Visceral Fat and Hypertension: A Link?

Visceral adipose tissue, rather than body mass index (BMI) or overall subcutaneous fat, was associated with the development of hypertension, researchers found.

In a multivariate analysis, BMI initially was associated with incident hypertension, with a relative risk of 1.24 (95% CI 1.12-1.36, P<0.0001) per standard deviation increase, according to Aslan T. Turer, MD, and colleagues from the University of Texas Southwestern Medical Center in Dallas.

However, after visceral adiposity and subcutaneous fat were included in the model, only visceral adipose tissue remained significant, with a relative risk of 1.22 (95% CI 1.07-1.39, P=0.004) for each standard deviation increase, the researchers reported in the Journal of the American College of Cardiology.

"There is growing evidence that [visceral adipose tissue] represents a pathological adipose tissue depot, which accumulates when subcutaneous depots are overwhelmed or otherwise unavailable for storage. Relative to [subcutaneous adipose tissue], visceral fat is more sensitive to lipolysis and secretes higher amounts of inflammatory cytokines," Turer and colleagues wrote.

The central mystery that the investigators sought to address is that hypertension has been clearly linked with obesity, yet not all obese individuals develop high blood pressure.

To see if the distribution, rather than quantity, of body fat could be implicated, the researchers analyzed data from the Dallas Heart Study, in which 903 participants had an initial evaluation between 2000 and 2002.

What’s wrong with abdominal fat?

Body fat, or adipose tissue, was once regarded as little more than a storage depot for fat blobs waiting passively to be used for energy. But research suggests that fat cells - particularly abdominal fat cells - are biologically active. It’s more accurate to think of fat as an endocrine organ or gland, producing hormones and other substances that can profoundly affect our health. One such hormone is leptin, which is normally released after a meal and dampens appetite. Fat cells also produce the hormone adiponectin, which is thought to influence the response of cells to insulin. Although scientists are still deciphering the roles of individual hormones, it’s becoming clear that excess body fat, especially abdominal fat, disrupts the normal balance and functioning of these hormones.

Scientists are also learning that visceral fat pumps out immune system chemicals called cytokines - for example, tumor necrosis factor and interleukin-6 - that can increase the risk of cardiovascular disease by promoting insulin resistance and low-level chronic inflammation. These and other biochemicals, some not yet identified, are thought to have deleterious effects on cells’ sensitivity to insulin, blood pressure, and blood clotting.

One reason excess visceral fat is so harmful could be its location near the portal vein, which carries blood from the intestinal area to the liver. Substances released by visceral fat, including free fatty acids, enter the portal vein and travel to the liver, where they can influence the production of blood lipids. Visceral fat is directly linked with higher total cholesterol and LDL (bad) cholesterol, lower HDL (good) cholesterol, and insulin resistance.