Albuminuria is strongly associated with the severity of calcified atherosclerotic plaque (CP) in white but not black individuals with type 2 diabetes, according to a new study. 

The study explored ethnic-specific relationships between albuminuria and CP involving the aorta and the coronary and carotid arteries in 1,228 subjects with type 2 diabetes: 835 Caucasians and 393 African Americans.

Adjusting for age, gender, glomerular filtration rate (GFR), and BMI, albuminuria was significantly associated with CP only in whites. Furthermore, ethnic differences in the relationship between proteinuria and atherosclerosis persisted after adjustment for BP, smoking, lipid levels and use of ACE inhibitors or angiotensin receptor blockers.

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“Proteinuria, a long accepted indicator of heart disease risk, has far less impact in blacks than it does in whites,” said lead investigator Barry Freedman, MD, Professor and Chief of Nephrology at Wake Forest University School of Medicine in Winston-Salem, N.C. “It is widely believed that the more protein in a patient’s urine, the greater the risk for heart disease and stroke, and this is true [only] in white populations.”

Dr. Freedman added: “There may be biological factors predisposing whites to develop atherosclerosis, or conversely, there may be biological factors that protect blacks from developing atherosclerosis.”

In the general community, black diabetics have more heart disease risk factors than whites, including higher BP, higher LDL cholesterol levels, and higher blood sugar levels than white diabetics. As such, blacks face overall higher risks for myocardial infarction (MI) and stroke. 

Dr. Freedman, however, cited large studies showing that, despite having more risk factors for atherosclerotic plaque, black men have significantly less calcium in their coronary arteries compared with white men.  In addition, diabetic blacks with access to equivalent health care as whites face only half the risk of suffering an MI, indicating that blacks appear to be somewhat protected from the cardiovascular effects of these risk factors. 

“Nephrologists need to understand that the effects of atherosclerotic risk factors, including those associated with kidney disease, may have differential impacts across ethnic groups,” Dr. Freedman told Renal & Urology News.

“We think that this study provides clues for detecting genes that lead to atherosclerosis in all populations. However, we expect the risk variants in these genes will more often be present in European Americans versus African Americans. Proteinuria is not an equivalent risk factor for heart disease between blacks and whites.  Biologically, this is a clue that proteinuria has different effects in various ethnic groups.”

Patients with type 2 diabetes were recruited from internal medicine clinics and community advertising for this study.  The mean age of African American participants was 56.7 years, compared with 61.7 years among European Americans. Diabetes durations were 10.4 years and 10.0 years, respectively.

The new report, published in Diabetes Care (2010;33:131-138), is the first to demonstrate ethnic differences in the effect of proteinuria, an accepted CVD factor, on development of atherosclerosis.  Dr. Freedman and his colleagues propose that there may be inherited factors in whites that contribute to their higher CVD or protective inherited factors in blacks.

The next phase of this study, known as the African American-Diabetes Heart Study, will attempt to identify gene variants that play a protective role against heart disease in blacks and/or variants that predispose whites to heart disease. “There are factors beyond environment exposure that lead to the development of heart disease,” Dr. Freedman said.

The vast majority of diabetic patients who develop end-stage renal disease and start dialysis have proteinuria for a number of years. Black patients, however, generally live longer on dialysis and have fewer MIs, despite having more risk factors and typically being seen by nephrologists later in the course of their kidney disease than their white peers.