Type 1 Diabetes

Intro

Type 1 diabetes (T1D) is a chronic autoimmune condition in which the immune system destroys the insulin-producing beta cells of the pancreas. Without insulin, the body cannot move glucose from the bloodstream into cells for energy, leading to dangerously high blood sugar levels. Type 1 diabetes accounts for roughly 5—10% of all diabetes cases and can be diagnosed at any age, though it is most commonly identified in children, adolescents, and young adults.

This guide provides a plain-language, evidence-based overview of Type 1 diabetes: what causes it, how it is diagnosed, how it is managed day to day, and what complications to be aware of. It is not a substitute for individual medical advice. If you’re unsure how Type 1 and Type 2 diabetes differ, see our overview explaining the distinction.

Key Points

Type 1 diabetes is an autoimmune condition — the immune system attacks the body’s own insulin-producing cells.
People with T1D require exogenous insulin for the rest of their lives; the condition cannot currently be managed with diet or oral medication alone.
Blood glucose monitoring (finger-stick or continuous glucose monitoring) is essential for safe day-to-day management.
Diabetic ketoacidosis (DKA) is a serious, potentially life-threatening complication that can develop quickly when insulin is insufficient.
Hypoglycaemia (low blood sugar) is the most common acute risk of insulin therapy.
Modern diabetes technology — continuous glucose monitors (CGMs), insulin pumps, and automated insulin delivery systems — has significantly improved quality of life and glycaemic outcomes.
T1D is distinct from Type 2 diabetes in cause, typical onset, and treatment approach.

Deep Dive

What Type 1 diabetes is

Type 1 diabetes is classified as an autoimmune disease. In most cases, the body produces antibodies that target and progressively destroy the beta cells in the islets of Langerhans within the pancreas. Once a critical mass of beta cells is lost (often estimated at around 80—90%), the body can no longer produce enough insulin to regulate blood glucose, and clinical symptoms appear.

The exact trigger for this autoimmune process is not fully understood. Research suggests it involves a combination of genetic susceptibility (particularly certain HLA gene variants) and environmental factors such as viral infections, though no single environmental cause has been definitively established.

Key characteristics of T1D include:

Absolute insulin deficiency — the pancreas produces little to no insulin.
Autoantibody markers — blood tests can detect islet autoantibodies (e.g., GAD65, IA-2, ZnT8, IAA) before and at diagnosis.
Onset at any age — while often diagnosed in childhood, adult-onset T1D (sometimes called latent autoimmune diabetes in adults, or LADA) is increasingly recognised.

Type 1 vs Type 2

Type 1 and Type 2 diabetes are both characterised by elevated blood glucose, but they differ in important ways:

Feature	Type 1	Type 2
Underlying cause	Autoimmune destruction of beta cells	Insulin resistance, often with progressive beta-cell decline
Insulin production	Little to none	Initially normal or elevated; declines over time
Typical onset	Childhood / young adulthood (any age possible)	Adulthood (increasingly seen in younger populations)
Body habitus at diagnosis	Often normal weight	Frequently associated with overweight/obesity
Primary treatment	Insulin (always required)	Lifestyle changes, oral medications, and sometimes insulin
Proportion of diabetes cases	~5—10%	~90—95%

Both types share the risk of long-term complications (eye, kidney, nerve, and cardiovascular disease), and both benefit from close blood glucose management.

Diagnosis

Type 1 diabetes is typically diagnosed through a combination of clinical presentation and laboratory tests.

Common presenting symptoms:

Excessive thirst (polydipsia)
Frequent urination (polyuria)
Unexplained weight loss
Fatigue and weakness
Blurred vision
In severe cases, nausea, vomiting, and abdominal pain (signs of DKA)

Diagnostic criteria (consistent with ADA guidelines):

Fasting plasma glucose of 7.0 mmol/L (126 mg/dL) or higher
Random plasma glucose of 11.1 mmol/L (200 mg/dL) or higher with classic symptoms
HbA1c of 48 mmol/mol (6.5%) or higher
Oral glucose tolerance test (OGTT) with a 2-hour value of 11.1 mmol/L (200 mg/dL) or higher

To confirm the autoimmune type, clinicians may test for islet autoantibodies and measure C-peptide levels (a marker of residual insulin production). Low or undetectable C-peptide in the presence of autoantibodies supports a T1D diagnosis.

Treatment & daily management

There is currently no cure for Type 1 diabetes. Management centres on replacing the insulin the body can no longer produce while keeping blood glucose within a target range.

Insulin therapy:

All people with T1D require insulin, delivered via multiple daily injections (MDI) or an insulin pump.
Insulin regimens typically include a long-acting (basal) insulin and a rapid-acting insulin taken at meals and for corrections.
Dosing is individualised and adjusted based on blood glucose readings, carbohydrate intake, physical activity, illness, and other factors. Specific dosing decisions should always be made with a healthcare team.

Blood glucose monitoring:

Regular monitoring is fundamental. This may involve finger-stick capillary glucose testing, continuous glucose monitoring (CGM), or both.
Most clinical guidelines recommend a target time-in-range (glucose 3.9—10.0 mmol/L / 70—180 mg/dL) of at least 70% for most adults with T1D.
HbA1c testing (typically every 3—6 months) provides a longer-term picture of glucose control.

Carbohydrate awareness:

Understanding the carbohydrate content of food is important for calculating mealtime insulin.
Many people with T1D learn carbohydrate counting as a core self-management skill.

Physical activity:

Exercise is encouraged for overall health but requires planning because it affects blood glucose levels, sometimes unpredictably.
Activity can cause blood glucose to drop (during and after aerobic exercise) or rise (during intense or anaerobic exercise).

