|
|
||||||||||
|
J Am Coll Cardiol, 2005; 46:457-463, doi:10.1016/j.jacc.2005.04.046
(Published online 14 July 2005). © 2005 by the American College of Cardiology Foundation |






* Atherosclerosis Imaging Research Program, Section of Cardiovascular Medicine, University Medical School, Madison, Wisconsin
Division of Cardiovascular Medicine, Duke University Medical Center, Durham, North Carolina
Tulane Center for Cardiovascular Health and Department of Epidemiology, Tulane University Health Sciences Center, New Orleans, Louisiana
Division of Vascular Ultrasound Research, Wake Forest University School of Medicine, Winston-Salem, North Carolina.
Manuscript received February 9, 2005; revised manuscript received March 30, 2005, accepted April 13, 2005.
* Reprint requests and correspondence: Dr. James H. Stein, Department of Medicine, Section of Cardiovascular Medicine, University of Wisconsin Medical School, 600 Highland Avenue, G7/341 CSC (MC 3248), Madison, Wisconsin 53792. (Email: jhs{at}medicine.wisc.edu).
| Abstract |
|---|
|
|
|---|
BACKGROUND: Metabolic syndrome is associated with subclinical atherosclerosis and increased cardiovascular risk in older and middle-aged adults; however, these associations have not been studied among young adults.
METHODS: Non-diabetic subjects from Bogalusa Heart Study, a longitudinal study of atherosclerosis in young adults, underwent B-mode ultrasonography of the carotid arteries. Metabolic syndrome was defined with the National Cholesterol Education Program Adult Treatment Panel III (MetSNCEP) and World Health Organization (MetSWHO) definitions. CIMT and MetS associations were evaluated with multivariable regression and area under receiver-operator characteristic curve (AUC) analyses.
RESULTS: Of 507 subjects (29% black, 39% male, mean [SD] age 32 [3] years), 67 (13%) had MetSNCEP and 65 (13%) had MetSWHO. Common (mean = 0.70 [0.11] mm vs. 0.66 [0.08] mm, p = 0.002) and internal CIMT (0.72 [0.21] mm vs. 0.68 [0.12] mm, p = 0.020) were higher among those with MetSNCEP than those without MetSNCEP. Common (0.69 [0.11] mm vs. 0.66 [0.08] mm, p = 0.020) and internal CIMT (0.73 [0.23] mm vs. 0.68 [0.12] mm, p = 0.012) also were higher among those with MetSWHO than those without MetSWHO. Composite CIMT increased with the number of MetS components present (MetSNCEP r = 0.997, p < 0.001; MetSWHO r = 0.946, p = 0.053). Metabolic syndromeNCEP (AUC = 0.557, 95% confidence interval [CI] 0.513 to 0.601) and MetSWHO (AUC = 0.539, 95% CI 0.495 to 0.584) both predicted composite CIMT
75th percentile.
CONCLUSIONS: In young adults, MetS is associated with increased atherosclerotic burden, and therefore, increased cardiovascular risk. These results support the importance of screening and early intervention in this population.
| |||||||||||||||
Although several studies have associated the presence of atherosclerosis risk factors with subclinical atherosclerosis in younger adults, no study has specifically evaluated MetS and atherosclerosis in young adults, a population that increasingly is becoming more overweight (712). Finding evidence of an increased burden of subclinical and potentially reversible vascular disease in young adults would emphasize the need for heightened awareness and early treatment of MetS. Additionally, comparing available definitions from the World Health Organization (MetSWHO) and the National Cholesterol Education Program Adult Treatment Panel III (MetSNCEP) (13,14) might help determine the relative utility of diagnostic criteria in this age group.
Carotid intima-media thickness (CIMT), a validated method for detecting subclinical atherosclerosis and predicting cardiovascular risk, was used to investigate the relationships between MetS and subclinical atherosclerosis in asymptomatic young adults from the Bogalusa Heart Study, applying and comparing both MetSNCEP and MetSWHO definitions (1315).
| Methods |
|---|
|
|
|---|
126 mg/dl or taking antiglycemic medications) or missing data necessary to determine diabetes status were excluded from further analysis (n = 12). All of the remaining 507 subjects were analyzed for the presence of MetSNCEP and then, in separate analysis, for MetSWHO. Study procedures. Study procedure protocols have been described previously (11). Subjects fasted for at least 12 h before assessments. Height and weight were measured in duplicate and averaged to calculate BMI. Waist circumference was measured midway between the rib cage and superior border of the iliac crest. Blood pressure (BP) was measured in triplicate in the right arm in a seated, relaxed position. Serum lipids were measured with a Technicon Auto Analyzer II (Technicon Instrument, Tarrytown, New York) with the standardized procedures of the Lipid Research Clinics Program (17). Plasma insulin levels were measured by radioimmunoassay (Phaadebas Insulin Kit, Pharmacia Diagnostics AB, Portage, Michigan). Plasma glucose was measured on a Beckman glucose analyzer by the glucose oxidase method.
