Type 2 diabetes

What it is

Type 2 diabetes (T2D) is the most common form of diabetes, accounting for 90–95% of all cases worldwide and affecting approximately 3 million Canadians — with a further 6–7 million estimated to have prediabetes. Also called adult-onset diabetes or T2D, it is a chronic metabolic condition in which the body's cells stop responding normally to insulin (insulin resistance) and the pancreas gradually loses the capacity to compensate with higher insulin output, resulting in chronically elevated blood glucose (hyperglycaemia).

Unlike type 1 diabetes, the pancreas continues to produce some insulin in T2D. The condition develops gradually, often over many years, and is frequently silent in its early stages — which is why up to 50% of people living with T2D remain undiagnosed. Long-term uncontrolled hyperglycaemia damages blood vessels and nerves throughout the body, leading to serious complications affecting the kidneys, eyes, heart, and feet. In Canada, Diabetes Canada estimates that diabetes and its complications cost the health system more than $3 billion annually.

Global prevalence has more than doubled since 1980, driven by rising rates of obesity, physical inactivity, and aging populations.

Causes and mechanism

T2D results from two interacting processes:

Insulin resistance — Peripheral tissues, particularly skeletal muscle, liver, and adipose tissue, lose their normal sensitivity to insulin. The liver continues releasing glucose into the bloodstream even when blood glucose is already elevated, and muscle cells fail to take up glucose efficiently after meals.

Beta cell failure — The pancreas initially compensates for insulin resistance by producing more insulin. Over years, this sustained demand exhausts the pancreatic beta cells, which progressively lose their secretory capacity.

A third contributor is incretin deficiency: the gut hormones GLP-1 and GIP, which normally stimulate insulin release and suppress glucagon after meals, are impaired in T2D.

Key risk factors include:

Risk factor	Notes
Obesity (visceral fat)	Strongest modifiable risk factor
Physical inactivity	Independent of weight
Age ≥ 45	Risk rises substantially after this threshold
Family history	First-degree relatives carry 2–3× higher risk
High-risk ethnicity	South Asian, East Asian, Middle Eastern, Indigenous, and Afro-Caribbean populations have significantly elevated rates in Canada
Gestational diabetes or prediabetes	Strong predictor of future T2D
PCOS	Driven by shared insulin resistance pathway
Sleep apnea	Independent metabolic risk
Certain medications	Corticosteroids, some antipsychotics

Symptoms and diagnosis

T2D often produces no symptoms for years, making routine screening essential. When symptoms do appear, they typically include increased thirst, frequent urination, unexplained fatigue, blurred vision, slow-healing wounds, recurrent urinary tract or skin infections, and tingling or numbness in the hands and feet. Acanthosis nigricans — dark, velvety skin patches in body folds — can signal underlying insulin resistance before a formal diagnosis.

Diabetes Canada recommends that all adults over 40 be screened every 3 years using a fasting plasma glucose or HbA1c test; high-risk individuals should be screened more frequently. Testing is available through LifeLabs and Dynacare across most provinces, and is covered under provincial health plans when ordered by a physician or nurse practitioner.

Diagnostic thresholds (Diabetes Canada 2024 guidelines):

Test	Prediabetes	Diabetes
Fasting plasma glucose	6.1–6.9 mmol/L	≥ 7.0 mmol/L (×2)
HbA1c	42–47 mmol/mol	≥ 48 mmol/mol (×2, or ×1 with symptoms)
2-hour OGTT (75 g)	7.8–11.0 mmol/L	≥ 11.1 mmol/L
Random plasma glucose	—	≥ 11.1 mmol/L with symptoms

A fasting lipid panel, kidney function tests, and urine albumin are typically ordered at diagnosis to assess cardiovascular and renal risk.

Treatment options

Management targets sustained glycaemic control alongside cardiovascular and kidney risk reduction.

Lifestyle interventions remain the most powerful tool at every stage. A low-glycaemic, high-fibre diet with reduced refined carbohydrates and processed foods, combined with at least 150 minutes per week of moderate aerobic activity plus resistance training, significantly improves insulin sensitivity. Weight loss of 5–15% of body weight can substantially improve — and in some cases normalize — blood glucose levels.

Pharmacological treatment follows a stepwise approach:

• Metformin — first-line for most patients; improves insulin sensitivity and reduces hepatic glucose output; inexpensive and widely covered by provincial formularies.
• SGLT2 inhibitors (empagliflozin, dapagliflozin, canagliflozin) — reduce HbA1c and carry proven benefits for heart failure hospitalization, kidney disease progression, and cardiovascular death, largely independent of glucose lowering. Current guidelines recommend them early when cardiovascular or kidney disease is present.
• GLP-1 receptor agonists (semaglutide, liraglutide) — reduce HbA1c, promote weight loss, and reduce cardiovascular events and kidney disease progression. Coverage varies by province; some formulations require special authorization.
• DPP-4 inhibitors (sitagliptin, saxagliptin) — modest glucose lowering with low hypoglycaemia risk and weight-neutral profile.
• Sulfonylureas (gliclazide) — effective and low-cost but carry a hypoglycaemia risk.
• Insulin — introduced when other agents cannot maintain adequate control; formulations range from long-acting basal to rapid-acting bolus insulin.

Complication prevention also requires blood pressure control (target below 130/80 mmHg), statin therapy for cardiovascular risk, ACE inhibitor or ARB therapy if albuminuria is present, and regular screening for retinopathy, neuropathy, nephropathy, and foot disease.

When to see a clinician in Canada

See a physician or nurse practitioner for T2D screening if you are over 40 with any risk factor (overweight, family history, hypertension), or at any age with multiple risk factors such as obesity, PCOS, a history of gestational diabetes, or membership in a high-risk ethnic group. Symptoms such as increased thirst, frequent urination, fatigue, or slow wound healing warrant prompt assessment regardless of age.

If you have been told you have prediabetes, this is the window in which lifestyle intervention is most likely to prevent or delay T2D. Virtual care platforms operating in Canada — including Felix, Maple, Cleo, and others — can facilitate initial screening conversations and referrals, though complex diabetes management typically requires in-person care with a family physician, endocrinologist, or diabetes educator.

Limitations and open questions

Research is still emerging on several fronts. The optimal HbA1c target for older adults and those with multiple comorbidities remains debated, and Diabetes Canada acknowledges that individualized targets are appropriate rather than a single threshold for all patients. The long-term durability of T2D remission after dietary intervention or bariatric surgery is not yet fully characterized — most remission data extend only 2–5 years. The mechanisms linking sleep disorders, gut microbiome composition, and T2D risk are active areas of investigation without definitive clinical guidance yet. Health Canada has not issued specific guidance on time-restricted eating or very-low-calorie diets as T2D management strategies, and evidence quality for these approaches varies. Coverage for newer agents such as GLP-1 receptor agonists remains inconsistent across provincial formularies, creating access inequities that are not yet resolved.