Monday, October 2, 2023
Type 2 diabetes mellitus (DM) and its associated long-term complications are emerging as critical, worldwide public health problems.[1] Although few groups have been spared increases in the burden of these conditions, indigenous populations around the world (defined by the United Nations as distinct, precolonial ethnic/cultural groups with strong attachments to ancestral territories) suffer from remarkably high rates of type 2 DM and related complications and risk factors.[1,2] This increasing burden of diabetes and associated morbidities among the world's indigenous groups highlights the urgent need for (1) comprehensive, evidence-based programs for the clinical management of type 2 DM in indigenous populations and (2) culturally appropriate, community-based intervention programs focusing on primary prevention. At the recent 66th Scientific Sessions of the American Diabetes Association (ADA) in Washington, DC, a joint International Diabetes Federation/ADA symposium[3] addressed the issue of diabetes in indigenous populations, focusing on 3 high-risk groups from different regions of the world: Aboriginal Canadians, Native Americans, and the people of the Torres Straight Islands, which extend from the tip of the Cape York Peninsula of Australia almost to the Papua New Guinea coastline.
Although the global pandemic of type 2 DM has left few populations untouched, the degree to which indigenous groups have been affected is remarkable. Stewart Harris, MD, MPH,[3] of the Centre for Studies in Family Medicine, The University of Western Ontario, London, Ontario, Canada, presented data indicating that, among the populations that have the highest reported prevalence rates of type 2 DM and impaired glucose tolerance (IGT), the vast majority are indigenous groups in the Americas or Asia-Pacific region. For example, the prevalence of type 2 DM is 2-3 times higher in Native Americans compared with US adults.[4] Between 1994 and 2002, the prevalence of clinically diagnosed diabetes increased 33.2% among Native Americans, with increases in all age and sex groups.[4,5] Similarly, findings from recent national surveys of self-reported diabetes in Canada indicated that the condition is more common in the Aboriginal population than in the general population in all age and sex categories.[6] Studies in the United States and Canada that have assessed diabetes status directly with standardized oral glucose tolerance testing protocols have documented that Native American and Aboriginal Canadian communities experience diabetes prevalence rates that are among the highest in the world.[6-12] Further, these studies have shown that the onset of diabetes in these groups occurs at a much younger age than in most other populations,[6,7] and that pediatric type 2 DM is emerging as an important health issue.[13,14] Finally, data from a recent community-based screening program among individuals age 15 years and older from 9 communities in the Torres Strait Islands indicate a diabetes prevalence rate of 26%, which is 6-fold higher than in the general population of Australia on the basis of data from the Australian Diabetes, Obesity and Lifestyle Study.[15]
The causes of this explosion of diabetes in indigenous populations have not been completely elucidated, although it is likely that a complex mix of genetics, lifestyle change, and psychosocial stress associated with colonization is playing a major role. It is notable that obesity, the strongest risk factor for type 2 DM identified to date, is very prevalent in indigenous populations worldwide.[2] Findings from national surveys in Canada have shown a very high prevalence of self-reported overweight and obesity among Aboriginal groups. An analysis of data from 2 cycles of the Canadian Community Health Survey (2000/2001 and 2003) indicate that Aboriginal men and women had the highest prevalence rates of overweight and obesity (defined as body mass index [BMI] ≥ 25 and 30, respectively) compared with other ethnic groups in the country, even when accounting for group differences in age, household income, education, and physical activity.[16] Epidemiologic studies that have used direct assessments of body composition also report high prevalence rates of both overall and especially central or abdominal obesity, relative to the general population.[17,18] Perhaps of greater concern is the dramatically increasing prevalence of obesity among children and youth in this population.[19] Very high prevalence rates of childhood obesity have been reported from several regional and community studies in Canada, with rates ranging from 29% to 64%, depending on the standard reference population used.[6,20,21]
Similarly, data from the United States have consistently demonstrated high prevalence rates of overweight and obesity among Native American populations.[19,22] Among adults, overweight and obesity prevalence rates tend to be higher among women and in certain tribal groups.[19,22] For example, the Strong Heart Study, which used a standardized examination protocol across a number of centers, reported a higher prevalence rate of overweight (defined as BMI > 27.8 for men and > 27.3 for women) among Indian adults in Arizona (~ 75%) compared with those in Oklahoma (~ 70%) and the Dakotas (~ 67%).[23] Further, data from the Behavioral Risk Factor Surveillance System indicated a steady increase in self-reported BMI between 1985 and 1996.[24] In addition, Native American children and youth are experiencing a dramatically increasing prevalence rate of obesity.[19] Findings from several large surveys have demonstrated high rates of overweight and obesity in these age groups, with the highest prevalence rates of weight gain in the youngest age categories.[19, 25-27] In addition, data from a study of Navajo youth indicated secular increases in the prevalence rate of overweight between 1955 and 1997 (0.5-1.0 units of BMI per decade).[28]
Data from a recent community-based screening program among individuals age 15 and older from 9 communities in the Torres Strait Islands indicate high prevalence rates of overweight (30%), obesity (51%), and especially central/abdominal obesity (70%). Obesity rates among Torres Strait Islanders in this study were 3-fold higher than those observed for the general population of Australia from the Australian Diabetes, Obesity and Lifestyle Study.[15]
Type 2 DM exacts its toll on the health of individuals and communities primarily through the induction of long-term micro- and macrovascular complications. In many settings, diabetes is the leading cause of lower extremity amputations and new cases of adult blindness,[29,30] and it accounts for a large proportion of incident cases of end-stage renal disease.[31] Individuals with diabetes are also at markedly increased risk for cardiovascular morbidity.
