Three definitions of metabolic syndrome applied to a sample of young obese men and their relation with plasma testosterone

Abstract

This study tested 60 men, aged <40 years, with a BMI 27–35 kg/m² to determine whether they had metabolic syndrome. The three definitions used to test this were from the National Cholesterol Education Program (NCEP), the World Health Organization (WHO) and the International Diabetes Federation (IDF). Further, the relationship between a positive definition and plasma testosterone (T) and calculated free T was analysed.

Using the above three definitions of metabolic syndrome (MetS), there was a large degree of overlap of identifying obese men as having the syndrome, but there were quantitatively significant differences as well. So, it is relevant in studies to identify which of the present definitions of the syndrome has been used. With aging there is an increasing prevalence of the syndrome and age itself might be a factor in the lower T levels encountered in these men. But low plasma total T and calculated free T were also consistent features of men <40 years with metabolic syndrome, regardless of which definition had been applied. Including low T levels in the definition of metabolic syndrome, may be helpful.

Keywords:

• Testosterone
• relations with MetS definitions
• obesity
• young men

Introduction

Obesity is a condition that is reaching epidemic proportions in both the developed and the developing world [1]. Approximately 80% of obese adults suffer from at least one, and 40% from two or more of the diseases associated with obesity, such as type 2 diabetes, hypertension, cardiovascular disease, gallbladder disease, cancers and diseases of the locomotor system, such as arthrosis).

A closer examination of obesity has revealed that a preferential accumulation of fat in the abdominal region is associated with an increased risk of non-insulin dependent diabetes mellitus (NIDDM) and cardiovascular disease, not only in obese subjects but even in non-obese subjects [2]. A large number of cross-sectional studies have established a relationship between abdominal obesity and cardiovascular risk factors such as hypertension, dyslipidemia (elevated levels of cholesterol, of triglycerides, of low-density lipoproteins and low levels of high density lipoproteins), impaired glucose tolerance with hyperinsulinemia, a cluster known as ‘insulin resistance syndrome’ or ‘metabolic syndrome' [3-6]. The term metabolic syndrome is now preferred. The main components of metabolic syndrome are abdominal obesity, insulin resistance, hypertension and dyslipidemia. There is a debate in the literature as to whether combining these components or conditions has an added diagnostic or prognostic value. Meanwhile, there are three main definitions of metabolic syndrome. These definitions overlap but differ in the points of emphasis of the components. The definition of the National Cholesterol Education program places equal emphasis on the various components of the metabolic syndrome [7]. The definition adopted by the WHO assigns greater value to insulin resistance as a required component of the metabolic derangements [8]. Increasingly, professional organizations have now proposed definitions. The International Diabetes Federation has drafted a singly unifying definition in April 2005. The main emphasis in this definition is central obesity defined by waist circumference and two or more of the following four factors: elevated triglycerides, reduced HDL-cholesterol, elevated blood pressure, and dysglycemia [9].

In this report we studied a group of 60 men between the ages of 20 to 40 years with overweight (BMI 27–35 kg/m²). We analysed who of these overweight men would be defined as suffering from metabolic syndrome using any of the three above definitions, and whether men classed as sufferers of the syndrome by one definition, would (largely) overlap with the other two definitions, or whether there are significant differences in outcome when using one of these three definitions.

Both cross-sectional and longitudinal epidemiological studies have convincingly established that low plasma testosterone/SHBG are correlated with/predict metabolic syndrome [10-14]. Adiposity with its associated hyperinsulinism suppresses SHBG synthesis and therewith the levels of circulating testosterone [15]. It also may affect the strength of LH signalling to the testis [16]. Further, insulin [17] and leptin [18] have a suppressive effect on testicular steroidogenesis. So, there are reasons to believe that adiposity is a significant factor in lowering circulating levels of testosterone.

The second question of this study was whether inclusion of the serum level of total T, or SHBG or calculated free T would lead to a more precise definition of metabolic syndrome in men. These men were between the ages of 20 and 40 years. Metabolic syndrome has usually been studied in middle-aged and/or older men. It is unlikely that in this cohort the age-related changes in the dynamics of the hypothalamo-pituitary-testicular axis [15] are playing a major role in the serum T levels associated with their obesity.

