Both types raise blood glucose, but they start in different ways and are treated differently. Here is what causes each one, who gets them and when, how doctors tell them apart, and why type 2 doesn’t turn into type 1.
Type 1 and type 2 diabetes share a name and a main sign: too much glucose in the blood. Underneath, they are different conditions. In type 1, the immune system destroys the beta cells in the pancreas. These cells make insulin, the hormone that lets glucose move out of the blood and into the body’s cells 1. In type 2, the body doesn’t use insulin well and can’t keep glucose at normal levels 2.
Type 2 is far more common. It makes up about 90% to 95% of diagnosed diabetes in the United States 2.
Here is what causes each type, who gets them, how they are diagnosed and told apart, and how treatment differs.
Type 1 is autoimmune, meaning the immune system attacks the body’s own tissue. The immune system destroys the insulin-making beta cells, and genes and factors in the environment may set this off 1. The World Health Organization (WHO) notes that neither the cause of type 1 nor a way to prevent it is known 8.
The process starts long before symptoms 10. In stage 1, autoantibodies (immune proteins aimed at the insulin-making islet cells) appear in the blood, but glucose is still normal. In stage 2, glucose tolerance becomes impaired. In stage 3, the signs and symptoms of clinical diabetes appear. Once someone is in stage 2, the chance of reaching stage 3 is about 75% within five years 10. When symptoms come, they usually develop quickly, over a few days or weeks 1.
Sometimes the first noticeable sign is diabetic ketoacidosis (DKA), a medical emergency in which the body runs short of insulin and acids called ketones build up 11. The US Centers for Disease Control and Prevention (CDC) says to go to the emergency room or call 911 right away if your blood sugar stays at 16.7 mmol/L (300 mg/dL) or above, your breath smells fruity, you are vomiting and can’t keep food or drinks down, you are having trouble breathing, or you have several signs and symptoms of DKA 11.
In type 2, the pancreas doesn’t produce enough insulin and the body has trouble using the insulin it has 1. That second problem is called insulin resistance: the cells in the muscles, fat and liver don’t respond well to insulin 1. Diabetes Canada’s 2024 guideline notes that the function and number of beta cells can decline in type 2, and that insulin needs are likely to rise as it progresses 6. Being overweight, not getting enough exercise and genetics all contribute 8. Symptoms tend to build slowly, over several years, and many people have none or barely notice them 1.
In plain terms: In type 1, the body stops making insulin because the immune system has destroyed the cells that make it. In type 2, the body still makes insulin, at least at first, but it doesn’t work well, and over time the pancreas may not keep up.
Type 1 is usually diagnosed in children and young adults, but it can be diagnosed at any age 2. Mayo Clinic describes two peaks in childhood, at ages 4 to 7 and 10 to 14 12. Adults are affected more often than many people think. In UK Biobank, a large British study, researchers used genetic risk to identify type 1 among 379,511 white European adults. Of those cases, 537 (42%) were diagnosed between ages 31 and 60. They made up only 4% of diabetes diagnosed after age 30, and the authors warn that later-onset type 1 is easily missed 3.
Type 2 develops over many years and is usually diagnosed in adults, though more and more often in children, teens and young adults 2. In the US SEARCH for Diabetes in Youth study, new type 2 cases among 10- to 19-year-olds rose by 5.3% a year between 2002 and 2018, compared with 2.0% a year for type 1. The most common age at diagnosis was 16 for type 2 and 10 for type 1 13.
Testing for type 2 is recommended for people with risk factors, such as being 35 or older, having overweight or obesity along with another risk factor, having had gestational diabetes, or belonging to certain racial and ethnic groups 14. Family history is much more common in type 2. Diabetes Canada puts it at about 75% to 90% of people with type 2, compared with 5% to 10% of people with type 1 4.
