- Email: [email protected]
Mortality from coronary heart disease and stroke for six ethnic groups in California, 1985 to 1990
ELSEVIER
Mortality from Coronary Heart 1985 to Groups in California, SARAH H. WILD, ANN N. VARADY,
Disease and Stroke for Six Ethnic
1990
MB, BCHIR, AMI LAWS, MD, MS, AND CHRISTOPHER
STEPHEN P. FORTMANN, D. BYRNE, MB, BCH, PHD
MD,
Coronary heart disease and stroke death rates were compared for six ethnic groups (non-Hispanic Chinese, Japanese, and Asian Indian) by sex and age (2.5 to white, Hispanic, African-American, census and 1985 to 1990 death 44, 45 to 64, 65 to 84, and 25 to 84 years old) using California data. African-American men and women in all age groups bud the highest rates of death from coronary heart disease, stroke, and all causes (except for coronary heart disease in the oldest men). Hispanics, Chinese, and Japanese in all age-sex groups had comparatively low death rates for coronary heart disease and stroke, although stroke was proportionally an important cause of death for Chinese and Japanese groups. Coronary heart disease was an important came of death for Asian Indians although death rates were generally not higher than those for other ethnic groups. Ethnic differences were most marked for women and younger age groups. Ann Epidemiol 1995;5:432-439. KEY WORDS:
Cerebrovascular
disorders, coronary disease, ethnic groups, mortality.
INTRODUCTION Ethnic differences in mortality from heart disease were described as early as 1931 when Schwab and Schulz (1) reported that deaths due to arteriosclerotic heart disease were 1.5 times more common in American whites than blacks. Further studies confirmed that variation exists between races in mortality from coronary heart disease (CHD) and stroke whether subjects remain in their native countries or migrate overseas (2-9). Many of these studies have been limited either to the comparison of only two ethnic groups or to the study of men (or both), and few studies performed in the United States included ethnic groups other than non-Hispanic whites and non-Hispanic blacks (subsequently referred to as whites and African-Americans, respectively). Furthermore most previous studies did not examine age-specific rates. Crude death rates give the impression of lower CHD rates in subpopulations with a larger proportion of young people (i.e., most ethnic minorities). The use of age-standardized rates for a large age range in
a population may also obscure the presence of important differences between
age groups.
From the Center for Research in Disease Prevention (S.H.W., S.P.F., A.N.V.), Division of General Internal Medicine (A.L., S.P.F.), and Falk Cardiovascular Research Center (C.D.B.), Stanford University School of Medicine, Stanford, CA. Address remint reauests to: Sarah H. Wild. MB. BChir. Eoidemioloev Unit, Department of’ Epidemiology and Po&ation Sci&&, L.ond& School of Hygiene and Tropical Medicine, Keppel __ Srreet. London WClE 7HT, Engla&. Received June 17, 1994; accepted December 7, 1994. Q 1995 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
Migration influences ethnic differences in mortality. For example, CHD risk is low for Japanese men in Japan, increases following migration to Hawaii, and increases further after migration to the US mainland, but remains below the CHD risk for white men in the United States (2, 3). The excess risk for CHD in Asian Indians over other ethnic groups may be exacerbated by migration to other countries (8). In contrast, the incidence of stroke is high in Japan and falls rapidly for Japanese people after migration to the United States (3, 9). An increasing proportion of the population of California and the United States is composed of ethnic minorities. In 1987 California received 26.1% of the total immigrants to the United States (10). According to the US Bureau of Census in 1988, the Hispanic population in California (approximately 80% of which are Mexican-Americans) is growing five times as fast as the population as a whole. In the 1990 California census 25.8% of the population was Hispanic and 57.2% was white. The proportions of African-Americans and Japanese in California remained stable between 1980 and 1990 and were 7 and 1.1% of the total population, respectively. The proportion of Chinese people in the state rose from 1.4% in 1980 to 2.4% in 1990. The Asian Indian population in California trebled in the decade prior to 1990 and came to represent 0.5% of the population. The total population of California as enumerated by censuses grew by over 6 million between 1980 and 1990 and was nearly 30 million people in 1990. Because an increasing proportion of the California and US populations is composed of ethnic minorities, it is important to quantify the mortality from CHD and stroke in 1047-2797/95/$9.50 SSDl 1047-2797(95)00058-F
AEP Vol. 5, NO. h
Wild et al. ETHNIC DIFFERENCES IN CHD AND STROKE M0RTALIl-Y
.Nowmber 1995: 432-439
433
TABLE 1. Population of California aged 25 to 84 years by sex for total population and six ethnic groups for 1980 and 1990 and median age of each subpopulation for 1990 1990 1980 Ethnic group
Median age (y)
Men
Women
%”
Men
Women
%”
Men
Women
Total White
6,667,810 4,802,551
7,143,078 5,186,283
100.0 72.3
9,004,684 5,686,514
1,004,607
1,018,824
14.7
1,912,701
100.0 63.5 10.4
‘,. ‘,:
Hispanic AfricanAmerican Chinese Japanese Asian Indian
9,293,248 5,931,094 1,813,802
32 ib 24
431,9.31 99,298 76,646 17,868
479,905 99,774 95,888 15,276
6.6 1.4 1.3 0.2
575,718 2 16,302 101,435 52,004
624,101 234,684 123,304 41,553
6.6 2.5 1.2 0.5
(_ ,\ \ Lit
20 ii 38 27
” The percent of the total population aged 25-84 comprised by each ethnic group (men and women combined).
these groups so that this information can be applied to the development of public health policies. Data from California death tapes and censuses provide an opportunity to simultaneously compare mortality rates for multiple ethnic groups with large sample sizes. Death certificate and census data are available for other states and for the entire United States but we limited the study to California because of the more marked and expanding ethnic diversity than in many other states. This study reports age-specific death rates from CHD and stroke by race, sex, and age in six ethnic groups in California from 1985 to 1990.
MATERIALS
AND
METHODS
Numbers of deaths with CHD (identified using International Classification of Diseases, 9th revision (ICD-9) classification numbers 410 to 4 14) and stroke (ICD-9 classification numbers 431 to 438) as the primary cause of death for six different ethnic groups (white, Hispanic, African-American, Chinese, Japanese, and Asian Indian) in California were obtained from death tapes for the years 1985 to 1990. The specified ethnic groups were chosen for the study either because of large population sizes or, in the case of the Asian Indian population, because previous studies outside the United States had revealed a high risk of CHD and stroke. The first year in which precise data regarding ethnicity were recorded on death certificates in California was 1985 and 1990 is the most recent year for which census data are available. Population sizes were calculated by linear interpolation between data collected in the 1980 and 1990 censuses. Ethnicity is self-reported on censuses; race is recorded on death certificates by the funeral director using state guidelines. The classification of race differs slightly between censuses and death tapes in that several small subpopulations (e.g., Bangladeshi, Pakistani, and Sri Lankan) are excluded from the group titled “Asian Indian” on the census but are in-
cluded in the “Indian” category on death tapes (which excludes American Indians). Age distributions vary within each ethnic group, with minority populations usually having a preponderance of younger persons, and comparison of crude death rates among ethnic groups may yield misleading results. Death rates in this study were calculated by stratifying the populations by sex and age (25 to 44, 45 to 64, 65 to 84, and 25 to 84 years) and by age standardization in 5-year age groups within each of these age groups, using the age distribution ofthe total population by sex in 1990 as the standard. Owing to the small numbers of deaths in some of the subpopulations, data from all years, 1985 to 1990, were combined and trends across the years were not examined. Standardized mortality ratios (SMRs) for each sex and age group were calculated by expressing as a percentage the age-standardized death rate from CHD or stroke in each ethnic group divided by the expected death rate (i.e., the comparable rate for the total population). Proportional mortality ratios (PMRs) for each sex and age group were calculated by dividing the proportion of deaths due to CHD or stroke in each ethnic group by the proportion of deaths due to CHD or stroke for the total population and are also expressed as a percentage. Calculation of the PMR is useful in that it does not use census data (thus preventing any miscalculations due to different reporting of race in death tape and census data) and it also provides an indication of the relative importance of CHD and stroke as causes of death in subpopulations. Using the Poisson assumption 95% confidence intervals were calculated for SMRs and PMRs for each sex and age group.
