What is the primary cause of type 2 diabetes mellitus?

In type 2 diabetes mellitus, the primary contributing factor is insulin resistance, which occurs when the body's cells fail to respond effectively to insulin. This leads to a reduced ability to transport glucose into the cells, as insulin is essential for facilitating glucose uptake by tissues, especially muscle and fat cells. Over time, this impaired glucose transport results in elevated blood glucose levels, which characterizes type 2 diabetes.

While insulin deficiency is also a feature of type 2 diabetes, it is typically secondary to the primary issue of insulin resistance. Initially, the pancreas compensates by producing more insulin; however, as the condition progresses, beta cell function may decline, leading to a deficiency in insulin. Autoimmune destruction of beta cells is primarily associated with type 1 diabetes rather than type 2. High levels of epinephrine can affect blood glucose levels and metabolism but are not a primary cause of type 2 diabetes. Thus, the defect in glucose transport due to insulin resistance is the most accurate reflection of the underlying pathophysiology of type 2 diabetes.