Relationship between changes in neck circumference and cardiovascular risk factors

Abstract

OBJECTIVE

Neck circumference (NC) is a simple screening measure for identifying overweight and obese patients. The main aim of the present study was to determine the relationship between changes in NC and changes in cardiovascular risk factors by evaluating some components of the metabolic syndrome.

METHODS

The present longitudinal cohort study included 364 subjects (155 men and 209 women) with no known major medical conditions and who were not receiving any medication. Main indicators included NC, waist circumference, waist-to-hip ratio, body mass index, and fasting lipoprotein, glucose and uric acid levels.

RESULTS

Pearson’s correlation coefficients indicated a significant association between changes in NC and changes in body mass index (men, r=0.67; women, r=0.69; each, P<0.0001), waist circumference (men, r=0.69; women, r=0.56; each, P<0.0001), waist-to-hip ratio (men, r=0.27; women, r=0.33; each, P<0.0001), and total cholesterol (men, r=0.68; women, r=0.64; each, P<0.0001), low density lipoprotein cholesterol (men, r=0.58; women, r=0.59; each, P<0.0001), triglyceride (men, r=0.48; women, r=0.44; each, P<0.0001), glucose (men, r=0.51; women, r=0.44; each, P<0.0001) and uric acid (men, r=0.42; women, r=0.47; each, P<0.0001) levels. The relative changes in NC contributed to independent significant changes in total cholesterol (8% for men and 1% for women), low density lipoprotein cholesterol (1% for men and 1% for women) and triglycerides (23% for men); it did not significantly contribute to changes in high density lipoprotein cholesterol, glucose or uric acid levels.

CONCLUSION

Changes in NC are positively correlated with changes in some factors of the metabolic syndrome and, therefore, are correlated with changes in the risk of cardiovascular disease.

Although obesity results in metabolic abnormalities, upper body obesity is more strongly associated with glucose intolerance, hyperinsulinemia, diabetes, hypertriglyceridemia, gout and uric calculus disease than lower body obesity (1–3).

Upper body obesity can be assessed by various techniques such as neck circumference (NC), waist circumference (WC), waist-to-hip ratio, waist-to-thigh ratio, subscapular-to-triceps skinfold ratio and abdominal sagittal diameter (4–8). In our previous study (4), NC was examined as an index of upper body obesity, and was found to be a simple and time-saving screening measure that could be used to identify overweight and obese individuals. It has been shown that men with an NC of less than 37 cm and women with an NC of less than 34 cm probably have a low body mass index (BMI). Patients above these levels require a more comprehensive evaluation of their status as overweight or obese (4).

We also examined the relationship between NC and risk factors for coronary artery disease by evaluating the components of the metabolic syndrome. Higher NC positively correlated with the factors of the metabolic syndrome; therefore, it is likely that a higher NC increases the risk of coronary artery disease (9).

Body weight and BMI, even when adjusted for changes in waist-to-hip ratio, change in parallel with changes in risk factors for cardiovascular disease (6,10–13). In addition, a change in NC is positively correlated to some cardiovascular risk factors, such as insulin, glucose, triglyceride and uric acid levels, but it is negatively correlated to changes in high density lipoprotein (HDL)-cholesterol levels in adults with severe obesity in a three-compartment (lean body mass, and subcutaneous and visceral adipose tissue masses) model (14).

Therefore, the aim of the present study was to determine whether changes in NC alone can predict changes in risk factors for cardiovascular heart disease in subjects who were not only severely obese by evaluating the association between changes in NC and changes in some components of the metabolic syndrome. The data on the association between changes in NC and hypertension are analyzed in a separate report (15).

PATIENTS AND METHODS

Four hundred thirty-one consecutive patients (187 men and 244 women) aged 18 years or older, with no known major medical conditions (eg, diabetes, coronary artery disease, hypertension, thyroid diseases or malignant disease) and not receiving prescription medication, were recruited for the present study. All subjects had attended a family health clinic in an Israeli urban district for any reason between January 1998 and December 2002. A total of 67 subjects were excluded; of these, three were wheelchair bound, 15 had a thyroid nodule, one had cervical kyphosis, seven refused to participate, and 26 women and 15 men had no changes in their weight; this left 155 men and 209 women in the study.

