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Neighborhood Socioeconomic Status Alone May Sway Stroke Survival

Samson, Kurt

doi: 10.1097/01.NT.0000427572.82352.d4
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In an analysis of data on stroke mortality from a longitudinal study on cardiavascular health, investigators found that living in the most disadvantaged neighborhood was associated with 77 percent greater risk of dying during the first post-stroke year, even when all other variables were taken into consideration.

The socioeconomic status of neighborhoods appears to have an independent influence on one-year survival after stroke, regardless of cardiovascular risk factors, biological and behavioral factors, age, race, gender, income, or education, researchers have found.

Investigators at the University of California, Los Angeles, and the University of Washington in Seattle, studied stroke mortality at one month and at one year in 4,701 participants in the Cardiovascular Health Study (CHS), a longitudinal, population-based study of cardiovascular disease, including stroke, in adults over age 65. None of the participants had a history of prior stroke at the study's outset. Over an average of 11.5 years, 806 people suffered strokes, the majority of which were ischemic.



Using an index of census-derived indicators to classify neighborhood socioeconomic status (NSES) based on income, education, employment, and wealth, the team divided patients into four neighborhood categories, ranging from the lowest to highest quartile.

They then adjusted mortality rates based on a number of health variables per patient, including subclinical cardiovascular disease, atrial fibrillation; and history of transient ischemic attacks (TIA), hypertension, diabetes, and high cholesterol; together with behavioral risk factors such as smoking, alcohol consumption, diet, and physical activity.

While no difference in mortality was observed at 30 days after stroke, living in the most disadvantaged neighborhood was associated with 77 percent greater risk of dying during the first year, even when all other variables were taken into consideration.

The findings were published in the Jan. 2 online edition of Neurology.

“Our study shows that neighborhood matters,” said lead author Arleen F. Brown, MD, PhD, associate professor of medicine at the David Geffen School of Medicine at the University of California, Los Angeles.

“If you live in a neighborhood with a low NSES score, your risk of dying within one year of a stroke is much higher than if you reside in a neighborhood with more socioeconomic advantages,” she told Neurology Today in a telephone interview.

Stroke epidemiologists have known for several decades that post-stroke survival rates are lower in disadvantaged communities, but few studies have been able to adequately measure the independent effects of neighborhood characteristics and individual factors on stroke survival. It remains unknown how neighborhood plays a role, or why.

“We did not find that behavioral and biological factors explained the association,” said Dr. Brown. “However, considering that this risk persisted after adjusting for demographic factors including individual income and education levels and other possible mediators, including biologic and behavioral characteristics, our findings suggest that factors unique to neighborhoods may play a role.”

She said additional work is needed to understand the structural and social characteristics of neighborhoods that may contribute to mortality in the first year after a stroke and the mechanisms through which these characteristics operate. The team is now conducting additional analyses and trying to “disentangle” the relationships between neighborhood characteristics, individual factors, and stroke survival.

The American Heart/Stroke Association and the National Institutes of Health funded the study.

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“This is an interesting and well-designed study that adds to a growing body of research showing neighborhood SES [socioeconomic status] plays a role in survival after stroke as well as other cardiovascular events,” said stroke epidemiologist Moira K. Kapral, MD, associate professor of medicine at the University of Toronto.

“Unfortunately, the mechanisms are not known,” she told Neurology Today in a telephone interview.

Factors might include lower adherence to medications in lower SES neighborhoods, especially because of their cost, as well as the potential for isolation and psychosocial stress, she said.

“We know that stress and depression can increase mortality, and these individuals can be especially vulnerable.”

She, too, noted that it was unfortunate that the study could not include stroke severity in its review, especially with regard to 30-day events.

“Early stroke mortality is driven to a large extent by stroke severity, and this is a limitation acknowledged by the authors. At one year, many risk factors come into play.”

