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Elimination of health disparities in the United States is a national health priority. Cardiovascular disease, diabetes, and obesity are key features of what is now referred to as the “cardiometabolic syndrome,” which disproportionately affects racial/ethnic minority populations, including Native Hawaiians and other Pacific Islanders (NHOPI). Few studies have adequately characterized the cardiometabolic syndrome in high-risk populations such as NHOPI. The authors systematically assessed the existing literature on cardiometabolic disorders among NHOPI to understand the best approaches to eliminating cardiometabolic health disparities in this population. Articles were identified from database searches performed in PubMed and MEDLINE from January 1998 to December 2008; 43 studies were included in the review. There is growing confirmatory evidence that NHOPI are one of the highest-risk populations for cardiometabolic diseases in the United States. Most studies found increased prevalences of diabetes, obesity, and cardiovascular risk factors among NHOPI. The few experimental intervention studies found positive results. Methodological issues included small sample sizes, sample bias, inappropriate racial/ethnic aggregation of NHOPI with Asians, and a limited number of intervention studies. Significant gaps remain in the understanding of cardiometabolic health disparities among NHOPI in the United States. More experimental intervention studies are needed to examine promising approaches to reversing the rising tide of cardiometabolic health disparities in NHOPI.
The prevalence of cardiometabolic disorders, including cardiovascular disease, diabetes, and obesity, has reached epidemic proportions worldwide. Prevalences of diabetes and cardiovascular disease among ethnic minorities in the United States exceed those seen in the general population (1–7). Because of the excess health burden of cardiovascular disease and diabetes in ethnic minorities, cardiometabolic risk, as the precursor of these diseases, provides a specific target for conducting investigations that aim to reverse and/or eliminate these disparities. Moreover, obesity, as one of the central pathophysiologic mechanisms underlying the syndrome of cardiometabolic risk, might constitute an earlier “upstream” target for treatment and prevention that could be effective in reducing excess morbidity.
In this review, we focused on cardiometabolic health disparities among Native Hawaiians and other Pacific Islanders (NHOPI). As a federal designation, “Native Hawaiian or Other Pacific Islander” refers to persons with origins in any of the original peoples of the islands of Polynesia, Micronesia, and Melanesia (8). The first Polynesian settlers of the Hawaiian Islands are thought to have migrated from the Marquesas Islands as early as 100 B.C.E., some 2,000 years ago (9). Hawaiians lived in isolation until 1778, when European explorers brought with them deadly foreign infectious diseases that decimated the Native population. Colonization and the eventual overthrow of the Hawaiian monarchy resulted in a loss of land and political power, as well as traditional practices and customs, including the near extinction of the Hawaiian language (9).
Events such as the cultural revival referred to as the “Hawaiian Renaissance,” the return of the island of Kahoolawe to the Hawaiian people, the formation of political bodies such as the Office of Hawaiian Affairs, the public recognition of the illegal overthrow of the Hawaiian monarchy, and the ongoing voyages of the Hokule‘a using historical navigation techniques of Native Hawaiians serve to highlight the resiliency and strength of this population. However, despite these positive social and political developments, NHOPI are overrepresented in lower socioeconomic groups, report greater difficulties in obtaining health care, and may be affected by internalized racism as a consequence of their historical experience of disenfranchisement and loss of power within their traditional homeland (10–12). In addition, NHOPI continue to bear a disproportionate burden of disease, including cardiovascular disease and diabetes.
Today, the state of Hawai‘i has the largest population of Native Hawaiians in the United States, followed by California. Among ethnic subgroups in Hawai‘i, Native Hawaiians have the highest prevalence of diagnosed diabetes (11.5%), with reported prevalences ranging from 19% to 22% for type 2 diabetes and from 16% to 35% for impaired glucose tolerance (5, 13, 14). Cardiovascular disease mortality among Native Hawaiians in 2004 was more than twice that in Japanese, who had the lowest rates (372 per 100,000 population vs. 167 per 100,000 population), and diabetes-related mortality was 3 times higher in Native Hawaiians than in Caucasians (39 per 100,000 population vs. 13 per 100,000 population) (6). The Native Hawaiian Health Research (NHHR) Project examined the relation between a clustering of cardiovascular risk factors and biochemical markers of insulin resistance (fasting insulin and C-peptide levels) (7). The investigators found that fasting insulin concentrations were correlated with body mass index, waist-to-hip ratio, blood pressure, and levels of triglyceride, high density lipoprotein cholesterol, and glucose. A significant correlation was also found between increasing insulin resistance and increased clustering of cardiovascular disease risk factors. The NHHR study, in addition to a limited number of other studies on NHOPI, suggests that significant disparities occur between and among these populations. The purpose of this review was to systematically assess the state of the science related to cardiovascular disease, diabetes, and adiposity among NHOPI.
