This non-promotional disease awareness website for members of the UK general public is developed and funded by Sanofi.

Woman standing outdoors holding a basket of toys and looking confidently ahead
Woman standing outdoors holding a basket of toys and looking confidently ahead

What is Autoimmune
Type 1 Diabetes (T1D)?

What is T1D, its causes and how it develops

Overview

  • Type 1 Diabetes is an autoimmune condition. This means the body’s immune system mistakenly attacks the insulin‑producing cells in the pancreas.1–3
  • Insulin is a hormone that helps move glucose from the blood into the body’s cells for energy.4
  • Over time, as more of these cells are lost, the body can no longer control blood sugar on its own, and insulin injections become necessary.3
  • T1D often develops slowly and quietly, with no obvious symptoms at first.2
  • Learning about the condition can help you and your family feel prepared and informed.
test

Key Facts About Type 1 Diabetes in the UK

  • Around 464,000 people in the UK live with Type 1 Diabetes.14
  • It can develop at any age, but is more commonly diagnosed in childhood or early adulthood.6–7 Read who may be at greater risk of T1D
  • T1D is an autoimmune condition and is not caused by lifestyle, diet, or personal choices .11,13
  • More than 1 in 4 children are diagnosed after developing diabetic ketoacidosis (DKA), a serious complication that needs urgent care.12 Know the symptoms and complications of T1D

How Does aT1D Develop?

Icon showing immune system activation attacking insulin-producing cells

1. Immune system activation

Normally, the immune system protects the body from infections. In T1D, it mistakenly identifies the insulin producing cells as harmful and begins to attack them.1–5

Icon illustrating the slow silent progression of type 1 diabetes

2. Autoimmune progression

This autoimmune process may continue for months or years without symptoms.2,4

Icon illustrating declining insulin production in the pancreas

3. Declining insulin production

As more insulin producing cells are lost, the pancreas produces less insulin. Blood glucose becomes harder to control naturally.2,10

Icon representing the emergence of symptoms in type 1 diabetes

4. Symptoms emerge

When insulin levels fall too low, symptoms such as thirst, weight loss, tiredness, and needing the toilet more often can start to appear. These are commonly known as the '4Ts' Toilet, Thirsty, Tired, and Thinner.4,15

Read more in our next section on the difference between T1D and T2D.
Icon representing lifelong insulin therapy for people with type 1 diabetes

5. Diagnosis & Lifelong Management

At diagnosis, individuals with T1D may require insulin therapy to maintain safe blood glucose levels and support normal metabolic function.3,6

What Causes Autoimmune Type 1 Diabetes?

Genetic factors

The exact cause of T1D is not fully understood. Current evidence suggests a combination of genetic and environmental factors.2,9 Read more about the common misconceptions and myths in the diagnosis of diabetes. Some people inherit genes that increase their likelihood of developing autoimmune conditions, including T1D. However, having these genes does not mean the condition will definitely occur.8

icon genetic factors

Environmental triggers

Environmental factors are believed to play a role in triggering this autoimmune response, although the exact causes are not fully understood. These include:6,11

  • Viral infections
  • Changes in the gut microbiome, which may affect immune regulation
  • Early‑life environmental exposures that influence immune system development
  • Other unknown environmental factors

However, these factors are not direct causes of T1D. Importantly, type 1 diabetes is not caused by diet, lifestyle, weight, or personal behaviours, and it cannot be prevented through lifestyle changes.13

icon environmental triggers
Woman sitting on a yoga mat indoors while checking the time on her smartwatch.

Know the Differences Between Type 1 and Type 2 Diabetes?

Find out why it's important
Woman standing in a shop holding a notebook with shelves of books and greeting cards behind her.

Am I or my family at risk?

Find out who may be at higher risk
Woman standing in a kitchen preparing food with organised meal containers on the counter.

Can T1D be detected early?

Explore how Early Detection can detect T1D before symptoms appear

If you are concerned about diabetes or its symptoms, please speak to your healthcare professional

References

  1. Smith DA, Germolec DR. Environ Health Perspect. 1999;107(Suppl 5):661–665.
  2. Insel RA, Dunne JL, Atkinson MA, et al. Diabetes Care. 2015;38(10):1964–1974.
  3. Diabetes UK. Differences between type 1 and type 2 diabetes. Accessed May 2026.
  4. Cleveland Clinic. Hyperglycemia (High blood sugar). Accessed May 2026.
  5. Sims EK, Besser REJ, Dayan C, et al. Diabetes. 2022;71(4):610–623.
  6. DiMeglio LA, Evans-Molina C, Oram RA. Lancet. 2018;391(10138):2449–2462.
  7. Gregory GA, Robinson TIG, Linklater SE, et al. Lancet Diabetes Endocrinol. 2022;10(10):741–760.
  8. Diabetes UK. What causes Type 1 Diabetes? Accessed May 2026.
  9. Weires MB, Tausch B, Haug PJ, et al. Exp Clin Endocrinol Diabetes. 2007;115(10):634–640.
  10. Atkinson MA, Eisenbarth GS, Michels AW. Lancet. 2014;383(9911):69–82.
  11. Bauer W, Gyenesei A, Krętowski A. Int J Mol Sci. 2021;22(14):7493.
  12. Besser REJ, Ng SM, Gregory JW et al. Arch Dis Child. 2022-107(9)-790-795.
  13. Breakthrough T1D. Fact checking myths and misconceptions about type 1 diabetes. Accessed May 2026.
  14. NICE. Diabetes - type 1 : How Common is it? Accessed May 2026
  15. Diabetes UK: Type 1 Diabetes Symptoms. Accessed May 2026
MAT-XU-2505056 (v1.0) | May 2026
Sanofi Logo

© Sanofi 2026 - All rights reserved

Privacy PolicyCookies PolicyTerms of UseContact UsAccessibilitySite MapCookie settings