The Evolving Diabetes Burden in the United States

Diabetes was first described in ancient times with the cardinal symptoms of polyuria, polydipsia, and polyphagia (1). The use of uniform diagnostic criteria provided a means to reliably track the disease and unveiled a worldwide epidemic that emerged during the second half of the 20th century and is now extending into the 21st century (2-4). This report examines the evolution of the diabetes epidemic in the United States and the burden imposed by its complications. Classification of Diabetes Mellitus There are 3 major types of diabetes (5). Type 1 diabetes usually involves children and was previously called insulin-dependent diabetes mellitus or juvenile-onset diabetes. It develops when the body's immune system destroys pancreatic cells, which make insulin. Type 1 diabetes accounts for 5% to 10% of all diagnosed cases of diabetes in the United States. Type 2 diabetes, previously called noninsulin-dependent diabetes mellitus or adult-onset diabetes, usually begins as insulin resistance, in which target tissues do not use insulin properly. It accounts for approximately 90% to 95% of all diagnosed cases of diabetes. Gestational diabetes is glucose intolerance diagnosed during pregnancy with return to a normal metabolic state after delivery. Other, lesser types of diabetes result from specific genetic conditions (such as maturity-onset diabetes of youth), surgery, drugs, malnutrition, infections, and other illnesses; these account for 1% to 5% of all diagnosed cases of diabetes (5). Diagnosis of Diabetes Uniform diagnostic criteria for diabetes were first recommended by the American Diabetes Association and the World Health Organization in 1979 and 1980 and were updated in the late 1990s (5, 6). Currently, when typical symptoms of diabetes are present (for example, polyuria, polydipsia, or unexplained weight loss), a casual (that is, at any time without regard to the last meal) plasma glucose level of 11.1 mmol/L (200 mg/dL) or greater confirms the diagnosis. In addition, the diagnosis can be made with a fasting plasma glucose level of 7.0 mmol/L (126 mg/dL) or greater or an oral glucose tolerance test with a 2-hour value of 11.0 mmol/L (200 mg/dL) or greater. A positive diagnostic test result should be followed by a repeated test on a different day to confirm the clinical diagnosis. In contrast, for epidemiologic studies, a single fasting plasma glucose or 2-hour oral glucose tolerance test measurement is used to estimate the prevalence of diabetes in a population. Tracking the Diabetes Epidemic Currently, 3 periodic national surveys track diabetes prevalence in the United States. The National Health Interview Survey and National Health and Nutrition Examination Survey (NHANES) use national population-based samples and query persons in face-to-face interviews about whether they have been told by their health care provider that they have diabetes. A third survey, the Behavioral Risk Factors Surveillance System, asks a similar question of state-based population samples during telephone interviews of residents. Unlike the other 2 surveys, NHANES includes a laboratory-based examination that measures glucose levels and identifies persons with undiagnosed diabetes. All 3 surveys provide national estimates of the prevalence of diagnosed diabetes. Only the Behavioral Risk Factors Surveillance System provides state-based estimates, and only NHANES provides estimates of undiagnosed diabetes. Prevalence In 2002, an estimated 6.3% of the U.S. population (about 18.2 million persons) had diabetes (7). Diabetes affects various sociodemographic groups unequally. According to data from the National Health Interview Survey, persons 65 years of age or older make up almost 40% of all persons with diagnosed diabetes, and the prevalence in this age group is more than 10 times that in persons younger than 45 years of age (8). Minority race and ethnic groups, including black persons, Hispanic persons, and Native Americans, are disproportionately affected; the prevalence of diagnosed diabetes is generally 2 to 4 times higher in these groups than in the majority population (Figure 1) (7, 8). Figure 1. Prevalence of diagnosed diabetes in people 20 years of age and older by age and race or ethnicity, United States, 2002. The longest running of the surveys, the National Health Interview Survey, found a 4- to 8-fold increase over the last half-century in the number of persons who received a diagnosis of diabetes (1.6 million in 1958 and 12.1 million in 2000) and the prevalence of diagnosed diabetes in the United States (0.9% in 1958 and 4.4% in 2000) (Figure 2) (8, 9). Increases occurred across all demographic categories, including sex, race or ethnicity, and age (8). Between 1990 and 2001, data from the Behavioral Risk Factors Surveillance System indicate that the largest relative increases in diagnosed diabetes occurred in persons 30 to 39 and 40 to 49 years of age (95% and 83%, respectively); increases in other