ConditionHormones & metabolism
Type 1 Diabetes
Type 1 diabetes is an autoimmune disease in which the immune system destroys the insulin-making beta cells of the pancreas, so the body can no longer control blood sugar. It usually starts in children and young adults, though it can begin at any age. Classic symptoms are extreme thirst, frequent urination, weight loss and tiredness. Without insulin it leads to diabetic ketoacidosis, which is life-threatening. With insulin, glucose monitoring and support, people live full, active lives.
Also called: Type 1 diabetes mellitus, T1D, insulin-dependent diabetes, juvenile diabetes, autoimmune diabetes
At a glance
- What it is
- Autoimmune destruction of insulin-producing cells, causing lifelong insulin deficiency.
- Who gets it
- Often diagnosed in childhood or young adulthood, but up to half of cases begin in adults.
- Warning signs
- Thirst, frequent urination, bedwetting, weight loss, tiredness, blurred vision.
- Emergency
- Diabetic ketoacidosis (vomiting, abdominal pain, deep breathing, drowsiness).
- Treatment
- Insulin by injection or pump, glucose monitoring, carbohydrate counting.
- Outlook
- Good control greatly reduces the risk of eye, kidney, nerve and heart complications.
When to get help
Call 911 or go to the ER
- Vomiting, abdominal pain, fruity-smelling breath, deep or fast breathing, drowsiness or confusion, especially with high blood sugar or ketones (possible diabetic ketoacidosis)
- Someone with diabetes who is unconscious, having a seizure or unable to swallow safely because of low blood sugar. Call 911. Give glucagon if available. Do not put food in their mouth
- Moderate or large ketones that do not fall after extra insulin and fluids, or vomiting that prevents keeping fluids down
See a doctor within a day or two
- A child or adult with increased thirst, frequent urination, bedwetting after being dry, and weight loss. Get a same-day blood or urine glucose test
- Blood sugar repeatedly over 250 mg/dL (13.9 mmol/L) with ketones
- Frequent or severe lows, or lows without warning symptoms
Book a routine appointment
- Rising HbA1c, problems with pump or sensor, or emotional burnout with diabetes care
- Annual eye, kidney, foot and thyroid checks
- Family members of someone with type 1 who want autoantibody screening
Usually safe to manage at home
- A mild low (below 70 mg/dL or 3.9 mmol/L) treated with 15 g of fast-acting sugar and rechecked after 15 minutes
What happens in type 1 diabetes
Insulin is the hormone that lets glucose move from the blood into cells for energy. In type 1 diabetes, T cells attack the beta cells in the islets of the pancreas. The process develops silently over months to years and can be detected early by islet autoantibodies in the blood. Doctors now describe stages:
| Stage | What is happening | Symptoms |
|---|---|---|
| Stage 1 | Two or more autoantibodies, normal blood sugar | None |
| Stage 2 | Autoantibodies plus abnormal blood sugar | None |
| Stage 3 | Enough beta cells lost to cause high blood sugar | Classic symptoms, possibly DKA |
Without insulin, the body cannot use glucose and breaks down fat instead, producing acidic ketones. This leads to diabetic ketoacidosis (DKA).
Symptoms
Symptoms often develop over days to weeks:
- excessive thirst and dry mouth
- frequent urination, including at night, and new bedwetting in children
- unexplained weight loss despite eating normally or more
- tiredness and weakness
- blurred vision
- irritability and mood changes
- yeast infections, such as thrush or diaper rash in toddlers
Signs of DKA
Nausea, vomiting, abdominal pain, fruity-smelling breath, deep sighing breathing, drowsiness and confusion. About a third of children are diagnosed only when they already have DKA, so knowing the early symptoms matters.
Causes and risk factors
The exact trigger is unknown. Contributing factors include:
- Genetics: certain HLA genes. A child with a parent or sibling with type 1 has a risk of about 1 in 20 to 1 in 30, compared with about 1 in 300 in the general population
- Environmental triggers: viral infections (such as enteroviruses) are suspected
- Other autoimmune conditions, such as Hashimoto's thyroiditis and celiac disease, which are more common in people with type 1
Type 1 diabetes is not caused by eating sugar or by lifestyle.
Type 1 vs type 2 diabetes
| Type 1 | Type 2 | |
|---|---|---|
| Cause | Autoimmune loss of insulin production | Insulin resistance plus declining insulin secretion |
| Typical onset | Children and young adults, but any age | Usually adults, increasingly younger people |
| Body weight | Any, often weight loss at diagnosis | Often overweight |
| Onset | Days to weeks | Gradual, often found on routine tests |
| Treatment | Insulin always required | Lifestyle, tablets, injectables, sometimes insulin |
| Autoantibodies | Present | Absent |
Adults with type 1 are sometimes misdiagnosed with type 2. Latent autoimmune diabetes in adults (LADA) is a slower-onset form of type 1.
