Why does type 2 diabetes cause glucose to accumulate in the blood?

In type 2 diabetes, glucose accumulates in the blood because the body’s cells—specifically muscle and adipose (fat) cells—become resistant to the effects of insulin.12

Normally, insulin acts as a key that triggers these cells to take up glucose from the bloodstream to be used for energy. In individuals with type 2 diabetes, this signaling process is impaired, meaning the cells do not respond effectively to insulin and therefore take up less glucose. Additionally, some patients may experience a deficiency in insulin production, where the pancreas fails to secrete enough of the hormone to compensate for this resistance.1324

Because the cells cannot efficiently absorb the glucose, it remains in the circulation, leading to hyperglycemia (high blood sugar). When blood glucose levels become sufficiently high, the excess sugar is excreted through the urine, which often results in increased urinary volume and thirst.12