All measurements were made by one investigator (LB) using standard techniques as follows (16): weight by digital scales (Hanson, England) to within 100 g, without heavy clothing; height by portable stadiometer (Holtain, Wales) to within 0.5 cm, while barefoot; and waist and hip circumferences to within 1 mm, with plastic tapes calibrated weekly, waist midway between the lowest rib and the iliac crest, the patient standing at the end of gentle expiration, and hips at the greater trochanter. NC was measured at mid-neck height, between mid-cervical spine and mid-anterior neck, to within 1 mm, with plastic tapes calibrated weekly. In men with a laryngeal prominence (Adam’s apple), it was measured just below the prominence (4). All circumferences were taken with the subjects standing upright and facing the investigator, having their shoulders relaxed.

Blood pressure (BP) was measured while subjects were sitting after 5 min of rest using a standardized Hawksley random-zero sphygmomanometer (WA Baum Co, USA). An appropriately sized cuff (cuff bladder encircling at least 80% of the arm) was used. The first and fifth phase Korotkoff sounds were criteria for systolic BP and diastolic BP, respectively. The average of the second and the third of three measurements was used (17,18).

After a 14 h fast, blood samples were sent to the clinical biochemistry laboratory at Soroka University Medical Center (Beer-Sheva, Israel) for analyses of blood glucose, total cholesterol, HDL-cholesterol, triglycerides and uric acid on a BM Hitachi automated clinical chemistry analyzer (Hitachi, Japan) by means of standard biochemical procedures. Low density lipoprotein (LDL)-cholesterol was calculated automatically:

$$\text{LDL}-\text{cholesterol}=\text{total}\hspace{0.17em}\text{cholesterol}-\text{HDL}-\text{cholesterol}-(\text{triglycerides}/5)$$

Measurements were performed at baseline (ie, cholesterol-1) and at follow-up or the end point of the study (ie, cholesterol-2), and relative changes were defined as the relative change in these values during the study (ie, the relative change in cholesterol equals cholesterol-2 minus cholesterol-1, divided by cholesterol-1).

During subsequent visits, the subjects were repeatedly weighed. Those who lost or gained at least 0.5 kg in weight, intentionally or unintentionally, regardless of the time during the study period, menopause, dietary energy intake and physical activity, underwent anthropometric measurements and their blood was sent for biochemical investigation. The research was continued until a reasonable number of patients for a subsequent analysis was achieved.

Statistical analysis

The significance of differences between continuous variables was assessed using Student’s t test. The pooled form of statistics tested equality of variance, and correction for unequal variances was performed when appropriate. All tests of significance were two tailed. Pearson’s correlation coefficients were used to analyze the interrelationships between anthropometric indexes and age, weight and various lipid, glucose and uric acid levels. The relative contributions of the variability of plasma lipids, glucose and uric acid to changes in NC and other anthropometric and demographic changes were analyzed by multiple regression analysis. The independent variables used in the model were demographic, anthropometric and biochemical data recorded initially, and their relative changes. A stepwise selection method was used to delineate a set of contributory variables to the variability of risk factors. Variables were added one by one to the model, and the F statistics for a variable to be added had to be significant at the 0.15 level. After a variable was added, the stepwise method looked at all of the variables included in the model and deleted any variable that did not produce an F statistic significant at the 0.05 level. Only after this check was made and the necessary deletions accomplished could another variable be added to the model. The stepwise process ended either when none of the variables outside the model had an F statistic significant at the 0.15 level or every variable in the model was significant at the 0.05 level, or when the variable to be added to the model was the one just deleted from it. The relative contribution of an independent (predictor) variable to the relative change of a risk factor was measured by partial squared correlation. The data were analyzed using PROC REG of SAS software (version 8.2, SAS Inc, USA) (19).

RESULTS

The mean age, waist-to-hip ratio, and total cholesterol, LDL-cholesterol and glucose levels were similar for men and women at baseline and follow-up. Compared with women, men were heavier and taller, had higher NCs, and had higher triglyceride and uric acid levels at baseline and at follow-up, whereas women had significantly higher WCs and higher HDL-cholesterol levels only at follow-up (Table 1).

TABLE 1.