The same blood tests diagnose diabetes whatever the type. A fasting test is done after no calories for at least 8 hours, a random test can be done at any time of day, and an oral glucose tolerance test (OGTT) measures glucose 2 hours after a 75 g glucose drink 4. A1c reflects average glucose over the past few months; our article on A1c, GMI and average glucose explains how. Diabetes Canada uses these cut-offs 4.
| Test | Diabetes | Prediabetes |
|---|---|---|
| Fasting plasma glucose | 7.0 mmol/L (126 mg/dL) or higher | 6.1 to 6.9 mmol/L (110 to 125 mg/dL) |
| A1c | 6.5% (48 mmol/mol) or higher | 6.0% to 6.4% (42 to 46 mmol/mol) |
| 2-hour glucose in a 75 g OGTT | 11.1 mmol/L (200 mg/dL) or higher | 7.8 to 11.0 mmol/L (140 to 199 mg/dL) |
| Random plasma glucose | 11.1 mmol/L (200 mg/dL) or higher | Not used |
US labs use the same diabetes cut-offs, but their prediabetes ranges start lower, at an A1c of 5.7% (39 mmol/mol) and a fasting glucose of 5.6 mmol/L (100 mg/dL) 14. Our mmol/L and mg/dL guide covers conversions.
Without symptoms of high glucose, a result in the diabetes range must be confirmed by a repeat lab test on another day. With symptoms, one result is enough 4. Diabetes Canada does not recommend A1c for diagnosis when type 1 is suspected, and says treatment should not wait for confirmatory tests when type 1 is likely 4. These tests show that someone has diabetes. They don’t show which type.
Diabetes Canada says no diagnostic test or clinical criteria can reliably make the distinction, though extra tests can help when a case doesn’t fit the usual pattern 4. This matters most in adults, in whom type 1 can develop slowly and look like type 2 1.
Age and insulin needs. In adults, a systematic review found that diagnosis before age 30 to 40, and needing insulin within one to two years, predicted type 1 better than body mass index (BMI) 4. In UK Biobank, among people diagnosed between 31 and 60, 89% of those with type 1 used insulin in their first year, compared with 6% of those with type 2. DKA occurred in 11% versus 0.3% 3.
Autoantibodies. A clinical lab can measure four islet autoantibodies, aimed at insulin and at three other proteins called GAD, IA-2 and ZnT8 10. Diabetes Canada says one or more autoantibodies points to type 1 and a need for insulin. Levels fall over time, though, and a negative result doesn’t rule type 1 out 4.
C-peptide. This blood test shows how much insulin the pancreas is still making 7. It is usually undetectable or low in type 1 and normal or high in type 2, but it isn’t helpful while glucose is acutely high 4.
Diabetes Canada summarizes the typical features of each type like this 4.
| Feature | Type 1 | Type 2 |
|---|---|---|
| Usual age at onset | Most before 25, but any age | Usually after 25, rising in teens |
| Body weight | Usually thin, but overweight is possible | More than 90% at least overweight |
| Family history of diabetes | Infrequent (5% to 10%) | Frequent (75% to 90%) |
| Islet autoantibodies | Usually present | Absent |
| C-peptide | Undetectable or low | Normal or high |
| DKA | Common | Rare |
| First-line treatment | Insulin | Non-insulin medicines; insulin may become needed over time |
Latent autoimmune diabetes in adults (LADA) has features of both type 1 and type 2 7. Diabetes Canada classes it under type 1 4. Cleveland Clinic says that between 4% and 12% of people first diagnosed with type 2 turn out to have LADA, that it is diagnosed in adults between 30 and 50, and that it is often misdiagnosed as type 2. Insulin may not be needed for months or years, but people usually move to it as the pancreas loses its ability to make insulin 7.
Maturity-onset diabetes of the young (MODY) is caused by a change in a single gene that affects how the body makes insulin. It is inherited, is most often diagnosed before age 30, and affects an estimated 2% to 5% of people with diabetes. It can be mistaken for type 1 or type 2, and genetic testing is the only definitive way to diagnose it. Depending on the form, treatment may include diet changes, tablets such as sulfonylureas, or insulin 15.
Gestational diabetes is high glucose that starts, or is first recognized, during pregnancy 4. Testing is recommended at 24 to 28 weeks of pregnancy, and people who had gestational diabetes should be tested for type 2 after the birth, usually within 12 weeks 14. It usually goes away after the baby is born 2. Even so, a 2020 BMJ analysis of 20 studies found that type 2 was almost 10 times more likely after gestational diabetes, a relative risk of 9.51 16.
