Classification and Pathophysiology of Diabetes
Most cases of diabetes fall into one of two categories, although overlap may occur and the distinction may not always be clear. Type-1 diabetes accounts for <10% of all cases of diabetes, tends to occur in younger subjects and is caused by severe insulin deficiency. The latter results from autoimmune destruction of the insulin-secreting beta cells of the pancreas. Type-2 diabetes, the predominant expression of the disease, is usually seen in older adults but is being diagnosed with increasing frequency in younger age groups, including children and adolescents.
Obesity and physical inactivity are major risk factors for type-2 diabetes in adults, adolescents and children (Table 1). Obesity, especially visceral obesity, induces insulin resistance, which predisposes to type-2 diabetes in genetically susceptible individuals. Insulin resistance and pancreatic islet beta-cell defect (leading to relative insulin deficiency) are the characteristic pathophysiologic findings in type-2 diabetes. The etiology of the insulin secretory defect in type-2 diabetes is not well understood, but genetic factors probably are involved.
Worldwide Epidemic of Type-2 Diabetes
Type-l diabetes is predominantly a disease of persons of European ancestry and is much less prevalent among persons of African, Asian and other non-European descent, whereas type-2 diabetes is disproportionately more prevalent in non-European than European populations. Because type-2 diabetes accounts for >90% of all cases of diabetes worldwide, the current diabetes epidemic is attributable predominantly to rising cases of type-2 diabetes. It has been estimated that the worldwide prevalence of diabetes in adults will increase to 300 million persons (5.4%) by the year 2025.
Table 1. Risk factors for type-2 diabetes
|Family history Racial/ethnic origin Older age||Obesity/weight gain Physical inactivity Overeating||History of hypertension History of dyslipidemia|
Currently, diabetes is still more prevalent in developed than in developing countries (with notable exceptions, such as the Pima Indians and Pacific Islanders of Kiribati, Nauru and other high-risk groups). However, the major part of the predicted increase will occur in developing countries. For example, over the period 1995-2025, the diabetes burden will increase from 51-72 million in the developed countries (an increase of 42%) but the projected increase in the developing countries will be from 84-228 million (170%). Thus, by the year 2025, more than three-quarters of all persons with diabetes will reside in developing countries. India and China are leading this surge in diabetes, and sub-Saharan Africa is following with a much lower prevalence rate, at this time. viagra uk online
The faster rate of increase in the prevalence of type-2 diabetes in developing countries may relate to the effect of westernization superimposed on latent genetic predisposition to diabetes. Studies where persons from nonwestern traditional cultures are relocated to westernized environments have reported marked escalation in the risks for obesity and diabetes. A greater burden of insulin resistance also has been reported among persons from non-European populations compared with Europeans.