Diabetes Mellitus is primarily caused by:

Diabetes Mellitus is primarily characterized by elevated blood glucose levels due to the body's inability to effectively utilize insulin or an insufficient production of insulin. Insulin is a crucial hormone produced by the pancreas that facilitates the uptake of glucose into cells, allowing for its use as energy. In Type 1 Diabetes, there is an autoimmune destruction of the insulin-producing beta cells in the pancreas, leading to a deficiency of insulin. In Type 2 Diabetes, although the pancreas may initially produce insulin, the body's cells become resistant to its effects, resulting in a relative insulin deficiency over time.

In both forms of Diabetes Mellitus, the key underlying problem is a deficiency of insulin function or production, which directly leads to hyperglycemia and the subsequent metabolic complications associated with the disease. The understanding of insulin's role is fundamental to grasping the pathophysiology of Diabetes Mellitus.