Stacking up abdominal fat increases CVD risk
medwireNews: Follow-up of the Framingham Heart Study Third Generation cohort shows that increases in visceral adipose tissue (VAT) over time are associated with worsening cardiovascular disease (CVD) risk factors.
During an average 6.1 years of follow-up, the 1106 study participants gained an average 703 cm3 of VAT volume, measured on computed tomography, and 602 cm3 of subcutaneous adipose tissue (SAT) volume. Ian Neeland and James de Lemos, from the University of Texas Southwestern Medical Center in Dallas, USA, note in an accompanying editorial that this represents respective 45% and 22% increases.
“The strikingly discordant relative increase in VAT compared with SAT in the present study should clue us in to a major premise—that the inability to expand the SAT depot in the face of caloric surplus, resulting in the greater relative expansion of VAT, may be the underlying physiological derangement predisposing to worsening CVD risk factors”, they say.
Each 500 cm3 increase in abdominal fat was associated with increases in the likelihood of participants developing new CVD risk factors. This was statistically significant for hypertension, hypercholesterolaemia, hypertriglyceridaemia, low high-density lipoprotein (HDL) cholesterol and the metabolic syndrome, and persisted after accounting for multiple confounders, including body mass index (BMI) and waist circumference.
The findings “support a growing body of data that clearly demonstrate that adipose tissue imaging, which allows anatomical characterization of regional fat depots, provides important information about cardiometabolic risk not contained in the simple BMI measurement”, say the editorialists.
These associations were stronger for changes in VAT than in SAT. For example, the risk of hypertension was raised 1.32-fold by increased VAT versus 1.21-fold by increased SAT. And the risk of hypercholesterolaemia and low HDL cholesterol was associated only with VAT increases.
Neeland and de Lemos note that the changes in VAT and SAT were not modelled jointly. “Thus, we are unable to tease out whether the associations seen with SAT are truly independent of VAT or whether they would be significantly attenuated when the confounding impact of VAT is taken into account.”
Increases in VAT and SAT were also significantly associated with adverse changes in existing CVD risk factors, including fasting plasma glucose, report Caroline Fox (National Heart, Lung, and Blood Institute, Framingham, Massachusetts, USA) and study co-authors.
Their results, published in The Journal of the American College of Cardiology, also show that decreases in VAT and SAT quality in Hounsfield units (HU) were associated with an increased risk of incident CVD risk factors and the worsening of existing ones.
But the editorialists say: “Although the theoretical concept that lower HU signifies greater lipid accumulation and overactive lipolysis is intriguing, the significance of fat attenuation is far from clear.”
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