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Stroke Mortality Among Alaska Native PeopleRonnie D. Horner, PhD, Gretchen M. Day, MPH, Anne P. Lanier, MD, MPH, Ellen M. Provost, DO, MPH, Rebecca D. Hamel, BSN, and Brian A. Trimble, MD

Although stroke has become a signicant health problem among the Alaska Native pop-ulation, its epidemiology remains poorly de-scribed. This is attributable, in part, not only tothe sparseness of the literature but also to itsfailure to consider Alaska Native people as a distinct cultural group, one among the manythat comprise the American Indian/Alaska Native designation. Despite these signicant limitations, several worrying patterns areemerging. Stroke mortality appears to be sig-

nicantly elevated among relatively younger American Indians/Alaska Natives comparedwith US Whites of similar age.13 Other reportsindicate that, compared with US White women,American Indian/Alaska Native women havegreater mortality from stroke, especially fromsubarachnoid hemorrhages.47 Of note, data for the 1990s indicate that stroke mortality hasdecreased in all racial/ethnic groups except for American Indians/Alaska Natives.8

The sparseness of the epidemiological data on stroke as it relates specically to Alaska

Native people hinders efforts at preventionand intervention in this unique cultural group.Stroke prevention and intervention strategiescan be most effectively designed and targetedwhen the higher-risk populations are identiedand the types of strokes and associated etio-logic factors are known. We begin the processof generating a more precise epidemiology of stroke among Alaska Natives by describing their stroke mortality between 1984 and2003 in terms of age, gender, time, and stroketype.

METHODS

This population-based stroke mortalitystudy uses death certicate data on Alaska Native people who resided inAlaska during the period 1984 through 2003, and comparesthese data with those for White Alaska resi-dents and the larger US White population. Inthat stroke mortality patterns among AlaskanWhites are virtually identical to those of thegeneral US White population, the latter

population is used as the primary referent population because it provides more preciserates with which to compare the stroke mor-tality patterns among Alaska Native people.

Study PopulationThe study population was dened as all

Alaska residents who self-identied as Alaska Native people. Alaska Native people comprisethose individuals whose ancestors occupiedthe geographic area that is now the state of Alaska. Traditionally, under federal reporting systems, the Alaska Native population is clas-sied into 3 major ethnic groups: Aleut,Eskimo, and Indian. Linguistic and culturalstudies, however, document many different subgroups within the major groupings of Eskimo and Indian, including Inupiat, Yupik,Cupik, and Sugpiaqunder the category Eskimoand Athabascan, Haida, Tlingit, and Tsimpsianunder the category Indian. On the basis of the US Bureau of the Census enumeration for the year 2000, there were 119499 Alaskan resi-dents who self-identied as an Alaska Native,of whom approximately 11% were Aleut, 50% Eskimo, and 39% Indian. Although the variousindigenous groups in the state differ in cultureand language, their social and economic indi-cators are similar.

Data SourceInformation on cause of death and demo-

graphic characteristics was obtained from theState of Alaska Bureau of Vital Statistics, whimaintains a database comprising the data ele-

ments recorded on the death certicate of any person dying in Alaska. From this database,information was collated on Alaska Nativeswho were indicated to be residents of Alaska and had died of stroke in the years 1984through 2003. An Alaska Native was dened by the death certicate race codes indicating Alaska Native, Eskimo or Canadian Eskimo,Indian or Canadian Indian, Aleut, or a mixturof any of these Alaska Native groups. Amongthose identied as Indian, there may be a smal percentage of individuals from American In-dian tribes of the contiguous United States.Although the number of such individuals isunknown, they are estimated to comprise 7% to12% of the total Alaska Indian population onthe basis of detailed US census data regardingtribal afliation of Native Americans in AlaskOverall, misclassication of deceased Alaska Natives as being of another racial/ethnic groupis estimated to be less than 5%.9

For Alaska Natives, Alaskan Whites, and UWhites, we identied stroke deaths by using International Classication of Disease, 9th

Objectives. We aimed to describe the epidemiology of stroke among AlaskaNatives, which is essential for designing effective stroke prevention and inter-vention efforts for this population.

