RESULTS â Rates of ischemic heart disease and atherosclerosis were found to be generally low among AI/AN although those in the 25- to 44 -yr age-group ...
Cardiovascular Disease Among American Indians and Alaska Natives THOMAS K. WELTY, MD, MPH JOHN L. COUUEHAN, MD, MPH
OBJECTIVE— To compare the regional differences in cardiovascular disease in Al/AN with the U.S. general population and determine the parity gap and preventable proportion of cardiovascular mortality. RESEARCH DESIGN AND METHODS— Age-adjusted cardiovascular disease mortality rates for 1981-1983 and hospital discharge rates for 1982-1984 reported by the IHS were compared with U.S. data for 1982 and 1983, respectively.
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tudies dating from early in this century have documented the low prevalence of ischemic heart disease among southwestern American Indians (1-11) and among Alaska Natives (12). Other American Indians have been less well studied, but it is clear that within the last generation, the rates of ischemic heart disease in some American Indian groups approached or exceeded that of the general U.S. population ( 1 3 15). Autopsy studies of southwestern Indians have also documented a very low prevalence of all types of atherosclerosis, including cerebrovascular disease (5,6). In these respects, southwestern Indians resemble the members of many traditional cultures in other parts of the world. Acute rheumatic fever and resulting rheumatic heart disease, formerly a serious problem among southwestern Indians, have become less of a problem in recent decades (16).
RESULTS — Rates of ischemic heart disease and atherosclerosis were found to be generally low among AI/AN although those in the 25- to 44 -yr age-group have higher death rates from cardiovascular disease than in the U.S. population. Although Both genetic and environmental the mortality rate from cardiovascular disease in AI/AN is 19% lower than the rate for the general U.S. population, the parity gap in individual regions of the U.S. ranges factors have probably contributed to refrom favorable to extremely unfavorable. There were also wide variations in the sistance to ischemic heart disease and other forms of atherosclerosis among preventable gap theoretically possible by reduction of the three major risk factors. southwestern Indians. Glucose intolerCONCLUSIONS— Changing nutrition and exercise patterns and the increasing ance, however, is a major risk factor for prevalence of diabetes in many Indian tribes may have adverse effects in the future, cardiovascular disease, estimated to conpossibly increasing the prevalence of heart disease. Regional differences in the tribute to 19% of all cardiovascular prevalence of some major cardiovascular risk factors (smoking, hypertension, hyper- deaths in the U.S., and an especially imcholesterolemia, and diabetes) are the probable explanation for these differences in portant risk factor for women (17). Diacardiovascular morbidity and mortality rates. Prevention and treatment of these risk betes is increasing among American Infactors will have the greatest impact in attempts to reduce cardiovascular disease dians (18), and the prevalence of among AI/AN. In addition, moderation in the use of alcohol, or abstinence, may diabetes in all IHS areas now exceeds the prevalence in the U.S., with the excepprevent sudden deaths resulting from acute intoxication. tion of the Alaska area (this issue, Valway et al., p. 271-76). The Pima Indians of Arizona have the highest recorded rate of diabetes in the world (20), and the rate ranges from moderate to high for most other southwestern Indians (21). Obesity FROM THE ABERDEEN AREA INDIAN HEALTH SERVICE, RAPID CITY, SOUTH DAKOTA; AND THE STATE is also common among the southwestern UNIVERSITY OF NEW YORK AT STONYBROOK, STONYBROOK, NEW YORK. Indians, and it contributes to the high ADDRESS CORRESPONDENCE AND REPRINT REQUESTS TO THOMAS K. WELTY, MD, MPH, ABERDEEN AREA rate of diabetes (22). In both the Pima INDIAN HEALTH SERVICE, 3200 CANYON LAKE ROAD, RAPID CITY, SD 57702. and Navajo, diabetes is a documented THE OPINIONS EXPRESSED IN THIS PAPER ARE THOSE OF THE AUTHORS AND DO NOT NECESSARILY REFLECT risk factor for acute myocardial infarcTHOSE OF THE INDIAN HEALTH SERVICE. tion, although infarction occurs infreAI/AN, AMERICAN INDIANS/ALASKA NATIVES; IHS, INDIAN HEALTH CENTER; NCHS, NATIONAL quently even among diabetic patients CENTER FOR HEALTH STATISTICS. (10,23).
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Hypertension contributes to 30% of all cardiovascular deaths in the U.S. (17). Hypertension was once thought to be uncommon among southwestern Indians (24), but recent population studies have indicated a prevalence of 7-22% for adults (25-32; this issue, Broussard et al., p. 292-96). Cigarette smoking contributes to 17% of all cardiovascular deaths in the U.S. (17). Although cigarette smoking (particularly "heavy" or regular smoking) remains uncommon among southwestern Indians, smoking prevalence exceeds 50% among Northern Plains Indians and Alaska Natives ( 3 4 - 3 7 ) . Cholesterol levels >219 mg/ml contribute to 10% of cardiovascular deaths in the U.S. (17). Mean serum cholesterol levels in southwestern Indians have historically been low; 50-60 mg/ml less than in Caucasian groups (38-44). The high rates of cardiovascular disease in most AI/AN groups outside the southwest compared with the rates in the southwest Indians may reflect differences in known risk factor patterns, longer exposure to factors that disrupt traditional culture and nutrition, or greater genetic admixture with the Caucasian population. No systematic crosssectional or longitudinal studies have been conducted among tribal groups to determine the prevalence of factors related to ischemic heart and cerebrovascular disease. RESEARCH DESIGN AND METHODS IHS The inpatient care system is the source of IHS and contract inpatient data on a patient's age, sex, diagnosis, and community of residence. One record is created per discharge. Because the California program office operates no hospitals and reports no contract hospital work load, the inpatient data presented in this article cover 11 of the IHS's 12 areas. IHS hospital discharge rates are age adjusted to
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permit comparison with the U.S. population and among areas. Data on patient care that is provided in Veteran's Administration Hospitals or is totally funded privately or funded by third-party resources are unavailable. AI/AN hospitalization rates are, therefore, understated. The IHS user population is used to calculate rates of inpatient services provided by the IHS, because the IHS has patient care data only on services funded by the IHS. AI/AN who are eligible for and who periodically use IHS services constitute the IHS user population (830,000 in 1985).