Clinical characteristics of the study subjects

	Baseline values		Follow-up values
	Men (n=155)	Women (n=209)	Men (n=155)	Women (n=209)
Age (years)	48.1±14.1	46.4±12.4	49.7±14.3	48.0±12.4
Weight (kg)	78.7±13.9*	70.9±13.9	77.4±11.4‡	70.4±14.6
Height (cm)	170.1±7.4*	158.3±6.7	169.6±7.4‡	157.7±6.7
Waist circumference (cm)	95.9±9.5	98.6±15.3	95.2±9.1§	98.6±15.0
Hip circumference (cm)	99.5±6.5*	103.2±8.2	99.0±6.7‡	102.9±8.3
Waist-to-hip ratio	0.96±0.1	0.95±0.1	0.97±0.1	0.96±0.1
Neck circumference (cm)	39.2±2.4*	35.0±2.3	39.0±2.3‡	35.0±2.2
BMI (kg/m2)	27.3±3.7†	28.3±6.2	26.9±3.6¶	28.4±5.4
Total cholesterol (mmol/L)	5.5±1.1	5.5±1.1	5.2±0.9	5.3±1.0
Triglycerides (mmol/L)	2.0±1.1*	1.5±0.8	1.7±0.9**	1.5±0.7
LDL-cholesterol (mmol/L)	3.4±1.0	3.5±1.0	3.3±0.8	3.4±0.8
HDL-cholesterol (mmol/L)	1.1±0.2	1.5±3.5	1.1±0.2‡	1.3±0.3
Uric acid (μmol/L)	362.6±83.5*	261.8±70.4	344.1±79.6‡	252.4±63.1
Glucose (mmol/L)	4.7±0.7	4.6±0.7	4.6±0.7	4.5±0.7

Values are means ± SD. Men versus women at baseline:

^*P<0.0001 for weight, height, hip and neck circumferences, and triglyceride and uric acid levels;

^†P<0.03 for body mass index (BMI). Men versus women at follow-up:

^‡P<0.0001 for weight, height, neck and hip circumferences, and high density lipoprotein (HDL)-cholesterol and uric acid levels;

^§P<0.01 for waist circumference;

^¶P<0.003 for BMI;

^**P<0.001 for triglycerides by Student’s t test. LDL Low density lipoprotein

The differences among subjects according to age and various variables at the significance of P=0.05 or less are shown in Tables 2 and 3.

TABLE 2.

Clinical characteristics of the men by age group

	Baseline values, mean ± SD (95% CI)			Follow-up values, mean ± SD (95% CI)
	Group 1 (n=65)	Group 2 (n=70)	Group 3 (n=20)	Group 1 (n=65)	Group 2 (n=70)	Group 3 (n=20)
Weight (kg)	80.0±12.9 (50.2–104.1)	78.1±10.4 (54.1–103.5)	76.9±13.6 (57.2–104.1)	79.1±12.7 (53.4–110.2)	76.4±9.7 (54.6–100.2)	75.1±12.4 (58.4–100.2)
Height (cm)	172.0±6.4* (152.1–188.3)	169.3±6.7 (152.6–186.6)	166.8±10.8* (148.1–197.0)	171.7±6.6† (152.1–188.3)	168.6±6.6† (152.6–186.6)	166.0±10.6† (148.1–196.8)
Waist circumference (cm)	94.2±11.5 (65.1–115.2)	96.7±8.1 (73.1–116.1)	99.0±5.9 (89.3–110.2)	94.0±10.5 (68.4–110.2)	95.7±8.4 (73.4–116.2)	98.0±6.7 (88.3–116.6)
Hip circumference (cm)	100.6±6.6 (79.2–113.3)	99.0±6.1 (85.3–112.8)	98.0±7.0 (86.4–112.2)	100.5±6.7 (86.1–116.6)	98.2±6.1 (84.2–114.5)	97.0±8.5 (76.6–117.0)
Waist-to-hip ratio	0.93±0.08† (0.73–1.1)	0.97±0.1† (0.79–1.1)	1.0±0.1† (0.9–1.2)	0.93±0.07† (0.75–1.1)	0.97±0.1† (0.7–1.1)	1.0±0.1† (0.9–1.3)
Neck circumference (cm)	39.1±2.7 (30.4–47.1)	39.2±2.2 (36.0–47.2)	39.4±2.0 (36.6–43.6)	39.0±2.6 (32.3–46.4)	39.1±2.2 (35.3–46.4)	39.1±1.9 (36.4–42.7)
Body mass index (kg/m2)	27.0±4.3 (16.3–34.5)	27.3±3.5 (20.0–35.0)	27.5±2.6 (24.0–34.2)	26.8±4.0 (17.4–34.7)	26.9±3.3 (18.9–37.2)	27.2±2.9 (21.8–33.2)
Total cholesterol (mmol/L)	5.0±1.1† (2.8–8.6)	5.7±1.1† (3.5–8.6)	5.9±1.1† (4.4–8.4)	4.8±1.0† (2.7–7.7)	5.4±0.8† (2.9–8.5)	5.4±0.7† (4.3–7.0)
Triglycerides (mmol/L)	2.0±1.2 (0.6–4.5)	2.1±1.0 (0.7–4.4)	1.6±0.7 (0.8–4.5)	1.7±0.9 (0.5–4.2)	1.9±0.89‡ (0.6–4.2)	1.3±0.4‡ (0.9–2.2)
LDL-cholesterol (mmol/L)	3.0±0.82† (1.4–5.2)	3.7±0.9† (2.0–6.0)	3.9±0.9† (2.7–5.7)	3.0±0.8† (1.7–5.5)	3.4±0.8† (1.5–5.7)	3.5±0.6† (2.4–4.3)
HDL-cholesterol (mmol/L)	1.1±0.2* (0.7–1.7)	1.1±0.2 (0.7–1.6)	1.2±0.4* (0.8–2.3)	1.1±0.2* (0.7–1.7)	1.2±0.3 (0.6–2.4)	1.2±0.2* (1.0–1.7)
Uric acid (μmol/L)	365.6±83.0 (166.5–559.1)	353.2±84.7 (208.2–541.3)	387.5±79.4 (226.0–511.5)	346.4±72.2 (178.4–523.4)	340.0±90.3 (172.5–636.4)	351.5±64.8 (214.1–452.1)
Glucose (mmol/L)	4.5±0.6† (3.5–6.4)	4.8±0.6† (3.8–6.6)	5.2±0.9† (3.9–7.1)	4.4±0.5† (3.4–6.1)	4.7±0.7† (3.3–7.8)	4.8±1.1† (3.6–7.4)

