Association between visceral and subcutaneous adipose depots and incident cardiovascular disease risk factors

Abstract

Background: Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) vary in volume and quality. We evaluated whether fat volume or attenuation (indirect measure of quality) predicts metabolic risk factor changes.

Methods and results: Framingham Heart Study Multi-detector Computed Tomography Substudy participants (n=1730, 45% women) were followed up over a mean of 6.2 years. Baseline VAT and SAT volume (in cm(3)) and attenuation (in Hounsfield units) were assessed. Outcomes included blood pressure, lipids, and glucose. We constructed multivariable regression models predicting change from baseline to follow-up. Baseline VAT was associated with metabolic risk factors at follow-up. Per 500-cm(3) increase in baseline VAT, glucose was 2.34 mg/dL higher (95% confidence interval, 1.71-2.97) and high-density lipoprotein was 1.62 mg/dL lower (95% confidence interval, 0.97-2.28) in women (P<0.0001 for both). These findings remained significant after adjustment for body mass index. Results for SAT were similar although less striking. Lower (more negative) fat attenuation was associated with more adverse metabolic profiles at follow-up. For example, per 5-unit decrease in baseline VAT Hounsfield units, log triglycerides increased by 0.08 mg/dL (95% confidence interval, 0.05-0.12; P=0.005), which remained significant after adjustment for baseline VAT. Among men, VAT and SAT Hounsfield units were associated with changes in cardiovascular disease risk factors but were mostly attenuated after baseline volume adjustment.

Conclusions: VAT volume and SAT volume are associated with incident metabolic risk factors beyond overall adiposity. Decreases in fat attenuation are also associated with incident risk factors. These findings suggest that both volume and quality of VAT and SAT contribute to metabolic risk.

Keywords: adipose tissue; epidemiology; population; risk factors.

Figure 1. Sex-specific incidence of risk factors stratified by VAT attenuation tertiles within BMI Categories

Normal weight defined as BMI < 25 kg/m2, overweight defined as BMI 25 to < 30 kg/m2, obese defined as BMI ≥ 30 kg/m2. VAT attenuation tertiles depicted as white bars (lowest tertile, i.e. most negative attenuation), gray bars (middle tertile) or black bars (highest tertile, i.e. least negative attenuation). Due to exclusion of individuals with the outcome present at baseline, the study populations differed for each outcome. For hypertension, the study populations consisted of 361, 171 and 116 women and 205, 370 and 153 men in the normal, overweight and obese categories, respectively. For metabolic syndrome, the study populations were 389, 162 and 89 women and 222, 348 and 82 men in each successive BMI category. For hypertriglyceridemia, the study populations were 370, 165 and 115 women, and 187, 271 and 113 men in each successive BMI category.

Figure 2. Sex-specific incidence of risk factors stratified by SAT attenuation tertiles within BMI Categories

Normal weight defined as BMI < 25 kg/m2, overweight defined as BMI 25 to < 30 kg/m2, obese defined as BMI ≥ 30 kg/m2. SAT attenuation tertiles depicted as white bars (lowest tertile, i.e. most negative attenuation), gray bars (middle tertile) or black bars (highest tertile, i.e. least negative attenuation). Due to exclusion of individuals with the outcome present at baseline, the study populations differed for each outcome. For hypertension, the study populations consisted of 361, 171 and 116 women and 205, 370 and 153 men in the normal, overweight and obese categories, respectively. For metabolic syndrome, the study populations were 389, 162 and 89 women and 222, 348 and 82 men in each successive BMI category. For hypertriglyceridemia, the study populations were 370, 165 and 115 women, and 187, 271 and 113 men in each successive BMI category.