Researchers analyzing data from a large ongoing stroke study in New York City found that living in an area with a greater than average proportion of the poor, unemployed and adults on public assistance is an independent risk factor for stroke. The finding holds true for blacks, whites and Hispanics. The study is the first using census tract data and individual socioeconomic variables to link living in a disadvantaged community to stroke.
"In stroke research, there have been a number of reports that African Americans and Hispanics have higher death rates than whites, leading to an ongoing debate over whether such differences are due to genes or the environment," says study lead author Bernadette M. Boden-Albala, Dr.PH.
"Our study suggests that some of the disparity may be due to population-level social resources. A white person living in a disadvantaged community does not fare well, just like a black or Hispanic living there," says Boden-Albala, research director for the stroke division in the department of neurology at Columbia University in New York City.
Boden-Albala hypothesizes that limited access to critical resources is the root of the problem and offers an analogy of two 60-year-old women with high blood pressure – a well-defined risk factor for stroke. One of the women lives in an affluent neighborhood, the other in a disadvantaged community.
"When the first woman's high blood pressure medication runs out, she gets in a car and refills her prescription," she says. "But the woman in a disadvantaged neighborhood may be less likely to get more medication. She may fear going out alone, there may not be a pharmacy nearby, or she may not be able to afford it."
The findings call for a rethinking of stroke-prevention programs, the researchers say.
"We need to add a new dimension to our thinking about stroke risk factors that includes community disadvantage, social supports, and community resources.
These conditions are just as important as some of the other well-known modifiable stroke risk factors such as hypertension and diabetes and have an impact across all race-ethnic groups," says senior author Ralph L. Sacco, M.D. professor of neurology and epidemiology and principal investigator of the Northern Manhattan Stroke Study (NOMASS).
"To truly make a difference in the impact of stroke, our prevention programs and healthcare systems will need to make special efforts to reach out to the particular needs of these disadvantaged communities," he says.
Boden-Albala and Sacco analyzed data from NOMASS, an ongoing study of 3,300 people who live in northern Manhattan. From 1993 to 1997, they identified 698 people who'd had an ischemic stroke. Ischemic strokes result from a blockage in an artery leading to the brain and are the most common type of stroke. The cases were compared to 1,270 healthy people living in the same area of Manhattan. The proportion of blacks, older people and women were similar in both groups. The average age of participants was 69. Twenty-two percent were white; 23 percent, black; and 55 percent, Hispanic.
The participants were then subdivided into 42 groups according to what census tract, or smaller community, within northern Manhattan they lived. Each census tract was assigned a community disadvantage rating based on poverty level, the number of adults on public assistance, the proportion of households headed by a female, unemployment levels and the proportion of children, minorities and immigrants.
"Unemployment and poverty levels were given the most weight, but all these factors contributed to a community's rating," Boden-Albala says.
Study participants were questioned about stroke risk factors including high blood pressure, high cholesterol, diabetes, smoking and physical activity. They were also asked about social factors known to affect stroke risk such as poor education, lack of health insurance and social isolation.
After adjusting for these known stroke risk factors, researchers found that people who lived in the most disadvantaged tracts were about twice as likely to have had a stroke, compared with those living in the least-disadvantaged areas.
When the researchers reanalyzed the data by racial group, the results were similar, Boden-Albala says. Whites who lived in the most-disadvantaged areas were 2.2 times more likely to have had a stroke, compared with whites living in the least-disadvantaged areas. Blacks in the most disadvantaged communities were 1.7 times more likely to have had a stroke and Hispanics in the most-disadvantaged areas were 1.6 times more likely to have had a stroke than their counterparts in the least-disadvantaged areas.
Average annual household income in the 42 communities studied ranged from about $12,000 to $40,000, Boden-Albala notes. "So even the least-disadvantaged communities we studied were not what one would typically call 'rich.' Presumably, if a really affluent community was studied, the differential in stroke risk (between the most- and least-disadvantaged areas) would be even greater."
NOMASS was funded by the National Institute of Neurological Disorders and Stroke.
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