Carotid ultrasonography. Images of common carotid, carotid bulb, and internal carotid artery (ICA) segments were recorded with a Toshiba Sonolayer SSH 160A (Toshiba Medical, Tustin, California) and a 7.5-MHz linear array transducer (11). Carotid artery segments were interrogated and measured with previously developed protocols for the Atherosclerosis Risk in Communities study (18). Certified readers conducted measurements with a semi-automated measurement program, as previously described (7). Mean values of three right and three left far-wall measurements were calculated separately for each of the three bilateral carotid segments. Right and left measurements for common carotid, carotid bulb, and ICA segments were averaged to create segmental and overall composite values.
Definition of MetS.
Metabolic syndromeNCEP was identified when three of the following five criteria were present: 1) waist circumference >102 cm in men or >88 cm in women; 2) triglycerides
150 mg/dl; 3) HDL-C <40 mg/dl in men or <50 mg/dl in women; 4) BP
130/
85 mm Hg or on antihypertensive medication; 5) fasting glucose
110 mg/dl (14). Metabolic syndromeWHO was identified if: 1) the insulin level was greater than the upper quartile of the study population or fasting plasma glucose
110 mg/dl; and 2) at least two of the following were present: a) BMI >30 kg/m2; b) serum triglycerides
150 mg/dl or HDL-C <35 mg/dl for men or <40 mg/dl for women; and c) BP
140/90 mm Hg or on BP medication (5,13). The latter criteria were modified from the original 1999 MetSWHO definition and recently were shown to accurately predict incident diabetes mellitus (19,20).
Statistical analysis. Statistical analyses were performed with the SAS system (SAS Institute, Cary, North Carolina). Two-tailed Student t tests were performed to compare continuously distributed variables (age, glucose, insulin, lipids, waist girth, BMI, weight, SBP, diastolic BP, and CIMT) between genders and races and to compare CIMT measurements between individuals with and without MetS. Exact binomial analysis was used to compare binomial variables (presence of MetS, hypertension, hyperlipidemia, smoking, family history) (21). To correct for potentially increased type I error rates with multiple testing, the Benjamini and Hochberg (22) false discovery rate adjustment was performed.
Unadjusted odds ratios (ORs) with 95% confidence intervals (CIs) and p values for trends of increasing MetS prevalence among increasing CIMT quintiles were formulated from Cochran-Armitage trend test models, in which CIMT quintiles were the independent variables. Subsequent adjustments for age and gender and then age, gender, race, and smoking were made to formulate adjusted OR and p values. Linear regression was used to assess the relationship between number of MetS components and increasing CIMT. Multiple regression analyses with the general linear model were used to ascertain the relative impact of each component of MetS on increased CIMT. Finally, two area under receiver-operator characteristic curves (AUC) were generated, with composite CIMT
75th percentile as the dependent variable, and the presence of MetSNCEP and MetSWHO as independent variables in respective models. Models were then compared after deriving 95% CIs (23).
| Results |
|---|
|
|
|---|
|
|
|
75th percentile did not differ significantly (MetSNCEP AUC = 0.557 [95% CI 0.513 to 0.601] vs. 0.539 [95% CI 0.495 to 0.584] for MetSWHO).
|
|
|
| Discussion |
|---|
|
|
|---|
Studies in middle-aged and older adults have demonstrated that MetS predicts cardiovascular disease and mortality. The Botnia Study, for instance, demonstrated that middle-aged adults with MetS have an approximately three-fold increased risk of incident coronary heart disease and more than a two-fold increased risk of stroke (4). A compelling finding was that the risk of coronary heart disease morbidity associated with MetS exceeded that associated with its individual components, suggesting that individuals with the constellation of metabolic abnormalities that characterize MetS should be targeted for aggressive primary prevention. Additionally, increased BP and dyslipidemia were the strongest predictors of vascular events (4). The present study demonstrated that the risk associations identified with MetS in middle-aged adults also are operant in young, asymptomatic adults.