RESULTS Population sizes for persons between 25 and 84 years old in California in 1980 and 1990 and the percentage of each ethnic subgroup are given in Table 1, with the ethnic groups
434
AEP Vol. 5, No. 6 November 1995: 432-439
Wild et al. ETHNIC DIFFERENCES IN CHD AND STROKE MORTALITY
TABLE
2. Number of observed deaths, standardized mortality ratio (SMR) for coronary heart disease (CHD), stroke, and all causes of death, and proportional mortality ratio (PMR) for CHD and stroke for ages 25 to 84 by sex for total population and six ethnic groups in California, 1985 to 1990
SeX
Ethnic crow
CHD
PMR
SMR
No. of observed deaths Stroke
All causes
CHD
Stroke
All causes
CHD
Stroke
Total
Metl Women
123,164 82,720
26,447 30,002
542,301 405,899
100 100
100 100
100 100
100 100
100 100
White
Men Women
102,507 67,948
20,069 23,578
420,555 325,430
108 103
97 98
103 104
107 102
98 98
Hispanic
Men Women
8168 5645
2229 2185
50,901 30,978
63 70
79 74
71 68
71 89
90 95
African-American
Men Women
7308 6599
2323 2798
46,142 33,817
113 154
165 180
150 151
70 96
103 112
Chinese
Men Women
1260 679
503 432
6631 4379
55 53
100 91
64 64
84 76
156 133
Japanese
Men Women
702 377
232 219
3461 2688
53 49
84 81
58 60
89 69
137 110
Asian Indian
Men Women
258 106
28 43
743 362
92 79
53 90
56 48
153 144
77 161
listed in order of decreasing population size. The median age of each population is also listed for 1990 and reflects the fact that the age structure of the different populations varies greatly, probably as a result of both different birth rates and differential immigration. The median age of the Hispanic population in California was the lowest of all ethnic groups and larger proportions of older people were found in the white and Japanese populations than in other ethnic groups. Numbers of deaths, SMRs, and PMRs from CHD, stroke, and all causes for the age range 25 to 84 by sex and ethnicity are presented in Table 2. Despite the considerably smaller population size for African-Americans than for Hispanics, it is interesting to note that larger numbers of CHD and stroke deaths were found to occur in African-American women than Hispanic women. For CHD and stroke, SMRs were highest for African-American men and women but PMRs for African-Americans were either lower than those for the total population (for CHD) or only slightly elevated (for stroke), consistent with the high SMR for deaths from
all causes for African-Americans. PMRs for stroke were high in Chinese and Japanese men and women. Age-standardized death rates per 100,000 population for CHD, stroke, and all causes are listed by sex in Table 3. African-Americans had the highest death rates for CHD, stroke, and all causes of death in all age-sex groups, except for CHD in the oldest men. In Hispanic, Chinese, and Japanese groups the rates for each cause of death were lower than for African-Americans and whites. The ethnic differences are more marked among the youngest age groups than across the larger age range. Figure 1 presents SMRs and 95% confidence intervals for CHD for men and women by ethnicity and age group and indicates that ethnic differences were most marked for women and younger age groups, although confidence intervals tended also to be wider in these groups. Similar results, which are not shown, were found for stroke, with the SMR being particularly high for African-American women in the youngest age group. Figure 2 shows PMRs for CHD and 95% confidence intervals for men and women by ethnicity
TABLE 3. Age-standardized death rates per 100,000 population for coronary heart disease (CHD), stroke, other, and all causes of death for ages 25 to 84 by sex for total population and six ethnic groups in California, 1985 to 1990
Cause of death CHD Stroke Other All
Total
White
AfricanAmerican
Hispanic
Chinese
Japanese
Asian Indian
M
W
M
W
M
W
M
W
M
W
M
W
M
W
280 62 858 1200
139 50 511 700
302 60 881 1243
143 49 534 726
175 49 632 856
97 37 344 478
316 102 1382 1800
214 91 755 1059
155 62 555 773
73 46 327 446
146 52 494 693
67 41 312 420
258 33 376 668
110 45 180 335
M, men; W, women.
AEP Vol. 5, No. 6 Notwnher 1997: 452-439
SMR
Wild
et ai.
435
ETHNIC DIFFERENCES IN CHD AND STROKE MORTAL:TV
and
95%CI
for
men
350 300 250 200 150 100 50 0
Age (years) SMR
25-44 and
95%CI
for
45-64
65-84
45-64
65-84
women
350 300 250 200 150 100 50 0
Age (years)
25-44
FIGURE 1. Standardized mortality ratio (SMR) and 95% confidence intervals (CI) for coronary heart disease (Cl-ID) for men (toe) and women (bottom) in California,
1985 to 1990, by ethnicity and age.
and age group. Although Asian Indians had the lowest death rates from all causes (see Table 3) of all the ethnic groups studied, PMRs for CHD were higher for Asian Indians than for other ethnic groups. CHD death rates in Asian Indian men were comparable to those for white men (see Table 3) and yet PMRs for CHD for Asian Indian men of all ages were considerably higher than for white men (see Figure 2, top). PMRs for CHD for middle-aged and older Asian Indian women were also significantly higher than for white women. Ethnic differences between PMRs for stroke in age-specific groups were less marked than for CHD (re-
sults not shown) but were generally higher for Chinese and Japanese in all age-sex groups than for other ethnic groups.
DISCUSSION The major findings of this study are that age-specific rates for CHD, stroke, and all-cause mortality in California were highest for African-Americans for all age-sex groups (except for CHD among the oldest men). CHD and stroke death rates in all Hispanic, Chinese, and Japanese age-sex groups
AEP Vol. 5, No. 6 November 1995: 432-439
Wild er al. ETHNIC DIFFERENCES IN CHD AND STROKE MORTALITY
436
PMR
and
95%CI
for
men
for
women
600 500 400 300 200 100 0
25-44
Age (years) PMR
and
95%CI
45-64
65-84
45-64
65-84
600 500 400 300
r
......... ......... .........
Age (years)
25-44
FIGURE 2. Proportional mortality ratio (PMR) and 95% confidence intervals (CI) for coronary heart disease (CHD) for men (top) and women (bottom) in California, 1985 to 1990, by ethnicity and age.