All comparisons are at P<0.05, with multiple comparison adjustment by the Tukey-Cramer method.

^*The aged 18 to 45 years group (group 1) is different from the older than 65 years group (group 3);

^†Group 1 is different from the aged 45 to 65 years group (group 2) and group 1 is different from group 3;

^‡Group 2 is different from group 3. All differences are at least at the 0.05 level. HDL High density lipoprotein; LDL Low density lipoprotein

TABLE 3.

Clinical characteristics of the women by age group

	Baseline values, mean ± SD (95% CI)			Follow-up values, mean ± SD (95% CI)
	Group 1 (n=86)	Group 2 (n=107)	Group 3 (n=16)	Group 1 (n=86)	Group 2 (n=107)	Group 3 (n=16)
Weight (kg)	67.4±14.1‡ (43.1–118.3)	73.6±13.5‡ (52.0–112.6)	71.1±12.1 (53.0–100.0)	67.3±13.2 ‡ (42.1–110.2)	73.1±13.1‡ (49.6–113.4)	70.0±10.8 (49.0–95.0)
Height (cm)	159.2±7.1* (141.0–177.2)	158.5±6.1 (145.2–175.4)	152.8±6.3* (141.8–168.3)	158.8±7.1§ (141.0–177.2)	157.7±6.0§ (144.5–175.2)	151.1±6.0§ (140.4–165.4)
Waist circumference (cm)	92.4±14.6† (59.1–132.3)	102.4±14.6† (70.0–149.3)	106.8±11.8† (85.2–137.1)	92.8±14.4† (58.9–132.2)	102.1±14.3† (72.1–151.2)	106.4±12.1† (82.7–136.1)
Hip circumference (cm)	102.1±7.6 (87.0–128.4)	104.2±8.9 (89.4–129.0)	101.9±6.7 (91.2–113.2)	102.1±7.6 (86.9–126.3)	103.8±8.9 (89.0–129.6)	101.6±7.3 (89.1–114.3)
Waist-to-hip ratio	0.90±0.1¶ (0.7–1.2)	0.98±0.1¶ (0.75–1.2)	1.1±0.1¶ (0.9–1.3)	0.91±0.1¶ (0.7–1.2)	0.98±0.1¶ (0.8–1.2)	1.1±0.1¶ (0.9–1.3)
Body mass index (kg/m2)	26.6±5.2† (18.3–44.4)	29.4±5.5† (20.1–50.4)	30.6±6.2† (23.5–49.7)	26.7±4.9† (17.6–41.3)	29.4±5.3† (20.4–46.5)	30.9±6.0† (22.9–48.2)
Neck circumference (cm)	34.2±2.3† (28.6–40.1)	35.4±2.1† (29.8–41.6)	36.7±2.2† (34.1–42.0)	34.3±2.3† (29.0–41.4)	35.3±2.0† (31.3–42.0)	36.6±1.8† (33.6–39.3)
Total cholesterol (mmol/L)	5.1±1.1† (3.1–8.6)	5.7±1.0† (3.2–8.2)	6.0±0.8† (4.3–7.1)	5.0±1.1† (2.6–7.5)	5.5±0.9† (3.1–7.7)	5.9±0.74† (4.4–7.6)
Triglycerides (mmol/L)	1.4±0.8 (0.5–4.5)	1.6±0.7 (0.6–4.2)	1.8±0.5 (1.2–2.9)	1.4±0.7 (0.5–4.2)	1.5±0.8 (0.5–4.6)	1.7±0.4 (0.9–2.2)
LDL-cholesterol (mmol/L)	3.2±0.98† (1.4–6.5)	3.6±0.9† (1.7–5.6)	4.0±0.7† (2.4–5.0)	3.1±0.9† (1.3–5.4)	3.5±0.8† (1.8–6.2)	3.9±0.6† (2.7–4.9)
HDL-cholesterol (mmol/L)	1.9±5.5 (0.7–52.0)	1.3±0.3 (0.8–2.3)	1.2±0.3 (0.8–2.2)	1.3±0.3 (0.6–2.3)	1.3±0.3 (0.7–2.4)	1.2±2.4 (0.9–1.7)
Uric acid (μmol/L)	241.9±59.3** (136.8–410.4)	275.0±74.6** (83.3–505.6)	275.5±76.4 (154.7–463.9)	236.7±65.9** (119.0–398.5.4)	263.9±66.9** (101.1–440.2)	260.6±69.0 (160.6–386.6)
Glucose (mmol/L)	4.5±0.7* (3.5–6.9)	4.7±0.6 (3.4–7.1)	5.1±0.9* (3.9–7.7)	4.4±0.7* (3.3–6.7)	4.6±0.7 (3.4–6.8)	4.9±0.9* (3.7–7.4)

