Correlation of neck circumference with abdominal circumference and BMI
A positive linear correlation of neck circumference with abdominal circumference and BMI was noted in men and women. This finding is consistent with those of previous studies (11, 14). A study in Turkey reported a correlation between neck circumference and waist circumference in adult men and women (Pearson’s correlation coefficients, r = 0.593 and r = 0.667, respectively). Moreover, the same study showed a correlation between neck circumference and BMI in men and women (r = 0.587 and r = 0.688, respectively). In both parameters, statistically significant associations were noted (p < 0.001) (11). Another outpatient study in the endocrinology department reported that the waist–neck index correlated with abdominal circumference (0.61 and 0.46 for men and women, respectively) and BMI (0.51 and 0.41 for men and women, respectively). Moreover, significant associations were observed in both parameters (p < 0.001) (14), albeit lower than those reported in a previous study. Although our study found practically similar correlation coefficients for men and women, men had greater values than women.
Our study evaluated patients with untreated metabolic syndrome; previous studies did not specify this criterion. This could explain why our study showed higher correlation coefficients because individuals with metabolic syndrome gain weight, BMI, and abdominal circumference over time, which could have resulted in an increased correlation among anthropometric parameters by the time these patients presented with an illness (15).
To the best of our knowledge, no study has yet evaluated patients with untreated metabolic syndrome. However, there is evidence in patients with other metabolic diseases (16, 17). For example, a recent study in patients with pre-diabetes reported a positive linear correlation between neck circumference and abdominal circumference (16). Moreover, another study reported a significant correlation between both variables in patients with type 2 diabetes (17). Despite the presence of metabolic disorders, the association between both parameters has been consistently reported.
Neck circumference is an anthropometric parameter that measures the distribution of subcutaneous fat in the upper body, thereby helping predict metabolic risk (8, 18). Several studies have supported the association between neck circumference and components of the metabolic syndrome, including abdominal circumference and BMI. A recent systematic review that addressed the association of neck circumference with cardiometabolic markers reported a significant association between neck circumference and abdominal circumference, fasting glycemia, the homeostatic model assessment of insulin resistance, and lipid profile (19).
Previous studies have consistently found that neck circumference is positively correlated with abdominal circumference, BMI, and other cardiovascular markers, such as the lipid risk profile, suggesting that neck circumference is a prognostic factor for mortality in patients with a high cardiovascular risk (6, 8, 19). Dai et. al. studied adults with two or more risk factors for cardiovascular disease and reported that an increased neck circumference was associated with a higher incidence of cardiovascular events and mortality (8).
Our study found that the correlation of neck circumference with abdominal circumference and BMI was higher in men than in women. The finding, however, is not homogeneous across studies worldwide. Several studies comparing the correlation between neck circumference and abdominal circumference according to sex have demonstrated higher coefficients in women than in men (11, 16), whereas others have shown otherwise (7, 14). Women tend to accumulate more subcutaneous fat, whereas men accumulate more visceral fat (20); this could justify a more robust association in males. However, in patients diagnosed with metabolic syndrome, sex may not play a key role in other factors. The current study found that women had a greater prevalence of hypertension and hyperglycemia, both of which are metabolic risk factors. Consequently, when analyzing the association between neck circumference and abdominal circumference after controlling for these parameters, women showed a greater decrease in the β coefficient than men.
Relevance to clinical practice and recommendations
Abdominal circumference is an anthropometric parameter traditionally used and recommended by international metabolic syndrome guidelines. However, certain disadvantages have been noted in its clinical use in patients at a risk of cardiovascular disease. For instance, a meta-analysis in older adults reported a J curve in the association between abdominal circumference and cardiovascular mortality, decreasing the reliability of this parameter (21). Conversely, neck circumference is an anthropometric parameter, which unlike abdominal circumference and BMI, does not have a measurement bias due to clothing and is simpler to measure. One study reported that a neck circumference of ≥38.5 cm had greater sensitivity for predicting metabolic syndrome, hyperglycemia, hypertension, hypertriglyceridemia, and low HDL cholesterol than an abdominal circumference of ≥90 cm in men and women (22). Therefore, clinicians should consider anthropometric and laboratory evaluations (fasting glucose and lipid profile) in patients with a high neck circumference value. Moreover, neck circumference assessment should be included in metabolic syndrome guidelines. Nonetheless, follow-up studies are warranted to continue identifying more robust methods of predicting cardiovascular events or mortality.
Our study should be interpreted considering the following limitations. First, the study design did not allow us to establish a timeframe for the measurement of neck circumference along with abdominal circumference and BMI. Berkson’s bias may exist by including only patients with access to the hospital, which would limit the extrapolation of results to other populations. Given that the patients studied were recruited from a community in the north of Peru, our findings may not be representative of all Peruvians with metabolic syndrome considering that dietary habits and other environmental exposures vary across Peru. However, despite these limitations, this study provides important evidence on the association of neck circumference with abdominal circumference and BMI in Peru and to our knowledge, is the first study of individuals with metabolic syndrome.