plays a crucial role in the metabolism of Se and in anti-oxidative defense. So, a decrease in the level of SEPP1 and selenoproteins causes various dysfunctions related to oxidative stress (Siato, 2019). The Aim of This work was to assess Selenoprotein-p as biomarker of selenium status in obese children and adolescents, and to evaluate the association between adiposity indices and selenium status in these children. This cross-sectional comparative study was carried out upon sixty children. The cases were collected from the out-patient clinic of Pediatric Clinical Nutrition Unit of Pediatric Department, Tanta University hospital in the period between January 2021 and December 2022. Informed written parental consent was obtained from every case that participated in this research. The study was approved by the Ethics committee of Faculty of Medicine, Tanta University. They were classified as follows: group 1 (Patient Group): included thirty obese children according to definition of Centers for Disease Control and Prevention (CDC) with BMI ≥ 95th percentile for age and sex (CDC, 2021). group 2 (Control Group): included thirty age and sex matched, apparently healthy children. All Children and adolescents with the study were subjected to: A. Full history taking including: Past history for systemic diseases, Drug administration (corticosteroids, antithyroid drugs, use of other drugs), family history of obesity, hypertension and diabetes, complete dietetic history including 24hr diet recall analysis and asking about food habits. B. Thorough clinical examination: Thorough medical examination (head & neck, chest, heart, abdomen, upper &lower limbs). C. Anthropometric measures: Weight, height, body mass index (BMI) and waist circumference. All measures were plotted on growth charts and Z-scores calculations were done. D. Blood pressure (Systolic and Diastolic) were measured carefully using a proper-sized cuff. E. Body composition analysis using Bioelectrical Impedance Analysis F. Investigations included: • Routine investigations [CBC, serum ALT and AST, blood urea, serum creatinine, serum Lipid profile (total cholesterol, triglycerides, High density lipoprotein cholesterol (HDL) and Low-density lipoprotein cholesterol (LDL)) and HOMA-IR]. • Calculation of VAI and diagnosis of metabolic syndrome based on IDF criteria. • Research investigation: Selenoprotien-p using Enzyme Linked Immunosorbent Assay (ElISA). This study revealed the following results: The percentage of female obese children twice males. While no significant difference between obese children and their controls as regard to age and sex. Onset of obesity was higher in those aged below 5 years (56.7%) and obese children with class I obesity higher percentage (86.6%) than those with class II (6.66%) and class III (6.66%). Significantly higher caloric intake, macronutrients intake as regard to carbohydrates, fats and proteins and selenium intake through 24hr diet recall in obese children than their controls with significantly higher percentage of carbohydrate consumption in obese children. Significantly higher consumption of sweetened beverage, large food portion, energy dense food in obese children than controls, while lower fruits and vegetables consumption in obese children than controls. A significant difference between both groups as regard to food preference with higher percentage in obese especially for noodles. Physical activity was significantly lower in obese children than controls, with higher percentage of obese children with mild physical activity than of those with moderate. Acanthosis nigricans was significantly higher in obese children than their control and it represented the higher percentage of clinical finding in obese children (73.35%). Anthropometric measurements including weight, BMI and waist circumference with their corresponding z-score and height z-score were significantly higher in obese children than controls. BIA analysis resulted that obese children were significantly higher in fat mass (FM), fat free mass (FFM) and their indices (FMI) and (FFMI), muscle mass, bone mass, total body water (kg) and basal metabolic rate (Kcal) than their controls; while they were significantly lower in total body water percentage than their control, while no significant difference between obese children and controls regarding to phase angle. Serum total cholesterol and triglycerides were significantly higher in obese children than controls; however, there was no significant difference in levels of HDL, LDL, CBC (Hb, TLC, PLT), blood urea and serum level of (creatinine, ALT, AST) between both groups. Metabolic syndrome was found in (13.4%) of obese children. Visceral adiposity index and HOMA-IR were higher in obese children than controls. Serum SEPP1 was significantly lower in obese children than controls. A significant negative moderate correlation between SEPP1 and free fat mass (FFM), Muscle mass, Bone mass, Total body water (TBW), Basal metabolic rate, Phase angle and HOMA-IR in obese children. The optimal cut-off value of SEPP1 for prediction insulin resistance was ≤6.73, with 66.67% sensitivity and 91.67% specificity.