Subjects and methods

Sixty overweight men between the ages of 20 and 40 years (BMI 27–35 kg/m²) were studied. They had been referred to the department of obesity and metabolic disorders of National Endocrinology Research Center for management of obesity. Exclusion criteria for participation in this study were diabetes mellitus, abnormalities of thyroid function, bulimia, severe liver or kidney disease, hormonal therapy present or in the three months before the investigation.

For each of these 60 men it was established whether this person would qualify as suffering from metabolic syndrome using one of the three mentioned definitions of the syndrome which are presented in Table I.

Table I.  The various definitions of metabolic syndrome.

Definition of metabolic syndrome
	NCEP (1) At least 2 of	WHO (2) At least 2 of	IDF (3)
Waist circumference (cm)	>102	≥94	≥94
Waist hip ratio		>0.90	>0.90
BMI		≥0.30	≥30
			And at least 2 of
Triglycerides (mg/dl)	≥150	≥150	≥150
HDL-cholesterol (mg/dl)	< 40	< 35	< 35
Blood pressure (mm Hg)	≥130/85 or medication	≥140/90 or medication	≥140/90 or medication
		AND
Fasting glucose (mg/dl)	≥110	≥110
Fasting insulin		Upper quartile of non-diabetic	Insulin resistance

(1) National Cholestrerol Education Program, JAMA 2001; 285: 2486–2497.

(2) World Health Organization, Diabetes Med 1999; 16: 442–3.

(3) International Diabetes, J Urol 2005; 174: 827–34.

triglycerides (mg/dL) ≥150 ( ≥1.7 mmol/L).

HDL-cholesterol (mg/dL) <40 (<1.7 mmol/L).

Fasting glucose (mg/dL) ≥110 ( ≥6.1 mmol/L).

All men's anthropometrical parameters such as waist circumference (WC), hip circumference (HC) and ratio WC/HC were determined. Further data were collected on body composition, and laboratory variables were measured (Table II).

Table II.  Characteristics of the patients (median [10–90% range]).

Age	31 (20–39)
BMI (kg/m^2)	32.6 (27.4–35.2)
Waist circumference (WC) (cm)	111 (96–118)
Hip circumference (HC) (cm)	113 (104–117.5)
WC/HC	0.97 (0.9–1.1)
L4 (cm^2) Visc. adip. tissue	201 (123–338)
L4 (cm^2) Subcut. adip. tissue	368 (254–354)
Triglycerides (mmol/L)	1.8 (1.0–4.4)
LDL-chol. (mmol/L)	3.2 (2.4–4.9)
HDL-chol. (mmol/L)	1.1 (0.8–1.6)
Cholesterol (mmol/L)	5.3 (4.2–7.0)
Glucose (mmol/L)	5.5 (4.7–6.5)
Testosterone (nmol/L)	12.2 (6.9–23.4)
Free T (calculated) pmol/L	267 (134–430)
SHBG (nmol/L)	29 (11–63)
Insulin (µME/ml)	10.9 (3.2–39.6)
Leptin (ng/ml)	20.8 (1.9–43.0)
DHEA-sulphates (µmol/L)	3.3 (1.6–5.6)
HOMA	2.8 (0.75–3.9)
Systolic BP (mm Hg)	130 (110–140)
Diastolic BP (mm Hg)	90 (80–100)

L4 (cm²), cross-sectional area visceral and subcutaneous adipose tissue; LDL/HDL, low/high-density lipoprotein; SHBG, sex hormone binding globulin; HOMO, the homeostatic model assessment.

Cross-sectional areas (CSAs) of visceral adipose tissue and subcutaneous abdominal fat were assessed using magnetic resonance tomography (Magnetom Impact, Siemens,Germany). Subcutaneous and visceral CSAs were measured by analysing a slice at the junction of the fourth and fifth lumbar vertebrae.

