Birth in South Raises Stroke Risk for Life
MONDAY Nov. 30, 2009 -- People born in the "stroke belt" of the southern United States have a lifelong higher risk of dying of stroke than others, even if they live elsewhere later, a new study shows.
Data on both black and white people born in the North and South Carolina, Georgia, Tennessee, Arkansas, Mississippi and Alabama show a consistently higher incidence of stroke compared to those born elsewhere, according to a report in the Dec. 1 issue of Neurology.
The higher stroke incidence in those seven states has been recognized for years, but why this is so, and why it persists, is not clear, said study author M. Maria Glymour, an assistant professor in the Harvard School of Public Health's division of society, human development and health.
"We think it's not genetic," Glymour said. "The hypotheses we have include the effect of social environment, what people eat and their access to medical care. There may be some element of socioeconomic risk."
Glymour and her collaborators used data from 1980, 1990 and 2000 U.S. national death records for people aged 30 to 80 who were born and lived in 49 states. They calculated stroke death rates by linking the data to U.S. census information.
What they found was that white people who were born and lived their adult lives in the stroke belt were 45 percent more likely to die of a stroke in the 1980 group, 29 percent more likely in the 1990 group and 34 percent more likely in the 2000 group than those who were born and lived outside the stroke belt. The figures were comparable for blacks: 55 percent, 47 percent and 34 percent higher risk for the respective groups.
Among whites who moved to the stroke belt as adults, the risk was 11 percent greater, according to the 2000 data, and 20 percent higher for those who were born in the stroke belt but later lived elsewhere.
The findings point out "the critical importance of early life exposures to lifelong health," said Dr. Mary Cushman, associate professor of medicine and pathology at the University of Vermont, lead author of a study published earlier this year that showed that conventional risk factors for stroke, such as obesity and diabetes, did not fully account for the regional differences.
"Other factors, such as genetic factors, environmental toxins and learned behavior [in youth, for example, from parents] could play a role," Cushman said.
The study had its weaknesses, she said, including "the inability to finely measure region of residence over lifespan and the reliance on administrative data for analysis."
"All we measured was where people were born," Glymour acknowledged. "But most people born in a state stay there at least through adolescence."
Still, the new study had a more solid base than earlier ones reporting the same association, Glymour said. One such study, which she led, had a much smaller sample and relied on self-reported stroke. "This one used strokes reported on death certificates and had national coverage," Glymour said.
More work is needed to determine why the stroke rate is higher in the South and to find ways to reduce the risk both regionally and nationally, she said.
"We think that understanding the causes of the phenomenon would be helpful in general to reduce stroke rates," Glymour said.
For more information on stroke, see the U.S. National Library of Medicine.
Posted: November 2009
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