Obesity has become a serious epidemic worldwide, estimated to be the fifth leading cause of death at global level, causing approximately 64 million deaths in 2015, 64% of those result from chronic illness unless urgent action is taken ^{1, 2, 3, 4, 5}. Moreover, the obesity in children and adolescents is also a major health issue, and its prevalence is increasing rapidly, mainly in developing countries. The International Obesity Task Force (IOTF) has stated recently that at least 500 million school children aged 5-17 years old are overweight or obese. Obesity is one of the Mets components which is a cluster of cardiovascular disease (CVD) risk factors including central obesity, diabetes, high serum cholesterol, high serum triglyceride, and high blood pressure ⁶. It is well established that this syndrome leads to reduce the quality of life and premature death ⁷. The association between the MetS and adolescents obesity has been reported in many published data ³. Obesity plays an essential role in the MetS through worsening of blood biochemical profile that leads the development of many non-communicable diseases such as CVD, diabetes, and stroke. There is an increasing evidence that the obesity and MetS among adolescents is associated with a number of health adverse consequences in adulthood such as type 2 diabetes mellitus and CAD ^{8, 9, 10}. The atherosclerosis process starts at an early age is linked to obesity and other components of MetS in childhood ¹¹. The association between childhood obesity and cardio-metabolic risk factors, i.e. abdominal obesity, glucose disorders, dyslipidaemia and hypertension in adolescents have been evaluated through many studies and substantial links have been shown ¹². Also, studies have demonstrated that increased body mass index (BMI) in adolescents has a significant link with type 2 diabetes mellitus and CVD incidence in adulthood ^{8, 13}.

There are other studies indicated that central obesity (abdominal obesity) in which fat accumulates in the abdominal cavity and around the viscera is associated with a much higher risk for CVD, stroke, and type-2 diabetes mellitus in adolescents than just excess accumulation of fat in the subcutaneous tissue ^{14, 15, 16, 17, 18, 19, 20, 21}. This type of fat is more metabolically active than subcutaneous fat and has been shown to have more adverse health consequences than overall obesity. Evidences suggest the importance of measuring central obesity besides overall obesity for the evaluation of health risks in the first decades of life ²². In addition, recent published data indicated that the percentage of patients who presented with Mets risk factors has almost doubled in the last ten years ²³. Therefore, it is highly urgent to develop valid and simple methods for identifying individuals with Mets mainly at a younger ages. Central obesity is measured by various anthropometrics methods such as WC, WHpR and WHtR, which is the main component of the MetS ^{19, 24, 25}. The relative risk for CVD and the (MetS) increases significantly with increasing the central obesity, defined as WC larger than 102 cm for men and 88 cm for women ²⁶. Also, several studies have proposed the use of WHpR for central obesity measurement indicated value ranging from 0.85 to 0.95 in men, and from 0.80 to 1.18 in women ²⁷. Recently, WHtR has been proposed as another simple index to measure the central obesity and a cut off value ≥0.5 was suggested for defining the obesity in children and adults ²⁸. This cut-off value was found to be strongly associated with cardiovascular risk factor ²⁹. It must be highlighted that the association between central obesity as accessed by the WC, and arterial blood pressure, has been largely reported in the adult population. However, until now, the predictive value of WC related to blood pressure levels has not been suggested for children and adolescents ³⁰. Meanwhile, prediction values for anthropometrics indicators were also not determined in the Syrian adolescents. Therefore, the aim of this study was to evaluate the predictive value of some central obesity anthropometric indicators such as the WC, HC, WHpR and WHtR, to MetS risk factors including BP, Chol, LDL, HDL, TG, and FBS.

The mean values (mean ± SD) of measured MetS components for 2064 adolescents participated in the current study were as follows: SBP (123.43±14.55 mm Hg), DBP (74.40±10.72 mm Hg), FBS (89.49±8.53 mg/100 ml), TG (91.84±44.06 mg/100 ml), Chol (136.36±33.04 mg/100 ml), HDL-C (57.11±5.63 mg/100 ml), LDL-C (62.04±29.34 mg/100 ml), and TG/HDL-C (1.61±0.78). The mean values of MetS risk factors in the studied group of Syrian adolescents by WC categories classified according to the weight status values are illustrated in Table 1. As shown in this table DBP, Chol, TG, and TG/HDL-C were significantly (p<0.05) higher in overweight and obese subjects in comparison to normal weight subjects. Meanwhile, SBP and FBS were significantly (p<0.05) higher in obese subjects than in normal participants, and LDL-C was significantly higher in overweight subjects than in normal once. However, there was no significant differences in HDL-C value among the three studied groups (normal, overweight and obese). WHtR (≥0.5) was found to be significantly (p<0.05) prevalent among participants with high BP (systolic and diastolic), FBG, TG, Chol, LDL-C and TG/HDL-C. Also, the participants with high WHpR (≥0.9) were shown significantly (p<0.05) higher BP (systolic and diastolic), TG, Chol, and TG/HDL-C. The results are shown in Table 2.

