By Annette M. Boyle
ATLANTA – While three-quarters of stroke patients are older than 65, a “brain attack” can affect people of any age.
For young American Indians and Alaskan Natives (AI/AN), that information is especially significant because they have two to two and a half times the risk of dying from stroke as their white counterparts in most regions and more than seven times the risk in Alaska.
“Several studies have found higher rates of smoking and higher body mass index in younger AI/AN,” said Linda J. Schieb, MSPH, of the national Centers for Disease Control and Prevention’s division for heart disease and stroke prevention in Atlanta. “These are strong risk factors for stroke.”
A number of previous studies have also found substantially higher rates of diabetes and physical inactivity among AI/AN populations generally and among younger AI/AN specifically.
Among whites aged 35 to 44 years, four in 100,000 died from a stroke in the 1990 to 2009 period. Within the AI/AN population nationwide, the rate was 10 in 100,000 for the same age group in contract health service delivery area (CHSDA) counties and 8.4 per 100,000 in all counties in the United States, according to research conducted by Schieb and her colleagues at the CDC and Mark Veazie, DrPH, of the Phoenix Area Indian Health Service. CHSDA counties include or border reservations, including specific counties in Michigan, Wisconsin and Minnesota; and the states of Alaska, Nevada and Oklahoma. 1
The breakdown by region shows even more significant differences in stroke death rate ratios for AI/AN persons compared to whites. In Alaska, young white people aged 35 to 44 have a death rate of 2.8 per 100,000. Their AI/AN contemporaries have a rate 7.4 times higher—20.8 per 100,000. By comparison, for the same age group in the Southwest, the rate ratio is 1.66.
Higher Mortality Rates
The researchers found higher rate ratios (RRs) for AI/AN persons compared to whites in all age groups (35-44, 45-54, 55-64, 65-74, 75-84 and 84+) except the oldest, in a study published in the June issue of the American Journal of Public Health.
The report also looked at the data for geographic disparities. In every region—Northern Plains, Alaska, Southern Plains, Southwest, Pacific Coast—all AI/AN groups under 75 years of age were found to have higher death rates than whites. Rate ratios declined with age, with the oldest AI/AN groups in the Northern Plains, Southwest, and Pacific Coast having lower death rates than whites.
The finding of higher mortality rates from stroke in AI/AN populations runs contrary to results seen in previous analyses of the National Vital Statistics System (NVSS) data, according to the study.
“While we can’t say for certain, I do believe that most of the differences we found in rates among AI/AN compared to previous studies are related to racial misclassification,” Schieb told U.S. Medicine. The researchers used NVSS data for 1990 to 2009 to identify stroke deaths in AI/AN and white adults older than age 35. They bridged single-race population estimates developed by the CDC and the U.S. Census Bureau with adjustment for population shifts following Hurricanes Katrina and Rita and limited analyses to non-Hispanic AI/AN persons and non-Hispanic whites.
To adjust for misclassifications, they used linkages with the Indian Health Service patient registration database and death certificate data to identify deaths marked as non-Native that were actually AI/AN. IHS provides care for about two-thirds of all AI/AN persons. This adjustment added 1033 AI/AN stroke deaths compared to the NVSS mortality records, raising the total number of deaths to 6937 from 5904.
Variation by Region
Overall, the researchers found similar stroke death rates for AI/AN men and women, 115.3 and 114.2 per 100,000, respectively, in the CHSDA counties. These rates were about 20% higher than those for white men and women in counties served by the IHS.
Across all age groups, AI/AN in Alaska had the highest death rate from stroke at 144.3 per 100,000 or 150% of the white rate for the state. In the CHSDA counties of the Pacific Coast, Southern Plains and Northern Plains regions, AI/AN had a 20% to 30% higher stroke death rate than whites. In the East, the AI/AN rate was 10% higher.
In the Southwest CHSDA counties, however, AI/AN adults had a lower rate of death from stroke than whites overall, mostly as a result of much lower rates in the two oldest age groups. In the 75 to 84 age group, AI/AN individuals had a 14% lower rate of stroke death, and in those over age 85, the rate was 23% lower than in whites. All younger AI/AN groups had higher rates than whites, but lower rates than AI/AN elsewhere in the country.
Schieb noted that a previous study using data from 2000 to 2006 showed that “American Indians in the Southwest had lower prevalence of current smoking than AI/AN in other regions. AI/AN in the Southwest also had lower prevalence of former smoking and higher prevalence of those who never smoked AI/AN in other regions or non-Hispanic whites in the U.S.” They had a lower percentage of individuals involved in no leisure time physical activity and lower percentages of AI/AN diabetic patients with high cholesterol, she added.
Stroke death rates declined over the study period for both AI/AN and white populations, although the rate rose 0.8% per year from 1990 to 2001 for AI/AN persons before dropping at a 4.3% per annum rate through 2009. Rates dropped more slowly in Alaska than elsewhere and more slowly among AI/AN than among whites.
Nationwide the lower mortality rates associated with stroke may be attributed to two factors, said Schieb. “The use of tPA [tissue plasminogen activator] for stroke treatment has increased since 2001. In addition, the importance of travel time to hospital and treatment is now better understood.”
Still, AI/AN stroke patients face significant hurdles in receiving timely care. The researchers noted that about half of the CHSDA counties are classified as rural, and Alaska counties are considered the most rural. Typically, rural residents must travel farther for care, and the extra time needed to access acute stroke care can mean the difference between life and death for stroke patients.
“People living in many rural areas, especially on tribal lands far from hospitals able to provide the best care for stroke, are at a great disadvantage in accessing appropriate timely treatment,” according to the study.
1 Schieb LJ, Ayala C, Valderram AL, Veazie MA. Trends and disparities in stroke mortality by region for American Indians and Alaska Natives. AM J Public Health. 2014 Jun;104 Suppl 3:S368-76.
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