Database searches were performed in PubMed and MED-LINE for the time period of January 1998 to December 2008, with keyword combinations of the following racial/ethnic groups in an “OR” search term: Native Hawaiian, Hawaiian, Pacific Islander, Samoan, Tongan, Micronesian, New Zealand, Maori, Melanesia, Chamorro, Guamanian, Fijian, and Polynesian (Figure 1). The racial/ethnic groups were then included in combination with the following terms defined as an “OR” function: minority, minorities, groups, ethnicity, and ethnicities. The above racial/ethnic AND minorities search term was identified as a “Set A” keyword search. Results from the Set A keyword search were then combined with Set B keywords as an “OR” search term which included the following: inequity, inequality, health disparities, health differences, cardiovascular, hypertension, heart, heart failure, heart disease, heart disease risk factors, cardiac, cardiomyopathy, diabetes, syndrome X, metabolic syndrome, insulin resistance, glucose intolerance, prediabetes, cardiometabolic, obesity, adiposity, overweight, physical inactivity, physical activity, nutrition, diet, and smoking in combination with United States.
Additional studies (n = 21) were also extracted from the reference lists of the articles identified in the initial search using Set A AND Set B keywords; these studies were reviewed for inclusion/exclusion. The searches were restricted to English-language articles on humans aged ≥19 years that had been published in peer-reviewed scientific journals. Articles were excluded from the review if they were letters, editorials, or literature reviews without new data; if they had been published in a foreign language; or if they were nonempirical.
Using this search strategy, we identified 311 citations, of which 98 were deemed relevant through review of the article title (performed by a single reviewer). All 98 articles underwent abstract review by 2 independent reviewers, using a standard checklist adapted from other reviews of the health-disparities literature (15). Of the 98 abstracts reviewed, 71 articles were selected for a full text review, which was performed by 2 independent reviewers to ensure compliance with all inclusion criteria, as well as ranking on the following study design criteria: 1) use of appropriate indicators for patient characteristics (e.g., race, ethnicity, or ancestry, sex, age, education, income); 2) inclusion of objective measures of the outcomes of interest (i.e., measured height, weight, and systolic and diastolic blood pressure; self-report of or medical chart review to determine obesity, cardiovascular disease, and/or diabetes status, etc.); 3) inclusion of well-defined measures of disease status; and 4) appropriate adjustment for patient comorbid conditions (i.e., age, sex, body mass index for diabetes outcomes, blood pressure for cardiovascular outcomes, etc.).
After full text review, a joint review meeting was convened to determine the final selection of articles to be included in this study. A total of 28 articles were excluded for 1 or more of the following reasons: 1) NHOPI were aggregated with other racial/ethnic groups (i.e., “Asians and Pacific Islanders” was a single category) (18% of articles); 2) the article was a review or editorial (36%); 3) the study included NHOPI but there was no specified outcome related to cardiometabolic diseases (21%); 4) the NHOPI study population lived outside of the United States (14%); 5) the study population was under age 19 years (i.e., children or youths) (7%); and 6) there was another miscellaneous reason for study exclusion (the article had been published in a non-peer-reviewed journal, no NHOPI population was included, etc.) (4%). Thus, the final number of articles included in this literature review of cardiometabolic health and health-care disparities among NHOPI was 43.
A total of 12 papers pertaining to cardiovascular disease or its risk factors were reviewed (Table 1). The majority of studies (n = 10) were cross-sectional. In 4 of the 10 cross-sectional studies, investigators had prospectively collected new data, and in 2 they had used retrospective data collected from administrative databases. A single prospective study included a cohort that had been followed for over 4 years. One study included qualitative data collected through focus groups of NHOPI. The only study in which researchers had proposed testing an intervention had had a quasi-experimental, pre-post study design without controls for testing of a Native Hawaiian cultural intervention designed to improve hypertension profiles. Fifty percent of the papers included a study sample of at least 300 participants of NHOPI ancestry.
