Diabetes mellitus

Diabetes mellitus is a long-term metabolic disease marked by raised blood glucose, called hyperglycemia. Normally the hormone insulin, released by beta cells in the islets of the pancreas, lets body cells take up glucose from the blood. In diabetes the pancreas makes too little insulin, the cells respond poorly to it, or both, so glucose builds up in the blood and spills into the urine, the sweet urine behind the name mellitus.

In type 1 diabetes the immune system destroys the insulin-making cells, so people need insulin every day. Type 2, by far the most common form, starts with insulin resistance and is linked to excess weight and physical inactivity; it often develops slowly and can go unnoticed for years. Gestational diabetes appears during pregnancy and raises the later risk of type 2. Classic symptoms are thirst, frequent urination, tiredness, blurred vision and weight loss.

Over years, high glucose damages blood vessels and nerves, leading to heart attack, stroke, kidney failure, vision loss and foot ulcers that can end in amputation. Diagnosis rests on blood tests such as fasting glucose and HbA1c, which reflects average glucose over the previous two to three months.