DALLAS, Sept. 9 -- African-Americans may need to become even stricter in controlling blood pressure if they hope to fight kidney disease, warn researchers today in the American Heart Association journal Hypertension.
The conclusion is based on an analysis of the National Institutes of Health Modification of Diet in Renal Disease Study (MDRD), the largest investigation of its kind to examine the effects of blood pressure control and diet in slowing the progression of intrinsic kidney disease, such as glomerulonephritis. The new results are based on part of the MDRD and include 495 whites and 53 African-Americans.
"African-Americans with intrinsic kidney disease may need to be more strict in controlling blood pressure than previously thought if they hope to slow progression of kidney disease," says Lee A. Hebert, M.D., one of the MDRD scientists and professor of medicine and director of the division of nephrology at Ohio State University in Columbus.
In recent years a level of blood pressure control of 140/90 millimeters of mercury (mmHg) would have been considered control. "Our study suggests that a new goal of about 125/75 mm Hg may be appropriate," says Hebert.
The participants in the study were followed for an average of two years to measure the decline in their glomerular filtration rates (GFR), a measure of the kidney's ability to filter waste products from the body.
"Blacks and whites showed the same rates of progression of renal disease when they achieve the lower blood pressure goal," Hebert says. However, in the usual blood pressure group, the mean rate of GFR decline was two times greater in blacks than in whites.
The findings suggest that achieving control of blood pressure to a level lower than that currently recommended for prevention of heart disease and stroke may be more important in slowing the progression of moderate kidney disease in blacks than in whites," he says.
The new blood pressure control, regarded as "strict blood pressure control," is particularly important for African-Americans with renal diseases that are characterized by large amounts of protein excretion by the kidney, says Hebert.
"The results are expected to be welcome news to African-Americans, who as a group, have a frequency of end-stage renal disease about six times greater than whites," he says. End-stage renal failure results in death unless dialysis or successful kidney transplant is performed.
Most of this difference between blacks and whites with respect to end-stage kidney failure is attributed to kidney disease caused by high blood pressure and diabetes. Individuals with kidney disease caused by diabetes were not studied in the MDRD.
In blacks, kidney disease from high blood pressure is now being studied in the national African-American Study of Kidney Disease and Hypertension (ASK). This study involves only patients with kidney disease from hypertension and will not consider the effects of diet on renal disease progression. Instead, it randomly assigns patients to either usual blood pressure control or to strict blood pressure control, and to one of three different blood pressure medications: ACE inhibitors, beta-blockers or calcium channel blockers. ASK will determine the level of blood pressure control needed to slow progression of kidney disease from hypertension. It will also look at whether some drugs are better than others in slowing progression. People interested in finding the closest center involved in the study should call 1-(800)-277-2275.
Media advisory: Dr. Hebert's office telephone number is (614) 293-4997. (Please do not publish his telephone numbers.)