There are various forms of diabetes (diabetes mellitus), with the commonest being type 1 and type 2 diabetes. Elevated blood glucose levels are common to all types of diabetes. Blood glucose levels may be high due to a lack of the hormone insulin and/or a reduction in the effect of the hormone. Insulin regulates the amount of blood glucose entering the cells. About 90 % of diabetics suffer from type 2 diabetes. About 537 million adults worldwide have diabetes, most of whom have type 2 diabetes, and this number is expected to rise to 783 million by 2045. Globally, the proportion of people living with undiagnosed diabetes is around 45%, but this figure ranges from 54% in Africa to 24% in North America and the Caribbean regions.

Type 2 diabetes is a condition caused by a reduction in sensitivity to insulin (insulin resistance) and a decrease in insulin production due to a persistently high insulin requirement, which ultimately overwhelms the insulin-producing cells in the pancreas. It often develops slowly and was formerly associated mainly with older adults but now occurs increasingly in younger people and adolescents as well. Risk factors are genetic predisposition, being overweight, lack of exercise, an imbalanced diet and smoking. Type 2 diabetes is associated with increased risk of both microvascular (of minute blood vessels) complications (i.e. retinopathy, neuropathy, and nephropathy) and macrovascular (of large blood vessels) complications (i.e. ischemic heart disease, cerebrovascular disease, and peripheral vascular disease).

Whilst in people with type 1 diabetes the absolute insulin deficiency is primarily treated with insulin, treatment of type 2 diabetes focuses initially on lifestyle changes such as increased exercise, a change in diet and weight normalization to improve insulin resistance and reduce the insulin requirement. If these changes are not enough, drug therapies are available, often administered in the form of tablets. If blood glucose control is still insufficient, insulin may also need to be administered to people with type 2 diabetes.