Plasma levels of fasting glucose and lipids (total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides were measured by an automatic analyser Hitachi 912 (Roche, France).

The levels of hormones (total testosterone, DHEA-sulfate, sex hormone binding globulin (SHBG), insulin and leptin) were measured in serum samples collected in the morning (8:30–10:30 am). Free testosterone values were calculated using the mathematical formula described by Vermeulen et al. [19] and available on-line at the ISSAM website, http://www.issam.ch/freetesto.htm.

Testosterone was analysed by enhanced chemiluminescent method (Ortho-Clinical Diagnostics, Johnson & Johnson Co., UK) using the automatic analyser Vitros Eci. Analytical sensitivity of the method is equal to 0.03 nmol/L. The intra-assay coefficients of variation for 52.7 nmol/L and 2 nmol/L were 2.5% and 3.1%, respectively. The inter-assay coefficients of variation for 52.7 nmol/L and 2 nmol/L were 4.9% and 7.1%, respectively. Reference range in our laboratory for total testosterone is 11.5–33 mol/L and for calculated free T 250–527 pmol/L.

SHBG and insulin were measured with the time-resolved delayed fluorescence method (Delfia) on analyser Autodelfia. For SHBG the intra-assay coefficients of variation for 57 nmol/L and 19.7 nmol/L were 1.6% and 2.4%, respectively. The inter-assay coefficients of variation for 57 nmol/L and 19.7 nmol/L were 4.8% and 5.9%, respectively. The sensitivity of this assay was 0.5 nmol/L.

For insulin, the intra-assay coefficients of variation for 30.2 µU/ml and 5.6 µU/ml were 1.7% and 2.4%, respectively. The inter-assay coefficients of variation for 30.2 µU/ml and 5.6 µU/ml were 3.5% and 2.3%, respectively. The sensitivity of this assay was 0.5 µU/ml.

Leptin was measured with solid-phase immune-enzyme analysis (ELISA, DSL-10–23100). Analytical sensitivity of the method is 0.05 ng/ml.

DHEA-sulphate was measured with solid-phase immune-enzyme analysis (ELISA, IBL, Germany). Analytical sensitivity of the method is 120 nmol/L.

The study was approved by the Ethic Committee at National Endocrinology Research Center following the guidelines of the Helsinki declaration and all subjects provided written informed consent.

Statistical analysis. Differences between the groups were analysed by Mann-Whitney test. Differences were considered statistically significant if p <0.05. Statistic analysis was performed using the statistical software application STATISTICA 6.0 (StatSoft Inc., USA).

Results

Baseline observations are presented in Table II. Results of the analysis are presented in Table III. Of the 60 men with a BMI 27–35 kg/m², 19 men were not defined as suffering from the syndrome by any of the definitions. The definition of the NCEP found 34 men positive, the WHO definition 23 men, and the IDF 27 men. In 17 cases the three definitions agreed, and in 9 cases two definitions were in agreement on diagnosing the syndrome.

Table III.  Overlap and differences of identifying men as having metabolic syndrome using three definitions of metabolic syndrome.

	NCEP+	NCEP−	WHO+	WHO−	IDF+	IDF−
NCEP+	34		19	15	24	10
WHO+	19	4	23	–	17	6
IDF+	24	3	17	10	27	–

As shown in Table III, when the definition of the NCEP was positive (34 men), the WHO definition was positive in 19 men, and negative in 15 men, and the IDF definition was positive in 24 men, and negative in 10 men. When the WHO definition was positive for metabolic syndrome (23 men), the definition of the NCEP agreed in 19 men, disagreed in 4 men and the IDF definition agreed in 17 men and disagreed in 6 men. When the IDF definition was positive (27 men) the NCEP definition was in agreement in 24 men and in disagreement in 3 men, and the WHO definition agreed in 17 men and disagreed in 10 men.

Plasma total T, SHBG and calculated free T were calculated for men who were positive and negative for each of the three definitions of metabolic syndrome (Table IV).

Table IV.  Relationship between a positive identification of metabolic syndrome and plasma T, SHBG and calculated free T.