All comparisons are at P<0.05, with multiple comparison adjustment by the Tukey-Cramer method.

^*The aged 18 to 45 years group (group 1) is different from the older than 65 years group (group 3);

^†Group 1 is different from the aged 45 to 65 years group (group 2) and group 1 is different from group 3;

^‡Group 1 is different from group 2;

^§Group 1 is different from group 3 and group 2 is different from group 3;

^¶Group 1 is different from group 2 and group 1 is different from group 3, and group 2 is different from group 3;

^**Group 1 is different from group 2. All differences are at least at the 0.05 level. HDL High density lipoprotein; LDL Low density lipoprotein

Significant differences were found between the mean differences at baseline and follow-up for age, weight, height, waist and hip circumferences, and total cholesterol, HDL-cholesterol and uric acid levels among men; and in age, height and glucose levels among women (Table 4).

TABLE 4.

The differences between the means at baseline and follow-up among men (n=155) and women (n=209)

	Men Mean (95 %CI)	Women Mean (95 %CI)
Age	0.04* (0.03 to 0.04)	0.04†† (0.03 to 0.04)
Weight	−0.02† (−0.02 to −0.005)	−0.002 (−0.01 to 0.008)
Height	−0.003* (−0.004 to −0.002)	−0.004†† (−0.005 to 0.003)
WC	−0.006‡ (−0.01 to −0.002)	0.001 (−0.004 to 0.006)
Hip circumference	−0.005‡ (−0.009 to −0.001)	0.002 (−0.005 to 0.009)
Waist-to-hip ratio	−0.001 (−0.004 to 0.002)	0.003 (−0.0007 to 0.007)
NC	−0.002 (−0.006 to 0.002)	−0.0006 (−0.005 to 0.004)
Body mass index	−0.008 (−0.02 to 0.002)	0.007 (−0.004 to 0.02)
Cholesterol	−0.003§ (−0.06 to −0.008)	−0.02 (−0.04 to 0.003)
Triglycerides	−0.01 (−0.05 to −0.02)	0.01 (0.03 to 0.06)
LDL-cholesterol	−0.02 (−0.05 to 0.02)	0.0006 (−0.03 to 0.03)
HDL-cholesterol	0.03¶ (0.004 to −0.56)	0.0006 (−0.02 to 0.03)
Glucose	−0.02 (−0.04 to 0.004)	−0.02‡‡ (−0.03 to 0.001)
Uric acid	−0.038** (−0.06 to −0.01)	−0.01 (−0.04 to 0.01)

Values for the differences between means. For men:

^*P<0.0001 for age and height;

^†P<0.003 for weight;

^‡P<0.01 for waist and hip circumferences;

^§P<0.009 for cholesterol;

^¶P<0.02 for high density lipoprotein (HDL)-cholesterol;

^**P<0.005 for uric acid. For women:

^††P<0.0001 for age and height;

^‡‡P<0.07 for glucose by paired t test. LDL Low density lipoprotein; NC Neck circumference; WC Waist circumference

There was no significant difference between the mean duration between examinations at baseline and follow-up in weight-gainers versus weight-losers (1.7±0.95 months versus 1.6±0.96 months, respectively).

