Non-Insulin-Dependent Diabetes Mellitus in Minorities in the United States

For some time, diabetes specialists have recognized that noninsulin-dependent diabetes mellitus is more prevalent in minority populations [1-12]. Recent information also shows increased complications and mortality from diabetes. We review the available literature on prevalence, incidence, complications, mortality, and interventions in black persons, Hispanic persons, Native Americans, and Asians and Pacific Islanders in the United States. Methods In June 1994, we searched the MEDLINE data-base through the PlusNet search system from 1976 to the date of the search. Using the key words noninsulin-dependent diabetes, African Americans, blacks, Hispanic, Mexican Americans, Native Americans, Asians, Pacific Islanders, minorities, socioeconomic status, acculturation, genetics, diet, complications, mortality, treatment, and intervention (lifestyle or medication), we found 268 unduplicated articles. In February 1996, we repeated the search and added the key words Asian and Pacific Islander; 22 more articles were identified. Ethnic-specific data were also included from Diabetes in America [13]. Several searches were done using noninsulin-dependent diabetes mellitus, a key word for one of the minority groups, and one each of the other key wordsfor example, noninsulin-dependent diabetes mellitus and African Americans and socioeconomic status. Articles cited in the original articles or encountered during the writing of this manuscript were also included. Only articles that discussed incidence, prevalence, complications, mortality, risk factors, or interventions were included. Papers on the basic physiology of obesity or diabetes or articles that did not include minority-specific data were not included. Data on diabetes-related complications and mortality, lifestyles, socioeconomic status, acculturation, and access to health care are scarce for some minority groupsparticularly Asians and Pacific Islanders, Arab-Americans, and other ethnic subgroups (such as Puerto Ricans, Cubans, and specific Native American tribes). Further, few prospective studies have assessed the incidence of noninsulin-dependent diabetes mellitus and associated risk factors. Finally, few studies have provided data on white persons for comparison. Prevalence and Incidence of Diabetes Most minority groups in the United States have higher rates of noninsulin-dependent diabetes mellitus than do white persons [2-47] (Table 1). The 1976-1980 National Health and Nutrition Examination Survey (NHANES II) [12] found the total prevalence of diabetes in black persons (diagnosed and undiagnosed) to be 1.5 times greater than that of white persons. Other estimated prevalences for black persons range from 1.4 to 2.2 times greater than the prevalences for white persons [13, 14]. The 1976 National Health Interview Survey [15] and a recent study of U.S. Army veterans [16] confirm this increased risk for black persons even after controlling for an increased prevalence of obesity. Table 1. Prevalence of Diabetes in the United States All Hispanic groups studied to date have a greater prevalence of diabetes than do white persons [17-23]. Data from the 1982-1984 Hispanic Health and Nutrition Examination Survey (HHANES) [17] show that, among Hispanic persons living in the United States, the prevalence of noninsulin-dependent diabetes mellitus is greatest for Puerto Ricans and Hispanic persons living in the southwest and is lowest for Cubans (Table 1). Epidemiologic studies in Texas (Laredo [18], Starr County [19], and San Antonio [20]) and in Colorado [21] and New Mexico [22], show a prevalence of diabetes in Hispanic persons that is two to five times higher than that in non-Hispanic persons (Table 1). The excess of diabetes in the Mexican-American population persists even when the greater overall and centralized obesity rates of the Mexican-American population when compared with those of white persons are considered [23]. Native Americans comprise more than 500 tribal organizations; in the 1990 census, about 1.9 million persons identified themselves as an American Indian or Alaska native [24]. High prevalences of diabetes among most Native American tribes have been reported [25-37]. The Pima tribe in Arizona has one of the highest rates in the world [25]. Variation of rates among tribes may be due to ascertainment methods (many rates are derived from clinical settings) or to true variation caused by genetic differences [8, 24-37]. Indian Health Service data indicate that the overall prevalence is 2.8 times the overall U.S. rate [8]. Only Alaska natives (Eskimo and Indian) have been shown to have prevalences less than or slightly greater than the overall rates of diabetes in the United States, but evidence suggests that the prevalence may be increasing in these groups [35, 37]. Asian Americans and Pacific Islander Americans are a diverse group with more than 20 population groups [38]. The Seattle Japanese-American Community Diabetes