Neck circumference (NC), a marker of upper body subcutaneous adipose tissue distribution, is a relatively new method of differentiating between normal and abnormal fat distribution. Central obesity being the main predictor of obesity-related disorders, body mass index (BMI) may not be the best indicator of functional consequences of obesity [1]. Calculating and interpreting BMI is also time consuming. On the contrary, measuring neck - and waist-circumference by a tape is relatively easy, and has not been explored adequately as anthropometric measure of overweight and obesity. We conducted this study to validate neck-and waist-circumference as anthropometric measures of overweight/obesity among adolescents, and to correlate these with BMI.

Weight was measured with light clothing and without shoes. Height without shoes was measured by stadiometer. Children were categorized according to their BMI using BMI percentile curves for Indian boys and girls from 5-17 years with 3rd, 10th, 25th, 50th, 85th and 95th percentiles, along with two additional percentiles corresponding to a BMI of 23 and 28 kg/m2 at 18 years [2]. Waist circumference (cm) was measured using plastic tape at midpoint between the costal margin and iliac crest in the mid-axillary line in standing position at the end of a gentle expiration [3]. Neck circumference was measured by using a flexible tape, with children in standing position; head held erect, at the level of the thyroid cartilage [4]. All anthropometric measurements were performed by two trained Medical Social Workers. Data were analyzed using SPSS version 20.0. Quantitative data were analyzed using independent samples t-test and Pearson’s correlation. Receiver Operating Characteristic (ROC) analysis was done to find the optimal and maximal sensitivity and specificity for neck/waist circumference against BMI. The cut-off values for these in school going adolescents were determined by Youden index (Sensitivity + Specificity -1) [5]. A P value of <0.05 was considered to be statistically significant.

The age of adolescents included in this study (n=1800; 51.7% boys) varied from 10-16 years with a mean (SD) age 13.0 (1.4) years. The study sample consisted of 1213 (67.4%) with normal BMI, 501 (27.8%) with overweight/obesity and 86 (4.8%) underweight adolescents. The mean (SD) BMI of boys and girls were18.5 (4.8) and 18.7 (4.4) kg/m2, respectively. The mean (SD) waist circumference for boys and girls were 68.5 (12.3) and 66.2 (9.5) cm, respectively; and the mean (SD) neck circumference for boys and girls were 29.9 (3.2) and 28.9 (2.7) cm, respectively. There was significant difference (P<0.001) in waist circumference and neck circum-ference between adolescents with normal and high BMI for both genders (Table I).

TABLE I	Anthropometric Measurements Among School-going Adolescents in Present Study

BMI was positively correlated with neck circumference (r=0.642 for boys, 0.615 for girls) and waist circumference (r=0.693 for boys, 0.682 for girls) at significant level (P<0.001). For boys, 3rd percentile of neck circumference was 25 cm and 97th percentile was 36.0 cm, and for girls, 3rd percentile was 24.2 cm and 97th percentile was 35 cm.

TABLE II	Performance of Neck Circumference in Detecting Overweight/obesity 

Table II shows the values of area under the curve (AUC) and cut-off values for waist circumference and neck circumference with their respective sensitivity and specificity levels in identifying children with overweight/obesity. Fig. I shows the comparison of neck circumference as a tool for detection of overweight/obesity as compared to waist circumference and BMI.

(a)	(b)
Fig. 1 ROC curve comparing neck circumference and waist circumference with body mass index (BMI) in boys (a), and girls (b). WC - waist circmference and NC - neck circumference.

In this study, we documented a significant difference in waist circumference and neck circumference among normal and overweight/obese children detected by BMI (P<0.001) in both boys and girls. Also, there was a strong positive correlation of neck circumference as well as waist circumference with BMI.

Limitations of present study include enrolment of adolescents from a small geographic area, sample size and lack of validation of these measurements with functional consequences of obesity.

We found that the cut-off value of neck circumference for screening adolescent obesity in boys and girls were 30.75 cm and 29.75 cm respectively, while cut-off values for waist circumference were 70.75 cm for boys and 69.25 cm for girls. These results were close to the estimates from previous studies, and small differences between the cut-offs could be explained by ethnic variation [4,6]. Correlation of neck circumference and waist circumference as with BMI, as observed in our study, has also been reported earlier [4,6,7]. We observed the area under the curve of more than 80% for both neck circumference and waist circumference among boys and girls, indicating accuracy in its ability to identify adolescents with a high BMI. Moreover, AUC for waist circumference was found to be more as compared to neck circumference in both boys (0.866 vs 0.823) and girls (0.850 vs 0.816) indicating that waist circumference may be a better measure of obesity in adolescents. However, several limitations have been documented in the literature, either related to its measurement [6], especially among the adolescents owing to body changes they experience during puberty or due to its variation throughout the day according to bowel function or menstrual period [8]. Measurement of neck circumference may be relatively simple, convenient and non-intimidating, especially for the adolescents. As compared to BMI and waist-to-hip ratio, neck and waist circumference have been shown to have higher accuracy in predicting the risk of atherosclerosis in the middle- aged adults [9].

We conclude that both neck- and waist-circumference are useful screening tools for adolescent overweight/obesity, and have a potential to be used as a screening tool for adolescent overweight/obesity.

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