NHOPI women were found to have a high frequency of hypertension and high cholesterol in comparison with whites and other ethnic groups (16, 17). Studies that examined hypertension along with other covariates in NHOPI found that hypertension was significantly related to degree of Hawaiian ancestry and especially diastolic blood pressure after controlling for other covariates (18). The sole genetic study found that increased corrected Q–T interval (Q-Tc), which has been associated with heart disease and sudden death, was associated with the angiotensin-converting enzyme insertion/insertion (ACE II) genotype, which is found with greater frequency among Native Hawaiians than in other ethnic groups (19). Verderber et al. (20) compared post-coronary artery bypass graft (CABG) complications across ethnic groups and found that NHOPI had similar early post-CABG complications (first 20 hours after CABG) but experienced significantly more ventricular arrhythmias requiring medical treatment on postoperative day 2 than Japanese. In another study, NHOPI men with acute coronary syndrome were significantly more likely to receive CABG (odds ratio = 1.8, 95% confidence interval: 1.2, 2.7) and less likely to receive percutaneous coronary intervention following their first hospitalization than were whites (21). No ethnic differences in endovascular treatment for acute coronary syndrome were found in women (21).
In the only longitudinal prospective cohort study, investigators were interested in examining measures of socioeconomic status and cardiovascular disease risk factors in American Samoans versus Western Samoans. Ezeamama et al. (22) found that high socioeconomic status was associated with increased odds of cardiovascular disease risk factors in Western Samoa but decreased odds in more developed American Samoa. The authors attributed this differential effect of socioeconomic status on cardiovascular disease risk factors to the heterogeneity across the Samoan Islands in specific exposures to economic development and the natural history of individual cardiovascular disease risk profiles.
The cardiovascular disease literature reviewed had a number of limitations. First, nearly all of the studies were observational studies with cross-sectional data, which does not permit a clear understanding of cause and effect for significant associations between outcomes and exposures. Half of the studies reviewed had relatively small sample sizes or had serious sample biases that confounded the study’s findings. Finally, several of the studies of sufficient quality were drawn from 2 research groups that have established cohorts in rural communities in Hawai‘i (Grandinetti et al. (19, 23)) and in Western and American Samoa (Ezeamama et al. (22)); those findings may not be generalizable to other NHOPI populations in the United States.
A total of 16 diabetes-related studies were reviewed. Most were cross-sectional investigations (10 studies), although 1 study was descriptive and 2 were retrospective (Table 2). Nine of the cross-sectional studies examined the population-based data of the NHHR Project, including a quasi-experimental study that was a nonrandomized concurrent intervention which included Native Hawaiians with diabetes or at risk for diabetes. Another quasi-experimental study compared “before” and “after” hemoglobin A1c levels in a small sample of Native Hawaiian, Samoan, and Tongan participants undergoing an intervention delivered by community health workers. Sample sizes ranged from 78 participants to more than 3,000. The 2 retrospective studies examined the incidence of macrosomia and gestational hypertension among NHOPI women.
Among studies using the NHHR data, Grandinetti et al. (5) found prevalences of type 2 diabetes and impaired glucose tolerance to be higher among NHOPI than among Caucasian participants. The overall prevalence of diabetes was 4 times higher in the NHHR participants than in the Second National Health and Nutrition Examination Survey population, and the prevalence of diabetes was also significantly higher among full Hawaiians than among part-Hawaiians. In comparison with global estimates of standardized prevalence rates (24), 1 study revealed that the prevalences of diabetes and impaired glucose tolerance among Hawaiians in the NHHR study were among the highest reported, except for Pima and Nauruan populations (5). Grandinetti et al. (5) also found that the age-adjusted prevalence of impaired glucose tolerance was higher in Hawaiian women than in men and was significantly associated with measures of adiposity (i.e., body mass index, waist circumference, and waist-to-hip ratio). Similarly, Kaholokula et al. (18) reported that increased Hawaiian blood quantum was significantly associated with higher fasting glucose concentration, body mass index, and waist-to-hip ratio.