Study [9, 10] found the prevalence of diabetes to be higher than that reported for the U.S. white population [12]. Filipinos had the highest prevalence of diabetes among the four largest ethnic Asian groups in Hawaii (Chinese, Filipino, Japanese, and Korean); all groups had higher prevalences than those of white persons [11]. In one pilot study of Arab Americans [39], the rates were also high. Although the prevalence of noninsulin-dependent diabetes mellitus is consistently higher in minorities, it is possible that prolonged durationand not an increased incidenceof noninsulin-dependent diabetes mellitus could be the explanation. Few incidence studies have been done, but thus far, incidence rates in the United States have been found to be higher in black persons [40], Mexican Americans [41, 42], the Pima tribe [43, 44] and Japanese Americans [45] than in white persons. Impaired glucose tolerance and gestational diabetes are recognized risk categories for progression to diabetes. Black persons, Hispanic persons, Native Americans, and Asian Americans have been shown to have higher rates of impaired glucose tolerance than white persons [2, 5-610, 46, 48]. Black persons, Hispanic persons, and Native Americans also have higher rates of gestational diabetes [49-53]. However, rates of gestational diabetes in Asians are similar to those of white persons in the United States [54]. Prevalence and Incidence of Complications and Mortality Table 2 lists the rates of complications between the primary minority subgroups and white persons. Table 2. Diabetes Complication Rates in Minorities and White Persons* Nephropathy Diabetic end-stage renal disease rates have been shown to be higher in all U.S. minority groups than in white persons [55-63]. The rate in black persons is 3.2 to 6.6 times higher than that in white persons; this value is reduced to 2.6 after adjustment for the underlying increased prevalence of diabetes [55]. After adjustment for systolic blood pressure, income, age, and other potential risk factors, black persons still had a 63% higher risk for developing end-stage renal disease [59]. Mexican Americans had a rate ratio for end-stage renal disease of 2.9 to 7 compared with white persons [60]. However, after adjustment for prevalence of diabetes, Mexican Americans no longer had an excess risk [64]. According to Medicare and United States Renal Data System data [61, 62], the age-adjusted incidence of diabetic end-stage renal disease is 6.3 times higher for Native Americans than for white persons in the United States; data from specific Native American tribes confirm this finding [65-69]. End-stage renal disease is the leading cause of death among diabetic Pima Indians, with incidence rates similar to those reported among persons with insulin-dependent diabetes mellitus [70]. Asians and Pacific Islanders had the lowest incidence of end-stage renal disease among minority groups, but this rate were still higher than those of white persons [62]. The mixture of insulin-dependent diabetes mellitus and noninsulin-dependent diabetes mellitus end-stage renal disease substantially differs between minorities and white persons. In a cohort study of diabetic end-stage renal disease in Texas [64], 93% of Mexican Americans with diabetic end-stage renal disease had noninsulin-dependent diabetes mellitus compared with 84% of black persons and 60% of white persons. Similarly, Cowie and colleagues [55] reported that 73% of cases of diabetic end-stage renal disease among black persons and 42% of cases among white persons were secondary to noninsulin-dependent diabetes mellitus. Survival among minority persons with diabetic end-stage renal disease who are treated with hemodialysis is better than for white persons [62, 71-73]. The reason of this survival advantage is unclear. Minorities receive transplants less often, leaving minority patients who are eligible for transplantation on dialysis [62, 74]. In addition, black persons have lower rates of voluntary withdrawal from dialysis than white persons [75]. It is not known whether this phenomenon occurs in other minorities. With regard to incipient nephropathy, Hispanic persons, black persons, and Native Americans have been found to have higher rates of proteinuria than do white persons [76-82]. Although fewer data are available for microalbuminuria, the available data also generally show higher rates for Pima Indians, Hispanic persons, and black persons [76-7880, 83-85]. Retinopathy Although minorities tend to have higher reported rates of retinopathy, this finding is not as consistent as that for end-stage renal disease. Age-standardized rates of blindness secondary to diabetes for nonwhite persons is double that for white persons [86]. Black adults with diagnosed diabetes have a higher prevalence of retinopathy [87, 88]. Two studies of retinopathy in Hispanic persons have conflicting results: One shows higher rates, and the other shows lower rates [77, 89]. Pima Indians and Native Americans in Oklahoma have also been s