Abdominal fat radiodensity, quantity and cardiometabolic risk: The Multi-Ethnic Study of Atherosclerosis
Introduction
Human obesity harbors distinct metabolic phenotypes within its traditional definition of a body mass index (BMI) > 30 kg/m2 [1], [2], [3]. Against a backdrop of “metabolically healthy” and “metabolically unhealthy” obese individuals, visceral adiposity is now a well-established cardiometabolic risk factor, which may differentiate human obesity phenotypes [3]. Although methods to measure adipose tissue (e.g., magnetic resonance imaging or positron emission tomography) have been proposed to examine adipose tissue lipid composition, metabolic activity, and inflammation, their implementation remains complex and relatively inaccessible to a population studies.
Most investigation in the field of ectopic fat has centered on the importance of visceral adipose tissue quantity [1], [3]. More recently, investigations in the Framingham Heart Study have demonstrated that the radiodensity of subcutaneous and visceral fat by computed tomography (CT; termed “fat quality”) is associated with cardiovascular, metabolic, and clinical risk, independent of fat volume [4], [5], [6]. However, whether fat radiodensity signifies something mechanistically important in adipose tissue remains an open question. As such, understanding the relationship between adipose tissue quantity and radiodensity, and their relative contributions to metabolic syndrome risk, is important to define a role for these imaging parameters in the pathophysiology of obesity.
To address this question, we investigated (1) the interrelationships between fat radiodensity and quantity in each compartment (visceral, subcutaneous, and intermuscular) and (2) the relationship between radiodensity in these compartments with established biomarkers of obesity-related cardiometabolic disease, as well as both prevalent and incident metabolic syndrome, in a well-characterized group of community-based, multi-racial individuals enrolled in the Multi-Ethnic Study of Atherosclerosis (MESA).
Section snippets
Participant population
The overall design of the MESA study has been described previously [7]. At baseline, the MESA consisted of 6814 men and women of White, African American, Chinese American, and Hispanic ethnicity enrolled from six sites in the United States who were free of clinical cardiovascular disease (history of myocardial infarction, angina pectoris, prior revascularization, heart failure, atrial fibrillation, stroke, or peripheral arterial disease) at enrollment. The study design, including demographics,
Baseline characteristics of the study population, stratified by radiodensity
The baseline characteristics of our study population, stratified by median radiodensity for each depot are shown in Table 1. In general, and for each fat depot, individuals with higher fat radiodensity had a consistently lower body mass index, waist circumference, insulin, CRP and prevalence of metabolic syndrome, while having higher adiponectin levels. In addition, MESA participants with higher fat radiodensity had lower fat quantity in each adipose tissue depot (e.g., higher visceral fat
Discussion
In a large, community-based, multi-racial, multi-ethnic population, we demonstrated a strong association between fat radiodensity and fat quantity in subcutaneous, visceral, and intermuscular fat depots. Specifically, we found that visceral fat radiodensity was strongly associated with visceral fat quantity, a finding that was similar for subcutaneous and intermuscular fat. In addition, we found that lower fat radiodensity was associated with higher levels of circulating biomarkers of
Acknowledgments
This research was supported by grant number R01 HL071739 and contracts N01-HC-95159 through N01-HC-95165 and N01 HC 95169 from the National Heart, Lung, and Blood Institute. The authors thank the other investigators, the staff, and the participants of the MESA study for their valuable contributions. A full list of participating MESA investigators and institutions can be found at http://www.mesa-nhlbi.org.
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Drs. Shah, Allison, and Murthy contributed equally to this work.