Three studies examined the relation between ethnicity, depressive symptoms, and diabetes among NHHR participants. Among Native Hawaiians with diabetes, depressive symptoms were associated with poorer physical functioning, poorer perception of general health, more severe and limiting bodily pains, less energy, and more emotional problems (25). NHHR participants with elevated hemoglobin A1c levels reported more depressive symptoms and a lower quality of life than participants with normal hemoglobin A1c levels (26, 27). Another cross-sectional study of NHHR participants examined dietary patterns, ethnicity, and the prevalence of diabetes and found that consumption of local ethnic foods was positively correlated with body mass index, smoking, waist-to-hip ratio, fasting glucose, and 2-hour glucose (28). Native Hawaiians were found to have significantly higher consumption of these foods and the highest total energy intake in comparison with all other ethnic groups. These results suggest that total energy intake may be a more significant risk factor for diabetes than a specific dietary pattern among Native Hawaiians (28). In the nonrandomized concurrent intervention study that enrolled Native Hawaiians with diabetes or at risk for diabetes, participants in a family support intervention were more likely than a standard intervention group to advance from the pre-action stage of change to the action/maintenance stage with regard to fat intake and physical activity (29).
Three additional studies examined diabetes-related conditions. Mau et al. (30) found that the prevalence of chronic kidney disease was higher among Native Hawaiians than among Asian and Pacific Islander participants in the National Kidney Foundation’s Kidney Early Evaluation Program community screening. In a retrospective study of perinatal outcomes in NHOPI women by Silva et al. (31), a higher percentage of NHOPI women required insulin during pregnancy and before 20 weeks’ gestation, suggesting that there may be a larger subset of NHOPI women with preexisting undiagnosed diabetes.
A major limitation of the diabetes-related research with NHOPI populations is the lack of studies that have tested the efficacy of interventions. A large number of studies were observational, cross-sectional studies that precluded causal inferences. Several of the studies also had small sample sizes, resulting in limited generalizability.
There were 15 obesity-related studies reviewed (Table 3). Four studies examined data from the Multiethnic Cohort Study, a population-based cohort study designed to examine risk factors for cancer (i.e., obesity) that included Asian, black, Hawaiian, Latino, and white adults from Hawai‘i and California. One additional study was a population-based prospective cohort study of ethnic groups residing in Hawai‘i. Another study pooled data from 18 population-based epidemiologic studies conducted in Hawai‘i over a period of 25 years to examine trends in body mass index among different ethnic groups in Hawai‘i and to explore associations between food intake and excess weight. Seven studies were cross-sectional. Two studies, 1 cross-sectional and 1 longitudinal, examined genetic associations with body mass index among Samoans residing in American Samoa. One study was qualitative; the researchers conducted focus groups with 32 Native Hawaiian community college students to explore facilitators and barriers to living a healthy lifestyle.
Prevalences of overweight and obesity were consistently higher among Native Hawaiians than in other ethnic groups (whites, blacks, Latinos, Asians, and Filipinos) across studies. Grandinetti et al. (32) reported a combined prevalence of 82% for overweight and obesity in NHHR study participants, as compared with a national prevalence of 53%; 49% were obese as compared with 21% nationally. Body mass index was also higher in persons with an ethnic admixture that included Native Hawaiian ancestry, as compared with most other ethnic combinations (32, 33). In pooled data from 18 population-based studies carried out over 25 years, Native Hawaiians had the highest prevalence of excess weight at all times (34).
Energy intake was consistently higher among NHOPI than in other ethnic groups in Hawai‘i. Both the NHHR and Multiethnic Cohort studies found that total dietary energy intake was significantly associated with Native Hawaiian ancestry and increased body mass index (32, 34). In 2 large population-based prospective studies, Native Hawaiians had the highest chronic disease risk scores in comparison with other ethnic groups, primarily because of high prevalences of overweight and obesity, higher rates of smoking, and chronic alcohol use (35). In the NHHR study, increased body weight was strongly associated with glucose intolerance (5). Despite the high prevalence of overweight and obesity, NHOPI reported a higher prevalence of physical activity in the 2001 Hawai‘i Behavioral Risk Factor Surveillance System survey than did other ethnic groups (36).