Dr. Kapral was lead author of a 2012 study, published in Neurology, that also found greater one-year mortality for stroke and transient iscemic stroke in poorest-versus-wealthiest neighborhoods, even after adjustment for age, sex, stroke type and severity, comorbid conditions, hospital and physician characteristics, and processes of care.

“This difference was even more significant after three years,” she said, citing ongoing follow-up data that has yet to be published.

The next step toward better understanding the phenomenon and improving survival rates would be to look at potential interventions to improve access to high quality acute stroke care, risk factor modification and secondary prevention in all neighborhoods, according to Dr. Kapral.

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“To our knowledge, [this study] is the first published study applying this sophisticated design on the question of post-stroke survival,” wrote Luciano A. Sposato, MD, director of the Stroke Center at the Institute of Neurosciences at the University Hospital in Buenos Aires, Argentina, and Olivier Grimaud, MD, of the French School of Public Health in Rennes, France, in an accompanying editorial.

The new study challenges “a widely accepted, but not proven, hypothesis that poor stroke outcomes found among lower SES are mostly related to a higher prevalence and poorer control of risk factors,” they wrote.

However the study had both strengths and weaknesses, they noted.

Its strength is the use of a statistical model that adequately combines individual and neighborhood socioeconomic status variables.

“When only neighborhood SES information is available, a negative association with outcome may entirely result from the fact that individuals with low SES tend to live in poorer neighborhoods. [The authors] were thus able to identify the specific association between neighborhood SES and mortality. To our knowledge, theirs is the first published study applying this sophisticated design on the question of post-stroke survival.”

The study's limitation, which they noted was acknowledged by the authors, was the lack of adjustment for stroke severity, a major determinant of stroke mortality.

However, they noted that in the September 2012 Neurology study, Dr. Kapral and colleagues did adjust for stroke severity and found that it accounted for just 13.9 percent of survival disparity between high- and low-income neighborhoods.

“Together, the two studies indicate that there is an independent association between neighborhood socioeconomic status and shorter survival, and that neither individual SES, nor do traditional risk factors seem to explain this association,” according to the editorial.

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Ralph L. Sacco, MD, chairman of neurology and executive director of the McKnight Brain Institute at the Miller School of Medicine of the University of Miami, said the findings add utility to predicting stroke outcomes.

Dr. Sacco served as president of the American Heart/Stroke Association during the 2010-2011 term, and has been principal investigator of the Northern Manhattan Study, an NIH-funded community-based, epidemiologic study of stroke incidence and risk factors in an elderly, multi-ethnic urban population.

“That the researchers divided neighborhoods into four quartiles, based on SES, and controlled for so many individual health variables, provided clear ‘dose-response’ data,” he told Neurology Today in a telephone interview. “They controlled for more than the usual suspects in a pretty robust model.”

However it is more difficult to modify neighborhood SES characteristics than individual care and follow-up treatment, he noted. “The socioeconomics of neighborhoods may be very important, and we need to think about changes that could improve these outcomes,” he said.

Improved access to medical care, more walking paths, and healthier food choices might help. “These are things in neighborhoods that could be modified,” he said. “The idea is to build an environment to make community characteristics healthier.”

Replicating the new study's data in other communities and neighborhoods is necessary, Dr Sacco said, as will be including stroke severity measures and future studies.

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• Brown AF, Liang LJ, Vassar SD, et al. Neighborhood socioeconomic disadvantage and mortality after stroke. Neurology 2013; E-pub 2013 Jan. 2.
    • Sposato LA and Grimaud O. Neighborhood socioeconomic status and stroke mortality: Disentangling individual and area effects. Neurology 2013; E-pub 2013 Jan. 2.
      • Grimaud O, Béjot Y, Heritage Z, et al. Incidence of stroke and socioeconomic neighborhood characteristics: an ecological analysis of Dijon stroke registry. Stroke 2011;42:1201–1206.
        • Kapral MK, Fang J, Chan C, et al. Neighborhood income and stroke care and outcomes. Neurology 2012;79:1200–1207.
          ©2013 American Academy of Neurology