Type 1 diabetes

What it is

Type 1 diabetes (T1D) is an autoimmune condition in which the body's immune system destroys the insulin-producing beta cells of the pancreas, affecting approximately 300,000 Canadians and requiring lifelong insulin therapy from the moment of diagnosis. Also called insulin-dependent diabetes or — historically — juvenile diabetes, T1D accounts for 5–10% of all diabetes cases worldwide and can develop at any age, with roughly 40% of new diagnoses occurring in adults over 30.

Without functioning beta cells, the pancreas cannot produce insulin — the hormone that enables cells to absorb glucose from the bloodstream for energy. Blood glucose rises to dangerous levels, and without insulin replacement, a person with T1D will develop diabetic ketoacidosis (DKA), a life-threatening emergency, within hours to days. With appropriate management, most people with T1D lead full, active lives.

T1D is a fundamentally different condition from type 2 diabetes. The table below summarizes the key distinctions:

Feature	Type 1 Diabetes	Type 2 Diabetes
Cause	Autoimmune beta cell destruction	Insulin resistance + gradual beta cell decline
Insulin production	Absent or near-absent	Reduced but often present initially
Lifestyle contribution	None	Significant
Insulin required at diagnosis	Always	Not always
Typical onset	Any age; peaks in childhood/adolescence	Predominantly adults
Autoantibodies present	Yes (GAD65, IA-2, ZnT8, IAA)	No

In Canada, T1D is managed under provincial diabetes programs, and Diabetes Canada publishes national clinical practice guidelines that inform care across all provinces.

Causes and mechanism

T1D results from autoimmune destruction of pancreatic beta cells in genetically predisposed individuals, likely triggered by environmental factors that are not yet fully characterized.

The immune attack involves T-lymphocytes and circulating autoantibodies directed against beta cell proteins — most commonly glutamic acid decarboxylase (GAD65), islet antigen-2 (IA-2), zinc transporter 8 (ZnT8), and insulin itself. By the time classic symptoms appear, approximately 80–90% of beta cells have already been destroyed.

Genetic susceptibility is substantial. Variants in the HLA (human leukocyte antigen) region on chromosome 6 — particularly the HLA-DR3 and HLA-DR4 haplotypes — account for roughly 40–50% of genetic risk. Having a first-degree relative with T1D raises personal risk to approximately 5% if a parent is affected, and somewhat higher if a sibling is affected.

Environmental triggers under investigation include enteroviral infections (particularly Coxsackie B virus), early-life gut microbiome composition, vitamin D deficiency, and infant feeding patterns. None of these has been confirmed as a direct cause, and T1D is not caused by diet, weight, or lifestyle choices.

Symptoms and diagnosis

Classic symptoms of T1D reflect severe insulin deficiency and typically develop rapidly over days to weeks:

• Polyuria (frequent, large-volume urination)
• Polydipsia (intense, persistent thirst)
• Polyphagia (increased hunger despite eating)
• Unexplained significant weight loss
• Extreme fatigue
• Blurred vision

T1D can also present as DKA — a medical emergency marked by nausea, vomiting, fruity-smelling breath, deep laboured breathing (Kussmaul respirations), and confusion. DKA is particularly common when the diagnosis has been missed or delayed.

Diagnosis is confirmed by:

1. Fasting blood glucose above 7.0 mmol/L, or a random glucose above 11.1 mmol/L with symptoms
2. HbA1c at or above 48 mmol/mol (6.5%) on two occasions, or once in the presence of symptoms
3. Islet autoantibodies (GAD65, IA-2, ZnT8, insulin autoantibodies) — confirm autoimmune aetiology and distinguish T1D from type 2
4. C-peptide — measures residual insulin secretion; low or undetectable in T1D
5. Blood or urine ketones — elevated in DKA

In Canada, diagnostic blood work is available through provincial laboratory networks including LifeLabs and Dynacare. Autoantibody testing is typically ordered by an endocrinologist when the type of diabetes is uncertain.

Treatment options

T1D requires lifelong insulin replacement. There is currently no established cure, though research is advancing rapidly.

Insulin therapy is the cornerstone of management. A basal-bolus regimen — combining a long-acting (basal) insulin for background coverage with rapid-acting (bolus) insulin at meals — is the standard approach. Insulin pump therapy (continuous subcutaneous insulin infusion, CSII) delivers insulin continuously through a small under-skin catheter and allows precise dose adjustments that can meaningfully improve glucose control and quality of life.

Continuous glucose monitoring (CGM) uses a small sensor worn on the skin to provide real-time glucose readings, trend arrows, and alerts for high and low values. CGM has substantially reduced hypoglycaemia risk and is now considered essential to modern T1D management.

Closed-loop systems (artificial pancreas) combine an insulin pump, a CGM, and a dosing algorithm that automatically adjusts insulin delivery in response to glucose readings. These systems represent a major advance, significantly improving time-in-range glucose control without requiring constant manual input.

Teplizumab — an anti-CD3 monoclonal antibody — is the first disease-modifying therapy for T1D. In high-risk individuals who test positive for two or more islet autoantibodies but have not yet developed clinical diabetes, teplizumab delays T1D onset by approximately 2–3 years. It does not prevent T1D but represents a meaningful step toward immune-based intervention.

Ongoing monitoring includes annual HbA1c, kidney function (urine albumin, eGFR), retinal examination, foot examination, blood pressure, and lipid panel — all recommended by Diabetes Canada's clinical practice guidelines.

When to see a clinician in Canada

Seek emergency care immediately if anyone — particularly a child or young adult — develops rapid-onset extreme thirst, frequent urination, unexplained weight loss, or signs of DKA (nausea, vomiting, fruity breath, laboured breathing, confusion). DKA is life-threatening and requires hospital treatment without delay.

See a physician promptly if blood glucose readings are consistently elevated on a home glucometer, if a child or adolescent has classical diabetes symptoms, or if you have a first-degree relative with T1D and are concerned about your own risk. The ADA and Diabetes Canada both recommend autoantibody screening for first- and second-degree relatives of people with T1D.

For ongoing management, a team approach — endocrinologist, diabetes educator, dietitian, and primary care provider — is the standard of care across Canadian provinces. Referral pathways vary by province; your family physician or nurse practitioner can initiate the process.

Limitations and open questions

Research is still emerging on the precise environmental triggers that initiate beta cell autoimmunity in genetically predisposed individuals. The roles of specific viruses, gut microbiome composition, and early-life nutrition remain under active investigation, and no single trigger has been confirmed.

Teplizumab is approved in the United States but Health Canada has not yet issued a regulatory decision on its use for T1D delay as of mid-2025; Canadian patients interested in immune-modulating therapies should discuss clinical trial eligibility with a specialist.

The long-term outcomes of closed-loop insulin delivery systems are promising but evidence beyond 2–3 years remains limited. Access to CGM and insulin pump technology varies significantly across Canadian provinces, with coverage policies differing under provincial drug benefit programs — a meaningful equity gap that Diabetes Canada has publicly flagged.

Islet cell transplantation and stem cell-derived beta cell therapies are in clinical trials but are not yet standard care. Whether any of these approaches will produce a durable functional cure remains an open question.