Elevated neck circumference and associated factors in adolescents

It is extremely important to evaluate adolescents considering, primarily, the pubertal stage, to the extent that this is a period of intense growth and development. However, to our knowledge, this is the first study evaluating the association between elevated neck circumference in adolescents with other factors, considering all pubertal stages (prepubertal, pubertal and postpubertal).

In this study it was found that the prevalence of females and males with elevated NC were 32.63 and 37.63%, higher than the study of Guo et al., who observed elevated NC in 11.4% of girls and 23.4% of boys. However, it is important to considerer that the Guo’s study was performed with Chinese children, and this population has lower rates of overweight and obesity than the population of our study [32].

Girls and boys postpubertal, who have completed pubertal stage, showed cutoffs values of NC that identify obesity equal to 32.65/33.90 cm, respectively, values close to those established by Ben-Noun et al., in other words, NC ≥34/37 cm in adult men and women, respectively, as pointed out obesity. This comparison is due to the fact that post pubertal individuals have physiological characteristics of adulthood, and the Ben-Noun’ study was done with adults [23].

In a turkish population-based study, the AUC showed NC for prepubertal girls like this study (0.884, 95% CI 0.828-0.927 vs 0.937, 95% CI 0.856-0.999, respectively), as well as in pubertal girls in both studies (0.896, 95%CI 0.857-0.928 vs 0.763, 95% CI 0.722-0.805). Among boys, the AUC found in two studies to prepubertal were (0.899, 95% CI 0.843-0.926 vs 0.888, 95%CI 0.812-0.964) and the pubertal (0.877, 95% CI 0.828-0.916 vs 0.693 95% CI 0.649-0.737) [33]. The fact that postpubertal girls had better AUC for NC than boys in the same pubertal stage should be emphasized, however there is the small number of boys at this stage.

Cutoff values that showed higher sensitivity and specificity for NC, for overweight prepubertal and pubertal girls, were 28.25 and 31.35 cm, respectively. For obese prepubertal our cutoff was higher than Hatipoglu et al. (29.75 vs 28.0 cm), however for pubertal were virtually the same (31.0 vs 31.15 cm). As for boys, the cutoff values for overweight were 29.75 (prepubertal), and 34.25 (pubertal), and for obese the opposit occurred, in relation to girls, that is, for the prepubertal cutoff value of NC was very similar to the turkish study (29.75 vs. 29.0 cm), and, for the pubertal, our values were higher than this turkish study (37.95 vs. 32.5 cm) [33].

Importantly, in this study postpubertal girls had better AUC for NC than boys. In general, cross-sectional and longitudinal studies indicate that girls have more fat deposits than boys, especially after puberty [34-37]. However, recent and important study by Katz et al., which aimed to examine the association between NC and markers of adiposity in children, and to develop reference data on NC for the Canadian pediatric population, assessed 936 girls and 977 boys Canadians and showed that NC values for the boys were higher than the NC values for the girls, which can be explained by the fact that all individuals in overweight and obesity were excluded from the sample, which considered only the healthy-weight individuals. Among healthy-weight individuals is expected that boys have larger neck circumference than girls, especially with increasing age. However, among overweight/obese individuals that does not necessarily happen that way. So, After excluding overweight/obese, ie, into an ideal healthy population is expected that boys have larger neck circumference than girl. Also, this Canadian study did not classified participants according to pubertal stage [38].

Anthropometric measurements showing high sensitivity and specificity in predicting overweight and fat accumulation in the upper body, such as the NC, for example, are feasible. NC is simple to perform, inexpensive, has no variation in its magnitude throughout the day, it is preferable in cold weather where individuals are wearing heavy clothing, and in some cases, such as obese or morbidly obese, which feature “belly apron” or various waistlines over the abdomen [39-42].

It is important to consider that NC has good intra and inter-observer, and does not require multiple measures, for accuracy and reliability, even when compared to waist circumference. Parameters in addition to BMI have been proposed long time with the aim of better defining the body composition of an individual [43], particularly with respect to fat accumulation in the central region, which is fully associated with the development of metabolic diseases including the metabolic syndrome, characterized by central obesity, dyslipidemia, hypertension and insulin resistance, while there are doubts in terminology, for children and adolescents, there is consensus regarding cardiometabolic risk [44].

