CVD in Asian Americans: Are There Disparities and Are They Important

In the National Heart, Lung, and Blood Institute (NHLBI) description of the topic of "Novel Methods of Monitoring Health Disparities" to be supported under the 2009 Request for Applications (RFA) for Grand Opportunities proposals, the following statement is made: "Population disparities in health and mortality have increased in the United States since the 1980s, with increases in mortality and poor health being most pronounced among the most disadvantaged many of whom are members of nonwhite minority subpopulations."[1] Asian Americans, as a group, however, have been considered to be a "model minority" to whom this generalization did not apply.[2] In general, studies of Asian Americans have treated them as a large, homogeneous group. Although the genetic admixture of most Asian American subgroups with whites is currently much more limited than in blacks and Hispanics, as pointed out in the manuscript by Palaniappan et al., within the Asian American population there is substantially more geographic, ethnic, cultural, and genetic diversity than is commonly recognized. The data on the health of the various components of this population are even more limited than that for Hispanics and African Americans.[3] Among Asian American populations, there appear to be striking, not fully understood disparities in the risk of cardiovascular disease (CVD). Abnormalities in some risk factors, such as glucose metabolism and type 2 diabetes, appear to be much more markedly influenced by the adoption of a "western" lifestyle in nonwhite immigrants than the effects of this lifestyle in whites.[4]

Overall, the causes of ethnic disparities in CVDs and their trends over time are poorly understood. Disparities may be due to differences in the prevalence of traditional risk factors such as diabetes, smoking, hypertension, and obesity, as well as dietary factors. Most involve the interaction between genetic and environmental contributors. Limited access to health care, socioeconomics, and culture may also enhance some differences. Nevertheless, as pointed out in the Palaniappan et al. manuscript, the Asian American differences can not be wholly attributed to differences in economic status or obesity.[3] However, the stresses of the current economic crisis may worsen some health disparities. Thus, variations in the potential for health care reform and the question of which areas such reforms would be most effective, are raised.

One factor that receives notably insufficient attention in most reports on health in Asian Americans is acculturation, partially because it is difficult to measure adequately. In truth, variation in stages of acculturation is so important that it may render many reported comparisons between Asian subgroups, as well as comparisons with other U.S. populations, difficult to decipher.

Although outlined in detail by Palaniappan et al.,[3] there have been two major waves of Asian American immigration into the United States. There was a large inflow of Asian American immigrants into the United States, the majority of which were Chinese and Japanese, beginning in the early 1800s and ending in the early 1900s. These individuals were largely poor and were brought in to perform hard labor in agriculture and construction. Many families of these original immigrants have done well economically and are well-established members of the middle and upper middle class in this country. Since the 1950s, a more economically varied group of Asians, from a wider array of Asian countries and socioeconomic backgrounds, have immigrated to the United States. Many came from countries in southern Asia. Some other groups, such as those from the Philippines, followed slightly different immigration patterns. Asian subgroups have had variable acculturation into an American lifestyle, as well as variations in ages, times, and generations of immigration. Thus, there are wide variations in current acculturation patterns among those from different subgroups and Asian countries. Palaniappan et al. give a number of examples of changes in risk and health associated with acculturation.[3]

There is evidence that, at least for some groups, later generations of fully acculturated Asian Americans may have very different health experiences than the first generation immigrants. This was well documented in the Honolulu Heart Program (HHP), a longitudinal follow-up of >8,000 Japanese American men.[5,6] For example, these first and second generation Japanese American men in Hawaii appeared to be healthier, have higher levels of function, and a longer life expectancy [7] and lower CVD rates [6] than other Americans in the mid-twentieth century. This documented relative good health contributed to the difficulty the HHP investigators experienced in obtaining funding to follow subsequent generations of Japanese Americans, so far less is known about the third and fourth generation Japanese American immigrant's health. Studies of several small groups of HHP Japanese American offspring, some with Japanese comparison groups in Japan, have been carried out. These have confirmed cardiovascular risk factors in the third generation Japanese American immigrants are becoming more similar to those in whites.[8,9] One such study of subclinical atherosclerosis indicates that 40 to 49 year old third generation Japanese offspring of the HHP cohort have as much or more severe atherosclerosis, as measured by Electron Beam Computed Tomography (EBCT), than a similarly aged white comparison group in Pittsburgh.[9] In addition, they have three times the rate of significant coronary calcification than does a Japanese comparison group in Japan.[10] This is despite a 50% smoking rate in the genetically very similar comparison group in Japan. The Japanese Americans were more obese and had much higher rates of diabetes, while both the Japanese in Japan and Japanese Americans, in contrast to their low cholesterol fathers, had similar serum cholesterol levels to whites. Despite extensive analysis of many traditional and nontraditional risk factors, no definitive explanation of these differences in atherosclerosis has yet been found. Understanding the causes of this difference could lead to factors that could be used to further reduce the incidence of CVD worldwide.

The combination or very different patterns of immigration among Asian subgroups, differences in culture, lifestyle, and genetic background, as well as profound changes in cardiovascular risk with increasing acculturation, means that most past and many present studies that aggregate all Asians, recent and established immigrants, as well as all acculturation levels, in analysis groups, are virtually uninterruptible as comparison groups. Their only utility is to characterize the health of the specific individuals in the particular location and study and the results cannot be generalized outside that study group to others of the same ethnicity.

Available data indicate there is a significant potential for an epidemic of diabetes and CVD and thus an acceleration of disparities in Asian American populations, as well as in these same groups, in their countries of origin.[11,12] If social and political policies slow immigration of the young into the United States, as is proposed by many, as the whole United States population continues to age and second and third generation immigrants become fully Americanized, there are likely to be significant effects on our economy. As the population inevitably rapidly ages, the average chronic disease burden will significantly increase and the workforce supporting that burden will become proportionately smaller in comparison to the current population age structure.

The current rapidly changing Asian American environment offers the possibility for studying a unique natural experiment that may be lost if we delay starting studies to examine it. Because the same health conditions are now being studied by governments in many Asian countries, extension of the area of study to the countries of origin through innovative collaborative studies, as has been done with the HHP offspring, at little cost to the United States taxpayer, offers a novel method for extending our observations into areas of the risk factor and disease distribution not easily studied in United States populations alone. For the large portion of the U.S. population that is Asian, there is no adequate, broad-based study in place to monitor health trends closely. Developing and using a network of scientists with expertise in the study of the Asian populations, as well as identifying existing data resources that can be pooled and analyzed to understand more about atherosclerotic diseases in this important population, is critical. Such a network can more rapidly provide a greatly increased understanding of social, biological, genetic, demographic, and economic influences on cardiovascular health. High-quality research generated by such a network working closely with the American Heart Association, National Institutes of Health, and other private and government entities could play a critical role in informing and evaluating public policy and clinical practice, both for Asian Americans and for the entire United States population, as well as in developed and developing countries in Asia and the rest of the world.

The availability of high-quality ethnic specific population data derived from carefully designed epidemiological and socioeconomic examinations and analyses will be essential for efforts to design changes in the U.S. health care system and in public health interventions that will reduce health disparities. A systematic strategy for monitoring key risk factors and the effects of health-related policies and reforms are urgently needed. The monitoring should be defined not only by geography but also by socioeconomic or sociocultural characteristics.