Visceral and subcutaneous fat quality and cardiometabolic risk

Abstract

Objectives: The aim of this study was to evaluate whether computed tomography (CT) attenuation, as a measure of fat quality, is associated with cardiometabolic risk factors above and beyond fat quantity.

Background: Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) are pathogenic fat depots associated with cardiometabolic risk. Adipose tissue attenuation in CT images is variable, similar to adipose tissue volume. However, whether the quality of abdominal fat attenuation is associated with cardiometabolic risk independent of the quantity is uncertain.

Methods: Participants were drawn from the Framingham Heart Study CT substudy. The VAT and SAT volumes were acquired by semiquantitative assessment. Fat quality was measured by CT attenuation and recorded as mean Hounsfield unit (HU) within each fat depot. Sex-specific linear and logistic multivariable regression models were used to assess the association between standard deviation (SD) decrease in HU and each risk factor.

Results: Lower CT attenuation of VAT and SAT was correlated with higher body mass index levels in both sexes. Risk factors were generally more adverse with decreasing HU values. For example, in women, per 1 SD decrease in VAT HU, the odds ratio (OR) was increased for hypertension (OR: 1.80), impaired fasting glucose (OR: 2.10), metabolic syndrome (OR: 3.65), and insulin resistance (OR: 3.36; all p < 0.0001). In models that further adjusted for VAT volume, impaired fasting glucose, metabolic syndrome, and insulin resistance remained significant. Trends were similar but less pronounced for SAT and for men. There was evidence of an interaction between HU and fat volume among both women and men.

Conclusions: Lower CT attenuation of VAT and SAT is associated with adverse cardiometabolic risk above and beyond total adipose tissue volume. Qualitative indices of abdominal fat depots may provide insight regarding cardiometabolic risk independent of fat quantity.

Figure 1. Visceral and Subcutaneous Adipose Tissue on Computed Tomography

VAT = Visceral Adipose Tissue, SAT = Subcutaneous Adipose Tissue. Computer generated Hounsfield units for VAT was −99.8 and for SAT was −109.4 for this scan.

Figure 2. Associations of HU (fat dens ity) within tertiles of absolute levels of VAT for women (Panel A) and men (Panel B)

In women, the cutpoint between tertile HU 1 and tertile HU 2 was −94.7. The cutpoint between tertile HU 2 and tertile HU 3 was −90.1. In men, the cutpoint between tertile HU 1 and tertile HU 2 was −97.7. The cutpoint between tertile HU 2 and tertile HU 3 was −93.9. VAT1 represented the lowest tertile of VAT volume and VAT3 represented the highest tertile of VAT volume.