ROC curves analysis of the WC, HC, WHpR and WHtR were performed for all studied MetS components. Regarding WC, AUC predicting metabolic abnormalities ranged between 0.37 and 0.69 and it was statistically significant (p>0.05) for SBP, DBP, Chol, TG, LDL-C and TG/HDL-C. The best WC cut-offs for the studied group were 73.15, 75.25, 79.90, 75.40, 75.40 and 76.83 cm for SBP, DBP, TG, Chol, LDL-C and TG/HDL-C, respectively, as illustrated in Table 3. AUC predicting metabolic abnormalities of HC ranged between 0.37 and 0.71 and it was statistically significant (p>0.05) for DBP, TG, Chol, LDL-C and TG/HDL-C. The best HC cut-offs for the studied group were 93.75, 94.75, 94.90, 95.95, and 94.75 cm for DBP, TG, Chol, LDL-C and TG/HDL-C, respectively, as indicated in Table 4. AUC predicting metabolic abnormalities of WHpR ranged between 0.43 and 0.65 and it was statistically significant (p>0.05) for SBP, DBP, Chol, TG, and TG/HDL-C. The best WHpR cut-offs for the studied group were 0.80, 0.81, 0.81, 0.81 and 0.81 for SBP, DBP, TG, Chol and TG/HDL-C, respectively, as shown in Table 5. AUC predicting metabolic abnormalities of WHtR ranged between 0.44 and 0.70 and it was statistically significant (p>0.05) for SBP, DBP, Chol, TG, LDL-C and TG/HDL-C. The best WC cut-offs for the studied group were 0.43, 0.44, 0.46, 0.46, 046 and 0.45 for SBP, DBP, TG, Chol, LDL-C and TG/HDL-C, respectively, as in Table 6.

In this cross-sectional study of Syrian adolescents aged 18-19 years a significantly higher values of anthropometric parameters of central obesity as measured by WC (≥94 cm), WHpR (≥0.9), and WHtR (≥0.5) were reported in those with high values of the Mets components. These values tended to increase as WC increased. These findings are in agreement with other studies which showed a strong correlation of WC with most of Mets components. The association of WC with a number of cardio metabolic risk factors, reported in this study and in a number of previous reports, encourage to propose to use this parameter as a simple method of identifying those who are at risk of developing CVD and type II diabetes mellitus ³⁵. Also, many studies have investigated the usefulness of WC as an alternative index for central obesity as that increase in WC predicts the risk for insulin resistance, adverse lipid profiles, high blood pressure and metabolic syndromeinadolescents ^{36, 37}. While Burgos et al. ³⁰ demonstrated a moderate correlation among these variables. However, Sarni et al. ³⁸ did not find correlation between WC and SBP or DBP in sample of 65 preschoolers of low socioeconomic status. In the present study the data, also, suggested a relative predictive value of WHpR, however, this value was not as high as WC and WHtR. In some published data the WHpR has been demonstrated a reliable predictor of health related parameters in adults, however, this ratio index was poor proxy central fatness in children and adolescents ³⁹. Peterson et al. ⁴⁰ reported that WHpR was found to be a significant predictor of HDL-C, total cholesterol/high-density lipoprotein cholesterol (TC/HDL-C) ratio, and TG.

In the current criteria for metabolic syndrome, we used a common cut-off value for the WC for Syrian adolescents. When using this cut-off threshold, it raises a problem in that the visceral fat area (VFA) for the adolescents is underestimated. Therefore, different cut-off values for the WC, WHpR and WHtR according to the age should be considered. The results of this study suggest that all used anthropometric indicators (WC, HC, WHpR and WHtR) are associated with one or more metabolic risk factors in adolescents. ROC curve analysis indicated that, among the indicators used to predict the presence of metabolic syndrome, DBP, TG, Chol, LDL-C, and TG/HDL-C have showed a great area under the ROC curve, but the TG was the index that showed the greatest area under the ROC curve. Based on the sensitivity, specificity, and ROC calculation, we found that WC, HC, WHpR and WHtR have a good accuracy for identifying adolescents with some metabolic risks including DBP, TG, Chol, LDL-C, and TG/HDL-C. This data suggest that, the best WC, HC, WHpR, WHtR cut-offs ranged between 73.15-79.90 cm, 93.75-101.10 cm, 0.80-0.81 cm, and 0.43 cm and 0.47 cm, respectively. These cut-off values of were lower than the current definitions recommended by the WHO ³².

However, the absolute risk currently determined by the multiple risk factors associated with body fat and its distribution may well reflect the phase of disease transition in a population. Hence, the thresholds for risk associated with WC or WHpR may vary with time. These considerations make it difficult to specify cut-off points on the basis of ethnicity ^{16, 41}. Cut-off points chosen vary considerably between countries; also, the variation is greater for WC than for WHpR. The cut-off points appear to be chosen based on disease risk and on hard outcomes such as mortality ⁴².

Males who have WC greater than 102 cm are considered to be at increased risk for CVD. This cut-off point was derived from a regression curve that identified the WC value associated with a body mass index (BMI) ≥30 kg/m² in primarily Caucasian men ⁴². The current recommendation for central adiposity as recommended by WHO WC ≥94 cm and a value WHpR is ranging from 0.85 to 0.95 in men ⁴². However, data indicate a lower WHpR cut-off point for Asians; for example, WC values of 85 cm, and WHpR values of 0.90, respectively ⁴³. Studies in populations of the Middle East Region have provided WC and WHpR cut-off points similar to those suggested for Europeans ⁴². In Japan, a WC of 80 cm has been established as one of various cutoff points for childhood obesity disease ⁴⁴.

Our findings indicate that central obesity as determined by the main anthropometric indicators WC, WHpR and WHtR have a significant association with the major components of MetS suggesting that visceral fat accessed by these indicators can be good predictors of this syndrome in Syrian adolescents. Based on ROC calculation for WC, HC, WHpR, and WHtR and some metabolic risk factors, the best cut-offs of these parameters were defined in this study. These cut-off values were lower than the values recommended by the WHO.

The authors equally contributed to this paper.

The authors wish to express their deep appreciation to the Director General of AECS Prof. I. Othman. This study was supported by the International Atomic Energy Agency under the Technical Research Contract No. SYR/6/012 is gratefully acknowledged.