Methods. We conducted an analysis of death certicate data for the state of Alaska for the period 1984 to 2003, comparing age-standardized stroke mortalityrates among Alaska Natives residing in Alaska vs US Whites by age category,gender, stroke type, and time.

Results. Compared with US Whites, Alaska Natives had signicantly elevatedstroke mortality from 1994 to 2003 but not from 1984 to 1993. Alaska Nativewomen of all age groups and Alaska Native men younger than 45 years of agehad the highest risk, although the rates for those younger than 65 years were

statistically imprecise. Over the 20-year study period, the stroke mortality ratewas stable for Alaska Natives but declined for US Whites.Conclusions. Stroke mortality is higher among Alaska Natives, especially

women, than among US Whites. Over the past 20 years, there has not been asignicant decline in stroke mortality among Alaska Natives. ( Am J Public Health. 2009;99:19962000. doi:10.2105/AJPH.2008.148221)

RESEARCH AND PRACTICE

1996 | Research and Practice | Peer Reviewed | Horner et al. American Journal of Public Health | November 2009, Vol 99, No. 11

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Revision (ICD-9 )10 and ICD-10 11 codes for cere- brovascular disease as the underlying cause of death (ICD-9 codes 430434 and 436438and ICD-10 codes I60.0I69.9). In addition to

examining cerebrovascular disease mortality broadly, we examined mortality for the 2 major types of stroke, dened by subsets of ICD-9 or ICD-10 codes as follows: hemorrhagic stroke(ICD-9 codes 430432 or ICD-10 codesI60I62) and ischemic stroke (ICD-9 codes434 and 436 or ICD-10 codes I63 and I64).ICD-9 and ICD-10 codes have been shown to be highly comparable in the classication of theunderlying cause of death from stroke; with ICD- 10 coding used as the standard, ICD-9 coding has a sensitivity of 92.6% and a specicity of 99.8%.12 Overall, the ICD-10 coding changes areestimated to have resulted in a 6% increase inthenumberof deathsattributable to stroke as theunderlying cause, primarily from the cause of death being classied as stroke rather than pneumonia.13

For the Alaska Native population, a singlesource of census data was not available for theentire study period. Consequently, the IndianHealth Service population estimates were usedfor theyears1984 through1993 andthe bridged2000 Alaska Native population, as calculated bythe National Cancer Institute Surveillance Epi-

demiology End Results (SEER) program, wasused for the years 1994 through 2003. 14 For both sources, the population data represent intercensal estimates. Data for the referent pop-ulation were obtained from the Centers for Disease Control and Prevention Wonder Pro-gram.15,16 The age and gender distributions of all3 populationsAlaska Natives, Alaskan Whites,and US Whitesare shown in Table 1.

Data AnalysisThe fundamental measure of occurrence

was the average annual age-adjusted strokemortality rate, where the numerator wasthe cumulative number of strokes and thedenominator the average annual population; both sums were for the specic time period(19841993 or 19942003) divided by thenumber of years within that time period. Ageadjustment was by the direct method, using the US 2000 standard population. Mortality rateswere calculated by age category, gender, stroketype, and time period. For age comparisons, weused 3 categories (

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Alaska Native population compared with 7% for US Whites.

During the period1984 to 1993, stroke mor-tality among Alaska Natives was similar to that of US Whites and Alaskan Whites, with theexceptionof hemorrhagic stroke (Table 2, upper half). The age-adjusted mortality rate for hem-orrhagic stroke was signicantly higher among

all Alaska Natives (by about 50%), but therate was almost double among Alaska Nativewomen. Duringthe period1994 to 2003 (Table2, lower half), stroke mortality, both overalland by type, was higher for Alaska Natives (for both men and women and for women only)than for US Whites, with no signicant differ-ences between Alaska Native men and women.

