Epidemiological studies had already identified "diabetes epidemic" in 1970s. The extraordinarily high prevalence of type 2 diabetes was reported in Pima Indians (18) and also in the Micronesian Nauruans in the Pacific (19), and subsequently in other Pacific and Asian island populations (20). These studies showed that transition from traditional lifestyle to Western way of life resulted in obesity, lack of exercise, profound changes in the diet, and finally to type 2 diabetes. Potential for a future global epidemic of diabetes were highlighted. Since the 1970s several other studies have shown that type 2 diabetes has reached epidemic proportions in several developing countries as well as in Australian Aboriginals (21), African-Americans, and Mexican Americans (22).
Table 2 shows the trends in the number of diabetic patients worldwide (23). Significant increase in the number of type 1 diabetic patients is expected, but the doubling of the number of diabetic subjects in the following 20 years is due to a huge increase in the number of type 2 diabetic patients. According to the estimation of the International Diabetes Federation (IDF) about 194 million people worldwide, or 5.1%, were estimated to have diabetes in the age group 20 to 79 years in 2003 (23). This estimate is expected to increase to some 333 million by 2025, or 6.3% of the adult population. Thus, the increase in the number of diabetic subjects will be almost twofold in the forthcoming 20 years. South East Asia has the most of the increase considering the size of the population (705 million in 2003 and 1081 million in 2025). People in Asia tend to develop diabetes with a lesser degree of obesity at younger ages. Similarly, childhood diabetes has increased substantially (24). The highest prevalence of diabetes was in 2003 in North America, and in 2025 about 10% of the people will have diabetes in this area of the world. Southeast Asia had the highest prevalence of IGT in 2003, and the percentage of people having IGT will be 13.5% in 2025. About 15% to 20% of people in different regions will have either DM or IGT in 2025.
The United States has the highest increase in the prevalence of DM on the basis of several follow-up studies. In the National Health and Nutrition Surveys (NHANES) II (1976-1980) the prevalence of diagnosed plus undiagnosed diabetes was 8.9%, but in the NHANES III (1988-1994) the prevalence was already 12.3% in the population 40 to 74 years of age (25). Prevalence of IFG increased from 6.5% to 9.7%. Figure 1 demonstrates a large difference between ethnic groups in diabetes prevalence in the U.S. population > 20 years of age. The prevalence of diabetes (known plus undiagnosed) was particularly high in Mexican American men (13.1%) and women (14.5%). IFG or diabetes was present in about 20% of Mexican Americans. Diabetes has become one of the most common chronic diseases in the United States, where in subjects > 60 years of age the prevalence is already 18.8%.
Until recently, type 2 diabetes was regarded as a disease of the middle-aged and elderly. However, evidence is accumulating that onset in subjects aged under 30 years is increasing. Even children and adolescent are diagnosed to have type 2 diabetes (26). For example, among children in Japan type 2 diabetes is already more common than type 1 and accounts for 80% of childhood diabetes (27). Between 8% and 45% of newly presenting children and adolescents in the United States have type 2 diabetes.
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