Is Neck Circumference A Better Measure for Determining Obesity? A Cross-Sectional Analytical Study to Assess Its Validity in Type II Diabetes Mellitus Patient

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INTRODUCTION
Obesity is defined as an enormous and unusual deposition of fat in the adipose tissue leading to health impairment. 1 Obesity is arbitrarily and dynamically interrelated to Type 2 diabetes and it is a modifiable risk factor. 2 Overweight and obesity combined with diabetes have the potential to double the risk of metabolic syndrome and cardiovascular events. Therefore weight reduction will be beneficial to the patients with type II diabetes not only in terms of glucose control, but to prevent cardiovascular events, and micro and macrovascular outcomes of diabetes. 3 Obesity can be evaluated by innumerable methods such as computed tomography, dual-energy X-ray absorptiometry, and magnetic resonance imaging by weighing body fat and fat distribution but these are costly and most advanced methods, and cannot be applied in routine primary care. 4 As an alternative, we can use several anthropometric measurements such as Body mass index (BMI), skin fold thickness, Waist circumference (WC), hip circumference (HC), waist-height ratio (WHtR), and Waist hip ratio (WHR) to measure obesity indirectly. 5 Among anthropometric parameters, BMI is the most convenient method of determining the prevalence of obesity at the population level, where weight in Kg is divided by Height in m². The advantage of BMI over other anthropometric parameters is, that it is completely age and sex independent and the disadvantage is that it does not account for variability in body fat distribution especially intra-abdominal fat mass. 6 For assessing intra-abdominal fat deposition, waist circumference and waist-hip ratio are the most definitive measure. Waist circumference proves to be a useful measure of central adiposity for a while and few studies depicted its strong correlation with cardiovascular and metabolic risks. 7,8 But the disadvantage of waist circumference is that it encompasses both visceral abdominal fat (VAT) and subcutaneous fat (SC) 9 , and the disadvantage of weight -hip ratio is that it takes time and involves more than one body part. Both anthropometric parameters are problematic in terms of environmental and cultural issues. 10 Therefore neck circumference(NC), which has been the recent anthropometric tool of interest is the unique marker of upper body subcutaneous adipose tissue distribution. 11 Neck circumference is also an excellent marker of visceral abdominal tissue (VAT) and insulin resistance compared to other anthropometric measures. 11 Insulin resistance accounts for the elevation of very-low-density lipoprotein (VLDL) and triglycerides levels leading to cardiovascular events in type II diabetes mellitus. 11 Few studies also depicted that individuals with larger neck circumference have been associated with cardiometabolic risk factors compared to individuals with less neck circumference. 12,13 Despite the fact that Neck circumference is an excellent indicator of insulin resistance and metabolic syndrome 13,14 , insulin resistance is usually higher in diabetics than in non-diabetics, and previous research has shown that NC cut off value varies between diabetic and Non-diabetic populations 11 . Therefore, determining the cut-off value of NC separately for Type II diabetes mellitus patient becomes more essential. This study aims to determine the validity of neck circumference as an anthropometric parameter of obesity and to estimate the cut-off points for obesity in type II diabetes mellitus patients.