Vital events The IHS derives mortality statistics from data furnished annually by the NCHS. The NCHS mortality data are based on official death certificates from state departments of health across the nation. The NCHS edit checks this information and determines values for missing items. The IHS calculates mortality rates for AI/AN who reside in counties where IHS has responsibility. Because death certificates do not indicate whether an individual used IHS services, the IHS service population (870,000 in 1982), rather than the user population, is the denominator for AI/AN mortality rates. The service population is estimated from the census of AI/AN who reside in geographic areas where the IHS has responsibilities. Populations between census years are projected from AI/AN birth and death statistics using linear regression techniques. Because deaths are infrequent occurrences that are associated with large random fluctuations, IHS uses a 3-yr period to analyze AI/AN deaths. Both the IHS and U.S. mortality rates are age adjusted to the 1940 U.S. census to make them comparable. Because census enumeration is based on self-reporting of race, census population estimates are subject to reporting error. AI/AN race on death certificates in California is known to be underreported and may also be underreported in other areas, such as the Portland and
Oklahoma areas. Mortality data from California are included in the overall IHS mortality rates. RESULTS— The age-adjusted total cardiovascular mortality rate among AI/AN is 19% lower than the U.S. rate (Table 1). Most of this difference is in the 30% lower rate for death from ischemic heart disease (Table 1). Overall mortality rates from cerebrovascular disease are similar in the AI/AN and total U.S. populations (Table 2). Annual hospital discharge rates indicate that, among AI/AN, the morbidity rate from cardiovascular diseases is proportionately even less than the mortality rate (Table 2). The hospital discharge rate is 48% of the U.S. rate. These lower rates are evenly distributed among acute myocardial infarction, cerebrovascular disease, and other cardiovascular diseases. Only acute rheumatic fever and chronic rheumatic heart disease cases are hospitalized more frequently in the IHS service population than in the U.S. population, but these two illnesses account for a very small proportion of all cardiovascular morbidity. Wide variations in cardiovascular morbidity and mortality rates exist in different IHS areas (Tables 1 and 2). Some of these individual rates are based on small populations, and in some cases identification of services or of Indian ancestry may be incomplete, so these values should be interpreted cautiously. Nonetheless, data indicate a continued low rate of cardiovascular disease among southwestern Indians, particularly in the Navajo and Albuquerque areas, where low morbidity and mortality are largely explained by the very low rates of acute myocardial infarction and death from ischemic heart disease. The Phoenix and Tucson areas (along with the Oklahoma City, Portland, and Alaska areas) appear to have intermediate rates of cardiovascular disease, somewhat lower than those of the total U.S. population. Finally, the Aberdeen, Bemidji, Billings, and Nashville areas have rates that are comparable
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Table 1—Cardiovascular mortality for AI/AN* TOTAL CARDIOVASCULAR
POPULATION
U.S. (1982)
DISEASE
ISCHEMIC HEART DISEASE
CEREBROVASCULAR DISEASE
ICD-9 CODE 390-448
ICD-9 CODE 410-414
ICD-9 CODE 430-438
N
RATEt
N
RATEt
N
RATEt
967,868
238.3
552,786
139.3
157,710
35.8
FOR 3 YR
FOR 3 YR
IHSt (1981-1983) ABERDEEN ALASKA ALBUQUERQUE BEMIDJI BILLINGS NASHVILLE NAVAJO OKLAHOMA PHOENIX PORTLAND TUCSON
4087 478 295 121 383 255 181 361 1069 363 358 66
192.3 351.7 206.3 117.9 413.8 339.1 244.7 103.3 177.4 207.9 210.4 188.0
2019 238 122 43 233 132 89 96 606 170 196 18
FOR 3 YR
98.2 178.7 91.1 45.7 263.2 178.1 123.9 30.5 102.4 100.1 115.6 54.6
715 76 63 27 46 32 38 70 188 59 69 9
32.3 52.2 44.2 25.5 45.9 40.6 50.9 19.1 29.9 33.0 41.3 25.1
*NCHS data for underlying cause of death. tAnnual age-adjusted rates/100,000 population (1940 standard). f IHS population, Al/AN living in counties that are served by IHS. California data are included in the overall IHS rate.
to and, in some cases, considerably above those of the U.S. population.
favorable in the Bemidji area. These differences are attributable partly to differences in the prevalence of four maCONCLUSIONS— Any generaliza- jor risk factors (smoking, hypertension, tions about cardiovascular morbidity and high serum cholesterol, and diabetes), mortality among AI/AN must be inter- but may also involve other genetic and preted in light of wide regional varia- environmental factors. The current Nations. The parity gap shows that AI/AN vajo area cardiovascular mortality is even have lower rates of cardiovascular dis- less than the theoretical best-projected ease and ischemic heart diseases than the U.S. rate (i.e., a 55% reduction in the general U.S. population and are at par for current rate) attainable if all people cerebrovascular disease (Table 3). How- stopped smoking, if all systolic blood ever, the mission of the IHS is to improve pressures were brought to < 139 mmHg, the health of AI/AN to the highest pos- and if all serum cholesterol levels were sible level and not just to attain parity. brought down to