were low in comparison to those for whites and AfricanAmericans. Although the absolute rates for CHD deaths were low in Asian Indians, total mortality was also low, and a higher proportion of all deaths in this ethnic group was due to CHD compared to the other ethnic groups. These findings underline the importance as causes of death of CHD and stroke for whites and African-Americans, of CHD for Asian Indians, and of stroke for Chinese and Japanese populations and reveal that ethnic differences tend to be more marked for women and younger age groups. We found CHD death rates were higher for AfricanAmerican than white men and women at all ages studied except the oldest age group for men. Our findings contrast
with some previous studies that found prevalence of CHD to be higher in white men than African-American men and similar in white women and African-American women (6, ll-13), and with the 30-year follow-up of the Charleston Heart Study which concluded that the mortality rates from CHD for whites and African-Americans were not significantly different (14). It should be noted, however, that these conclusions were drawn from studies using a variety of methods that differed from ours; for example, the Charleston Heart Study was a closed cohort study that represented the age and ethnic distribution of the particular population studied in 1960. The 1986 Report of the Secretary’s Task Force on African-American and Minority Health found
AEP Voi. 5, No. 5 November 1995: 432.-439
that CHD mortality rates were similar among AfricanAmerican men and white men but were higher for AfricanAmerican women than white women (15). US statistics for 1986 revealed that age-adjusted death rates for ischemic heart disease overall were lower in African-American men than white men but higher for African-American women than white women (16). In the younger age groups (up to age 65 in men and age 75 in women), however, death rates from ischemic heart disease were higher in both AfricanAmerican men and women, compared to whites (16). We used the more conventional group of ICD codes (410 to 413) to describe CHD. The code 429.2, which denotes hypertensive disease, is included in some studies and we believe that the inclusion of this code in the present study would not have affected the conclusions and may indeed have extended the differences between African-Americans and whites. Reasons for the discrepancies among African-American/ white differences in previous studies have been reviewed (17, 18) and include the difference between crude, agestandardized, and age-specific rates. Our results show that ethnic differences appear much less marked for the age range of 25 to 84 years than for the 25- to 44-year age group and thus indicate the importance of studying age-specific death rates. The findings of our study concur with those of other studies that showed stroke death rates to be much higher for African-Americans than for whites (19). This effect was particularly marked in this study for women aged 25 to 44 for whom the stroke death rate was 5.5 times higher for African-Americans than whites. The increased CHD mortality for African-Americans may be explained by differences in prevalence of certain risk factors; for example, there is a higher prevalence of hypertension and diabetes mellitus in African-Americans than whites (20). However, onestudy found that adjustment for age, hypertension, and diabetes mellitus did not fully explain the excess incidence of stroke in African-Americans over whites (21). Obesity is prevalent in African-American women and is associated with a cluster of risk factors, which may partially account for an increased risk of CHD (22, 23). Other factors that may influence the excess mortality include lower sociofrom all causes for African-Americans economic status, poor survival rates (24), differential access to and seeking of health care (25), the presence of other diseases, and possibly other physiologic, psychological, and behavioral differences. Hispanics in various parts of the United States have been shown to have a lower prevalence of CHD than do whites, in spite of an apparently higher prevalence of CHD risk factors (7, 26-29). Differences in mortality exist between subgroups of the Hispanic population (26) but we did not investigate these because the majority (80% in the 1990 census) of Hispanics in California are Mexican-Americans. Non-insulin-dependent diabetes mellitus (NIDDM) is more
‘Y&idet ;ri
437
ETHNIC DIFFERENCES IN CHD AND STROKE MCXTALITl
common in Hispanics than whites (30-33) and is known to be a major risk factor for CHD in whites (34,35). However, a low prevalence of CHD has been found in Hispanics with NIDDM, particularly in men (28), and this paradox remains unexplained. The low death rates for CHD, stroke, and all causes of death in Hispanics in this study are thus consistent with findings of studies elsewhere in the United States. The low mortality from all causes (except homicide) for Hispanics compared to whites in the United States may be due, at least in part, to a combination ofthe “healthy migrant effect” (a selection process analogous to the “healthy worker effect” whereby recent migrants tend to be healthier than more established populations (36)), underreporting of certain conditions, incorrect recording of ethnicity on death certificates, and the possibility that Mexican-born persons in the United States tend to return to Mexico when they become older or ill (26). Chinese and Japanese populations have a reduced risk of CHD when compared to whites (9, 37). However, Japan has had the highest stroke rates in the world, although in the two decades leading up to 1985 there was a rapid fall in stroke rates in Japan (9, 38). The low risk of CHD compared to whites was found to persist in Japanese-Americans (3). Our study showed death rates to be iow in Chinese and Japanese populations in California for both CHD and stroke, particularly at younger ages. However, stroke was proportionally an important cause of death in Chinese- and Japanese-Americans, although this can, :n part, be explained by the low overall mortality in these ethnic groups. Asian Indians have been reported to have higher odds ratios for developing and dying from CHD than do Chinese, Africans, and Europeans (4,8,39-41) and Asian-Americans born in India and Pakistan have been found to be at high risk of coronary disease hospitalization (42). The excess risk of CHD seems to apply to migrants from all parts of the Indian subcontinent and can not be fully explained by the increased prevalence of established risk factors after migration (8, 39). In contrast to these reports, the death rate for CHD for Asian Indians in California in this study was not significantly different from that of white men. The discrepancy in classification of Asian Indian subgroups between the census and death tapes would, if anything, result in an overestimation of death rates in this ethnic group and is therefore not responsible for this unexpected finding. The population of Asian Indians in California has trebled in the years 1980 to 1990 and it is likely that these recent migrants are generally healthier than are more established populations. This theory is supported by rhe fact that the mortality of Asian Indians in California from all causes is the lowest of all ethnic groups in this study. The “healthy migrant effect” and the effect of different methods of data collection used in censuses and death tapes can be overcome by examining the proportion of all death:; that are due to
438
Wild et al. ETHNIC DIFFERENCES
IN CHD
AND
STROKE
AEP Vol. 5, No. 6 November 1995: 432-439
MORTALITY
a specific cause, that is, PMR. PMRs for CHD were high for all age-sex groups of Asian Indians (with the exception of the women aged 25 to 44); this finding indicates the importance of CHD as a cause of death for Asian Indians. Stroke mortality in Asian Indian men has also been reported to be higher than the average for England and Wales (41); our study found no consistent difference between death rates or PMRs for stroke for Asian Indians compared to whites. This finding may partly be due to the fact that there were only a small number of stroke deaths in the Asian Indian population studied. Interpretation of the findings of this study relies on the accuracy of the data recorded on the death certificates and we assumed that no systematic differences exist among races in recording of race or cause of death. It is possible that the low death rates found in all ethnic minorities except African-Americans may, in part, reflect misclassification of race on death certificates. However, a study of the validity of demographic characteristics on death certificates found that the agreement between race recorded on the death certificate and the Census Bureau’s population surveys was 99.4% overall, 98.7% for Hispanic origin, and 82.4% for Asian/Pacific Islanders (43). Mortality rates occur as a function ofboth incidence of disease and case fatality, and ethnic differences may influence both of these factors. Evidence exists to suggest that lower incidence of myocardial infarction (rather than a lower case fatality) is more likely to cause the comparatively low mortality from cardiovascular disease in Mexican-Americans (44) and a recent study found that case fatality after myocardial infarction was actually greater among Mexican-Americans than among whites (45). Socioeconomic status data were not available for subjects in this study and socioeconomic status is known to have an important influence on mortality from heart disease (46). Differences in socioeconomic status may account for some of the observed ethnic differences, especially between African-Americans and other ethnic groups. Whether a socioeconomic gradient exists in the United States in ethnic groups other than whites and African-Americans (for whom a reverse relationship is known to exist between socioeconomic status and mortality (47)) is not known. We have shown the importance of examining age-specific rates to quantify ethnic differences and the presence of major differences in mortality from CHD and stroke for several minority populations. CHD is the leading cause of death among US residents (48,49) regardless of ethnic origin, and is a major public health problem. As a consequence it is imperative that attempts be made to identify and reduce risk in all populations. As the nonwhite population of the United States continues to grow, there is a greater need for studies of risk factors in groups other than white middleaged men who have, to date, provided the basis for the majority of the research into CHD. Research into ethnic differences is required not only to facilitate health care plan-
ning but also to investigate the relative importance of risk factors for CHD and stroke in population subgroups and to enable the development of appropriate primary and secondary prevention programs.
This work wassupportedby
Public Health Service grant HL 21906 from the National Heart, Lung, and Blood Institute. Sarah H. Wild was supported in part by the Stanford University Dean’s Postdoctoral Fellowship. Christopher D. Byrne was supported by the Peel Medical Research Trust and the Parke Davis/Cambridge University International exchange fellowship. The comments of Dr. R. Gillum and Dr. P. McKeigue on an earlier version of the manuscript are acknowledged with gratitude.
REFERENCES I. Schwab EH, Schulz VE. The incidence of heart disease and of the etiological types in a Southern dispensary, Am Heart J. 1931;7:223234. 2. Gordon T. Mortality experience among the Japanese in the United States, Hawaii and Japan, Public Health Rep. 1957;72:543-553. 3. Marmot MG, Syme SL, Kagan A, Kate H, Cohen JB, Belsky J. Epidemiologic studies of coronary heart disease and stroke in Japanese men living in Japan, Hawaii and California: Prevalence of coronary and hypertensive heart disease and associated risk factors. Am J Epidemiol. 1!$5;102:514-525. heart disease in seven racial groups in Singapore, 4. Muir CS. Coronary Br Heart J. 1960;22:45-53. of cardiovascular disease in India. II. Isch5. Padmavati S. Epidemiology emit heart disease, Circulation. 1962;25:711-717. infarction in 6. Weisse AB, Abiuoso PD, Thind IS. Acute myocardial Newark, NJ: A study of racial incidence, Arch Intern Med. 1977;137: 1402-1405. 7. Markides KD, Coreil J. The health of Hispanics in the south-western United States: An epidemiologic paradox, Public Health Rep. 1986; 101:253-265. PM, Miller GJ, Marmot MG. Coronary 8. McKeigue South Asians overseas: A review, J Clin Epidemiol.
heart disease in 1989;42:597-609.
