Diabetes mellitus

Glucose is an important source of energy, and the hormone insulin—made by the pancreas—helps it move from the bloodstream into cells. Diabetes develops when the pancreas does not produce enough insulin or the body cannot use the insulin effectively. As a result, blood glucose can remain abnormally high. Diabetes is a group of related disorders rather than a single condition, and its causes and course vary by type.

The three main types are type 1, type 2 and gestational diabetes. Type 1 usually results from an autoimmune reaction that destroys insulin-producing cells in the pancreas, leaving the body with little or no insulin; people with type 1 need insulin every day to survive. In type 2, the body's cells do not respond normally to insulin, and over time the pancreas may not produce enough to keep blood glucose in the normal range. Type 2 is the most common form and can occur at any age. Gestational diabetes is diagnosed during pregnancy and often has no noticeable symptoms. Other, less common forms also exist.

Possible symptoms include increased thirst, frequent urination, tiredness, blurred vision and unintentional weight loss. They can develop quickly in type 1, while type 2 may progress gradually and go unnoticed for years. Long-standing high blood glucose can damage blood vessels and nerves and raise the risk of problems affecting the heart, eyes, kidneys and limbs. Risk factors vary by type. Type 2 risk is associated with factors including family history, overweight and physical inactivity, although it can affect people with different body types and at any age. Healthy eating and regular physical activity can help prevent or delay some cases of type 2 diabetes; type 1 is not currently known to be preventable.

Management depends on the form of diabetes and a person's circumstances. It may include monitoring blood glucose, food and activity choices, medicines, regular clinical follow-up and screening or treatment for complications. Insulin is essential for people with type 1 diabetes; care for type 2 and gestational diabetes is individualized and may also involve medication. Timely diagnosis and continuing care can reduce the risk of serious complications, but diabetes requires ongoing management rather than a one-time treatment.