The Relationship Between Bone Metabolism, Body Composition And Glucolipid Metabolism In Obese Children And Adolescents

Part I: The relationship between bone metabolism, body composition and glucolipid metabolism in obese children and adolescentsObjective This part was aimed to evaluate the incidence of vitamin D deficiency of obese children and adolescents according to their levels of serum 25-hydroxyvitamin D(25-OHD), and analyze the relationship between serum 25-OHD, osteocalcin and body composition, glucolipid metabolism, other bone turnover indicators.Method We used cross-sectional baseline data from the obese children and adolescents who accepted the follow-up intervention in the Department of Clinical Nutrition in Shanghai Xinhua Hospital affiliated to Shanghai Jiao Tong University School of Medicine in 2011~2014. On their first visits, all subjects underwent measurements of height, weight, body composition analysis and blood pressure, and also received ultrasonic detection of calcaneal bone mineral density(BMD), abdominal ultrasonography detection of fatty liver and periumbilical abdominal fat thickness(PAFT). Fasting and 2-hour postprandial blood samples were collected the next morning for biochemical indicators of liver function, glucose, lipid and bone metabolism, such as alanine aminotransferase(ALT), alkline phosphatase(AKP), fasting blood glucose(FBG) and insulin(FINS), 2 hour postprandial blood glucose(2h PBG) and insulin(2h PINS), triglyceride(TG), total cholesterol(TC), 25-hydroxyvitamin D(25-OHD), parathyroid hormone(PTH), osteocalcin(OC), β-isomerized form carboxy-terminal telopeptide of type I collagen(β-CTX), and total propeptide of type I procollagen(T-PINP). Insulin resistance was estimated using the homeostasis model assessment of insulin resistance(HOMA-IR) index.Results This study recruited 126 obese children and adolescents aged 4~17 years, 83 males(65.87%) and 43 females(34.13%), including 20 preschool children, 89 school-aged children and 17 adolescents. The average concentration of serum 25-OHD was(17.35±5.04)ng/ml. In sequence serum 25-OHD levels of 30ng/ml, 20ng/ml and 10ng/ml were defined as the cut-off points of vitamin D sufficient, insufficient, deficiency and severe deficiency, the incidence of which was 1.6%, 26.2%, 65.1%, 7.1%, respectively.The obese whose serum 25-OHD<20ng/ml were classified as vitamin D deficiency(VDD) group and 25-OHD≥20ng/ml as non-deficiency(VDND) group. To eliminate the difference of age between two groups, only those obese children aged 7~12 years were counted in. Compared with VDND group, PAFT, serum FINS level and HOMA-IR of VDD group were significantly higher(p<0.05).Pearson correlation analysis showed that age was an important factor associated with serum 25-OHD(r=-0.317, p<0.001). After adjustment for age and gender, serum 25-OHD was negatively correlated with parameters such as weight, BMI, waist circumference(WC), hip circumference(HC), percentage of fat mass(FM%), and PAFT(p<0.05), and it was positively correlated with percentage of soft lean mass(SLM%)(p<0.05). It was also negatively associated with indicators of glucose metabolism such as FINS, HOMA-IR and 2h PINS(p<0.01), and was negatively associated with serum PTH(p=0.043).Serum OC had significant positive correlations with age and serum 25-OHD(p>0.05). After adjustment for age and gender, serum OC had significant positive correlations with height, SLM% and percentage of skeletal mass(SMM%)(p<0.01), and had negative correlations between diastolic blood pressure(DBP) and FM%(p<0.05). Serum OC was also positively associated with AKP, PTH(p<0.01), and had high positive correlations with β-CTX(r=0.781, p<0.001) and T-PINP(r=0.778, p<0.001).Conclusion The incidence of vitamin D deficiency in obese children and adolescents was very high. Serum 25-OHD level significantly decreased with age, and closely related with many anthropometric indicators such as BMI, WC, HC, FM% and so on. It had significant negative correlations with indicators of glucose metabolism, such as FINS, HOMA-IR and 2h PINS, but had no significant correlation with indicators of lipid metabolism. Osteocalcin was significantly correlated with indicators of body composition(FM%, SLM%, etc.), and had high positive correlations with indicators of bone formation and resorption.Part II: Changes of bone metabolism and glucolipid metabolism in obese children and adolescents after a summer weight-loss campObjective Through a prospective cohort study, observing changes in body composition, gluocolipid and bone metabolism of obese children and adolescents in a summer weight-loss camp, this study was to explore the relationship between changes of bone and glucolipid metabolism, which could provide evidence for promoting bone health, prevention and treatment of obese children and adolescents. This study also focused on whether serum 25-OHD level