T, Komachi Y, Inada H, et al. Trends for coronary 9. Shimamoto disease and stroke and their risk factors in Japan, Circulation. 79:503-515.
heart 1989;
and Naturalization Service. 1987 Statistical Yearbook of 10. Immigration the Immigration and Naturalization Service. Washington, DC: US Government Printing Office; 1988. 11. Keil JE, Loadholt CB, Weinrich MC, Sandifer SH, Boyle E Jr. Incidence of coronary heart disease in African-Americans in Charleston, South Carolina, Am Heart J. 1984;108:779-786. 12. Langford HG, Oberman A, Borhani NO, Entwisle G, can-American-white comparison of indices of coronary and myocardial infarction in the stepped-care cohort of sion Detection and Follow-up Program, Am Heart J. 801.
Tung B. Afriheart disease the Hyperten1984;108:797-
13. McDonough JR, Hames CG, Stulb SC. Coronary heart disease among Negroes and whites in Evans County, Georgia, J Chronic Dis. 1965; 18:443-468. 14. Keil JE, Sutherland SE, Knapp RG, Lackland DT, Gazes PC, Tyroler HA. Mortality rates and risk factors for coronary disease in AfricanAmericans as compared with white men and women, N Engl J Med. 1993;329:73-78. 15. US Department of Health and Human Services. Executive summary. In: Report of the Secretary’s Task Force on African-American and
AEP Vol. 5, No. C ?Jovemher1995: 4 12-431)
ETHNIC
Minority Health. v. 1. DHHS Publication Washington, DC: US Government Printing
No. 186-620-638:40716. Office, 1986:llO.
16. National Center for Health Statistics. Vital Statistics of the United States, 1986. v. II. Mortality, Part A. DHHS Publication No. (PHS) 89-1101. Washington, DC: US Government Printing O&e; 1989. populations. 17. Gillum RF. Coronary heart disease in African-American I. Mortality and morbidity, Am Heart J. 1982;104:839-851. 18. Cooper RS, Ghali JK. Coronary heart disease: African-Americanwhite differences, Cardiovasc Clin. 1991;21:205-225. 19. Gillum
RF. Stroke
in African-Americans,
Stroke.
1988;19:1-9.
DIFFERENCES
IN CHD
AND
STROKE
population. The San Luis Valley 1989;129:295-311.
Diabetes
33. Haffner SM, Hazuda HP, Mitchell II diabetes in Mexican-Americans,
Wild et ai. MORTALITY
Study,
BD. Increased Diabetes Care.
439
Am J Epidemiol. incidence of type 1991;14:102-108.
34. Kannel WB, McGee DL. Diabetes and cardiovascular Framingham Study, JAMA. 1979;241:2035-2038
disease. The
35. Assman G, Schultz H. The prospective cardiovascular Munster (PRO CAM) study: Prevalence of hyperlipidemia in persons with hypertension and/or diabetes mellitus and the relationship to coronary heart disease, Am Heart J. 1988;116:1713-1724.
20. Gillum RF, Grant CT. Coronary heart disease in African-American populations. II. Risk factors, Am Heart J. 1982;104:852-864.
36. McMichael AJ, Haynes SC, Tyroler HA. Observations on the evaluation of occupational mortality data, J Occup Med. 1975;17:128-1 il.
21. Kittner SJ, White LR, Losonczy KG, Wolf PA, Hebel JR. AfricanAmerican-white differences in stroke incidence in a national sample. The contribution of hypertension and diabetes mellitus, JAMA. 1990; 264:1267-1270.
of coronary 37. Woo K-S, Donnan SP. Epidemiology the Chinese, Int J Cardiol. 1989;24:83-93.
22. Beckles CL, Miller GJ, Alexis SD, et al. Obesity in women in an urban Trinidadian community. Prevalence and associated characteristics, Int J Obesity. 1985;9:127-135. 23. Dawson DA. Ethnic differences 1985 National Health Interview 78:1X6-1329.
in female overweight: Data from the Survey, Am J Public Health. 1988;
24. Tofler GH, Stone PH, Muller JE, et al. Effects of gender and race on prognosis after myocardial infarcrion: Adverse prognosis for women, particularly African-American women, J Am Co11 Cardiol. 1987;9: 473.-482.
38. Bonita R, Stewart AW, Beaglehole R. International 1970-1985, Stroke. 1990;32:989-992, mortality:
arterial
disease in
trends in stroke
and other charac39. Miller GJ, Beckles CL, Maude GH, et ai. Ethnicitv teristics predictive of coronary heart disease in a developing community: Principal results of the St. James Survey, Trmidad, Inr J Epidemiol. 1989;18:808-817. 40. Hughes LO, Raval U, Rafter, EB. First myocardial Asians/whites, BMJ. 1989;298:1345.
rnfarction
in British
from rschaemic heart dis41. Balarajan R. Ethnic differences in mortality ease and cerebrovascular disease in England and Wales, BMJ. 1991; 302560-564.
25. Haywood LJ. Coronary heart disease mortality/morbidity and risk in African-Americans, II: Access to medical care, Am Heart J. 1984;108: 794 -796.
MA, Sidney S. The risk of hospital42. Klatsky AL, Tekawa I, Armstrong ization for ischemic heart disease among Asian Americans in northern California, Am J Public Health. 1994;84:1672- 1675.
I. Mortality among Hispanics 26. Shai D. Rosenwaike Chicago: An examination based on vital statistics Dis. 1987;40:445-451.
43. Sorlie PD, Rogot E, Johnson tics on the death certificate,
27. Sorlie PD, Backlund status in the United
in metropolitan data, J Chronic
E, Johnson NJ, Rogot E. Mortality States, JAMA. 1993;270:2464-2468.
by Hispanic
28. Rewers M, Shetterly SM, Baxter J, Marshall ]A, Hamman RF. Prevalence of coronary heart disease in subjects with normal and impaired glucose tolerance and non-insulin dependent diabetes mellitus in a biethnic Colorado population. The San Luis Valley Diabetes Study, Am J Epidemiol. 1992;135:1321-1330. 29. Goff DC Jr, Ramsey DJ, Labarthe DR, Nichaman MZ. Acute myocardial infarction and coronary heart disease mortality among Mexican Americans and non-Hispanic whites in Texas, 1980 through 1989, Ethnicity Dis. 1993;3:64-69. 30
Hanis CL, Americans 672.
Rerrell RE, Barton SA, et al. Diabetes among Mexican in Starr County, Texas, Am J Epidemiol. 1983;118:659-
31
Samet JM, Co&as DB, Howard CA, Skipper BJ, Hanis CL. Diabetes, gallbladder disease, obesity and hypertension among Hispanics in New Mexico, Am J Epidemiol. 1988;128: 1302-1311.
32. Hamman RF, Marshall of non-insulin-dependent
]A,
Baxter J, et al. Methods and prevalence diabetes mellitus in a biethnic Colorado
NJ. Validity of demographic characterisEpidemiology. 1992;3:181-184.
Stern MP. Myo44. Mitchell BD, Hazuda HP, HafItter SM, PattersonJK, cardial infarction in Mexican-Americans and non-Hispanic whites. The San Antonio Heart Study, Circulation. 199!;83:45-51. 45. Goff DC Jr, Ramsey DJ, Labarthe DR, Nichaman MZ. Greater case fatality after myocardial infarction among Mexican-Americans and women than non-Hispanic whites and women. ‘The Corpus Christi Heart Project, Am J Epidemiol. 1994;139:474-46 I. aspects 46. Young RF, Wailer JB, Kahana E. Racial and socioeconomic of myocardial infarction recovery: Studving confounds, Am J Prev Med. 1991;7:438-444. 47
Pappas G, Queen S, Hadden W, Fisher G. The mcreasing disparity in mortality between socioeconomic groups m the IJnited States, 1960 and 1986, N Engl J Med. 1993;329:103-.109.
48. Vital Statistics of the United States, 1988. v. It. Mortality, Part B. DHHS Publication No. 90-l 102. Washington, DC: US Government Printing Office; 1990. 49. Vital Statistics of the United States, 1988. v. Ii. Mortaiity, Part A. DHHS Publication No. 91-1101. Washington, DC’: US Government Printing Office; 1991.
