Differences in Heart Attack Risk Is Not Black-and-White

An analysis of the historic Dallas Heart Study conducted by statisticians from Rice University and medical researchers from the University of Texas Southwestern Medical Center at Dallas has ruled out one of the most prominent theories for why elevated levels of a fat-carrying protein called lipoprotein(a) lead to increased risks for heart attacks among whites but not among African Americans.

The theory is based on earlier lab studies that showed lipoprotein(a), often referred to as Lp(a), has a tendency to stick to some of the tissues that line blood-vessel walls. Some researchers believe the adhesive property causes a chain reaction in which, first, LDL (“bad” cholesterol) and then calcium build up on the inner walls of blood vessels. Although African Americans typically have two to four times more Lp(a) in their blood than whites, the Lp(a) proteins in whites tend to be shorter and stickier than that in African Americans.

The researchers looked for a relationship between increased levels of Lp(a) and increases in coronary calcium, a leading indicator of coronary atherosclerosis, but found no independent relationship between plasma levels of Lp(a) and coronary calcium in either whites or African Americans. “This indicates that some other mechanism is at work,” says Rudy Guerra, professor of statistics at Rice and the lead author of the paper. “We also found no evidence to support a relationship between the protein’s size and related levels of atherosclerosis in any of the groups we studied.”

The Dallas Heart Study is a groundbreaking multiethnic investigation of cardiovascular disease involving thousands of Dallas County residents, and it contains the most representative sample of African American subjects of any other statistical dataset ever used to study Lp(a) and coronary artery calcium levels. In the Rice-led study, scientists looked at the records of 1,288 subjects over the age of 40—380 black women and 241 white women over 45 and 381 black men and 286 white men over 40—whose coronary calcium levels had been determined via electron beam computer tomography and whose Lp(a) levels were determined via blood tests.

The researchers say their analysis, which appeared in a recent issue of the journal Circulation, points to the need for further research to determine whether African Americans have a genetic mechanism that protects them from the risks of Lp(a). If such a mechanism is found, doctors might be able to use the information to develop therapies and drugs that reduce heart attack risks for everyone.

The research was supported by the Donald W. Reynolds Foundation and the National Institutes of Health.

—Jade Boyd