BMI positively correlated with all variables studied, except with age among men at baseline and follow-up, as well as HDL-cholesterol among women at baseline and in both sexes at follow-up (Table 5).

TABLE 5.

Relationship between body mass index (BMI) and various variables in men (n=155) and women (n=209)

	BMI at baseline				BMI at follow-up
	Men		Women		Men		Women
	r	P	r	P	r	P	r	P
Age	0.13	0.1	0.36	0.0001	0.12	0.13	0.37	0.0001
Weight	0.83	0.0001	0.90	0.0001	0.81	0.0001	0.83	0.0001
Height	−0.39	0.08	−0.21	0.0001	−0.15	0.06	−0.23	0.0009
NC	0.79	0.001	0.74	0.001	0.73	0.001	0.70	0.001
WC	0.83	0.0001	0.89	0.0001	0.82	0.0001	0.89	0.0001
Hip circumference	0.72	0.001	0.69	0.0001	0.69	0.0001	0.72	0.0001
Waist-to-hip ratio	0.51	0.001	0.71	0.001	0.45	0.0001	0.67	0.0001
Total cholesterol	0.46	0.0001	0.39	0.0001	0.37	0.0001	0.31	0.0001
Triglycerides	0.44	0.0001	0.48	0.0001	0.27	0.0006	0.31	0.0001
LDL-cholesterol	0.33	0.0001	0.30	0.0001	0.19	0.02	0.26	0.0002
HDL-cholesterol	0.20	0.01	−0.10	0.14	−0.07	0.40	0.01	0.89
Uric acid	0.39	0.0001	0.52	0.0001	0.32	0.0001	0.45	0.0001
Glucose	0.25	0.002	0.40	0.0001	0.32	0.0001	0.34	0.0001

Pearson’s correlation coefficients and their statistical significance. LDL Low density lipoprotein; HDL High density lipoprotein; NC Neck circumference; WC Waist circumference

WC correlated positively with weight (men, r=0.78; women, r=0.85; each, P<0.0001), BMI (men, r=0.84; women, r=0.89; each, P<0.0001), NC (men, r=0.75; women, r=0.71; each, P<0.0001), total cholesterol (men, r=0.46; women, r=0.35; each, P<0.0001), LDL-cholesterol (men, r=0.33; women, r=0.29; each, P<0.0001), triglyceride (men, r=0.42; women, r=0.36; each, P<0.0001), glucose (men, r=0.21, P<0.01; women, r=0.34, P<0.0001), uric acid (men, r=0.31; women, r=0.44; each, P<0.0001), systolic BP (men, r=0.48; women, r=0.61; each, P<0.001) and diastolic BP (men, r=0.57; women, r=0.48; each, P<0.0001).

NC correlated significantly with weight, waist and hip circumferences, waist-to-hip ratio, BMI, and total cholesterol, triglyceride, LDL-cholesterol, uric acid and glucose levels at baseline and follow-up both in men and women. No significant correlation was found between NC and HDL-cholesterol levels at baseline and follow-up in men and in women (Table 6).

TABLE 6.

Relationship between neck circumference (NC) and various variables in men (n=155) and women (n=209)

	NC at baseline		NC at follow-up
	Men (r)	Women (r)	Men (r)	Women (r)
Age	0.12	0.38***	0.37	0.398***
Weight	0.76***	0.76***	0.73***	0.75***
Height	−0.21**	0.04	0.11	0.04
Waist circumference	0.75***	0.71***	0.73***	0.70***
Hip circumference	0.62***	0.52***	0.57***	0.53***
Waist-to-hip ratio	0.47**	0.61**	0.43***	0.58**
Body mass index	0.79***	0.74***	0.73***	0.70***
Total cholesterol	0.52***	0.53***	0.29***	0.45***
Triglycerides	0.46***	0.45***	0.39***	0.31***
LDL-cholesterol	0.46***	0.46***	0.41*	0.41***
HDL-cholesterol	−0.13	−0.13	−0.12	−0.0009
Uric acid	0.52***	0.50***	0.35***	0.48***
Glucose	0.33**	0.33***	0.36***	0.32***

^*P<0.05;

^**P<0.01;

^***P<0.001. HDL High density lipoprotein; LDL Low density lipoprotein

Correlations of changes from baseline to follow-up indicate that BMI and NC correlated positively with waist and hip circumferences, waist-to-hip ratio, and total cholesterol, triglyceride, LDL-cholesterol, uric acid and glucose levels (Table 7).

