(Published in LINKS: Minority Research & Training - Fall 2010 )
Poverty may predict chronic kidney disease (CKD) in African Americans but not whites according to a study recently conducted by investigators at the NIA, Johns Hopkins University School of Medicine, and University of California San Francisco (UCSF) and San Francisco General Hospital (SFGH). The research, published in the June 2010 issue of American Journal of Kidney Diseases, was one of the first to look at how the relationship between CKD and socioeconomic status (SES) varies by race.
Approximately 20 million people in the United States (or 10 percent of the population over the age of 20) have CKD, a condition in which the kidneys are unable to properly filter blood. CKD can lead to other serious diseases including cardiovascular disease, bone disease, and anemia. It is also a risk factor for death. As CKD progresses, it can cause complete kidney failure, known as End Stage Renal Disease. Low SES and being African American are well-established, independent risk factors for End Stage Renal Disease—African Americans were nearly four times more likely to develop End Stage Renal Disease than whites in 2007.
"The impact of SES and race on a person’s risk for earlier stages of CKD was less clear, which is what motivated this investigation," explains Deidra C. Crews, M.D., Sc.M., at Johns Hopkins University School of Medicine in Baltimore, Maryland.
To determine the relationship between SES, race, and CKD, the NIA, Hopkins, and UCSF/SFGH scientists used data collected through NIA’s Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS) study. The Baltimore, Maryland HANDLS study investigates differences in rates and risks for diseases and other conditions associated with aging among African American and white participants initially between the ages of 30 and 64 and living in varying socioeconomic communities. For this study, scientists analyzed data on creatinine levels (high levels in the blood are a sign of CKD) and presence of albumin in the urine (another sign of CKD) from 2,375 participants: 1,420 African Americans (713 low SES) and 955 whites (347 low SES). Approximately 6 percent, or 142 participants, had CKD.
Researchers found that race was not independently associated with CKD among study participants. However, similar to national statistics, African American HANDLS participants were more likely to have advanced stages of CKD compared to white HANDLS participants. "We found low SES to be associated with CKD, after adjusting for demographics, health insurance status, and co-morbid diseases. Notably, when we stratified these data by race, we found that African Americans living below the poverty line were 33 percent more likely to have CKD than low SES whites. We concluded that poverty may be a stronger predictor of CKD in African Americans than in whites," says Crews.
Researchers are considering several possible explanations for their study findings. For instance, they are identifying ways that poverty may affect African Americans differently than whites that would lead to their increased risk for CKD. Researchers already know that African Americans living in poverty have an increased prevalence of low birth weight, which is a known risk factor for End Stage Renal Disease and perhaps influences risk of CKD. Poverty is also more strongly associated with high blood pressure, unhealthy waist-to-hip ratio, and other "biological risk profiles" for African Americans than for whites. These risk profiles are associated with increased prevalence of CKD. In addition, African Americans may also have different mechanisms for coping with poverty than whites--leading to unhealthy behaviors. This may influence their risk.
The investigators note that more research is needed to explain their study findings. Ultimately, they hope this research will lead to more effective strategies for preventing CKD, especially among high-risk groups.
To learn more about NIA’s HANDLS study, read "HANDLS—Bringing Health Disparity Research to the Neighborhood " in the fall 2009 issue of Links.