Causes of type 2 diabetes are multifactorial and complex. Insulin resistance and abnormal insulin secretion are at the center to the development of type 2 diabetes. Many studies suggest that insulin resistance occurs before an insulin secretory defect and diabetes develops only when insulin secretion becomes inadequate. The genetic factor in development of type 2 diabetes is very strong in compare to type-1 diabetes. Environmental factors also play a strong role in causation of type-2 diabetes.

Genetic factor in causation of type 2 diabetes:

The genetic factor in causation of type 2 diabetes is very strong. The concordance of type 2 diabetes in identical twins is between 70% and 90%. If both parents have type 2 diabetes, the risk of development of type-2 diabetes among children is approximately 40%. Many first degree relatives of type-2 diabetes patients have reduced glucose utilization in skeletal muscles without diabetes, due to insulin resistance.

Environmental factors in causation of type-2 diabetes:

Environmental factors are equally important, if not more important than genetic factor in causation of type 2 diabetes. Factors such as obesity and overweight, over nutrition, and physical inactivity are important causative factors of type 2 diabetes.

Obesity, especially central or visceral obesity (accumulation of fat in the viscera and in the abdomen) is important in causation of type 2 diabetes. The increased fat cell mass results in increased circulating free fatty acids and other products of fat cells, such as nonesterified free fatty acids, retinol-binding protein 4, leptin, TNF-alpha etc. The fat cell products modulate insulin sensitivity; regulate body weight, appetite, as well as energy expenditure. Increased free fatty acids and other fat cell products may lead to insulin resistance in skeletal muscle and liver, by impairing glucose utilization in skeletal muscle, increased production of glucose in liver and by impairing function of beta cells of pancreas, which secrete insulin. Increased fat cell mass reduce production of adiponectin, an insulin-sensitizing peptide and contribute to insulin resistance. Fat cell products may also cause inflammatory state.

Over-nutrition and physical inactivity mostly acts as causative factors by indirectly promoting obesity.