In middle age, black Americans are four times more likely to die of stroke than whites, a U.S. study suggests.

But the reason doesn't appear to be differences in care after a stroke. Instead, it's because African-Americans have more strokes at age 45 and throughout middle age, the study found.

"This is important because it implies that the changes we have to make to reduce the disparity are community-based efforts to prevent and control risk factors, rather than hospital-based approaches about differences in the care of stroke patients," said lead study author Dr. George Howard of the University of Alabama at Birmingham.

To assess racial disparities in stroke rates and survival odds, Howard and colleagues analyzed data on more than 29,000 people living in the southern U.S.

During an average follow-up period of almost seven years, there were 1,168 strokes including 242 that were fatal, researchers report in the journal Stroke, online June 2.

By age 55, blacks were about three times more likely to die of stroke than whites. The odds of death from stroke were roughly doubled for blacks at age 65 compared to whites.

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On a case by case basis, however, blacks had slightly lower rates of death following stroke than whites. The higher mortality among blacks was almost entirely due to higher rates of stroke, although that disparity steadily declined with age.

From ages 45 to 54, blacks were about three times more likely to have a stroke. But there isn't much difference in the odds of having a stroke by the time people reach ages 75 to 84, the study found.

Roughly 40 percent of the racial disparity in the odds of having a stroke between ages 45 and 65 may be explained by risk factors such as hypertension or diabetes, the authors note. Both of these risk factors were more common among blacks than whites at those ages.

Overall, 71 percent of blacks in the study had hypertension, compared with 51 percent of whites. About 31 percent of blacks had diabetes, as did 16 percent of whites.

It's also possible that these risk factors impact African-Americans differently, or that they might experience certain conditions like hypertension over longer periods of time than whites, Howard said.

"To affect this, we need to make changes to prevent blacks from becoming hypertensive and diabetic, and then have better control of risk factors (blood pressure levels and glucose levels) in blacks," Howard added.

The rest of the disparity in stroke rates may be explained by problems such as limited awareness of risk factors and early symptoms for stroke or social and economic issues such as access and affordability of care, the authors note.

The disparity in stroke outcomes may disappear over time because blacks who live to old age are healthier than elderly white people, said Dr. Daniel Lackland, a researcher at the Medical University of South Carolina in Charleston who wasn't involved in the study.

"Most African-Americans do not survive as long, so you are comparing the healthiest surviving African-Americans with Caucasians at older ages," Lackland said by email.

At the same time, the study findings point to the importance of stroke prevention for black people at younger ages, Lackland said.

"Given the excess risks, it is critical for African-Americans to manage risk factors - in particular high blood pressure," Lackland said.

SOURCE: http://bit.ly/28kvZ0Y

Stroke 2016.