**2. Definition**

Type 1 diabetes mellitus is an autoimmune disease in which the pancreas is unable to respond to secretagogue stimulation with appropriate insulin secretion. Hyperglycemia develops when more than 70-90% of the insulin-producing beta cells are destroyed. An autoimmune destructive process, which plays a central role in the development of type 1 diabetes mellitus, is facilitated by the subject's own genetic susceptibility and by non-genetic factors. Non-genetic factors include viral infections, toxic chemicals, and others. Vitamin D deficiency is a non-genetic factor that appears to be associated with an increased risk of developing type 1 diabetes mellitus.

Type 1 diabetes mellitus complications are classified into acute and chronic. The acute complications include life-threatening conditions like severe hypoglycemia or diabetic ketoacidosis (DKA). Chronic diabetic complications can be divided into microvascular complications (retinopathy, neuropathy and nephropathy) and macrovascular complications (cardiovascular, cerebrovascular and peripheral vascular disease). Severe microvascular and macrovascular complications can lead to renal failure (the most common cause of hemodialysis in the US), blindness or lower extremity amputations.

Overall, uncontrolled diabetes mellitus in patients over 50 years of age reduces life expectancy in males and females by 7.5 and 8.2 years respectively (Franco et al.,2007).
