Neck circumference as a potential marker of metabolic syndrome among college students

OBJECTIVE: to relate neck circumference with metabolic syndrome and its criteria among college students. METHOD: cross-sectional study conducted with 702 college students in Fortaleza, CE, Brazil from September 2010 to June 2011. Socio-demographic data, waist circumference and neck circumference were collected together with blood pressure, fasting blood sugar, triglyceride levels, and HDL-C. RESULTS: 1.7% of the studied sample presented metabolic syndrome. Of these, 58.3% presented altered neck circumference (p<0.006). As neck circumference decreases, pressure levels improve (p<0.001). Additionally, college students with high fasting blood sugar (p=0.003) and high triglyceride levels (p<0.001) presented higher values of neck circumference. CONCLUSION: neck circumference is a potential predictive marker in the detection of metabolic syndrome and its components among college students.


Introduction
The National Priorities for Research and the Research Agenda in the health field gives priority in one of its sub-agendas to non-communicable diseases (NCDs), such as hypertension, diabetes mellitus and obesity (1) . Metabolic syndrome (MS) is also added to this context, the diagnosis of which may include these diseases; the disease also increases the risk for developing cerebrovascular and coronary artery diseases (2) . Metabolic syndrome is defined as a separate entity based on risk factors for cardiovascular diseases and type-2 diabetes mellitus (DM2). Factors related to MS include visceral obesity, dyslipidemia, arterial hypertension, and insulin resistance. MS should be recognized before the clinical manifestation of DM2 in order to implement primary prevention through lifestyle modifications and should specifically treat each of the syndrome components (3)(4) .
There are various sources providing criteria for identifying MS (3)(4) , however, those established by the National Cholesterol Education Program -Adult Treatment Panel III (NCEP ATP III) and recommended by the I Brazilian Guideline for the Diagnosis and Treatment of Metabolic Syndrome, are more frequently used in clinical studies due to their practicality. These programs consider the presence of three or more criteria to indicate the presence of metabolic syndrome, namely: waist circumference greater than 88cm in women and 102 cm in men, triglycerides above 150mg/ dl, HDL cholesterol below 40 mg/dl in men or 50mg/ dl in women, blood pressure above or equal to 130/85 mmHg, and circulating glucose greater than or equal to 110 mg/dl (3) .
The search for easily applicable clinical criteria to identify MS led researchers to consider the importance of investigating other anthropometric parameters to integrate or replace some of those already established (5) . Therefore, neck circumference (NC) began to be investigated under the argument that there are limitations in regard to waist circumference measurement (i.e. lack of a standard measurement technique, variations in certain health conditions) and also because neck measurements, under normal conditions, do not oscillate throughout the day (6)(7)(8) .
Hence, neck circumference is now considered a risk marker for MS, even though further investigation with different populations is still recommended (8)(9)(10)(11) .
In Brazil, neck circumference was investigated as part of the Brazilian Metabolic Syndrome Study (BRAMS) that included adult outpatients (between 18 and 60 years old) undergoing treatment for DM2, metabolic syndrome and/or obesity. The results found so far show that neck circumference is an innovative and additional parameter to determine the distribution of body fat, which is associated with visceral fat, to metabolic syndrome's components and insulin resistance, especially among women (12) .
The city of Fortaleza, CE, Brazil was included in BRAMS, but neck circumference as an MS marker has not yet been studied in predominantly young populations.
Hence, considering anthropometry as a tool to be used in Nursing consultations and also that the National Priorities for Research and the Research Agenda in the health field point to the need to develop and use healthpromoting methods in addition to preventive, diagnostic, and early treatment methods (1) , this study's objective was to relate neck circumference to metabolic syndrome and its criteria among college students.

Method
This cross-sectional study was performed at the Federal University of Ceará (UFC) in the campuses of Fortaleza, CE, Brazil. The sample was calculated using a formula for infinite populations. A prevalence of 50% was adopted because it provides the maximum sample size, with a level of significance of α=0.05 and an absolute sampling error of 4%. To minimize potential losses, 10% was added to the sample size (n=702 college students).
The participants were distributed in the following fields: Association of Business and Research) (13) , and with whom the individual lives with (parents, relatives, friends, spouse/partner, alone).
The following were established for anthropometric, clinical and biochemical variables: central obesity (waist circumference [WC] greater than 102cm for men and 88cm for women); neck circumference [NC] greater than or equal to 39cm for men and greater than or equal to 35cm for women) (12) ; high blood pressure (greater or equal to 130/85 mmHg); high triglycerides level (greater or equal to 150 mg/dl); low HDL cholesterol level (below 40mg/dl for men and below 50mg/dl for women); and circulating glucose greater than or equal to 110mg/dl) (3) .
The researcher assistants (two doctoral and two master's students along with two undergraduate students) responsible for collecting data received 30 hours of training to ensure the reliability of data. Data collection was performed from September to November 2010 and from February to June 2011 in private rooms on the university's premise.
The students were recruited in classrooms after the study's objectives and methodology was clarified. with an inelastic tape placed on the skin at the midpoint between the iliac crest and the last rib at the end of the expiratory breathing (16)(17) . Blood pressure was measured in accordance with Brazilian guidelines (18) .

Results
Of the 702 college students, 62.7% were women; 53.3% were aged between 20 and 24 years old When comparing the averages of association between NC and the socio-demographic data, statistically significant association was found in regard to sex (p<0.001), age (p=0.009), and occupational situation (p<0.001). Therefore, male students aged ≥ 25 years old and those who worked besides studying presented the highest measure of neck circumference.
The NC of men and women who presented high WC was greater than that of individuals with normal NC (p<0.001). Additionally, as NC decreases, the BP of the participants improves (p<0.001). Individuals with high FBS (p=0.003) and TG (p<0.001) presented higher NC, as opposed to what happened with HDL-C (Table 1).
These values were lower among those with normal biochemical measures and NC (Table 1).  Table 3).

Discussion
The relationship between NC and sex showed that men presented higher neck circumference values. Other studies, however, found this association in both sexes and this issue has not been totally clarified (9,12,14) . It is possible that the predominance of excess weight among women explains the greater female vulnerability to higher NC (19) .
Despite the prevalence of MS being low among college students, a significant association was found with high NC. Additionally, those with one or two MS components, also presented a higher average NC; however, more robust evidence was detected in regard to NC and WC, NC and BP, and NC and TG. In this sense, this study's results are in agreement with those found in recent literature (20)(21)(22)(23) .
Hence, the measurement of NC may help to diagnose MS and various health problems, such as central obesity, pre-hypertension, hypertension and dyslipidemia, in addition to indicating the condition of being overweight and obese (24) . One study addressing the relationship between NC and relative muscle force and cardiovascular risk factors among sedentary women showed that NC predicts cardiovascular risk (25) . On the other hand, another study with nursing professionals indicates that NC is not sensitive enough to capture metabolic deviations related to blood lipoprotein, as in other measures of body composition (26) .

Conclusions
Neck circumference was associated with MS and all its criteria according to NCEP/ATP III. Therefore, NC is a potential marker as an additional parameter to screen for MS among college students.