What Is Type 2 Diabetes?
Type 2 diabetes (T2D) is a metabolic disorder in which the body's cells become resistant to insulin, and the pancreatic beta cells can no longer compensate with sufficient insulin production. The result is persistently elevated blood glucose levels that damage blood vessels and nerves over time. T2D accounts for 90–95% of all diabetes cases, affecting over 37 million Americans.
How Is It Diagnosed?
- HbA1c ≥ 6.5% — reflects average blood glucose over 2–3 months
- Fasting plasma glucose ≥ 126 mg/dL
- 2-hour glucose ≥ 200 mg/dL during oral glucose tolerance test
- Random glucose ≥ 200 mg/dL with classic symptoms (polyuria, polydipsia, unexplained weight loss)
Prediabetes is diagnosed at HbA1c 5.7–6.4% or fasting glucose 100–125 mg/dL. At this stage, intervention can prevent or significantly delay progression to T2D.
Prevention: The Diabetes Prevention Program
The landmark Diabetes Prevention Program (DPP) trial showed that intensive lifestyle intervention (7% weight loss + 150 min/week of moderate exercise) reduced the incidence of T2D by 58% in high-risk individuals with prediabetes — more effective than metformin (31% reduction). For every kilogram of weight lost, T2D risk fell by 16%. These benefits persist for over a decade after the intervention.
Management
Lifestyle Foundation
A diet low in refined carbohydrates and processed foods, regular aerobic exercise (150+ min/week), and sustained weight loss form the cornerstone of T2D management. A Mediterranean or low-carbohydrate diet can reduce HbA1c by 0.5–1.0% beyond medication effects alone.
Metformin
Metformin remains the preferred first-line oral medication — it lowers hepatic glucose production, is weight-neutral or causes modest weight loss, has an excellent safety profile, is inexpensive, and reduces cardiovascular events. It is contraindicated in severe kidney disease (eGFR <30).
GLP-1 Receptor Agonists
Semaglutide (Ozempic/Wegovy), liraglutide (Victoza/Saxenda), and dulaglutide (Trulicity) lower HbA1c by 1–2%, cause significant weight loss (6–15%), and reduce major cardiovascular events and kidney disease progression. They are now recommended as second-line agents for patients with established cardiovascular disease or obesity.
SGLT2 Inhibitors
Empagliflozin (Jardiance), dapagliflozin (Farxiga), and canagliflozin (Invokana) lower blood sugar by causing the kidneys to excrete glucose in the urine. They also reduce heart failure hospitalisations by ~35% and slow CKD progression — benefits that are largely independent of glucose lowering.
Monitoring and Targets
The standard HbA1c target for most adults is <7% (53 mmol/mol), though targets should be individualised — less strict for older patients with multiple comorbidities, more strict for younger patients early in their disease. Continuous glucose monitors (CGM) are increasingly used to identify postprandial glucose spikes and guide medication adjustments.
Long-Term Complications
Uncontrolled T2D damages the kidneys (diabetic nephropathy — leading cause of dialysis), retina (retinopathy — leading cause of blindness), peripheral nerves (neuropathy causing pain and loss of sensation), and blood vessels (increasing heart attack and stroke risk 2–4-fold). Good glycaemic control, blood pressure management, and statin therapy dramatically reduce complication risk.