Mortality from Coronary Heart 1985 to Groups in California, SARAH H. WILD, ANN N. VARADY,
Disease and Stroke for Six Ethnic
1990
MB, BCHIR, AMI LAWS, MD, MS, AND CHRISTOPHER
STEPHEN P. FORTMANN, D. BYRNE, MB, BCH, PHD
MD,
Coronary heart disease and stroke death rates were compared for six ethnic groups (non-Hispanic Chinese, Japanese, and Asian Indian) by sex and age (2.5 to white, Hispanic, African-American, census and 1985 to 1990 death 44, 45 to 64, 65 to 84, and 25 to 84 years old) using California data. African-American men and women in all age groups bud the highest rates of death from coronary heart disease, stroke, and all causes (except for coronary heart disease in the oldest men). Hispanics, Chinese, and Japanese in all age-sex groups had comparatively low death rates for coronary heart disease and stroke, although stroke was proportionally an important cause of death for Chinese and Japanese groups. Coronary heart disease was an important came of death for Asian Indians although death rates were generally not higher than those for other ethnic groups. Ethnic differences were most marked for women and younger age groups. Ann Epidemiol 1995;5:432-439. KEY WORDS:
Cerebrovascular
disorders, coronary disease, ethnic groups, mortality.
INTRODUCTION Ethnic differences in mortality from heart disease were described as early as 1931 when Schwab and Schulz (1) reported that deaths due to arteriosclerotic heart disease were 1.5 times more common in American whites than blacks. Further studies confirmed that variation exists between races in mortality from coronary heart disease (CHD) and stroke whether subjects remain in their native countries or migrate overseas (2-9). Many of these studies have been limited either to the comparison of only two ethnic groups or to the study of men (or both), and few studies performed in the United States included ethnic groups other than non-Hispanic whites and non-Hispanic blacks (subsequently referred to as whites and African-Americans, respectively). Furthermore most previous studies did not examine age-specific rates. Crude death rates give the impression of lower CHD rates in subpopulations with a larger proportion of young people (i.e., most ethnic minorities). The use of age-standardized rates for a large age range in
a population may also obscure the presence of important differences between
age groups.
From the Center for Research in Disease Prevention (S.H.W., S.P.F., A.N.V.), Division of General Internal Medicine (A.L., S.P.F.), and Falk Cardiovascular Research Center (C.D.B.), Stanford University School of Medicine, Stanford, CA. Address remint reauests to: Sarah H. Wild. MB. BChir. Eoidemioloev Unit, Department of’ Epidemiology and Po&ation Sci&&, L.ond& School of Hygiene and Tropical Medicine, Keppel __ Srreet. London WClE 7HT, Engla&. Received June 17, 1994; accepted December 7, 1994. Q 1995 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
Migration influences ethnic differences in mortality. For example, CHD risk is low for Japanese men in Japan, increases following migration to Hawaii, and increases further after migration to the US mainland, but remains below the CHD risk for white men in the United States (2, 3). The excess risk for CHD in Asian Indians over other ethnic groups may be exacerbated by migration to other countries (8). In contrast, the incidence of stroke is high in Japan and falls rapidly for Japanese people after migration to the United States (3, 9). An increasing proportion of the population of California and the United States is composed of ethnic minorities. In 1987 California received 26.1% of the total immigrants to the United States (10). According to the US Bureau of Census in 1988, the Hispanic population in California (approximately 80% of which are Mexican-Americans) is growing five times as fast as the population as a whole. In the 1990 California census 25.8% of the population was Hispanic and 57.2% was white. The proportions of African-Americans and Japanese in California remained stable between 1980 and 1990 and were 7 and 1.1% of the total population, respectively. The proportion of Chinese people in the state rose from 1.4% in 1980 to 2.4% in 1990. The Asian Indian population in California trebled in the decade prior to 1990 and came to represent 0.5% of the population. The total population of California as enumerated by censuses grew by over 6 million between 1980 and 1990 and was nearly 30 million people in 1990. Because an increasing proportion of the California and US populations is composed of ethnic minorities, it is important to quantify the mortality from CHD and stroke in 1047-2797/95/$9.50 SSDl 1047-2797(95)00058-F
AEP Vol. 5, NO. h
Wild et al. ETHNIC DIFFERENCES IN CHD AND STROKE M0RTALIl-Y
.Nowmber 1995: 432-439
433
TABLE 1. Population of California aged 25 to 84 years by sex for total population and six ethnic groups for 1980 and 1990 and median age of each subpopulation for 1990 1990 1980 Ethnic group
Median age (y)
Men
Women
%”
Men
Women
%”
Men
Women
Total White
6,667,810 4,802,551
7,143,078 5,186,283
100.0 72.3
9,004,684 5,686,514
1,004,607
1,018,824
14.7
1,912,701
100.0 63.5 10.4
‘,. ‘,:
Hispanic AfricanAmerican Chinese Japanese Asian Indian
9,293,248 5,931,094 1,813,802
32 ib 24
431,9.31 99,298 76,646 17,868
479,905 99,774 95,888 15,276
6.6 1.4 1.3 0.2
575,718 2 16,302 101,435 52,004
624,101 234,684 123,304 41,553
6.6 2.5 1.2 0.5
(_ ,\ \ Lit
20 ii 38 27
” The percent of the total population aged 25-84 comprised by each ethnic group (men and women combined).
these groups so that this information can be applied to the development of public health policies. Data from California death tapes and censuses provide an opportunity to simultaneously compare mortality rates for multiple ethnic groups with large sample sizes. Death certificate and census data are available for other states and for the entire United States but we limited the study to California because of the more marked and expanding ethnic diversity than in many other states. This study reports age-specific death rates from CHD and stroke by race, sex, and age in six ethnic groups in California from 1985 to 1990.
MATERIALS
AND
METHODS
Numbers of deaths with CHD (identified using International Classification of Diseases, 9th revision (ICD-9) classification numbers 410 to 4 14) and stroke (ICD-9 classification numbers 431 to 438) as the primary cause of death for six different ethnic groups (white, Hispanic, African-American, Chinese, Japanese, and Asian Indian) in California were obtained from death tapes for the years 1985 to 1990. The specified ethnic groups were chosen for the study either because of large population sizes or, in the case of the Asian Indian population, because previous studies outside the United States had revealed a high risk of CHD and stroke. The first year in which precise data regarding ethnicity were recorded on death certificates in California was 1985 and 1990 is the most recent year for which census data are available. Population sizes were calculated by linear interpolation between data collected in the 1980 and 1990 censuses. Ethnicity is self-reported on censuses; race is recorded on death certificates by the funeral director using state guidelines. The classification of race differs slightly between censuses and death tapes in that several small subpopulations (e.g., Bangladeshi, Pakistani, and Sri Lankan) are excluded from the group titled “Asian Indian” on the census but are in-
cluded in the “Indian” category on death tapes (which excludes American Indians). Age distributions vary within each ethnic group, with minority populations usually having a preponderance of younger persons, and comparison of crude death rates among ethnic groups may yield misleading results. Death rates in this study were calculated by stratifying the populations by sex and age (25 to 44, 45 to 64, 65 to 84, and 25 to 84 years) and by age standardization in 5-year age groups within each of these age groups, using the age distribution ofthe total population by sex in 1990 as the standard. Owing to the small numbers of deaths in some of the subpopulations, data from all years, 1985 to 1990, were combined and trends across the years were not examined. Standardized mortality ratios (SMRs) for each sex and age group were calculated by expressing as a percentage the age-standardized death rate from CHD or stroke in each ethnic group divided by the expected death rate (i.e., the comparable rate for the total population). Proportional mortality ratios (PMRs) for each sex and age group were calculated by dividing the proportion of deaths due to CHD or stroke in each ethnic group by the proportion of deaths due to CHD or stroke for the total population and are also expressed as a percentage. Calculation of the PMR is useful in that it does not use census data (thus preventing any miscalculations due to different reporting of race in death tape and census data) and it also provides an indication of the relative importance of CHD and stroke as causes of death in subpopulations. Using the Poisson assumption 95% confidence intervals were calculated for SMRs and PMRs for each sex and age group.
