Medically reviewed by Dr. Raymond Osei, MD, MPH
Senior Medical Advisor · Last reviewed January 2025

Diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both. According to the CDC's National Diabetes Statistics Report, approximately 37.3 million Americans — 11.3% of the population — have diabetes. An estimated 96 million have prediabetes.

Type 1 Diabetes

Type 1 diabetes is an autoimmune condition in which the immune system destroys the insulin-producing beta cells of the pancreas, resulting in absolute insulin deficiency. It accounts for approximately 5–10% of all diabetes cases and typically presents in childhood or young adulthood, though onset can occur at any age. Individuals with Type 1 diabetes require lifelong insulin therapy. Modern management options include multiple daily injections (MDI) and continuous subcutaneous insulin infusion (CSII/insulin pump), often guided by continuous glucose monitoring (CGM).

Type 2 Diabetes

Type 2 diabetes — accounting for 90–95% of all diabetes — is characterized by insulin resistance (cells do not respond normally to insulin) combined with progressive beta-cell dysfunction. It is strongly associated with excess adiposity, physical inactivity, and genetic factors. Unlike Type 1, Type 2 diabetes can often be prevented or delayed with lifestyle modification and can sometimes be put into remission with intensive lifestyle intervention or bariatric surgery.

Diagnosis Criteria

Diabetes is diagnosed by any of the following: fasting plasma glucose ≥126 mg/dL; 2-hour plasma glucose ≥200 mg/dL during an oral glucose tolerance test; HbA1c ≥6.5%; or random plasma glucose ≥200 mg/dL with symptoms of hyperglycemia. Prediabetes is defined by fasting glucose 100–125 mg/dL, 2-hour OGTT glucose 140–199 mg/dL, or HbA1c 5.7–6.4%.

Diabetes and Mental Health

Depression affects approximately 15–25% of individuals with diabetes — two to three times the general population rate. The bidirectional relationship is well-documented: depression impairs self-management behaviors (medication adherence, dietary choices, physical activity), worsening glycemic control; and the burden of chronic disease, hypoglycemia episodes, and fear of complications contribute to depression. See our article on diabetes and mental health for a detailed discussion.