TABLE 7.

The correlation between changes in neck circumference (NC), body mass index (BMI) and various variables at follow-up in men (n=155) and women (n=209)

	BMI at follow-up		NC at follow-up
	Men (r)	Women (r)	Men (r)	Women (r)
Age	−0.29	−0.09	0.17*	0.03
Weight	0.98	0.76***	0.68***	0.70**
Height	−0.12	0.015*	0.16	0.04
Waist circumference	0.68***	0.69***	0.69***	0.56***
Hip circumference	0.66***	0.69***	0.62***	0.57***
Waist-to-hip ratio	0.22***	0.41**	0.27***	0.33***
BMI			0.67***	0.69***
Total cholesterol	0.67***	0.77***	0.68***	0.64***
Triglycerides	0.43***	0.55***	0.48***	0.44***
LDL-cholesterol	0.59***	0.68***	0.58***	0.59***
HDL-cholesterol	−0.12	−0.13	−0.09	−0.07
Uric acid	0.40***	0.47***	0.42***	0.47***
Glucose	0.54**	0.57***	0.51***	0.44***

^*P<0.05;

^**P<0.01;

^***P<0.001. HDL High density lipoprotein; LDL Low density lipoprotein

The model for the relative changes in lipid, glucose and uric acid levels after the stepwise elimination procedure shows that the relative changes in NC contributed to significant independent changes in total cholesterol (8% for men and 1% for women), LDL-cholesterol (1% for men and 1% for women) and triglyceride levels (23% for men); the relative NC changes did not significantly contribute to changes in HDL-cholesterol, glucose or uric acid levels (Tables 8 and 9).

TABLE 8.

A model for total cholesterol, low density lipoprotein (LDL)-cholesterol and triglyceride relative changes after a stepwise elimination procedure

Dependent variable (relative changes)	Independent variable	Partial R2	Model R2	P
Total cholesterol
Men	Weight (relative change)	0.49	0.49	0.0001
	NC (relative change)	0.08	0.57	0.0001
	Initial cholesterol	0.04	0.60	0.0002
	Initial DBP	0.01	0.62*	0.04
Women	Weight (relative change)	0.60	0.60	0.0001
	Hip circumference (relative change)	0.04	0.64	0.0001
	Initial glucose	0.01	0.65	0.009
	NC (relative change)	0.01	0.66	0.01
	Initial height	0.01	0.67*	0.02
LDL-cholesterol
Men	Weight (relative change)	0.38	0.38	0.0001
	Initial LDL-cholesterol	0.13	0.50	0.0001
	WC (relative change)	0.02	0.53	0.007
	Initial total cholesterol	0.02	0.55	0.007
	NC (relative change)	0.01	0.56*	0.04
Women	Weight (relative change)	0.48	0.48	0.0001
	Initial LDL-cholesterol	0.05	0.53	0.0001
	WC (relative change)	0.02	0.56	0.001
	Age	0.03	0.58	0.0006
	Initial glucose	0.02	0.60	0.006
	Initial total cholesterol	0.01	0.61	0.01
	NC (relative change)	0.01	0.62	0.04
	Initial height	0.01	0.63*	0.05
Triglycerides
Men	NC (relative change)	0.23	0.23	0.0001
	Initial triglycerides	0.06	0.29	0.0005
	Initial DBP	0.02	0.31*	0.04

^*Maximal variation was partly explained by the variables included in the model (model R²). Relative changes in high density lipoprotein cholesterol were not correlated to relative changes in neck circumference (NC) or other anthropometric factors. In all regression models, age and changes in age (at baseline and at follow-up) were entered as independent variables. In most models, except LDL-cholesterol for women, age and changes in age were found to be noncontributory (nonsignificant) and, therefore, were dropped from the model during the stepwise elimination procedure. DBP Diastolic blood pressure; WC Waist circumference

TABLE 9.