RESULTS Population sizes for persons between 25 and 84 years old in California in 1980 and 1990 and the percentage of each ethnic subgroup are given in Table 1, with the ethnic groups
434
AEP Vol. 5, No. 6 November 1995: 432-439
Wild et al. ETHNIC DIFFERENCES IN CHD AND STROKE MORTALITY
TABLE
2. Number of observed deaths, standardized mortality ratio (SMR) for coronary heart disease (CHD), stroke, and all causes of death, and proportional mortality ratio (PMR) for CHD and stroke for ages 25 to 84 by sex for total population and six ethnic groups in California, 1985 to 1990
SeX
Ethnic crow
CHD
PMR
SMR
No. of observed deaths Stroke
All causes
CHD
Stroke
All causes
CHD
Stroke
Total
Metl Women
123,164 82,720
26,447 30,002
542,301 405,899
100 100
100 100
100 100
100 100
100 100
White
Men Women
102,507 67,948
20,069 23,578
420,555 325,430
108 103
97 98
103 104
107 102
98 98
Hispanic
Men Women
8168 5645
2229 2185
50,901 30,978
63 70
79 74
71 68
71 89
90 95
African-American
Men Women
7308 6599
2323 2798
46,142 33,817
113 154
165 180
150 151
70 96
103 112
Chinese
Men Women
1260 679
503 432
6631 4379
55 53
100 91
64 64
84 76
156 133
Japanese
Men Women
702 377
232 219
3461 2688
53 49
84 81
58 60
89 69
137 110
Asian Indian
Men Women
258 106
28 43
743 362
92 79
53 90
56 48
153 144
77 161
listed in order of decreasing population size. The median age of each population is also listed for 1990 and reflects the fact that the age structure of the different populations varies greatly, probably as a result of both different birth rates and differential immigration. The median age of the Hispanic population in California was the lowest of all ethnic groups and larger proportions of older people were found in the white and Japanese populations than in other ethnic groups. Numbers of deaths, SMRs, and PMRs from CHD, stroke, and all causes for the age range 25 to 84 by sex and ethnicity are presented in Table 2. Despite the considerably smaller population size for African-Americans than for Hispanics, it is interesting to note that larger numbers of CHD and stroke deaths were found to occur in African-American women than Hispanic women. For CHD and stroke, SMRs were highest for African-American men and women but PMRs for African-Americans were either lower than those for the total population (for CHD) or only slightly elevated (for stroke), consistent with the high SMR for deaths from
all causes for African-Americans. PMRs for stroke were high in Chinese and Japanese men and women. Age-standardized death rates per 100,000 population for CHD, stroke, and all causes are listed by sex in Table 3. African-Americans had the highest death rates for CHD, stroke, and all causes of death in all age-sex groups, except for CHD in the oldest men. In Hispanic, Chinese, and Japanese groups the rates for each cause of death were lower than for African-Americans and whites. The ethnic differences are more marked among the youngest age groups than across the larger age range. Figure 1 presents SMRs and 95% confidence intervals for CHD for men and women by ethnicity and age group and indicates that ethnic differences were most marked for women and younger age groups, although confidence intervals tended also to be wider in these groups. Similar results, which are not shown, were found for stroke, with the SMR being particularly high for African-American women in the youngest age group. Figure 2 shows PMRs for CHD and 95% confidence intervals for men and women by ethnicity
TABLE 3. Age-standardized death rates per 100,000 population for coronary heart disease (CHD), stroke, other, and all causes of death for ages 25 to 84 by sex for total population and six ethnic groups in California, 1985 to 1990
Cause of death CHD Stroke Other All
Total
White
AfricanAmerican
Hispanic
Chinese
Japanese
Asian Indian
M
W
M
W
M
W
M
W
M
W
M
W
M
W
280 62 858 1200
139 50 511 700
302 60 881 1243
143 49 534 726
175 49 632 856
97 37 344 478
316 102 1382 1800
214 91 755 1059
155 62 555 773
73 46 327 446
146 52 494 693
67 41 312 420
258 33 376 668
110 45 180 335
M, men; W, women.
AEP Vol. 5, No. 6 Notwnher 1997: 452-439
SMR
Wild
et ai.
435
ETHNIC DIFFERENCES IN CHD AND STROKE MORTAL:TV
and
95%CI
for
men
350 300 250 200 150 100 50 0
Age (years) SMR
25-44 and
95%CI
for
45-64
65-84
45-64
65-84
women
350 300 250 200 150 100 50 0
Age (years)
25-44
FIGURE 1. Standardized mortality ratio (SMR) and 95% confidence intervals (CI) for coronary heart disease (Cl-ID) for men (toe) and women (bottom) in California,
1985 to 1990, by ethnicity and age.
and age group. Although Asian Indians had the lowest death rates from all causes (see Table 3) of all the ethnic groups studied, PMRs for CHD were higher for Asian Indians than for other ethnic groups. CHD death rates in Asian Indian men were comparable to those for white men (see Table 3) and yet PMRs for CHD for Asian Indian men of all ages were considerably higher than for white men (see Figure 2, top). PMRs for CHD for middle-aged and older Asian Indian women were also significantly higher than for white women. Ethnic differences between PMRs for stroke in age-specific groups were less marked than for CHD (re-
sults not shown) but were generally higher for Chinese and Japanese in all age-sex groups than for other ethnic groups.
DISCUSSION The major findings of this study are that age-specific rates for CHD, stroke, and all-cause mortality in California were highest for African-Americans for all age-sex groups (except for CHD among the oldest men). CHD and stroke death rates in all Hispanic, Chinese, and Japanese age-sex groups
AEP Vol. 5, No. 6 November 1995: 432-439
Wild er al. ETHNIC DIFFERENCES IN CHD AND STROKE MORTALITY
436
PMR
and
95%CI
for
men
for
women
600 500 400 300 200 100 0
25-44
Age (years) PMR
and
95%CI
45-64
65-84
45-64
65-84
600 500 400 300
r
......... ......... .........
Age (years)
25-44
FIGURE 2. Proportional mortality ratio (PMR) and 95% confidence intervals (CI) for coronary heart disease (CHD) for men (top) and women (bottom) in California, 1985 to 1990, by ethnicity and age.