MATERIAL AND METHODS
This analytical cross-sectional study was conducted among Type II diabetes patients attending rural and urban health training centre non-communicable disease clinic of Sri Ramachandra Institute of higher education and research (SRIHER), Chennai -600116. Type II diabetes patients with a duration of illness of more than 1 year and those who granted informed consent were included. The study has no exclusion criteria. With the intense review of previous literature, the sensitivity and specificity of Neck circumference for diagnosing obesity were taken as 55% and 77% with a relative precision of 20% and 15% and a Z value of 1.96, the sample size calculated was 115. 15 About 20% of the sample size [23] was added to take care of any refusal to participate in this study and the sample size arrived for the study was 138.
Through the Universal sampling method, all the type II diabetes patients who were present during data collection days were included i.e., 141. The data on anthropometric parameters such as height and weight are measured using a stadiometer and calibrated weighing machine. Waist circumference, Hip circumference, and Neck circumference were measured to the nearest 0.1 cm using a flexible measuring tape in those wearing light clothing and standing straight. 16 To measure the neck circumference, the patients were asked to hold their heads erect and shoulders down without hunching and the flexible measuring tape was placed horizontally around the neck at the level of the mid-cervical spine and midanterior neck, and the readings were taken. 11,17 Waist circumference was measured with the patient in the standing position and at the end of normal expiration, the flexible measuring tape was placed horizontally at the level halfway between the inferior margin of the lowest rib and iliac crest, and the readings were taken. 10,18 Body mass index (BMI) was calculated by dividing weight in Kilogram by Height in metre² and the patient was divided into two categories based on WHO appropriate body mass index cut-off points for Asians 19 into overweight/obese (BMI >23Kg/m²) and Normal (BMI <23Kg/m²). Waist Hip ratios were given by simply dividing Waist circumference by Hip circumference. Ethical clearance was procured from the institutional ethics committee of Sri Ramachandra Medical College and Research Institute (SRIHER) [CSP-MED/19/JUN/53/65] before the commencement of the study. Written informed consent from all participants was obtained before the interview.
Statistical Analysis: Data entry was done in excel and analysis was completed using the statistical package for social sciences (SPSS) 16 version software. Continuous variables such as age, height, and weight were depicted in mean and standard deviation. Independent T-test and Pearson's Correlation coefficient were used as tests of significance for analysing the data and the p-value of ≤ 0.05 was taken as statistically significant. Receiving operating characteristic curve (ROC) was generated to find out the sensitivity and specificity of Neck circumference against BMI.

RESULTS
In this study, 141 Type II diabetes patients were recruited. Among 141 participants 52 are males and 89 are females. The mean age of females was higher than the male and the difference was not statistically significant (55.44±11.15 years in males vs. 57.52±8.45 years in females, P=0.212). The mean ± SD of weight in males was higher compared to females and it was statistically significant (66.5±13.35 Kg in males vs. 60.05±10.31 Kg in females, P<0.01*).    The patients were divided into two groups overweight/obese and normal based on the BMI cut-off points (BMI <23 Kg/m²) and NC was compared between these two categories. In male diabetic patients, the mean ± SD of NC was higher for over  Figure 3: Receiver operating characteristic curve related to neck circumference and obesity (BMI >23 Kg/m²) in male diabetic patients weight/obese (39.15±2.94 cm) compared to diabetic patients with normal BMI (34.75±1.34 cm), and the difference was statistically significant. Similarly in female diabetic patients, the mean ± SD of NC (35.08±2.80 cm) was found to be higher in overweight/obese than normal BMI patients (31.85±1.66 cm) and the difference was statistically significant. The results were tabulated in Table 3.
ROC curve analysis was done to define cut-off values of NC for overweight/ obesity (based on BMI>23 Kg/m²) for both genders respectively. The area under curve (AOC) for NC and overweight/obesity was 0.931(95% CI: 0.859 -1.00) in male diabetic patient and 0.844 (95% CI: 0.759 -0.930) in female diabetic patient. NC ≥36.5 cm is the best cut-off value to ascertain overweight/obesity with a sensitivity of 84% and specificity of 93% in diabetic male patients. In the case of diabetic females, NC ≥33.2 cm is the perfect cut-off value to determine overweight/obesity with a sensitivity of 68% and specificity of 85%. The results were shown in Figure 3 and 4.

CONCLUSION
This analytical study deduced that NC is a valid anthropometric measurement for diagnosing obesity among Type II diabetes mellitus with plausible sensitivity and specificity. NC acts as an outstanding marker in differentiating obese from those with normal BMI with a cut-off value of ≥36.5 cm for males and ≥33.2 cm for females in Type II diabetes mellitus patients. Keeping count on its simplicity, applicability, affordability, and cultural consideration, it can be a perfect tool for diagnosing obesity among Type II diabetes mellitus patients in primary health care.

LIMITATION
Present study has a few limitations. This study does not consider separate cut-off points for determining overweight and obesity independently. The established cut-off points for identifying obesity can be applied only to the Asian Diabetic population, hence the generalizability is the issue. This study identified the diagnostic ability of NC concerning the BMI, in the future more studies involving a large sample size will be required to identify cut-off points relative to other anthropometric measurements as well.