Sep. 24, 2008 American Indians have a higher incidence of stroke compared to white and black Americans and their first strokes may be more deadly, according to a study published in Circulation: Journal of the American Heart Association.
The findings, from the largest longitudinal, population-based study of cardiovascular disease and risk factors in American Indians showed that the stroke incidence rate was 679 per 100,000 person years for American Indians. Previous studies in persons of similar age found the stroke incidence rate 306 per 100,000 person years for whites and 607 per 100,000 person years for blacks.
Moreover, first strokes appear to be more deadly in American Indians, said Ying Zhang, M.D., Ph.D., study lead author and assistant professor at the College of Public Health at the University of Oklahoma Sciences Center in Oklahoma City. The death rate was 18 percent within one month of stroke and 32 percent within one year of stroke.
Researchers analyzed data from the Strong Heart Study, an observational study of adult members of 13 American Indian tribes living in southwestern Oklahoma, central Arizona, and North and South Dakota.
The stroke sub-study analyzed data from 4,507 participants, ages 45 to 74, with no history of stroke when they were recruited for the study from 1989 to 1992. Nearly, 60 percent of the participants were women.
During more than 13 years of follow-up, 306 participants suffered a first stroke, usually when in their mid-60s. Just as in whites and blacks, ischemic stroke – stroke caused by a blockage that cuts off blood supply to the brain – was more common than hemorrhagic or bleeding stroke, 86 percent versus 14 percent.
Researchers cited high rates of hypertension, diabetes, and cigarette smoking in this population as a possible reason for the higher stroke incidence. They did not find an association between alcohol use and stroke incidence in this group.
Each of these risk factors provides important avenues for intervention to reduce risk, researchers said.
Researchers also found a strong association between stroke and protein in the urine which is a marker for kidney dysfunction that is often associated with diabetes. Researchers concluded further studies of the association between kidney function and stroke incidences are needed.
Although the data indicate a higher stroke incidence among American Indians, the numbers were too small to compare stroke prevalence in this population with stroke prevalence in whites and blacks, she said.
Incidence refers to the frequency of development of a new illness in a population in a certain period of time. Prevalence refers to the current number of people suffering from an illness in a given period of time, usually one year.
Among American Indians age 18 and over, about 5.8 percent have had a stroke, compared to 3.4 percent of African-Americans and 2.3 percent among whites, according to the American Heart Association/American Stroke Association.
Clinicians who care for American Indian patients can use the information to reduce their risk of stroke by providing appropriate treatment and by advising them to modify their lifestyle.
Co-authors are: James M. Galloway, M.D.; Thomas K. Welty, M.D.; David O. Wiebers, M.D.; Jack P. Whisnant, M.D.; Richard B. Devereux, M.D.; Jorge R. Kizer, M.D., MSc; Barbara V. Howard, Ph.D.; Linda D. Cowan, Ph.D.; Jeunliang Yeh, Ph.D.; Wm. James Howard, M.D.; Wenyu Wang, Ph.D.; Lyle Best, M.D.; and Elisa T. Lee, Ph.D. Individual author disclosures can be found on the manuscript.
The National Heart, Lung and Blood Institute funded the study.
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