were low in comparison to those for whites and AfricanAmericans. Although the absolute rates for CHD deaths were low in Asian Indians, total mortality was also low, and a higher proportion of all deaths in this ethnic group was due to CHD compared to the other ethnic groups. These findings underline the importance as causes of death of CHD and stroke for whites and African-Americans, of CHD for Asian Indians, and of stroke for Chinese and Japanese populations and reveal that ethnic differences tend to be more marked for women and younger age groups. We found CHD death rates were higher for AfricanAmerican than white men and women at all ages studied except the oldest age group for men. Our findings contrast
with some previous studies that found prevalence of CHD to be higher in white men than African-American men and similar in white women and African-American women (6, ll-13), and with the 30-year follow-up of the Charleston Heart Study which concluded that the mortality rates from CHD for whites and African-Americans were not significantly different (14). It should be noted, however, that these conclusions were drawn from studies using a variety of methods that differed from ours; for example, the Charleston Heart Study was a closed cohort study that represented the age and ethnic distribution of the particular population studied in 1960. The 1986 Report of the Secretary’s Task Force on African-American and Minority Health found
AEP Voi. 5, No. 5 November 1995: 432.-439
that CHD mortality rates were similar among AfricanAmerican men and white men but were higher for AfricanAmerican women than white women (15). US statistics for 1986 revealed that age-adjusted death rates for ischemic heart disease overall were lower in African-American men than white men but higher for African-American women than white women (16). In the younger age groups (up to age 65 in men and age 75 in women), however, death rates from ischemic heart disease were higher in both AfricanAmerican men and women, compared to whites (16). We used the more conventional group of ICD codes (410 to 413) to describe CHD. The code 429.2, which denotes hypertensive disease, is included in some studies and we believe that the inclusion of this code in the present study would not have affected the conclusions and may indeed have extended the differences between African-Americans and whites. Reasons for the discrepancies among African-American/ white differences in previous studies have been reviewed (17, 18) and include the difference between crude, agestandardized, and age-specific rates. Our results show that ethnic differences appear much less marked for the age range of 25 to 84 years than for the 25- to 44-year age group and thus indicate the importance of studying age-specific death rates. The findings of our study concur with those of other studies that showed stroke death rates to be much higher for African-Americans than for whites (19). This effect was particularly marked in this study for women aged 25 to 44 for whom the stroke death rate was 5.5 times higher for African-Americans than whites. The increased CHD mortality for African-Americans may be explained by differences in prevalence of certain risk factors; for example, there is a higher prevalence of hypertension and diabetes mellitus in African-Americans than whites (20). However, onestudy found that adjustment for age, hypertension, and diabetes mellitus did not fully explain the excess incidence of stroke in African-Americans over whites (21). Obesity is prevalent in African-American women and is associated with a cluster of risk factors, which may partially account for an increased risk of CHD (22, 23). Other factors that may influence the excess mortality include lower sociofrom all causes for African-Americans economic status, poor survival rates (24), differential access to and seeking of health care (25), the presence of other diseases, and possibly other physiologic, psychological, and behavioral differences. Hispanics in various parts of the United States have been shown to have a lower prevalence of CHD than do whites, in spite of an apparently higher prevalence of CHD risk factors (7, 26-29). Differences in mortality exist between subgroups of the Hispanic population (26) but we did not investigate these because the majority (80% in the 1990 census) of Hispanics in California are Mexican-Americans. Non-insulin-dependent diabetes mellitus (NIDDM) is more
‘Y&idet ;ri
437
ETHNIC DIFFERENCES IN CHD AND STROKE MCXTALITl
common in Hispanics than whites (30-33) and is known to be a major risk factor for CHD in whites (34,35). However, a low prevalence of CHD has been found in Hispanics with NIDDM, particularly in men (28), and this paradox remains unexplained. The low death rates for CHD, stroke, and all causes of death in Hispanics in this study are thus consistent with findings of studies elsewhere in the United States. The low mortality from all causes (except homicide) for Hispanics compared to whites in the United States may be due, at least in part, to a combination ofthe “healthy migrant effect” (a selection process analogous to the “healthy worker effect” whereby recent migrants tend to be healthier than more established populations (36)), underreporting of certain conditions, incorrect recording of ethnicity on death certificates, and the possibility that Mexican-born persons in the United States tend to return to Mexico when they become older or ill (26). Chinese and Japanese populations have a reduced risk of CHD when compared to whites (9, 37). However, Japan has had the highest stroke rates in the world, although in the two decades leading up to 1985 there was a rapid fall in stroke rates in Japan (9, 38). The low risk of CHD compared to whites was found to persist in Japanese-Americans (3). Our study showed death rates to be iow in Chinese and Japanese populations in California for both CHD and stroke, particularly at younger ages. However, stroke was proportionally an important cause of death in Chinese- and Japanese-Americans, although this can, :n part, be explained by the low overall mortality in these ethnic groups. Asian Indians have been reported to have higher odds ratios for developing and dying from CHD than do Chinese, Africans, and Europeans (4,8,39-41) and Asian-Americans born in India and Pakistan have been found to be at high risk of coronary disease hospitalization (42). The excess risk of CHD seems to apply to migrants from all parts of the Indian subcontinent and can not be fully explained by the increased prevalence of established risk factors after migration (8, 39). In contrast to these reports, the death rate for CHD for Asian Indians in California in this study was not significantly different from that of white men. The discrepancy in classification of Asian Indian subgroups between the census and death tapes would, if anything, result in an overestimation of death rates in this ethnic group and is therefore not responsible for this unexpected finding. The population of Asian Indians in California has trebled in the years 1980 to 1990 and it is likely that these recent migrants are generally healthier than are more established populations. This theory is supported by rhe fact that the mortality of Asian Indians in California from all causes is the lowest of all ethnic groups in this study. The “healthy migrant effect” and the effect of different methods of data collection used in censuses and death tapes can be overcome by examining the proportion of all death:; that are due to
438
Wild et al. ETHNIC DIFFERENCES
IN CHD
AND
STROKE
AEP Vol. 5, No. 6 November 1995: 432-439
MORTALITY
a specific cause, that is, PMR. PMRs for CHD were high for all age-sex groups of Asian Indians (with the exception of the women aged 25 to 44); this finding indicates the importance of CHD as a cause of death for Asian Indians. Stroke mortality in Asian Indian men has also been reported to be higher than the average for England and Wales (41); our study found no consistent difference between death rates or PMRs for stroke for Asian Indians compared to whites. This finding may partly be due to the fact that there were only a small number of stroke deaths in the Asian Indian population studied. Interpretation of the findings of this study relies on the accuracy of the data recorded on the death certificates and we assumed that no systematic differences exist among races in recording of race or cause of death. It is possible that the low death rates found in all ethnic minorities except African-Americans may, in part, reflect misclassification of race on death certificates. However, a study of the validity of demographic characteristics on death certificates found that the agreement between race recorded on the death certificate and the Census Bureau’s population surveys was 99.4% overall, 98.7% for Hispanic origin, and 82.4% for Asian/Pacific Islanders (43). Mortality rates occur as a function ofboth incidence of disease and case fatality, and ethnic differences may influence both of these factors. Evidence exists to suggest that lower incidence of myocardial infarction (rather than a lower case fatality) is more likely to cause the comparatively low mortality from cardiovascular disease in Mexican-Americans (44) and a recent study found that case fatality after myocardial infarction was actually greater among Mexican-Americans than among whites (45). Socioeconomic status data were not available for subjects in this study and socioeconomic status is known to have an important influence on mortality from heart disease (46). Differences in socioeconomic status may account for some of the observed ethnic differences, especially between African-Americans and other ethnic groups. Whether a socioeconomic gradient exists in the United States in ethnic groups other than whites and African-Americans (for whom a reverse relationship is known to exist between socioeconomic status and mortality (47)) is not known. We have shown the importance of examining age-specific rates to quantify ethnic differences and the presence of major differences in mortality from CHD and stroke for several minority populations. CHD is the leading cause of death among US residents (48,49) regardless of ethnic origin, and is a major public health problem. As a consequence it is imperative that attempts be made to identify and reduce risk in all populations. As the nonwhite population of the United States continues to grow, there is a greater need for studies of risk factors in groups other than white middleaged men who have, to date, provided the basis for the majority of the research into CHD. Research into ethnic differences is required not only to facilitate health care plan-
ning but also to investigate the relative importance of risk factors for CHD and stroke in population subgroups and to enable the development of appropriate primary and secondary prevention programs.
This work wassupportedby
Public Health Service grant HL 21906 from the National Heart, Lung, and Blood Institute. Sarah H. Wild was supported in part by the Stanford University Dean’s Postdoctoral Fellowship. Christopher D. Byrne was supported by the Peel Medical Research Trust and the Parke Davis/Cambridge University International exchange fellowship. The comments of Dr. R. Gillum and Dr. P. McKeigue on an earlier version of the manuscript are acknowledged with gratitude.
REFERENCES I. Schwab EH, Schulz VE. The incidence of heart disease and of the etiological types in a Southern dispensary, Am Heart J. 1931;7:223234. 2. Gordon T. Mortality experience among the Japanese in the United States, Hawaii and Japan, Public Health Rep. 1957;72:543-553. 3. Marmot MG, Syme SL, Kagan A, Kate H, Cohen JB, Belsky J. Epidemiologic studies of coronary heart disease and stroke in Japanese men living in Japan, Hawaii and California: Prevalence of coronary and hypertensive heart disease and associated risk factors. Am J Epidemiol. 1!$5;102:514-525. heart disease in seven racial groups in Singapore, 4. Muir CS. Coronary Br Heart J. 1960;22:45-53. of cardiovascular disease in India. II. Isch5. Padmavati S. Epidemiology emit heart disease, Circulation. 1962;25:711-717. infarction in 6. Weisse AB, Abiuoso PD, Thind IS. Acute myocardial Newark, NJ: A study of racial incidence, Arch Intern Med. 1977;137: 1402-1405. 7. Markides KD, Coreil J. The health of Hispanics in the south-western United States: An epidemiologic paradox, Public Health Rep. 1986; 101:253-265. PM, Miller GJ, Marmot MG. Coronary 8. McKeigue South Asians overseas: A review, J Clin Epidemiol.
heart disease in 1989;42:597-609.