age groups were 40% in persons 18 to 29 years of age, 49% in persons 50 to 59 years of age, 42% in persons 60 to 69 years of age, and 33% in persons 70 years of age or older (10, 11). Although the magnitude of the increase varied, the prevalence of diagnosed diabetes among adults increased in every state in the United States (Figure 3). Trends are also disturbing in children and adolescents, in whom type 2 diabetes is increasingly being recognized, but as yet less commonly than type 1 diabetes (12). Studies of estimates of the incidence of type 1 diabetes in the United States, which are limited by sparse data, do not find a consistent patternsome show an increase, some show a decrease, and some remain unchanged (13). Figure 2. Prevalence of diagnosed diabetes and the number of people with diagnosed diabetes in the United States, 1958 to 2000. Figure 3. Prevalence of diagnosed diabetes (including gestational diabetes) by state in the United States, 1990 to 2001. The NHANES found that diabetes is undiagnosed in approximately one third of all persons with diabetes and that this fraction has changed little over time (14). Many factors may have affected these uptrends in the prevalence of diabetes, including changes in diagnostic criteria, improved or enhanced detection, decreasing mortality, changes in demographic characteristics of the population (for example, aging), and growth in minority populations in whom the prevalence and incidence of diabetes are increasing. Diabetes Complications Morbidity Cardiovascular Disease Data on cardiovascular disease among the diabetic population are scant. However, in 2000, 37.2% of diabetic persons age 35 years and older reported receiving a diagnosis of a cardiovascular disease (8). Prevalence of ischemic heart disease among persons with diabetes was about 14 times the rate among those without diabetes in persons 18 to 44 years of age (2.7% vs. 0.2 %), 3 times as high in persons 45 to 64 years of age (14.3% vs. 4.7%), and almost twice as high in those 65 years of age or older (20% vs. 12%) (15). Other studies have shown that the absolute rates of cardiovascular disease in persons with diabetes are higher in men than in women (as in the general population), but the relative risk (comparing those with and without diabetes) is higher in women than in men (relative risk, 2 to 4 for women and 1.5 to 2.5 for men) (16, 17). Eye, Kidney, and Lower-Extremity Disease Visual impairment and blindness are major disabling complications of diabetes. Diabetic retinopathy, the leading cause of blindness (visual acuity 20/200) in persons age 20 to 64 years, accounts for 12% of all new cases of blindness and leads to 12 000 to 24 000 new cases each year in the United States (18). Considerable visual impairment (best corrected [for example, with glasses] visual acuity in either eye < 20/40) among persons with diabetes is much more common than blindness and is associated with reduced functional status. A national population-based survey based on self-reports found that 25% of all persons with diabetes had considerable visual impairment, approximately double the proportion among persons without diabetes (19). Impairment among persons with diabetes can have several causes. Some are specific to diabetes, such as macular edema and diabetic retinopathy, and others are not specific to diabetes but occur more commonly in diabetic than in nondiabetic persons. Examples of conditions not specific to diabetes are cataracts (32% vs. 20% in persons 65 to 74 years of age) and glaucoma (6.0% vs. 2.3% in persons 65 to 74 years of age) (20-23). In the United States in 2000, diabetic nephropathy accounted for more than 40% of new cases of end-stage renal disease (that is, kidney failure that requires dialysis or transplantation) (8). Persons with diabetes are the fastest-growing group of recipients of dialysis and transplantation (8). Several factors may account for the increase in incidence, including greater recognition of the etiologic role of diabetes, more use of treatments for end-stage renal disease, a true increase in the incidence of diabetes-related end-stage renal disease, or a combination of these factors. Lower-extremity disease, which includes peripheral neuropathy and peripheral arterial disease or both, results in elevated rates of lower-extremity amputations among persons with diabetes. An estimated 15% of persons with diabetes will have a diabetic foot ulcer during their lifetime (24); of these, 6% to 43% will ultimately undergo a lower-extremity amputation (25). Among persons with diabetes who have had an amputation, as many as 85% may have had a preceding foot ulcer (25). Currently, more than half of all nontraumatic lower-extremity amputations in the United States occur among people with diagnosed diabetes (8). An analysis of the 1999 to 2000 NHANES found that an estimated 8.1% of the diabetic population age 40 years or older have peripheral arterial disease (defined as an ankle to brachial artery blood pressure ra