Subjects
In this study, a total of 683 students aged 8-15 years were selected from two nine-year schools via the stratified cluster sampling methods, including 317 girls (46.4%) aged at (10.98±1.83 years)and 366 boys (53.6%) aged at (10.77±1.80 years).
Measurement
The medical staff who received standardized training measured the participants’ body weight, height, sitting height (SH), Diastolic blood pressure (DBP), Systolic blood pressure (SBP), WC and AST. The participants kept have an empty stomach when they were measured, and were requested barefoot, dressed in light clothes and stood straight. An electronic scale was used to measure weight, and the reading was accurate to 0.1 kg. Height and SH were measured using Mechanical height measure, and the readings were accurate to 0.1 cm. Blood pressure was measured on the right arm with an appropriately sized cuff using mercury sphygmomanometer after having a rest for at least 10 min. DBP was defined as the fifth Korotkoff sound (K5), SBP was defined as the onset of the Korotkoff sound (K1). The blood pressure was measured twice at interval of 2 min. Waist circumference (WC) was measured along a horizontal line at 1 cm above the belly button using a Nylon tapes, the reading was accurate to 0.1cm. Abdominal skinfold thickness (AST) was measured at the intersection of the horizontal umbilicus and the right midclavicular line, the reading was accurate to 0.1 mm.
The children and adolescents after at least 8 h of overnight fasting were collected 3 mL venous blood samples by nurses received standardized training. The enzyme-linked immunoassay method was used to detect HDL-C. Enzymatic methods were used to detected TG and FBG levels.
Definition of Metabolic Syndrome (MS)
In this study, MS was diagnosed according to the amended NCEP-ATP III criteria [21]. high fasting blood glucose(FBG)≥110mg/dL; abdominal obesity: WC≥ 90th age-and sex-specific percentile for Chinese children [22]; high blood pressure: SBP and/or DBP ≥90th percentile for gender and age [23]; low high-density lipoprotein cholesterol (HDL-C)≤40 mg/dL; high triglycerides(TG)≥110mg/dL; when three or more of the five components were present that MS was identified.
Calculation of the Derivative Variables
Children’s lipid accumulation product (CLAP) = WC (cm) × AST (mm) × TG (mmol/L) / 100; BMI=weight (kg)/ height2 (m2); WHtR = waist circumference (cm) / height (cm); Relative children’s lipid accumulation product per height (RCLAP-H) = WC (cm) × AST (mm) × TG (mmol/L) / height (cm); Relative children’s lipid accumulation product per sitting height (RCLAP-SH) = WC (cm) × AST (mm) × TG (mmol/L) / sitting height (cm); Relative children’s lipid accumulation product per weight (RCLAP-W) = WC (cm) × AST (mm) × TG (mmol/L) / weight (kg).
Surveys of Behavioral Indexes
We investigated dietary behaviors which included the frequency of breakfast, milk, fresh vegetables, fruits, nuts, fried foods, carbonated drinks, eating out, western-style fast food, high-energy snacks. Each of the dietary behavior items was assigned 6 grades including never (0 points), 1 time per month (0.25 points), 2 time per month (0.5 points), 1–3 times per week (2 points), 4–6 times per week (5 points), and 1 time per day (7 points). The total scores of healthy dietary behaviors (including breakfast, milk, fruits, nuts, fresh vegetables) and risk dietary behaviors (including fried foods, eating out, carbonated drinks, high-energy snacks, western-style fast food) were defined as ≥the 75th percentile (P75) and < 75th percentile (P75) two grades. Children’s Leisure Activities Study Survey (CLASS) questionnaire was used to investigate Physical activities [24]. The moderate-to-vigorous physical activity was defined as <60min and ≥60min two grades, and sedentary activity time was defined as <120min and ≥120min two grades [25].
Statistical Analysis
Data were analyzed using the SPSS 23.0 software. The data were described using rate (or proportion) or mean ± standard deviation. The height, siting height, weight, WC, AST, BMI, WHtR, logarithmic CLAP, RCLAP-H, RCLAP-SH, RCLAP-W, SBP, and DBP was standardized for genders and ages using Z-score method (Abbreviations of above standardized indexes: SH, SSH, SW, SWC, SAST, SBMI, SWHtR, SlnCLAP, SRCLAP-H, SRCLAP-SH, SRCLAP-W, SSBP, SDBP, respectively). The t-test, chi-square test and logistic regression models were used to analyze the associations of SBMI, SWHtR, SlnCLAP, SRCLAP-H, SRCLAP-SH, SRCLAP-W with MS, respectively. Receiver Operating Characteristic (ROC) curves were used to evaluate the predictive efficiency of above indexes for predicting MS. P < 0.05 was considered statistically significant.