Major Finding: Conventional risk factors accounted for 13% of the excess incidence of stroke among blacks, whereas the addition of socioeconomic status to the analysis accounted for 23%.
Data Source: A population-based study of more than 30,000 white and black participants.
Disclosures: The study was supported by the National Institute of Neurological Disorders and Stroke. Dr. Howard reported that he has no relevant financial relationships.
SAN ANTONIO — Although large racial differences in conventional risk factors for cerebrovascular disease and socioeconomic factors exist, these differences do not fully account for the greater incidence of stroke that is seen in blacks.
In a proportional hazards mediation analysis, at age 45 years the addition of conventional risk factors accounted for 13% of the excess incidence among blacks, George Howard, Dr.P.H., reported at the annual International Stroke Conference. The addition of socioeconomic status to the analysis accounts for 23% of the excess incidence in blacks.
“The things that we tend to think about as largely driving the black-white differences account for less than a quarter of the differences that we're observing,” said Dr. Howard, chair of biostatistics at the University of Alabama at Birmingham.
The findings come from the REGARDS (Reasons for Geographic and Racial Differences in Stroke) study, which involves a national cohort of 30,239 white and black participants.
“One of the great mysteries in stroke is the huge racial disparities in stroke mortality,” Dr. Howard said.
It is estimated that stroke mortality is 40% greater in blacks than in whites, he noted. “These are massive differences in mortality.”
Study participants have been selected from a commercially available list and were recruited by mail and telephone. The researchers use a computer-assisted telephone interview that includes cardiovascular disease history. This is followed by a home visit for venipuncture, ECG, and physical measures.
Participants are followed at 6-month intervals for stroke surveillance. Suspected events are adjudicated centrally. Currently, there are 352 events among 26,610 participants, who were stroke and/or TIA free at baseline.
In this study, the researchers performed a proportional hazards mediation analysis, estimating the excess risk in blacks, adjusting for possible factors, and evaluating how much of the excess risk is accounted for by the inclusion of these factors.
The REGARDS population is generally reflective of the U.S. population. The assessed demographic factors included age, sex, and region. Risk factors included hypertension, diabetes, atrial fibrillation, dyslipidemia, previous MI, current smoking, alcohol use, and weekly exercise. Socioeconomic factors included education and income.
In terms of risk factors, 70% of blacks had hypertension, compared with 49% of whites. Likewise, 29% of blacks had diabetes, compared with 15% of whites.
A clear age effect has been observed as well, with a 300% stroke mortality rate for blacks younger than 65 years.
In this analysis, at age 65 the addition of risk factors accounted for 31% of the excess incidence among blacks. The addition of socioeconomic status accounts for 42% of the excess incidence in blacks.
“Depending on the age, these factors account for less than half of the racial disparity in incidence. So something else is accounting for the other half,” Dr. Howard said.