Treatment decisions belong to you and your care team; this section summarizes what guidelines and studies say.
People with type 1 need insulin to survive 8. Diabetes Canada’s 2025 guideline recommends offering automated insulin delivery (AID) to everyone with type 1 who is willing and able to use it. AID systems use an algorithm to combine an insulin pump with real-time continuous glucose monitoring (CGM). When AID isn’t possible or chosen, the guideline recommends CGM with a pump or injections 17. In adults, other glucose-lowering medicines, such as metformin, GLP-1 receptor agonists or SGLT2 inhibitors, may be considered in addition to insulin 17. Our guide to insulin on board explains how long a rapid-acting dose keeps working.
Teplizumab is approved in the United States to delay type 1 from progressing from stage 2 to stage 3. In a TrialNet trial, people who took it developed stage 3 about two years later, on average 10. Health Canada approved teplizumab (Tzield) on May 5, 2025, as the first treatment that can delay the onset of type 1 in people whose immune system is already attacking their beta cells 18.
Diabetes Canada’s 2024 guideline describes physical activity, nutrition therapy, self-management education and support, and weight management as important parts of care from diagnosis on. It recommends metformin as the first glucose-lowering medicine 6. It recommends a GLP-1 receptor agonist, an SGLT2 inhibitor or both, with proven benefit, for people at high cardiovascular risk, and an SGLT2 inhibitor for people with heart failure or chronic kidney disease. Insulin is recommended as the first medicine for people with metabolic decompensation, a serious loss of glucose control 6. It’s also not unusual for people with type 2 to start insulin later because the pancreas stops making enough 5.
Some people with type 2 reach remission. The DiRECT trial enrolled 306 adults through 49 general practices. All had been diagnosed within the past 6 years, had a BMI of 27 to 45 and were not using insulin. The program used a low-calorie formula diet, a stepped return to ordinary food and withdrawal of diabetes and blood pressure medicines. After a year, 46% of the program group were in remission, compared with 4% with usual care, and 86% of people who lost 15 kg or more were in remission 9.
An international expert group defines remission as an A1c below 6.5% (48 mmol/mol) at least 3 months after stopping glucose-lowering medicine. Because high glucose frequently comes back, the group advises against the word cure and recommends checking A1c at least once a year 19.
In type 1, the immune system destroys the cells in the pancreas that make insulin 1. In type 2, the body’s cells respond poorly to insulin and the pancreas can’t make enough 1. Type 1 needs insulin from the start, while type 2 is usually treated first with healthy behaviours and medicines such as metformin 6, 8.
No. Type 1 is autoimmune and type 2 involves insulin resistance, so one is not a later stage of the other 5. Some adults first diagnosed with type 2 turn out to have LADA, an autoimmune form that is often misdiagnosed as type 2 7.
Yes. In a UK Biobank analysis, 42% of genetically defined type 1 cases were diagnosed between ages 31 and 60 3. In some adults, symptoms develop slowly and look like type 2 1.
Type 2. It makes up about 90% to 95% of diagnosed diabetes in the United States 2, and WHO says more than 95% of people with diabetes have type 2 8.
Some people reach remission, defined as an A1c below 6.5% (48 mmol/mol) at least 3 months after stopping glucose-lowering medicine 19. In the DiRECT trial, 46% of people in an intensive weight-management program were in remission after a year 9. High glucose frequently comes back, so regular checks continue 19.
Whatever your type, it helps to see what happened around your glucose. In Glyve’s day view, the glucose line shows your own target range shaded, with logged meals, insulin, exercise, sleep and stress placed on it. You can log by typing, voice or photo, and each estimate is a draft you check before saving. The week view shows whether a pattern repeats, and the time in range guide explains the bigger picture. Glyve reads glucose from Apple Health, and Dexcom and FreeStyle Libre readings through those companies’ sharing services. Glyve is not a medical device and gives no advice. It can’t tell you which type of diabetes you have or what caused a reading.
How we write about diabetes. Spotted a mistake? Email info@glyve.ca and we’ll check it against the source.
Glyve keeps glucose, food, insulin, exercise, sleep and stress on one timeline.
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