Sick-day management:

Illness, infection, and physiological stress can raise blood glucose significantly and increase the risk of DKA.
People with T1D are advised to have a sick-day plan developed with their healthcare team.

Diabetes technology

Technology has transformed T1D management over the past two decades.

Continuous glucose monitors (CGMs):

Small sensors worn on the body that measure interstitial glucose every few minutes and transmit readings to a receiver or smartphone.
Provide trend data, alerts for highs and lows, and detailed reports.
Widely recommended by guidelines for people with T1D on intensive insulin therapy.

Insulin pumps:

Small devices that deliver rapid-acting insulin continuously (basal rate) and in boluses at mealtimes.
Allow more flexible dosing and can reduce the number of daily injections.

Automated insulin delivery (AID) / hybrid closed-loop systems:

Combine a CGM and an insulin pump with an algorithm that automatically adjusts basal insulin delivery based on sensor glucose readings.
Users still need to bolus for meals, but the system helps manage glucose between meals and overnight.
Clinical trials have shown improvements in time-in-range and reductions in hypoglycaemia with AID systems.

Digital tools:

Apps for logging food, insulin doses, and glucose data.
Cloud-based platforms that allow data sharing with healthcare teams and family members.

Risks & complications

Acute complications:

Diabetic ketoacidosis (DKA): Occurs when there is not enough insulin in the body, leading to a buildup of ketones (acidic byproducts of fat breakdown). DKA is a medical emergency with symptoms including nausea, vomiting, abdominal pain, fruity-smelling breath, rapid breathing, and confusion. It can develop within hours and requires urgent hospital treatment.
Hypoglycaemia: Blood glucose falling below approximately 3.9 mmol/L (70 mg/dL). Mild episodes cause shakiness, sweating, and hunger. Severe hypoglycaemia can lead to confusion, seizures, or loss of consciousness and may require assistance from another person.

Long-term complications (associated with prolonged elevated blood glucose):

Retinopathy — damage to blood vessels in the retina, a leading cause of vision loss.
Nephropathy — kidney damage that can progress to kidney failure.
Neuropathy — nerve damage, most commonly in the feet and hands (peripheral neuropathy) or affecting digestion and heart rate (autonomic neuropathy).
Cardiovascular disease — increased risk of heart attack, stroke, and peripheral arterial disease.
Foot complications — reduced sensation and poor circulation increase the risk of ulcers and infections.

Regular screening (eye exams, kidney function tests, foot checks, cardiovascular risk assessment) is recommended to detect complications early when interventions are most effective.

Living with Type 1 diabetes

Type 1 diabetes is a lifelong condition that requires continuous self-management. Key aspects of daily life include:

Routine and flexibility: Balancing consistent habits (meal timing, monitoring) with the ability to adapt to changing circumstances.
Education: Structured diabetes education programmes (such as DAFNE in the UK or equivalent programmes elsewhere) help people develop the skills to manage their condition confidently.
Mental health: The psychological burden of T1D is well documented. Diabetes distress, anxiety, depression, and fear of hypoglycaemia are common and should be addressed as part of holistic care.
Support networks: Peer support, diabetes charities, and online communities can be valuable sources of information and encouragement.
Workplace and school: People with T1D are generally able to participate fully in education and employment, though accommodations (e.g., time for blood glucose checks and insulin administration) may be needed.
Driving: Many jurisdictions have specific medical requirements for drivers with insulin-treated diabetes, typically involving regular blood glucose checks before and during driving.
Pregnancy: With careful planning and close monitoring, people with T1D can have healthy pregnancies. Pre-conception counselling and tight glycaemic control before and during pregnancy are strongly recommended.

FAQ

Q: Can Type 1 diabetes be prevented? A: Currently, there is no proven way to prevent Type 1 diabetes in the general population. Research into immunotherapy and other interventions (such as teplizumab, which has been shown to delay onset in high-risk individuals) is ongoing.

Q: Is Type 1 diabetes caused by eating too much sugar? A: No. Type 1 diabetes is an autoimmune condition. Diet does not cause it. This is a common misconception that conflates T1D with Type 2 diabetes risk factors.

Q: Can people with Type 1 diabetes eat sugar and carbohydrates? A: Yes. People with T1D can eat a varied diet, including foods that contain sugar and carbohydrates, as long as they adjust their insulin accordingly. There are no foods that are strictly off-limits.

Q: What is the difference between Type 1 and Type 1.5 (LADA)? A: LADA (latent autoimmune diabetes in adults) is a form of autoimmune diabetes diagnosed in adulthood that progresses more slowly than classic Type 1. It is sometimes called Type 1.5, though it is not a formally distinct type in most classification systems. LADA is managed similarly to T1D once insulin dependence develops.

Q: How is Type 1 diabetes different from gestational diabetes? A: Gestational diabetes develops during pregnancy in people who did not previously have diabetes and usually resolves after delivery. Type 1 diabetes is a permanent autoimmune condition that is present before, during, and after pregnancy.

Q: What happens if someone with Type 1 diabetes stops taking insulin? A: Without insulin, blood glucose rises uncontrollably, and the body begins breaking down fat for energy, producing ketones. This leads to diabetic ketoacidosis (DKA), which is life-threatening without prompt treatment. People with T1D must take insulin every day.

Q: Is a cure for Type 1 diabetes being researched? A: Yes. Active areas of research include islet cell transplantation, stem-cell-derived beta cells, immune modulation to halt or reverse the autoimmune process, and bioartificial pancreas devices. Progress is being made, but no cure is currently available for routine clinical use.

Q: At what age is Type 1 diabetes typically diagnosed? A: T1D can be diagnosed at any age. There are two peak periods of diagnosis: one between ages 4 and 7, and another between ages 10 and 14. However, roughly half of all T1D diagnoses now occur in adults.