To date, no studies have been published that specifically addressed the relationship between MetS and subclinical atherosclerosis in young adults, although associations between CIMT and atherosclerosis risk factors, some of which are MetS components, have been described (79,11,12,16,24,25). Recent reports indicated that the presence of such components in childhood are associated with increased adult CIMT (11,12). In the Bogalusa Heart Study, childhood BMI was one of the strongest predictors of increased adult CIMT (11), whereas in the Young Finns study, BMI and SBP predicted increased adult CIMT (12). In the Atherosclerosis Risk in Young Adults study of white 27- to 30-year-olds, BMI predicted common carotid artery CIMT; however, after adjustment for age, gender, and BMI, components of the MetS such as BP, triglycerides, and waist/hip ratio, did not predict CIMT (9). This study was limited because CIMT was measured only in the common carotid artery, a segment that usually lags the bulb and ICA in the development of atherosclerosis (9,26).
In the Atherosclerosis Risk Factors in Male Youngsters study of 17- to 18-year-old white men, MetS components of elevated diastolic BP and low HDL-C predicted increased CIMT (10). Body mass index was not higher in individuals with increased CIMT; however, this study was small and included few overweight individuals (mean body mass index 22.5 kg/m2) (10). In the Muscatine Study, multivariate analysis showed that CIMT was associated with SBP, increasing age, and LDL-C in women and with smoking in men (27). Significant univariate correlations included BMI in men only, waist/hip ratio and triglycerides in women, but not HDL-C, glucose, or fasting insulin (27). These subjects, almost exclusively, were white; more than one-half were men >38 years old, and nearly one-half smoked cigarettes, limiting the generalizability of these data. On the basis of these previous studies, the relationships between MetS, MetS components, and CIMT could not be ascertained. Finally, MetS by modified NCEP criteria (using BMI instead of waist circumference) predicted the presence of coronary artery calcium among a population that included individuals as young as 20 years (adjusted OR 1.40, 95% CI 1.05 to 1.87, p = 0.02).(28). The mean age (52.7 [9.9] years) of the cohort, however, was notably older than in our study. Our study is the first to analyze the relationship between MetS as a diagnostic entity and subclinical atherosclerosis in young, asymptomatic adults.
Carotid intima-media thickness values were similar among those with MetSNCEP or MetSWHO. The lack of a significant difference in composite CIMT between those with and without MetSWHO appears to have been due to the lack of a significant difference between bulb CIMT values, because common and internal carotid CIMT measurements did differ significantly. It is unclear why bulb CIMT was higher among those with MetSNCEP but not those in the MetSWHO group. One reason might be that bulb CIMT images anatomically are more difficult to obtain and measurements are more variable than in the common carotid artery; however, these issues should not have differentially affected the MetS definitions. Another consideration is that more than one-half of those meeting criteria for either MetSNCEP or MetSWHO (61%) were different subjects and those with MetSNCEP tended to include more smokers and subjects on therapy for hypertension, qualities that have been shown to differentially increase bulb CIMT thickness (29). Despite these differences, trends for increasing composite CIMT were associated with increasing numbers of either MetSNCEP or MetSWHO components. Additionally, both NCEP and WHO criteria identified subjects with composite CIMT
75th percentile equally well, thus confirming their clinical value in primary cardiovascular disease prevention and intervention.
Direct comparisons with previous studies are difficult because of differing definitions of MetS. The WHO was the first to specify diagnostic criteria in 1999; however, the practical difficulties in meeting some of the criteria, such as using the insulin clamp method to measure insulin resistance or assessing impaired glucose tolerance with oral glucose tolerance testing, have limited the use of the strict definition (13). Additionally, inclusion of microalbuminuria among the diagnostic criteria has been controversial (19,20). Subsequent groups have employed modified MetSWHO definitions (36). The NCEP definition, which was presented more recently, is based on more easily measurable components; however, it has been criticized for being less sensitive for detecting insulin resistance, which is associated with cardiovascular risk factors in the absence of MetS (30,31). Nevertheless, despite differences in criteria used between studies, associations of MetS and increased CIMT in middle-aged adults have been fairly consistent. For example, the Atherosclerosis and Insulin Resistance study showed that middle-aged white men with MetSWHO had increased CIMT, and the Brunek Study of middle-aged and elderly adults demonstrated that carotid atherosclerosis was significantly higher in individuals with MetSWHO (using a modified WHO definition) and MetSNCEP (3,6). Our study provides the first analysis of the impact of MetS on the anatomic burden of subclinical atherosclerosis in young, asymptomatic adults. Furthermore, it provides a comparison of the established definitions of MetS and suggests that both sets of criteria are useful for detecting subclinical atherosclerosis in this age group. This is an important area of interest, especially given the increasing prevalence of childhood obesity, insulin resistance, and predicted cardiovascular risk (32).