T, Komachi Y, Inada H, et al. Trends for coronary 9. Shimamoto disease and stroke and their risk factors in Japan, Circulation. 79:503-515.
heart 1989;
and Naturalization Service. 1987 Statistical Yearbook of 10. Immigration the Immigration and Naturalization Service. Washington, DC: US Government Printing Office; 1988. 11. Keil JE, Loadholt CB, Weinrich MC, Sandifer SH, Boyle E Jr. Incidence of coronary heart disease in African-Americans in Charleston, South Carolina, Am Heart J. 1984;108:779-786. 12. Langford HG, Oberman A, Borhani NO, Entwisle G, can-American-white comparison of indices of coronary and myocardial infarction in the stepped-care cohort of sion Detection and Follow-up Program, Am Heart J. 801.
Tung B. Afriheart disease the Hyperten1984;108:797-
13. McDonough JR, Hames CG, Stulb SC. Coronary heart disease among Negroes and whites in Evans County, Georgia, J Chronic Dis. 1965; 18:443-468. 14. Keil JE, Sutherland SE, Knapp RG, Lackland DT, Gazes PC, Tyroler HA. Mortality rates and risk factors for coronary disease in AfricanAmericans as compared with white men and women, N Engl J Med. 1993;329:73-78. 15. US Department of Health and Human Services. Executive summary. In: Report of the Secretary’s Task Force on African-American and
AEP Vol. 5, No. C ?Jovemher1995: 4 12-431)
ETHNIC
Minority Health. v. 1. DHHS Publication Washington, DC: US Government Printing
No. 186-620-638:40716. Office, 1986:llO.
16. National Center for Health Statistics. Vital Statistics of the United States, 1986. v. II. Mortality, Part A. DHHS Publication No. (PHS) 89-1101. Washington, DC: US Government Printing O&e; 1989. populations. 17. Gillum RF. Coronary heart disease in African-American I. Mortality and morbidity, Am Heart J. 1982;104:839-851. 18. Cooper RS, Ghali JK. Coronary heart disease: African-Americanwhite differences, Cardiovasc Clin. 1991;21:205-225. 19. Gillum
RF. Stroke
in African-Americans,
Stroke.
1988;19:1-9.
DIFFERENCES
IN CHD
AND
STROKE
population. The San Luis Valley 1989;129:295-311.
Diabetes
33. Haffner SM, Hazuda HP, Mitchell II diabetes in Mexican-Americans,
Wild et ai. MORTALITY
Study,
BD. Increased Diabetes Care.
439
Am J Epidemiol. incidence of type 1991;14:102-108.
34. Kannel WB, McGee DL. Diabetes and cardiovascular Framingham Study, JAMA. 1979;241:2035-2038
disease. The
35. Assman G, Schultz H. The prospective cardiovascular Munster (PRO CAM) study: Prevalence of hyperlipidemia in persons with hypertension and/or diabetes mellitus and the relationship to coronary heart disease, Am Heart J. 1988;116:1713-1724.
20. Gillum RF, Grant CT. Coronary heart disease in African-American populations. II. Risk factors, Am Heart J. 1982;104:852-864.
36. McMichael AJ, Haynes SC, Tyroler HA. Observations on the evaluation of occupational mortality data, J Occup Med. 1975;17:128-1 il.
21. Kittner SJ, White LR, Losonczy KG, Wolf PA, Hebel JR. AfricanAmerican-white differences in stroke incidence in a national sample. The contribution of hypertension and diabetes mellitus, JAMA. 1990; 264:1267-1270.
of coronary 37. Woo K-S, Donnan SP. Epidemiology the Chinese, Int J Cardiol. 1989;24:83-93.
22. Beckles CL, Miller GJ, Alexis SD, et al. Obesity in women in an urban Trinidadian community. Prevalence and associated characteristics, Int J Obesity. 1985;9:127-135. 23. Dawson DA. Ethnic differences 1985 National Health Interview 78:1X6-1329.
in female overweight: Data from the Survey, Am J Public Health. 1988;
24. Tofler GH, Stone PH, Muller JE, et al. Effects of gender and race on prognosis after myocardial infarcrion: Adverse prognosis for women, particularly African-American women, J Am Co11 Cardiol. 1987;9: 473.-482.
38. Bonita R, Stewart AW, Beaglehole R. International 1970-1985, Stroke. 1990;32:989-992, mortality:
arterial
disease in
trends in stroke
and other charac39. Miller GJ, Beckles CL, Maude GH, et ai. Ethnicitv teristics predictive of coronary heart disease in a developing community: Principal results of the St. James Survey, Trmidad, Inr J Epidemiol. 1989;18:808-817. 40. Hughes LO, Raval U, Rafter, EB. First myocardial Asians/whites, BMJ. 1989;298:1345.
rnfarction
in British
from rschaemic heart dis41. Balarajan R. Ethnic differences in mortality ease and cerebrovascular disease in England and Wales, BMJ. 1991; 302560-564.
25. Haywood LJ. Coronary heart disease mortality/morbidity and risk in African-Americans, II: Access to medical care, Am Heart J. 1984;108: 794 -796.
MA, Sidney S. The risk of hospital42. Klatsky AL, Tekawa I, Armstrong ization for ischemic heart disease among Asian Americans in northern California, Am J Public Health. 1994;84:1672- 1675.
I. Mortality among Hispanics 26. Shai D. Rosenwaike Chicago: An examination based on vital statistics Dis. 1987;40:445-451.
43. Sorlie PD, Rogot E, Johnson tics on the death certificate,
27. Sorlie PD, Backlund status in the United
in metropolitan data, J Chronic
E, Johnson NJ, Rogot E. Mortality States, JAMA. 1993;270:2464-2468.
by Hispanic
28. Rewers M, Shetterly SM, Baxter J, Marshall ]A, Hamman RF. Prevalence of coronary heart disease in subjects with normal and impaired glucose tolerance and non-insulin dependent diabetes mellitus in a biethnic Colorado population. The San Luis Valley Diabetes Study, Am J Epidemiol. 1992;135:1321-1330. 29. Goff DC Jr, Ramsey DJ, Labarthe DR, Nichaman MZ. Acute myocardial infarction and coronary heart disease mortality among Mexican Americans and non-Hispanic whites in Texas, 1980 through 1989, Ethnicity Dis. 1993;3:64-69. 30
Hanis CL, Americans 672.
Rerrell RE, Barton SA, et al. Diabetes among Mexican in Starr County, Texas, Am J Epidemiol. 1983;118:659-
31
Samet JM, Co&as DB, Howard CA, Skipper BJ, Hanis CL. Diabetes, gallbladder disease, obesity and hypertension among Hispanics in New Mexico, Am J Epidemiol. 1988;128: 1302-1311.
32. Hamman RF, Marshall of non-insulin-dependent
]A,
Baxter J, et al. Methods and prevalence diabetes mellitus in a biethnic Colorado
NJ. Validity of demographic characterisEpidemiology. 1992;3:181-184.
Stern MP. Myo44. Mitchell BD, Hazuda HP, HafItter SM, PattersonJK, cardial infarction in Mexican-Americans and non-Hispanic whites. The San Antonio Heart Study, Circulation. 199!;83:45-51. 45. Goff DC Jr, Ramsey DJ, Labarthe DR, Nichaman MZ. Greater case fatality after myocardial infarction among Mexican-Americans and women than non-Hispanic whites and women. ‘The Corpus Christi Heart Project, Am J Epidemiol. 1994;139:474-46 I. aspects 46. Young RF, Wailer JB, Kahana E. Racial and socioeconomic of myocardial infarction recovery: Studving confounds, Am J Prev Med. 1991;7:438-444. 47
Pappas G, Queen S, Hadden W, Fisher G. The mcreasing disparity in mortality between socioeconomic groups m the IJnited States, 1960 and 1986, N Engl J Med. 1993;329:103-.109.
48. Vital Statistics of the United States, 1988. v. It. Mortality, Part B. DHHS Publication No. 90-l 102. Washington, DC: US Government Printing Office; 1990. 49. Vital Statistics of the United States, 1988. v. Ii. Mortaiity, Part A. DHHS Publication No. 91-1101. Washington, DC’: US Government Printing Office; 1991.