Elsevier

Metabolism

Volume 63, Issue 2, February 2014, Pages 218-225
Metabolism

Clinical Science
An examination of sex and racial/ethnic differences in the metabolic syndrome among adults: A confirmatory factor analysis and a resulting continuous severity score

https://doi.org/10.1016/j.metabol.2013.10.006Get rights and content

Abstract

Objective

The metabolic syndrome (MetS) is typically diagnosed based on abnormalities in specific clustered clinical measures that are associated with increased risk for coronary heart disease (CHD) and Type 2 diabetes mellitus (T2DM). However, current MetS criteria result in racial/ethnic discrepancies. Our goals were to use confirmatory factor analysis (CFA) to delineate differential contributions to MetS by sub-group, and if contributions were discovered, develop sex and racial/ethnic-specific equations to calculate MetS severity.

Research Design and Methods

Using data on adults from the National Health and Nutrition Examination Survey 1999–2010, we performed a CFA of a single MetS factor that allowed differential loadings across groups, resulting in a sex and race/ethnicity-specific continuous MetS severity score.

Results

Loadings to the single MetS factor differed by sub-group for each MetS component (p < 0.001), with lower factor loadings among non-Hispanic-blacks for triglycerides and among Hispanics for waist circumference. Systolic blood pressure exhibited low factor loadings among all groups. MetS severity scores were correlated with biomarkers of future disease (high-sensitivity C-reactive-protein, uric acid, insulin resistance). Non-Hispanic-black-males with diabetics had a low prevalence of MetS but high MetS severity scores that were not significantly different from other racial/ethnic groups.

Conclusions

This analysis among adults uniquely demonstrated differences between sexes and racial/ethnic groups regarding contributions of traditional MetS components to an assumed single factor. The resulting equations provide a clinically-accessible and interpretable continuous measure of MetS for potential use in identifying adults at higher risk for MetS-related diseases and following changes within individuals over time. These equations hold potential to be a powerful new outcome for use in MetS-focused research and interventions.

Introduction

With rising rates of cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM), there has been significant focus on risk prediction. One way clinicians can identify individuals at higher risk for disease progression is by assessing for the metabolic syndrome (MetS)[1], [2], a cluster of cardiovascular risk factors that is associated with insulin resistance [1], [3] and that correlates with underlying inflammation [4], [5], [6], [7] and oxidative stress [7], [8], [9], [10], [11]—additional risk factors for CVD and T2DM. Compared to those without MetS, individuals who are classified as having MetS and followed for 10 years have an odds ratio of 1.2–1.8 for progressing to CVD [12], [13] and 4.1 for progressing to T2DM [14], demonstrating its utility as a clinical tool.

Nevertheless, there are significant racial/ethnic differences in MetS that limit its use over time [15], [16], [17], [18]. Non-Hispanic blacks have a low prevalence of MetS despite having more insulin resistance, more T2DM and more death from CVD than non-Hispanic whites [17], [18], [19], [20], [21], [22], [23]. The binary nature of MetS may contribute to these observed racial/ethnic differences, as it requires extreme values (e.g., triglycerides greater than 150 mg/dL or HDL less than 40 mg/dL for males) that may not be appropriate for all groups, particularly if certain groups have on average lower values of any of the components of MetS (e.g., lower triglyceride levels among non-Hispanic blacks)[24]. Furthermore, a binary MetS classification makes it difficult to follow for a worsening condition over time. Because of this, some have advocated for continuous scores for MetS [25]. The majority of these scores have been composed of a sum of z-scores of the various components of MetS (blood pressure, waist circumference [WC], etc.)[26], [27], [28]. This approach does not take into account weighting of how these components correlate together as a manifestation of the processes underlying MetS, nor do they take into account that such weighting may vary by sex or race/ethnicity [29], [30], [31].

Our goal was to examine the differences between sexes and among racial/ethnic groups with respect to how the traditional MetS components correlate with a single MetS “factor” via a confirmatory factor analysis, utilizing data from adults in the National Health and Nutrition Examination Survey (NHANES). Rather than explore whether or not there are multiple factors or examine whether additional components should be added to MetS, we instead operated under the framework that a single metabolic syndrome exists and is made up of the components utilized in common definitions such as the Adult Treatment Panel III (ATP-III)[1], [32]—namely WC, systolic blood pressure (SBP), triglycerides, HDL-cholesterol, and fasting blood glucose. Such a statistical exploration then would not only allow for an examination of sex- and racial/ethnic differences in how these components correlate with the hypothesized single MetS factor, but it also would take into account any observed differences in producing a continuous MetS score from this analysis — thus providing in essence a sex- and race/ethnicity-specific risk or severity score that can be followed over time in individuals either clinically or in research settings. Our hypothesis was that the contribution of MetS components to such a factor would vary by sex and race/ethnicity in a way that could improve on correlations between MetS and clinically-relevant measures related to insulin resistance, CVD risk and disease diagnosis.

