Diabetes mellitus is a chronic disease where the body has high blood sugar because it either doesn't produce enough insulin, or can't use it effectively.

The main types are:

Type 1: Autoimmune, body destroys insulin-producing cells, requires insulin.

Type 2: Most common, body is insulin resistant or doesn't make enough, linked to lifestyle.

Gestational: Develops during pregnancy.

Symptoms include increased thirst, frequent urination, fatigue, and blurred vision. Diagnosis is via blood tests. Treatment involves lifestyle changes, medication, and/or insulin to control blood sugar and prevent serious complications like heart disease, kidney damage, and nerve damage.