We found that the prevalence of obesity, as measured by BMI, increased among AI/AN adults with diabetes during the study period. A greater increase in BMI was observed among adults in the younger age categories. We found a greater percentage increase in obesity among men relative to women. While the sex difference in the prevalence of obesity has decreased, women remained more obese than men in every year studied. Notably, the increase in obesity has resulted in a large increase in the proportion of people with the most extreme degree of obesity.
The trends in obesity observed in this study may have important clinical and public health implications. The combination of diabetes and high BMI has been associated with increased risk for the development of more severe degrees of hyperglycemia, hypertension, dyslipidemia, retinopathy, and progressive loss of renal function (17
). The relationship between obesity and cardiovascular disease morbidity and mortality are complex and nonlinear; however, obesity in its most extreme degrees is associated with higher all-cause and possible coronary cardiovascular disease mortality (20
). The increase in obesity among adults with diabetes in this study could have implications for the burden of morbidity and mortality among AI/AN people with diabetes.
Obesity has been increasing among U.S. adults. Analysis of Behavioral Risk Factor Surveillance System (BRFSS) data shows a trend of increasing prevalence of extreme obesity compared with other classes of obesity in the U.S. population (22
). BRFFS data and American Indian oversamples have described similar trends among American Indian adults. Between 1999 and 2003, 1000 American Indian adults aged 18 years and older living on or near the seven reservations in Montana were interviewed each year using an adapted BRFSS survey. During this period, the prevalence of obesity increased from 34% to 39% (23
). The Strong Heart Study, an epidemiological study of cardiovascular disease risk factors in four American Indian communities, also documented the high prevalence of obesity, particularly among participants in the younger age groups (24
). The trends in obesity in our study are also consistent with trends in the prevalence of obesity and extreme obesity among people with diabetes. Among adults with diabetes in an epidemiologic study in Rochester, Minn, the proportion of obesity increased from 33% to 49%, and extreme obesity nearly doubled from 5% to 9% over approximately 20 years (21
Because our study was cross-sectional, we cannot determine the cause or causes of our observations. It is possible that AI/AN adults with diabetes have become more obese during the study period just as U.S. adults have become more obese. Treatment of diabetes may limit weight loss, and some pharmacologic agents used to treat people with diabetes are associated with weight gain (25
). In longitudinal studies among the Pima Indians of Arizona, pharmacologic treatment had a statistically significant limiting effect on weight loss in people after the onset of diabetes (26
), and clinical trial data from the United Kingdom Prospective Diabetes Study showed the greatest increase in weight among people using insulin and certain pharmacologic agents (27
). With more interest in using intensive therapies since publication of the findings of the United Kingdom Prospective Diabetes Study, which were released during the study period, changes in treatment practice toward improved glycemic control (10
) could explain some of the observed trends. Such treatment changes, however, would not explain the increase in mean BMI found in patients who were not treated with such agents (). Alternatively, the observed increases in obesity could reflect unintentional changes in who was included in the DCOA or how the audit was conducted. For example, an unrecognized selection bias toward participants with greater BMIs or a bias toward collection of data from participants with higher BMIs over time could create a temporal trend. To examine this possibility, we analyzed the percentage of participants who were missing BMI data during the study period and did find that the percentage of participants with missing data decreased from 17.6% in 1995 to 4.5% in 2004. However, the inclusion and exclusion criteria remained the same during the study period and never included weight restrictions, so the decrease in the number of patients with missing BMI values likely reflects better medical record documentation and less likely reflects differences in data reporting or in participant selection. Confounding due to other cohort differences is also unlikely to explain the results because adjustment for age, sex, diabetes duration, treatment type, and treatment facility did not substantially change our observations. Furthermore, the large dataset and the large number of different auditors should limit the chance of a one-way systematic selection bias toward more obese patients for inclusion. Still, changes based on modifications of health care usage bias, diagnostic criteria, or case ascertainment of diabetes cannot be fully excluded. Longitudinal studies would be required to fully address these and other questions about the cause of our observations.
Health care programs can be tailored to meet the lifestyle, preferences, and resources of individuals with obesity. Options include dietary and physical activity interventions with behavioral modification strategies, antiobesity drugs, and, for certain individuals, surgical interventions (28
). Public health approaches to weight management may also have a role, particularly if they are combined with interventions directed at individuals (29
). By documenting increasing trends in obesity among people with type 2 diabetes, this study helps to focus both clinical and public health attention on a major health challenge facing health professionals serving not only American Indian and Alaska Native people but also Latino, African American, and other communities that are experiencing an increase in prevalence of obesity and type 2 diabetes (30
). The challenge will be to better understand the physiologic, socioeconomic, and lifestyle factors influencing obesity in adults with type 2 diabetes and to design, develop, implement, and evaluate effective and culturally appropriate interventions to address the trends in obesity in these high-risk groups.