Neck circumference as a simple tool for identifying the metabolic syndrome and insulin resistance: results from the Brazilian Metabolic Syndrome Study

Objective: To investigate the relationship of the neck circumference (NC) with the metabolic syndrome (MetS) and insulin resistance (IR) in a large Brazilian population-based sample, within a wide range of adiposity and glucose tolerance, and to establish cut-off values of the NC for MetS and IR.

Context: The NC correlates with cardiovascular risk factors, IR and components of MetS. Upper-body subcutaneous (sc) fat, as estimated by the NC, is associated with cardiovascular risk factors as much as abdominal fat, which is usually estimated by the waist circumference (WC). There are few epidemiological population-based studies on the clinical significance of the NC to MetS and IR.

Design: This is a cross-sectional study.

Patients: About 1053 Brazilian adults (18-60 years).

Measurements: Patients with BMI 18.5-40.0 kg/m(2), with normal glucose tolerance or type 2 diabetes (T2DM), were submitted to anthropometric measurements including waist circumference (WC), NC and BMI. Abdominal visceral fat (VF) was assessed by ultrasound. Insulin sensitivity (IS) was assessed by euglycaemic-hyperinsulinaemic clamp (10% of total sample) and HOMA-IR. Spearman correlations were used to evaluate the association between NC and IR and MetS risk factors. Receiver operating characteristic (ROC) curves were used for gender-specific cut-off values for the prediction of IR and MetS. Binary logistic regression analysis was used to assess the chance of developing IR or MetS according to the enlargement of NC and WC.

Results: The sample consisted of 28.6% men, with a mean age of 39.4 (12 years). T2DM diagnosis was present in 306 individuals, of whom 34% were men. NC correlated with WC and BMI in both men and women (P < 0.001). In both genders, NC showed a positive correlation with triglycerides, fasting glucose, fasting insulin and HOMA-IR, and NC had a negative association with high-density lipoprotein (HDL). NC and IS showed a moderate negative correlation. A significant correlation was demonstrated between VF and NC. In the ROC curves, NC presented the largest AUC for IR in women (P < 0.001), while NC presented a large AUC for MetS in both genders.

Conclusions: Neck circumference measurements are an alternative and innovative approach for determining body fat distribution. The NC is positively associated with MetS risk factors, IR and VF, with established cut-off values for the prediction of MetS and IR.