Section snippets

Methods

Data were obtained from NHANES (1999–2010), a complex, multistage probability sample of the US population [33]. These annual cross-sectional surveys are conducted by the National Center for Health Statistics (NCHS) of the Centers for Disease Control (CDC), with randomly-selected subjects undergoing anthropometric and blood pressure measurements, answering questionnaires and undergoing phlebotomy. The NCHS ethics review board reviewed and approved the survey and participants gave informed

Results

The sample of participants utilized in the series of confirmatory factor analyses consisted of 6870 male and female non-Hispanic blacks, non-Hispanic whites, and Hispanics aged 20–64 years old with complete data for MetS components (Supplementary Table 1). The overall prevalence of MetS in this sample was 25.8% according to ATP-III criteria [1]. The prevalence of ATP-III-based MetS was considerably lower among non-Hispanic-black males.

In performing confirmatory factor analysis of MetS components

Discussion

We report here a comprehensive analysis showing that under the assumption of a single MetS factor, the components that make up the traditional MetS definition are correlated differently according to sex and race/ethnicity. This analysis allows for the utilization of a continuous MetS severity score that is tailored to how MetS is manifest among particular sex- and racial/ethnic groups. While racial/ethnic differences have long been noted in individual components of MetS [17], [24] and while a

Conflicts of Interest

The authors have no conflicts of interest.

The following are the Supplementary data related to this article.

. NHANES 1999-2010 Characteristics: Adults 20–64 Years Old with Data on all Metabolic Syndrome Components (n = 6870).

Acknowledgments

This work was supported by NIH grants 5K08HD060739-03 (MDD), U54GM104942 (MJG) and 1R21DK085363 (MDD and MJG). MJG and MDD conceptualized the study, designed the analysis, and wrote the manuscript. MJG conducted the analysis. CLL assisted in the conceptualization of the analysis, contributed to and reviewed the analysis, and reviewed and edited the manuscript. MNO contributed to the conceptualization of the study, reviewed the analysis, and reviewed and edited the manuscript. MJG is the

References (41)

  • L.B. Andersen et al.

    Physical activity and clustered cardiovascular risk in children: a cross-sectional study (The European Youth Heart Study)

    Lancet

    (2006)
  • W.B. Kannel

    Elevated systolic blood pressure as a cardiovascular risk factor

    Am J Cardiol

    (2000)
  • S.D. Pierdomenico et al.

    Prognostic relevance of metabolic syndrome in hypertensive patients at low-to-medium risk

    Am J Hypertens

    (2007)
  • S.M. Grundy et al.

    Diagnosis and management of the metabolic syndrome: an American Heart Association/National Heart, Lung, and Blood Institute scientific statement

    Circulation

    (2005)
  • J. Arnlov et al.

    Impact of BMI and the metabolic syndrome on the risk of diabetes in middle-aged men

    Diabetes Care

    (2011)
  • DeBoer MD, Dong L, Gurka MJ: Racial/ethnic and sex differences in the ability of metabolic syndrome criteria to predict...
  • M.D. DeBoer et al.

    Diagnosis of the metabolic syndrome is associated with disproportionately high levels of high-sensitivity C-reactive protein in non-Hispanic black adolescents: an analysis of NHANES 1999–2008

    Diabetes Care

    (2011)
  • P. Rein et al.

    Roles of the metabolic syndrome, HDL cholesterol, and coronary atherosclerosis in subclinical inflammation

    Diabetes Care

    (2010)
  • J.M. Dekker et al.

    Metabolic syndrome and 10-year cardiovascular disease risk in the Hoorn Study

    Circulation

    (2005)
  • A.J. Hanley et al.

    Prediction of type 2 diabetes mellitus with alternative definitions of the metabolic syndrome: the Insulin Resistance Atherosclerosis Study

    Circulation

    (2005)
  • Cited by (0)

    View full text