Diagnosis
- Blood glucose: random glucose of 200 mg/dL (11.1 mmol/L) or higher with symptoms, or fasting glucose of 126 mg/dL (7.0 mmol/L) or higher.
- HbA1c of 6.5% or higher (may be normal early in rapid-onset cases).
- Ketones in blood or urine.
- Islet autoantibodies (GAD65, IA-2, ZnT8, insulin) confirm autoimmune diabetes.
- C-peptide shows how much insulin the body still makes.
Children with symptoms should have a fingerstick glucose the same day and, if high, be referred urgently, rather than waiting for routine tests.
Treatment
Insulin
Everyone with type 1 needs insulin for life, given as:
- Multiple daily injections: long-acting (basal) insulin once or twice a day plus rapid-acting (bolus) insulin with meals and to correct highs
- Insulin pumps: deliver rapid-acting insulin continuously through a small tube or patch
Glucose monitoring
- Continuous glucose monitors (CGMs): a small sensor under the skin reads glucose every few minutes and alerts to highs and lows. Recommended for most people with type 1.
- Fingerstick meters as backup.
Automated insulin delivery
Hybrid closed-loop systems connect a CGM and pump with software that adjusts insulin automatically. They improve time in range and reduce lows, especially overnight.
Daily management
- carbohydrate counting and matching insulin to meals
- adjusting for exercise, illness, stress and alcohol
- sick day rules: never stop basal insulin, check ketones, drink fluids, and call your team if ketones rise
- always carrying fast-acting sugar and having glucagon available
Targets
Typical goals for many people are HbA1c below 7% and at least 70% of CGM readings between 70 and 180 mg/dL (3.9 to 10 mmol/L), with less than 4% below 70. Goals are individualized.
Newer treatments
- Teplizumab, an immune therapy, can delay the onset of stage 3 type 1 diabetes by about 2 to 3 years in people aged 8 and older with stage 2 disease.
- Islet cell transplantation is an option for a small number of adults with severe, unpredictable lows. Stem cell-derived islet therapies are in clinical trials.
Complications
Short-term
- Hypoglycemia (low blood sugar): shakiness, sweating, hunger, confusion. Treat with 15 g of fast-acting sugar and recheck after 15 minutes.
- Diabetic ketoacidosis.
Long-term
High glucose over years damages blood vessels and nerves:
- eyes: diabetic retinopathy
- kidneys: diabetic nephropathy
- nerves: peripheral neuropathy and foot problems
- heart attack and stroke
Landmark studies showed that keeping glucose close to target markedly reduces these complications.
Regular checks
Annual eye exams, kidney tests (urine albumin and creatinine), foot exams, blood pressure, cholesterol, thyroid function, and celiac screening when indicated.
Living with type 1 diabetes
People with type 1 diabetes work, play sports, travel and have healthy pregnancies with planning. Diabetes education, a care team, school care plans for children, and mental health support for diabetes distress all help. Peer support communities are valuable for many families.
Frequently asked questions
What are the first signs of type 1 diabetes?
The first signs are usually extreme thirst, frequent urination (including bedwetting in children who were dry), unexplained weight loss, tiredness and blurred vision. Nausea, vomiting, abdominal pain and heavy breathing suggest diabetic ketoacidosis, which is an emergency.
What causes type 1 diabetes?
It is caused by the immune system attacking the insulin-producing cells of the pancreas. Genes play a role, and environmental triggers such as viral infections are suspected. It is not caused by eating too much sugar or by lifestyle choices.
Can adults get type 1 diabetes?
Yes. Many people are diagnosed as adults, sometimes in their 30s, 40s or later. Adult-onset type 1 can develop more slowly and is sometimes mistaken for type 2. Autoantibody tests help make the correct diagnosis.
Can type 1 diabetes be cured?
Not yet. It is managed lifelong with insulin. Teplizumab can delay onset in people at high risk, and islet transplants help a small number of adults. Research into stem cell-derived islets and immune therapies is active and promising.
Can type 1 diabetes be prevented?
There is no proven way to prevent it. Screening relatives for autoantibodies can identify early-stage disease, which allows monitoring to prevent DKA at diagnosis and gives the option of teplizumab to delay the onset of symptoms.
Sources
This guide was written from current patient and clinical guidance, including:
- American Diabetes Association: Standards of Care in Diabetes (2026)
- National Institute of Diabetes and Digestive and Kidney Diseases: What Is Diabetes? Type 1 diabetes
- CDC: Type 1 Diabetes
- Breakthrough T1D (formerly JDRF): Type 1 diabetes facts
- International Society for Pediatric and Adolescent Diabetes: Clinical Practice Consensus Guidelines (2022)