Type 2 diabetes
This form of diabetes was previously called as non- insulin dependent diabetes mellitus (N1DDM) or maturity onset diabetes. Although the specific causes of this form of diabetes are not known, autoimmune destruction of beta cells does not occur. Two factors, namely deficiency of insulin secretion and resistance to insulin action in various tissues, play varying roles in causation of this heterogeneous disorder. At one end of the spectrum, there is a predominant insulin secretory defect. In these individuals, the actual (absolute) level of insulin in blood is low. At the other end of the spectrum there is predominant insulin resistance with (relative rather than absolute) insulin in the blood that may be normal or even high, compared to normal individuals. However, it is relatively inadequate (deficient) to normalise the blood glucose level. At least initially, or even throughout their life time, these individuals do not need insulin treatment to survive.
Type 2 diabetes occurs virtually in all racial and ethnic groups. Some population groups like Pima Indians of Arizona, USA, Micronesians of the Pacific islands have a very high prevalence, up to 55 percent of the population. The world wide prevalence of type 2 diabetes is increasing with an alarming speed and is expected to double, between 1995 and 2025 to 2 crores and 70 lacs. This increase will be mainly in the developing countries like India.
Both secretory defect and insulin resistance may be inherited by many mechanisms. Environmental factors like high intake of refined
Carbohydrates, fats, urbanization, sedentary life style are also important. For insulin to act on various tissues, it must first fit into certain sites on the cell surface which are called insulin receptors. If the insulin receptors decrease insulin cannot act effectively, even if present in adequate quantity. In some individuals the defect in insulin action may be at the level of receptor. Certain factors like obesity and physical inactivity worsen insulin resistance.
Type 2 diabetes is the most frequent form of diabetes worldwide and accounts for more than 90 to 95 per cent of diabetes in India. Asian Indians as a group, have a high susceptibility to type 2 diabetes. Further, in Asian Indians, the onset of diabetes is believed to start a decade earlier compared to Western population. Type 2 diabetes affects both sexes and the rich and the poor.
The prevalence (number of persons having the disease in a particular place at a particular date) of diabetes in India, is reaching alarming proportions. Large population surveys in India have shown that diabetes affects around 12-14% of adults above the age of 20 years. More disturbingly, the prevalence of the so-called borderline diabetes (or impaired glucose tolerance) is also around 12-14%, a third of these individuals are expected to develop frank diabetes over time. An increasing number of Indians in their twenties and thirties are developing diabetes. The prevalence in urban areas is 3-4 times that in rural areas. For every diagnosed diabetic, there could be two or three undiagnosed diabetics. It is a myth that it is a disease only of the urban and affluent class.
Most patients are detected after 30 years of age of onset, a decade earlier than in the west. With increasing global prevalence of obesity in children and adolescents, type 2 diabetes is now seen in those age groups.
This form of diabetes frequently goes undiagnosed for many years. This is because the rise in blood glucose occurs gradually and is initially not severe enough to produce any complaints. Nevertheless, such patients are at an increased risk of developing various long-term complications and in fact may present with them. Accumulation of ketones in the blood seldom occurs spontaneously; When seen, it usually arises in association with the stress of another illness such as infection.
Many patients with this form of diabetes are obese. Patients who are not obese by traditional weight criteria may have an increased percentage of body fat distributed predominantly around the waist. The waist to hip ratio that is the smallest circumference between the rib cage and pelvic bone divided by the largest circumference around the hips, is normally about 0.72. If it exceeds 1.0 in males and 0.9 in females, it is suggestive of insulin resistance. Insulin resistance may improve with weight reduction in obese individuals and/or drugs but is seldom restored to normal. Insulin resistance often present as a velvety, brownish-black pigmentation called acanthosis nigricans. This is typically seen in the nape of the neck, armpits, groins and other skin folds. Women with insulin resutance may have associated unwanted male pattern hair over face, chest, abdomen, back and thighs. Such women may have excess oiliness of skin, acne, irregular menses and difficulty in conceiving. The risk of developing this form of diabetes increases with age, obesity and lack of physical activity. It occurs more frequently in women who have developed diabetes in pregnancy and individuals with high blood pressure and abnormal blood lipids (fats in blood). It has been proposed that a low birth weight reflects poor foetal development of various organs including the pancreas, liver and muscle. This may lead to diabetes in adult life especially if there is accompanying obesity.