The obesity-related studies reviewed had several limitations. First, the cross-sectional design of many of the studies did not allow for determination of causal relations. Second, many of the studies were questionnaire-based and may have been vulnerable to recall bias or a propensity towards giving socially desirable answers. Finally, investigators in several studies were unable to measure confounding variables, which limited the potential for understanding the true association between exposure and disease.
Studies of cardiometabolic disparities among NHOPI are sparse. The 43 studies in this review were published in the last 10 years and provide growing evidence that NHOPI are one of the highest-risk US populations affected by cardio-metabolic diseases. Some progress has been made in addressing these disparities, as evidenced by the handful of studies that have shifted from observational research towards program development and then to experimental and clinical trial-type studies that include NHOPI. However, there were a number of methodological issues apparent during the course of this literature review. For example, there were several studies that were limited by sample bias (convenience samples, etc.) and relatively small sample sizes (i.e., <50 subjects). NHOPI comprise less than 1% of the US population, and thus recruitment of NHOPI into research studies remains a challenge. Despite these challenges, a number of research teams have been successful in enrolling sufficient-sized samples or have taken advantage of existing data or administrative databases to better understand cardiometabolic diseases in this population. Moreover, recent developments in the use of community engagement approaches have served to increase the participation of this population in research activities and ensure that studies are relevant and translatable to NHOPI communities.
Aggregation of NHOPI with Asian Americans in several publications limited the number of available studies for this review. There was also a paucity of experimental studies that were adequately designed to reduce treatment bias (i.e., randomization) and longitudinal prospective cohort studies that would allow elucidation of cause-and-effect relations in cardiometabolic diseases. However, a few focus groups and quasi-experimental studies provided preliminary data that offer potential for designing intervention studies in the future.
Several studies (29, 37–40) provided initial insights on promising approaches in NHOPI populations, such as social and/or family support and the inclusion of cultural and/or traditional healing methods as alternatives or supplements to conventional medical regimens. Other studies provided empirical evidence with which to develop scientifically informed and culturally specific diet-based interventions for prevention and treatment of cardiometabolic disparities. Health care differences in cardiovascular disease treatment suggest that more study is needed in order to determine the best medical treatments for high-risk ethnic groups such as NHOPI (20, 21). Further investigation is needed to examine both provider factors and patient factors that may underlie the treatment differentials between patients who may receive different treatments and hence have different outcomes.
There remain significant gaps in our understanding as to why cardiometabolic diseases occur more frequently in the NHOPI population in the United States (Figure 2). Any number of factors, alone or in combination, may contribute to the creation of disparities in health within this population. Compared with most other US ethnic groups, NHOPI are overrepresented in the lower socioeconomic strata, under-represented in higher education, and more likely to be marginalized from the larger society (41). Behavioral risk factors for diabetes and cardiovascular disease, such as tobacco use and psychological distress, are highly prevalent in NHOPI (42). In the case of Native Hawaiians, many health professionals have suggested that the health disparities experienced by Native Hawaiians are associated with their lower social status and adverse historical relations with Western governments (43, 44). Thus, it would seem appropriate in future studies to explore psychosocial stressors that may contribute to health disparities in NHOPI.
Future research aimed at eliminating cardiometabolic disparities in health and health care among NHOPI needs to move beyond observational studies into intervention studies that will engage NHOPI communities in the process while maintaining scientific rigor. Researchers should consider the whole spectrum of types of scientific studies—ranging from genetic, bench studies to clinical studies to effectiveness studies that test interventions in real-world settings. NHOPI can participate in this research not only as study subjects but also as investigators. In this way, they can both obtain health equity and, more importantly, help to promote health and wellness for all.
This work was supported by the Center for Native and Pacific Health Disparities Research, Department of Native Hawaiian Health, John A. Burns School of Medicine, University of Hawai‘i at Manoa; The Myron Pinky Thompson Endowed Chair (grant S21 MD 000228); the National Center on Minority Health and Health Disparities (grants P20 MD000173 and R24 MD 001660); and the National Heart, Lung, and Blood Institute (grant U01HL 079163).
Conflict of interest: none declared.