Stroke mortality rates were signicantly higher for the Alaska Native population thanfor US Whites across most age categories for the period1994 to 2003 (Table 3). Rate ratios between the 2 populations declined with in-creasing age. For all strokes, however, Alaska Natives overall and Alaska Native women hadsignicantly higher mortality rates than USWhites in all age categories. For Alaska Nativemen, a signicantly elevated mortality rate wasfound only for the youngest age category (

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patterns similar to those identied here arereported for American Indian residents of Montana.4 It remains to be determined whether the numerous cultural groups that comprise theAlaska Native population have stroke mortality patterns similar to those foundfor Alaska Natives

in general. Understanding the epidemiology of stroke

among Alaska Natives is essential for devel-oping effective prevention and interventionstrategies to reduce the burden of stroke inthis population. We have begun the process of identifying the characteristics of those indi-viduals within the Alaska Native populationwho are at higher risk of death from strokeand the types of stroke for which the risk iselevated. Notably, Alaska Natives aged youn-ger than 45 years and Alaska Native womenof all ages are at signicantly greater risk of stroke mortality than their White counter- parts. This elevated risk is found for hemor-rhagic stroke and appears to occur for ische-mic stroke as well, although the mortality ratesfor ischemic stroke in those aged younger than65 years are based on too few stroke deathsto yield statistically precise rates. The observedage, gender, and time effects suggest that theetiologic factors are more prevalent among younger individuals than among older individ-uals and more common among women.

An explanation for the observed occurrenceof stroke among Alaska Native people mayreect the substantial lifestyle changes that have been occurring in this cultural group over the last several decades, specically those re-lated to the shift from a subsistence diet to a

more Westernized diet. Younger Alaska Na-tives have been moving away from the tradi-tional diet, which is associated with better cardiovascular health.18,19 These dietarychanges are associated with an increasing prev-alence of overweight, glucose intolerance, and hypertension.20,21 Hypertensiona risk factor for both ischemic and hemorrhagic strokesandfactors associated with elevated blood pressuresuch as overweight may therefore be the focal points for intervention.

As a mortality study, our ndings are subject to a number of limitations inherent to the use of death certicate data. Using stroke as the un-derlying cause of death may yield conservativemortality rates compared with a proposedstrategy of including any death where stroke isindicated to be a related cause, whether direct or otherwise.22 Misclassication of stroke type isalso a recognized limitation of death certicatedata. Although such misclassication may yieldunderestimates of the true rates for stroke types,this should not affect the comparison of racial/ethnic populations unless there is differential

misclassication of stroke type by the decedentrace/ethnicity. Misclassication of the decedentrace/ethnicity is yet another potential limitationof our data 6 ; however, for the broad category oAlaska Native, ethnic misclassication has beenreported to be minimal in Alaska death les.9

Still another limitation is the relatively smanumber of stroke deaths on which the mortal-ity rates for Alaska Natives are based. This presents the challenge of low statistical powefor assessing differences vis-a `-vis the referent population, differences between men andwomen or other subgroups of the population,and changes over time. It must also be recog-nized that the denominators for the rates in the2 time periods are from different sources,whichmay account, in part, for variations in therates. It is uncertain to what extent this is a factor, but the differences appear to be rela-tively small and unlikely to substantially inuence the observed rates. When we comparedstroke mortality rates for the years for which both Indian Health Service and SEER population data were available (19901993), the rates based on the denominators from each of thesesources were statistically similar: 70.9 (per 100000) versus 68.1 for men and women,61.9 versus 60.4 for men only, and 77.6 versus74.1 for women only, respectively. Finally, thechange in coding from ICD-9 to ICD-10 may

TABLE 3Average Annual Age-Specic Stroke Mortality Rates (per 100000) for Alaska Natives andUS Whites, by Stroke Type and Gender: 19942003

Men and Women Men Women

Stroke Type Alaska Natives US Whites RR (95% CI) Alaska Natives US Whites RR (95% CI) Alaska Natives US Whites

All

Age 044 y 6.6 1.6 4.0 (3.0, 5.4) 5.5a 1.7 3.2 (2.0, 5.0) 7.7 1.5 5.0 (3.4, 7.4)

Age 4564 y 33.8 20.8 1.6 (1.2, 2.1) 25.5 23.4 1.1 (0.7, 1.7) 42.0 18.3 2.3 (1.6, 3.2)