of the obese could be elevated after intervention to guide vitamin D supplement.Method The subjects were recruited from the children and adolescents participating in weight-loss camp lasting 6 weeks in July ~ August, 2014. In the morning before intervention, blood samples were collected from all subjects to test glucose, lipid and bone metabolism. And then all subjects accepted anthropometry and blood pressure measurements, and bone mineral density detection. Anthropometry measurement included height, weight, waist circumference, hip circumference, triceps skinfold thickness(TST) and scapular skinfold thickness(SST). Finally, all subjects received exercise load test to ensure safe and effective physical exercise. All subjects accepted closed-off management. Aerobic exercise was the main intervention method on the basis of appropriate caloric control. In the exercise, heart rate was monitored to ensure the small-medial load aerobic exercise. All kinds of exercise were conducted indoor, twice per day, 6 day per week, and lasting for 2 hours every time.On the basis of meeting the daily energy physiological requirement, basal metabolic rate was calculated to formulate diet project according to Harris-Benedict formula,. The diet was composed of 20% protein, 30% fat and 50% carbohydrates. After 6 weeks of training, fasting blood samples were collected again to test biomarkers and all subjects accepted the measurement as before intervention. During the intervention, all subjects never supplemented any kinds of nutritional supplements like vitamin D and calcium.Results At the beginning of this study, we recruited 75 obese children and adolescents(9~17 years old), whose average age was(13.4±1.9) years old. Serum 25-OHD levels of all subjects were lower than 20ng/ml, and the average level was(13.81±2.38)ng/ml. At last, there were 53 of them finished the weight-loss intervention of 6 weeks including 35 males and 18 females, and their mean age was(13.6±1.8) years old.After intervention, nearly all kinds of anthropometric indcators, glucose and lipid metabolism indicators, and blood pressure were improved significantly(p<0.001). Weight decreased by 11.9%(87.1kg vs. 76.7kg), BMI decreased by 15.1%(31.82kg/m2 vs. 27.0kg/m2), DBP decreased by 10.5%(70mm Hg vs. 62 mm Hg), and SST decreased by 32.6%(38.9mm vs. 26.2mm). TC decreased by 20.1%(4.50mmol/L vs. 3.50mmol/L), TG decreased by 50.4%(1.52mmol/L vs. 0.74mmol/L), FINS decreased by 64.0%(136.3pmol/L vs. 49.8pmol/L), and HOMA-IR decreased by 67.35%(4.40 vs. 1.53).Serum 25-OHD level elevated to nearly twice as much as the level before intervention(13.81ng/ml vs. 26.82ng/ml, p<0.001). The incidence of vitamin D deficiency(VDD) was 100% before intervention, while after intervention the incidence of VDD was 3.8%(2/53), and 24.5% of them(13/53) reached vitamin D sufficiency. Serum PTH levels increased by 128%(20.6pg/ml vs. 45.9pg/ml, p<0.001), and serum OC increased by 44%(45.69ng/ml vs. 66.56ng/ml, p<0.001). Bone alkaline phosphatase(BALP) decreased by 41.0%(66.0 ng/ml vs. 40.4 ng/ml, p<0.001), and T-PINP decreased by 43.6%(147.9 ng/ml vs. 96.0 ng/ml, p<0.001). Serum β-CTX increased by 33%(0.88ng/ml vs. 1.88 ng/ml).BMD and Z-score were significantly higher after intervention(p<0.001).The change percentage of serum 25-OHD(delta% 25-OHD) was significantly positively correlated with delta% weight(r=0.281, p=0.041) and delta% SST(r=0.305, p=0.305). Delta% 25-OHD was significantly negatively correlated with delta% TC(r=-0.276, p=0.045), and had no significant correlation with delta% OC(r=0.224, p=0.106). Delta% OC was significantly correlated with delta% weight(r=0.309, p=0.024), delta% SST(r=0.338, p=0.013), delta%DBP(r=-0.452, p=0.001), delta% TC(r=-0.434, p=0.001), delta% TG(r=-0.376, p=0.005), delta% BMD(r=0.302, p=0.035). After adjustment for age and gender by partial correlation analysis, delta% 25-OHD was still significantly correlated with delta% weight, delta% SST and delta% TC, moreover, it was significantly positively correlated with delta% OC. Delta% OC was still correlated significantly with the above indicators except delta% BMD.Conclusion After the intervention for 6 weeks, weight, BMI, and skinfold thickness of the obese children and adolescents reduced significantly, and glucolipid metabolic indicators improved comprehensively. Serum 25-OHD levels elevated to twice as much as the level before intervention, serum OC level also increased signifiantly. After adjustment for age and gender, ?%25-OHD was significantly positively correlated with ?%OC. Both ?%25-OHD and ?%OC was significantly associated with ?%weight, ?%SST, and ?%TC, and ?%OC also had significantly negative correlations with ?%DBP and ?%TG. After intervention, bone mineral density and the level of bone absorption indicators of the obese increased significantly, but bone formation indicators decreseased significantly.