Vitamin A protein may reveal hidden body fat

By Will Boggs, MD

NEW YORK (Reuters Health) - Measuring blood levels of a chemical transporter for vitamin A may be useful in estimating a person's "intraabdominal fat," a type of fat inside the abdomen that it not visible, but still adversely affects health, new research shows.

In addition, measuring levels of this chemical transporter, called retinol-binding protein (RBP4), may help identify patients with insulin resistance, a disturbance in sugar metabolism associated with the development of type 2 diabetes, according to a report in the journal Cell Metabolism.

Increased blood levels of RBP4 "appear to be a very good indicator of insulin resistance and increased intraabdominal fat, two risk factors that are notoriously difficult to assess...since they require complicated biochemical testing and advanced imaging techniques," Dr. Timothy E. Graham from Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, told Reuters Health.

In the current study, which involved 196 subjects, Graham showed that RBP4 is much more abundant in intraabdominal fat than in fat beneath the skin, which can be easily seen.

As noted, increased levels of the protein were seen in subjects with high amounts of intraabdominal fat and in those with insulin resistance. In fact, RBP4 was a better predictor of intraabdominal fat and insulin resistance than several other blood tests that were evaluated.

Monitoring RBP4 levels "may one day provide a simple tool for assessing these risks and tailoring treatments in patients," Graham concludes. In addition, the current RBP4 findings may help explain why high levels of intraabdominal fat increase the risk of heart attack and stroke.

SOURCE: Cell Metabolism, July 2007.