Type 2 diabetes is characterized by insulin resistance and relative insulin deficiency, either of which may be present at the time that diabetes becomes clinically manifest. The specific reasons for the development of these abnormalities are not yet known.

The diagnosis of type 2 diabetes usually occurs after the age of 40 years but could occur earlier, especially in populations with a high diabetes prevalence. Type 2 diabetes can remain undetected, i.e. asymptomatic, for many years and the diagnosis is often made from associated complications or incidentally through an abnormal blood or urine glucose test.

Possible factors
Type 2 diabetes is often, but not always, associated with obesity, which itself can cause insulin resistance and lead to elevated blood sugar levels. It is strongly familial, but major susceptibility genes have not yet been identified. There are several possible factors in the development of type 2 diabetes. These include:

• Ethnicity
• Obesity, diet and inactivity
• Insulin resistance
• Family history
• Intrauterine environment
  

In contrast to type 1 diabetes, persons with type 2 diabetes are not dependent on exogenous insulin and are not ketosis-prone, but may require insulin for control of hyperglycaemia if this is not achieved with diet alone or with oral hypoglycaemic agents.

Type 2 diabetes constitutes about 85 to 95% of all diabetes in developed countries, and accounts for an even higher percentage in developing countries.