April 23, 1997
Media Contact: Gary Stephenson
Although hypertension and low income already are linked to an increased risk of end-stage renal disease (ESRD) for both African-American and white men, the two factors may help explain the four-fold higher incidence of ESRD found in blacks, compared to whites, according to a study led by Johns Hopkins researchers published in the April 23 issue of The Journal of the American Medical Association. These results also may help physicians design more effective treatment strategies, says Michael J. Klag, M.D., Hopkins associate professor of medicine and principal investigator for the study.
"These results indicate that interventions designed to address the markedly higher incidence of end-stage renal disease in African-American men need to focus on ethnic disparities in blood pressure and socioeconomic status," he says.
In the study, data were analyzed from 332,544 men (300,645 white, 20,222 African-American, 11,677 other ethnic groups) aged 35 to 57 years who had been screened for the Multiple Risk Factor Intervention Trial, a study designed to examine the effects of various interventions on coronary heart disease. The incidence of ESRD was assessed using the Health Care Financing Administration national ESRD Treatment Registry. Death from renal disease was assessed using data from the National Death Index and the Social Security Administration.
Over a mean follow-up of 16 years, the age-adjusted ESRD incidence was 13.90 per 100,000 person-years in white men and 44.22 per 100,000 person-years in African-American men. However, this large difference was substantially reduced after taking into account differences in blood pressure, serum cholesterol level, cigarette smoking, history of heart attack, medication use for diabetes and family income. When all of these factors were considered, the relative risk of ESRD in African-American men compared with white men was reduced from 3.20 to 1.87.
Of these factors, higher blood pressure and lower family income had the largest impact on reducing the difference between the rates of ESRD incidence among African-Americans and whites. When differences in systolic blood pressure were taken into account, the relative risk was reduced to 2.56; after adjusting for income, the relative risk was 2.73.
Klag notes that other factors, not addressed in the study, also may account for the persistent increased risk of ESRD in African-American men compared with white men. These include greater exposure to occupational toxins, viral infections, adverse health behaviors and possible genetic predisposition to ESRD.
End-stage renal disease is the most advanced form of kidney failure. It occurs when both kidneys gradually cease to function. Diabetes mellitus and hypertension are the most common causes of chronic renal failure.
Hopkins collaborators in the study were Paul K. Whelton, M.D., and Frederick L. Brancati, M.D. Other collaborators included Bryan L.Randall, M.S., and James D. Neaton, Ph.D., at the University of Minnesota, Minneapolis, and Jeremiah Stamler, M.D. at Northwestern University Medical School in Chicago.