Unfortunately, the most sensitive methods to identify and complete the accumulation of body fat are expensive, difficult to be implemented in clinical practice, such as computed tomography, the DEXA (dual-energy X-ray absorptiometry), ultrasound [45]. So many authors have been engaged in developing technical protocols to better assess the distribution of body fat, especially in the pediatric age group, more cheaply and accessible to health professionals. During puberty, for example, the change in body composition is too large, depending on the stage of growth spurt, even among age-matched subjects. This makes references proposed for this assessment taking into account the pubertal stage [46]. Now there is controversy in the literature about which is the best method and technique used for the evaluation of visceral obesity in adults, stages of growth and development, such as adolescence, the difficulties are much higher [40,41].

It is widely known that the measurement of waist circumference (WC) has good ability to determine central obesity, both in adults and in children and adolescents, having already shown that in these individuals there are also good relationship with central fat [10,17,18]. In the present study the WC after being adjusted significantly correlated to overweight (p = 0.024), which did not occur when the adjustment was made in obesity (p = 0.305). In addition, WC does not have international standard classification cutoffs for classification of abdominal adiposity, much less specific to the pediatric population, and presents difficulties in measurement, that can vary significantly throughout the day, in the postprandial period in menstrual period, according to bowel function, and diverge as to the best measurement technique: the midpoint between the last intercostal arch and iliac - crest, the upper border of the iliac crest, the smallest circumference abdomen, above the umbilicus, depending on posture, respiratory phase, long after the meal [39-41].

It was observed that sex correlates significantly even when adjusted. In relation to BMI, it was found that normal individuals showed greater association with elevated NC when set this way, greater concern should be directed to these individuals, which had 2.63 greater chance to have high NC (OR: 2.63; 95%CI 1.28-5.37). Regarding circumferences, the one that presented the highest association, unilateral or adjusted, was the arm circumference (AC), in other words, the adolescent who provide high AC has a 13% more chance to present high NC (p = 0.002), and 7% chance to presenting high NC to obesity (p = 0.008), in accordance with the adjusted model. AC is important to assess subcutaneous fat and muscle mass, which may reflect a reduction in cases of malnourished individuals, or an increase in cases of obese individuals, both, respectively. In a previous study conducted with 8020 adolescents in the city of Sao Paulo, the cutoff values of the AC demonstrated for female and male high sensitivity and specificity. This shows how this measure is correlated with adiposity [9].

Although there was a significant association of NC with high blood pressure changed only in the univariate analysis, both for overweight, and for obesity, it emphasizes the importance of this issue, because it was high prevalence of this change in sistolic blood pressure (22.19%) and diastolic blood pressure (25.17%). Some studies have documented changes in blood pressure in children and adolescents (14.4%) [47-49], but less high than among adolescents in the present study. Work of Guo et al. [32], which examined whether there was an association according to nutritional status between NC and high risk of change in BP, noted that, among eutrophic participants, elevated NC was significantly associated with a greater chance for change in BP (OR = 1.637; 95% CI 1.288-2.08) in univariate analysis, and this result remained significant after adjustment for BMI and WC (OR = 1.439; 95% CI 1.118-1.853).

Study by Ferretti et al., which evaluated 917 adolescents in a specialized center in Adolescents in the city of São Paulo showed that elevated blood pressure in adolescents is highly prevalent, even among healthy-weight individuals, which can be explained by style of teenage life, characterized by high consumption of foods high in salt, sugar and fat, in addition to physical inactivity, contributing to the increase in blood pressure and various metabolic disorders, even in apparently healthy individuals [50].

To our knowledge, this is the first study to determine cutoff values for NC with Brazilian Adolescents that identify overweight and obesity and its association with associated factors. These data demonstrate the importance of NC in adolescents. However, the cross-sectional nature of this study prevents the firm causal conclusions.

Study limitations are considered, as not questioning about sleep disturbances, although the focus of this study was not sleep disturbances, recent studies have shown that sleep deprivation may be related to increased neck circumference in adults. In addition, metabolic assessment would be required, and control of internal quality of the data was not performed, intra and inter-rater reability [13,15,51].