Type 2 Diabetes: Definition, Signs and Symptoms, and Causes
Type 2 diabetes is a metabolic disorder characterized by chronic hyperglycemia resulting from a combination of decreased insulin secretion and decreased insulin sensitivity (insulin resistance), accounting for 90-95% of all diabetes cases worldwide. 1
Definition
Type 2 diabetes is defined by the following diagnostic criteria:
- Fasting plasma glucose ≥ 7.0 mmol/L (126 mg/dL), or
- 2-hour plasma glucose ≥ 11.1 mmol/L (200 mg/dL) during an oral glucose tolerance test, or
- Hemoglobin A1C ≥ 6.5% 1
Unlike type 1 diabetes, which involves absolute insulin deficiency due to autoimmune destruction of pancreatic β-cells, type 2 diabetes involves:
- Relative insulin deficiency (rather than absolute)
- Peripheral insulin resistance
- Progressive loss of β-cell function over time 1
Signs and Symptoms
Many people with type 2 diabetes remain undiagnosed for years because symptoms develop gradually and may not be severe enough to be noticed. Common symptoms include:
- Polyuria (excessive urination) 1
- Polydipsia (excessive thirst) 1
- Polyphagia (increased hunger, sometimes) 1
- Unintentional weight loss 1
- Blurred vision 1
- Fatigue 1
- Slow-healing wounds or frequent infections 1
In the early stages, type 2 diabetes is often asymptomatic, which is why screening high-risk individuals is important 1. Even undiagnosed patients are at increased risk for developing macrovascular and microvascular complications 1.
Severe acute complications can include:
- Hyperglycemic hyperosmolar state (HHS) - more common in type 2 diabetes 1
- Diabetic ketoacidosis (DKA) - less common in type 2 diabetes but can occur during severe stress, infection, or with certain medications 1
Causes and Risk Factors
Type 2 diabetes develops from a complex interaction of genetic and environmental factors:
Primary Causes:
- Insulin resistance: Decreased biological response to insulin in target tissues 1, 2
- β-cell dysfunction: Progressive failure of pancreatic β-cells to secrete adequate insulin 3, 2
Major Risk Factors:
- Overweight or obesity (especially abdominal/visceral obesity) 1
- Physical inactivity 1
- Age (risk increases with age) 1
- Family history of diabetes (genetic predisposition) 1
- Race/ethnicity (higher risk in African Americans, Hispanic/Latino, Native Americans, Asian Americans, and Pacific Islanders) 1, 3
- History of gestational diabetes 1
- Polycystic ovary syndrome 1
- Hypertension or dyslipidemia 1
- Prediabetes (impaired fasting glucose or impaired glucose tolerance) 1
Pathophysiological Mechanisms:
- Ectopic fat deposition in liver, muscle, and pancreas 1, 2
- Chronic inflammation 2, 4
- Endoplasmic reticulum stress 2
- Oxidative stress 2, 5
- Impaired incretin effect 5
- Abnormal adipokine production 4, 5
Screening and Prevention
Screening for type 2 diabetes is recommended for:
- Adults of any age with BMI ≥25 kg/m² (or ≥23 kg/m² in Asian Americans) who have one or more additional risk factors 1
- Adults 45 years of age or older 1
Prevention strategies include:
- Weight management through healthy diet 3
- Regular physical activity (can reduce HbA1c by 0.4-1.0%) 3
- Medication (e.g., metformin) in high-risk individuals 6, 3
Long-term Complications
If not properly managed, type 2 diabetes can lead to:
- Microvascular complications: retinopathy, nephropathy, neuropathy 1, 3
- Macrovascular complications: cardiovascular disease, peripheral arterial disease, cerebrovascular disease 1, 3
- Other complications: increased susceptibility to infections, sexual dysfunction, gastrointestinal issues 1
Early diagnosis and proper management are essential to prevent or delay these complications and improve quality of life 3.