Age 65 y 496.1 403.0 1.2 (1.1, 1.4) 490.8 406.5 1.2 (0.97, 1.5) 494.0 395.9 1.2 (1.0, 1.5)

Hemorrhagic

Age 044 y 5.0 1.3 3.7 (2.6,5.2) 3.7a 1.2 3.0 (1.7,5.4) 5.7 1.3 4.2 (2.4,7.3)

Age 4564 y 17.9 10.6 1.7 (1.2,2.4) 10.2a 11.0 0.9 (0.5,1.9) 42.2 12.7 3.3 (2.2,5.1)

Age 65 y 65.9 60.8 1.1 (0.8,1.5) 46.8a 64.5 0.7 (0.4,1.4) 65.6 58.5 1.1 (0.6,2.0)

Ischemic

Age 044 y 1.4a 0.3 4.5 (2.3, 8.7) 1.5a 0.3 4.4 (1.8, 10.8) 1.3a 0.3 4.5 (1.7, 12.1)

Age 4564 y 12.1a 8.4 1.4 (0.9, 2.3) 11.5a 10.3 1.1 (0.6, 2.1) 12.7a 6.7 1.9 (1.0, 3.5)

Age 65 y 323.9 270.5 1.2 (1.01, 1.4) 271.7 268.4 1.0 (0.8, 1.4) 352.7 267.8 1.3 (1.1, 1.6)

Note. CI = condence interval; RR = rate ratio. For US Whites, the study period is 1994 to 2004. For the overall population, the age-specic rates are gender adjusted.a Based on fewer than 20 stroke deaths.

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yield higher rates because of the potential of the latter codes to identify approximately 6% more deaths as being caused by stroke; how-ever, this effect should apply to the referent

groups as well as to Alaska Natives.With due regard for the inherent limitationsto this investigation, we believe these ndingsadvance current knowledge regarding the ep-idemiology of stroke among Alaska Natives, providing an initial departure point for studiesof potential strategies for stroke prevention andintervention in this population. j

About the AuthorsRonnie D. Horner is with the Department of Public Health Sciences, University of Cincinnati Academic Health Center, Cincinnati, OH. At the time of the study,

Gretchen M. Day and Anne P. Lanier were with the Ofce of Alaska Native Health Research, Alaska Native Tribal Health Consortium, Anchorage. Ellen M. Provost is with the Alaska Native Epidemiology Center, Alaska Native Tribal Health Consortium, Anchorage. At the time of the study, Rebecca D. Hamel and Brian A. Trimble were with the Division of Neurology, Department of Internal Medicine, Alaska Native Medical Center, Anchorage.

Correspondence should be sent to Brian A. Trimble, MD,Neurology Service, Alaska Native Medical Center, 4315 Diplomacy Dr, Anchorage, AK 99508 (e-mail: btrimble@anthc.org). Reprints can be ordered at http://www.ajph.org by clicking the Reprints/Eprints link.

This article was accepted January 26, 2009.

ContributorsR.D. Horner and G.M. Day contributed to the studydesign, data analysis and interpretation, and drafting andrevision of the article. A.P. Lanier was responsible for the study concept and contributed to the design, data interpretation, and drafting and revision of the article.E.M. Provost and B.A. Trimble contributed to data interpretation and to drafting and revision of the article.R.D. Hamel helped to draft and revise the article.

AcknowledgmentsThis work was performed as part of the ofcial dutiesof A.P. Lanier, E.M. Provost, B.A. Trimble, G.M. Day,and R.D. Hamel as employees of the Ofce of Alaska Native Health Research, Alaska Native EpidemiologyCenter and the Alaska Native Medical Center, all a part of the Alaska Native Tribal Health Consortium. The

Alaska Native Epidemiology Center receives support through a cooperative agreement with the US IndianHealth Service.

Human Participant ProtectionThis project was reviewed by the Alaska Native TribalHealth Consortium and was deemed not to constituteresearch with human subjects.

References1. Harris C, Ayala C, Dai S, Croft JB. Disparities indeaths from strokeamongpersons aged

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