A distinctive feature of the epidemiology of the complications of diabetes is the wide variation in the prevalence of specific conditions both within and between ethnic groups. Data presented by Dr. Harris indicated that, although indigenous groups tend to have a similar or slightly lower burden of diabetic retinopathy compared with reference populations, they experience disproportionate burdens of diabetic kidney complications, lower extremity amputations, and -- more recently -- macrovascular outcomes. For example, it has been demonstrated that Native Americans, Aboriginal Canadians, and indigenous Australians experience dramatically higher incidence rates and earlier onset of diabetic end-stage renal disease compared with the general populations of their respective countries.[32-34] In addition, lower extremity amputation rates are substantially higher among Native Americans and Torres Strait Islanders compared with general populations of the United States and Australia, respectively.[35,36]
Comprehensive, evidence-based clinical care is of critical importance in reducing the incidence of diabetes complications as well as long-term morbidity and mortality in people who have diabetes. Many indigenous groups around the world live in areas that are remote and/or underserviced, and therefore they are much less likely to receive optimal diabetes care. Despite this sometimes discouraging clinical picture, a number of innovative approaches targeting indigenous populations do exist, and the speakers at the symposium presented some excellent examples of initiatives that have improved diabetes care in these settings.
Kelly Moore, MD,[3] of the Indian Health Service (IHS), Albuquerque, New Mexico, presented data on the Special Diabetes Program for Indians, which began in 1997 with the overall objective of improving prevention and treatment services in American Indians and Alaska Native communities. Recent evaluation of this program by the IHS demonstrated a number of positive outcomes, including increases in screening, diagnostic and treatment services, and the availability of diabetes care teams (including diabetes nurse educators and dieticians) and culturally appropriate education materials. In addition, clinical data from this evaluation indicated improvements in glycemic control, blood pressure, total and low-density lipoprotein (LDL) cholesterol and triglycerides, and other cardiovascular and renal risk factors.[37]
Ashim Sinha, MD,[3] of the Cairns Diabetes Centre in Cairns, Australia, presented the results of a randomized cluster trial to improve diabetes care in Torres Strait Islander communities. The intervention involved the establishment of registries, the training of local healthcare workers to manage the registries, recall and reminder systems, and care plans plus basic training in clinical diabetes care.[38,39] Results indicated a 40% reduction in diabetes-related hospitalizations in the intervention group.[38] Findings from this trial were disseminated to clinicians and managers in this region, and after 3 years, clinical audit data indicated improvements in proportions of patients with good glycemic and blood pressure control, increases of 18% to 25% and 40% to 64%, respectively, and reductions in diabetes-related hospitalizations.[39]
Initiation and expansion of comprehensive, evidence-based programs for the clinical management of type 2 DM will begin to address long-standing deficits in secondary and tertiary prevention of diabetes complications and outcomes among indigenous patients with diabetes. However, these initiatives will not address what is perhaps a more important objective, namely, the primary prevention of diabetes in these populations. Primary prevention activities can be targeted either at high-risk individuals (in the case of type 2 DM the most common target is IGT) or at entire populations. Strategies to target high-risk individuals in indigenous populations have been successful in a limited number of applications to date. Perhaps the best example is the Diabetes Prevention Program, which documented that intervention with lifestyle or metformin reduced the incidence of type 2 DM in subjects with IGT in all ethnic groups, including Native Americans.[40]
However, in light of the very high prevalence rates of obesity and type 2 DM in indigenous communities, more broadly focused, community-based primary prevention strategies are preferred. These approaches are also more consistent with the holistic worldview of indigenous populations. Several excellent examples of these types of programs were presented, including the Zuni Diabetes Prevention Program,[41] the Pathways Project,[42] the Kahnawake Schools Diabetes Prevention Project (KSDPP),[43] and Sandy Lake Health and Diabetes Project (SLHDP).[44] A common theme in all of these programs is a community-wide focus, with activities in local schools, including in most cases the development of school curricula, as well as other interventions in the community, such as radio/TV programming, grocery store interventions (shelf labeling, tours, and demonstrations), and partnerships and networking with existing community agencies. A key element in all of these programs is the use of a participatory research approach, in which responsibility, control, and decision making are shared by both the community and the researchers. Although it is too early to tell whether these programs will stem the tide of diabetes in their respective communities, they have yielded encouraging data on intermediate outcomes, including reductions in intake of unhealthy foods, increases in physical activity, and improvements in psychosocial indicators that relate to knowledge and confidence in making healthy food choices and in being more physically active.[41-44] Despite these successes, a number of challenges remain for community-based approaches to diabetes prevention, including sustainability of the programs and long-term, stable funding models.
The combination of early diabetes onset, the advancing age of a demographically young population, and the progression of a disease process that frequently involves devastating micro- and macrovascular complications will pose an extremely serious challenge to indigenous communities and their associated health systems in the coming years. Recent examples of community-based primary prevention approaches and strategies to improve clinical management of diabetic patients are promising, although there is an urgent need for wider dissemination and institutionalization of these programs.
