What happens in the body
In type 1 diabetes, T-lymphocytes of the immune system attack and gradually destroy the islets of Langerhans — clusters of pancreatic cells responsible for producing insulin. When insulin becomes critically scarce, glucose can no longer be taken up by cells and builds up in the blood, causing hyperglycemia. This type was formerly called "insulin-dependent" or "juvenile" diabetes, since it most often appears in children, teenagers, and young adults, though it can develop at any age.
Global prevalence
According to estimates from the IDF Diabetes Atlas (11th edition, 2025), around 9.5 million people worldwide live with type 1 diabetes — 13% more than in 2021. This type accounts for roughly 5–10% of all diabetes cases. Incidence varies significantly by region: Scandinavia diagnoses 30–60 new cases per 100,000 children each year, while East Asia and South America see only 1–3 cases per 100,000. Since the mid-20th century, the number of new cases worldwide has been rising by roughly 3–4% a year.
Causes and risk factors
The exact cause of the autoimmune reaction hasn't been fully established, but genetic predisposition — particularly the HLA gene region — is known to play a major role. If one parent has type 1 diabetes, the risk to a child is roughly 1–9%; if a sibling has it, 6–7%; and among identical twins, concordance reaches 30–70%. This shows that genes alone don't fully determine the disease — environmental factors (such as certain viral infections) likely play a role too, though their impact hasn't been conclusively proven.
Symptoms
Symptoms usually develop quickly — over days or a few weeks — and can be quite pronounced. Typical signs include:
- intense thirst (polydipsia) and dry mouth;
- frequent urination (polyuria); in children, sudden bedwetting;
- increased appetite (polyphagia) alongside weight loss;
- fatigue, irritability, blurred vision;
- in rapid-onset cases — nausea, abdominal pain, a fruity smell on the breath (signs of diabetic ketoacidosis, which requires emergency care).
Course and possible complications
Without insulin, the resulting deficiency leads to diabetic ketoacidosis — a dangerous state in which the body starts breaking down fat into acidic ketone bodies. Estimates suggest this complication occurs in the range of 1–5 episodes per 100 person-years and is a leading cause of death among people with type 1 diabetes under age 58. Severe hypoglycemia (a dangerous drop in blood sugar) is also a risk, and can cause loss of consciousness or seizures. Over the long term, chronically elevated blood sugar is linked to a higher risk of cardiovascular disease, eye damage (retinopathy), kidney damage (nephropathy), and nerve damage (neuropathy) — read more on the diabetes complications page.
How it's typically managed medically
The foundation of treatment is lifelong replacement insulin therapy — combining short-/rapid-acting insulin (before meals) with long-acting insulin, delivered by injection or an insulin pump. Regular glucose monitoring plays a key role — using a glucometer or continuous glucose monitoring (CGM) systems — along with periodic HbA1c testing to assess long-term disease control. In some cases, the medical literature also mentions additional approaches, such as pancreas or islet cell transplantation, but these are highly specialized options, not typical first-line therapy.