Researchers funded by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) report that reducing blood pressure to a mean arterial pressure of less than 92, or about 125/75 millimeters of mercury (mmHg), slowed kidney disease in people who had more than 1 gram of protein in the urine. At higher blood pressures the disease advanced more quickly, especially in blacks, who lost kidney function 7 times faster than whites, according to researchers. The study appears in the September 9 issue of Hypertension.
"What we found is that it is important to control blood pressure, especially in blacks with protein in the urine," said Lee A. Hebert, lead author of the study and head of nephrology at Ohio State University Medical Center in Columbus.
Hebert and colleagues compared the effects of normal (below 140/90) and low (about 125/75) blood pressure in a group of 53 African Americans and 495 whites with moderate kidney disease. These men and women are a subset of the original 840 patients who took part in NIDDKís Modification of Diet in Renal Disease (MDRD) Study, which ended in 1993.
However, because the study data came from a subset of MDRD patients and because some other studies have shown contradictory results and cardiovascular problems in some patients when they reduced blood pressure, doctors arenít ready to recommend the lower blood pressure level for all patients. "These results are important, but itís not appropriate to base major health policy on a secondary analysis," said Lawrence Agodoa, a nephrologist and co-author of the report. "You really need a larger study to settle the question."
"We think everyone with hypertension can help protect the kidneys and the heart by controlling blood pressure, but we still donít know what level is best," said Hebert. "And we donít know what will happen in kidney disease due to hypertension," he added. Relatively few people in the study had this type of disease even though it is the major cause of kidney disease in African Americans and causes a high percentage of kidney disease in whites.
In contrast to other kidney diseases, which "come from problems within the kidney itself," Hebert explains, "kidney disease from high blood pressure comes from the outside. If we can remove the external causeóthe hypertension--we might be able to stop the kidney disease in its tracks."
Researchers hope to finally settle the debate with another NIDDK trial, the African American Study of Kidney Disease and Hypertension (AASK), which is now enrolling patients. AASK is comparing low and normal blood pressure and specific classes of blood pressure drugs to control hypertension and protect the kidneys. Patients can call (800) 277-2275 for more information on AASK.
Media Contacts (phone numbers not for publication):
Lawrence Agodoa, M.D., NIDDK End-Stage Renal Disease Program Director (301) 594-1932
Lee Hebert, M.D., Ohio State University in Columbus (614) 293-4997