Metabolic syndrome (MetS)
	NCEP+	NCEP−	WHO+	WHO−	IDF+	IDF−
Total T (nmol/L)	11.2 ± 4.0*	16.3 ± 6.8	10.9 ± 4.4*	15.0 ± 6.3	11.2 ± 4.6*	15.3 ± 63
SHBG (nmol/L)	29.7 ± 21.5**	45.2 ± 32.0	33.9 ± 27.2	37.4 ± 28.0	31.4 ± 223**	40.4 ± 30.7
Calc f T (pmol/L)	249 ± 94***	294 ± 129	230 ± 95***	295 ± 120	236 ± 85***	296 ± 125

MetS+ versus MetS−*p < 0.05.

MetS+ versus MetS−**p < 0.05.

MetS+ versus MetS−***p < 0.05.

Though the overlaps between the three definitions was very incomplete, plasma total T and calculated free T were consistently significantly lower in men defined as having metabolic syndrome by each of the three definitions. Plasma SHBG was also significantly lower in the men with metabolic syndrome compared to the men not defined as having the syndrome when the definitions of the NCEP and the IDF were used but not with the WHO definition. Table V shows that men with the syndrome more often have ( ≥ 50%) plasma T levels below the reference range than men classified as obese.

Table V.  Number of men (%) with low testosterone levels (<11.5 mol/L) with and without metabolic syndrome (MetS) according to three definitions of metabolic syndrome.

Hormones	NCEP		WHO		IDF
	MetS	Obesity	MetS	Obesity	MetS	Obesity
Total T	50	31	52	30	59	30
calc. fT	44	35	42	27	41	36

Discussion

In this study of 60 men with varying degrees of obesity (BMI 27–35 kg/m²) we analysed who would qualify as suffering from metabolic syndrome using three definitions of the syndrome which have been widely used and adopted. Twenty men were not defined as suffering from metabolic syndrome. At least one of the three definitions qualified the remaining 40 men as having the syndrome. As expected there was an overlap: the three definitions were in agreement on 16 cases and in another 12 cases two definitions classed the men as positive. But the definitions certainly did not agree on all cases. It is not surprising that there are differences in defining men as having the syndrome. These definitions differ in the points of emphasis of the components. The definition of the NCEP puts equal emphasis on the various components of metabolic syndrome [7]. The definition adopted by the WHO assigns greater value to insulin resistance [8]. The main emphasis of the definition of the IDF is central obesity defined by waist circumference and two or more of the following four factors: elevated triglycerides, reduced HDL-cholesterol, elevated blood pressure, and dysglycemia [9]. The results of this study emphasize the significance of which definition has been used to define the syndrome in a study since there may be a considerable variation in labelling an obese person as suffering from metabolic syndrome.

A second part of the study was to analyse whether plasma T levels related to the presence of the syndrome using the various definitions. Whatever definition was used, men who were classed as having the syndrome had consistently lower plasma total T and lower calculated free T. Men identified as having the syndrome by the definitions of the NCEP and IDF had also significantly lower plasma SHBG levels, but this was not the case with the WHO definition. These findings suggest that low plasma total T and low calculated free T are consistent features of metabolic syndrome and are worthwhile to be considered as a diagnostic feature. The combination of low plasma T and SHBG and metabolic syndrome has been repeatedly reported in the literature [10],[11],[14],[20],[21].and it has been argued earlier to include hypotestosteronemia as a characteristic of the syndrome [22].

This study was conducted in young men: all subjects were below the age of 40 years. It is reasonable to assume that age-related decline of plasma total T and calculated free T [15] has not been the predominant factor in the lower plasma T levels in men with a BMI > 25 kg/m², and that the lower levels of plasma total T and calculated free T are indeed features of metabolic syndrome.

Conclusion

Using three definitions of metabolic syndrome there was a large degree of overlap of identifying obese men as having the syndrome, but there were quantitatively significant differences as well. So, it is relevant to identify in studies which of the present definitions of metabolic syndrome has been used. Low plasma total T and calculated free T were consistent features of men with the syndrome <40 years, regardless of which definition had been applied.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.