Conclusions. Identification of MetS in young, otherwise healthy adults is an important marker of increased subclinical atherosclerosis and, therefore, increased cardiovascular risk. The burden of subclinical atherosclerosis in young adults increases with an increasing burden of components of MetS, and increased BP and low HDL-C are especially powerful predictors of increased CIMT. Both NCEP and WHO definitions identify those with more advanced subclinical atherosclerosis equally well. Because MetS characteristics and the magnitude of subclinical atherosclerosis are modifiable, they might be appropriate targets for intervention in young adults.
| Footnotes |
|---|
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
N. Mattsson, T. Ronnemaa, M. Juonala, J. S.A. Viikari, E. Jokinen, N. Hutri-Kahonen, M. Kahonen, T. Laitinen, and O. T. Raitakari Arterial structure and function in young adults with the metabolic syndrome: the Cardiovascular Risk in Young Finns Study Eur. Heart J., March 2, 2008; 29(6): 784 - 791. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. E. O'Neil and T. A. Nicklas State of the Art Reviews: Relationship Between Diet/ Physical Activity and Health American Journal of Lifestyle Medicine, December 1, 2007; 1(6): 457 - 481. [Abstract] [PDF] |
||||
![]() |
A. G. Bertoni, N. D. Wong, S. Shea, S. Ma, K. Liu, S. Preethi, D. R. Jacobs Jr, C. Wu, M. F. Saad, and M. Szklo Insulin Resistance, Metabolic Syndrome, and Subclinical Atherosclerosis: The Multi-Ethnic Study of Atherosclerosis (MESA) Diabetes Care, November 1, 2007; 30(11): 2951 - 2956. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. A. Morrison, L. A. Friedman, and C. Gray-McGuire Metabolic Syndrome in Childhood Predicts Adult Cardiovascular Disease 25 Years Later: The Princeton Lipid Research Clinics Follow-up Study Pediatrics, August 1, 2007; 120(2): 340 - 345. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. Ingelsson, L. M. Sullivan, J. M. Murabito, C. S. Fox, E. J. Benjamin, J. F. Polak, J. B. Meigs, M. J. Keyes, C. J. O'Donnell, T. J. Wang, et al. Prevalence and Prognostic Impact of Subclinical Cardiovascular Disease in Individuals With the Metabolic Syndrome and Diabetes Diabetes, June 1, 2007; 56(6): 1718 - 1726. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. Kivimaki, M. Hintsanen, L. Keltikangas-Jarvinen, M. Elovainio, L. Pulkki-Raback, J. Vahtera, J. S.A. Viikari, and O. T. Raitakari Early Risk Factors, Job Strain, and Atherosclerosis Among Men in Their 30s: The Cardiovascular Risk in Young Finns Study Am J Public Health, March 1, 2007; 97(3): 450 - 452. [Abstract] [Full Text] [PDF] |
||||
![]() |
J.-P. Empana, M. Zureik, J. Gariepy, D. Courbon, J. F. Dartigues, K. Ritchie, C. Tzourio, A. Alperovitch, and P. Ducimetiere The Metabolic Syndrome and the Carotid Artery Structure in Noninstitutionalized Elderly Subjects: The Three-City Study Stroke, March 1, 2007; 38(3): 893 - 899. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. T. Flynn What Is the Significance of Increased Carotid Intima Media Thickness in Hypertensive Adolescents? Hypertension, July 1, 2006; 48(1): 23 - 24. [Full Text] [PDF] |
||||
![]() |
J. L. Menezes Oliveira, C. Marques-Santos, J. A. Barreto-Filho, R. Ximenes Filho, A. V. de Oliveira Britto, A. H. Oliveira Souza, C. M. Prado, C. R. Pereira Oliveira, R. M. C. Pereira, T. de Almeida Ribeiro Vicente, et al. Lack of Evidence of Premature Atherosclerosis in Untreated Severe Isolated Growth Hormone (GH) Deficiency due to a GH-Releasing Hormone Receptor Mutation J. Clin. Endocrinol. Metab., June 1, 2006; 91(6): 2093 - 2099. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. N. DeMaria, O. Ben-Yehuda, D. Berman, G. K. Feld, G. S. Ginsburg, B. H. Greenberg, W. Y.W. Lew, D. Sahn, and S. Tsimikas Highlights of the Year in JACC 2005 J. Am. Coll. Cardiol., January 3, 2006; 47(1): 184 - 202. [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | SUBSCRIPTIONS | CURRENT ISSUE | PAST ISSUES | CARDIOSOURCE | SEARCH | HELP | FEEDBACK |