A model for glucose and uric acid relative changes after a stepwise elimination procedure

Dependent variable (relative changes)	Independent variable	Partial R2	Model R2	P
Glucose
Men	Weight (relative change)	0.31	0.31	0.0001
	Initial glucose	0.10	0.41	0.0001
	WC (relative change)	0.03	0.44*	0.007
Women	Weight (relative change)	0.34	0.34	0.0001
	WC (relative change)	0.06	0.39	0.0001
	Initial glucose	0.01	0.41*	0.04
Uric acid
Men	WC (relative change)	0.20	0.20	0.0001
	Initial uric acid	0.09	0.29	0.0001
	Initial cholesterol	0.03	0.32	0.02
	Initial WC	0.03	0.35*	0.007
Women	Weight (relative change)	0.38	0.38	0.0001
	Initial uric acid	0.07	0.45	0.0001
	Hip circumference (relative change)	0.04	0.49	0.0001
	Initial waist-to-hip ratio	0.02	0.51	0.002
	Initial triglycerides	0.01	0.52*	0.02

^*Maximal variation was partly explained by the variables included in the model (model R²). WC Waist circumference

DISCUSSION

The present study indicates a correlation between NC and risk factors for cardiovascular disease, as well as between changes in NC and changes in these factors. Changes in NC were correlated with changes in BMI (total fatness index), WC, waist-to-hip ratio (upper body obesity indexes), and total cholesterol, LDL-cholesterol, triglyceride, fasting glucose and uric acid levels. No significant correlation was found between changes in NC and changes in HDL-cholesterol levels, and we conclude that changes in HDL-cholesterol levels are unaffected by changes in NC.

The Third Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) highlighted the importance of treating patients with the metabolic syndrome to prevent cardiovascular diseases (20–22). The elements of the current definition of the metabolic syndrome include WC, fasting glucose, BP, triglycerides and HDL-cholesterol (20). NC is a reliable, simple, time-saving screening measure that can be used, among numerous other methods, to identify overweight and obese patients (4). Therefore, the contribution of the present report lies in the indication of the correlation between changes in NC and changes in some of the factors of the metabolic syndrome. As stated previously, data on changes in NC and changes in BP are presented in a separate report (15).

On average, subjects were 1.6 years older at the second observation. It seems that these small changes in age did not significantly affect the changes between various variables and their associations. Because NC changes parallel with changes in weight (9), the present study only deals with individuals who lost or gained at least 0.5 kg in weight, regardless of time, dietary energy intake, a change in body composition and physical activity. Changes in weight were higher than changes in hip circumference, with no changes in NC and WC in women. It may be assumed that these findings were due to small changes in weight. Greater changes in weight correspond to greater changes in other measured circumferences.

Age did not correlate with BMI at baseline and follow-up in men. In addition, at baseline, a significant negative correlation was found between NC and height among men, but not in women. These findings can be explained by the different bodily structures between sexes.

Several studies (6,23–26), but not all (27–29), have observed that weight reduction induces a decrease in the waist-to-hip ratio. In the present study, changes in weight and NC are strongly correlated with changes in waist-to-hip ratio. Therefore, it can be assumed that in this population, waist and hip circumferences changed proportionally (eg, if WC decreased or increased by 2 cm, hip circumference also changed by a similar amount).

The relationship between visceral adipose tissue and muscle fat content and NC was not evaluated. This issue requires further research.

The regression procedure, with nonsignificant variables removed from the model, indicated that weight and NC in men, and weight, hip circumference and NC in women contributed to total cholesterol levels. Moreover, weight, WC and NC contributed to LDL-cholesterol levels in both men and women, whereas NC contributed to triglyceride levels only in men. Therefore, it can be concluded that NC makes a more significant contribution to the variability of total cholesterol and LDL-cholesterol in both sexes, and to triglycerides only in men. Thus, a change in NC is a significant predictor of a change in triglyceride levels. NC does not contribute to HDL-cholesterol, glucose or uric acid levels.

We observed a consistent reduction in stature in both men and women. It seems that this reduction was associated with different backgrounds, such as the physical activity level and the food habits of the population studied.

The evaluation of the components of the metabolic syndrome was based on the guidelines of the Adult Treatment Panel III (20). Other variables such as heart variability, plasma insulin, leptin, interleukin-6, C-reactive protein, and urinary excretion of cortisol and catecholamines metabolites, which can be increased in the metabolic syndrome (30–32), were not examined in the present study. In addition, the present study included only subjects who lost or gained their weight, regardless of dietary energy activity and change in body composition. For these reasons, the above-mentioned variables were not evaluated.

In the present study, changes in NC and cardiovascular risk factors were not controlled for age and ethnic origin. Ethnic origin may affect the relationship between changes in NC and changes in cardiovascular risk factors. This issue requires further research.

In conclusion, changes in NC are positively correlated with changes in some factors of the metabolic syndrome and, therefore, are correlated with changes in risk for cardiovascular disease.