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There are two types of diabetes. In both, the body cannot regulate the level of glucose in the blood. This is because the body either stops producing the hormone insulin or does not respond properly to the insulin that is being made.
This model shows the structure of insulin. It is a complex protein hormone. Image courtesy of: T. Blundell & N. Campillo / Wellcome Images
Symptoms: develop quickly. Tiredness, excessive urine production, weight loss, increased thirst and blurred vision.
Symptoms: same as for type 1 but less severe and may go undetected for many years.
Diabetes does not have just one cause. Many factors influence whether a person develops diabetes or not. These include lifestyle, diet and genetic make-up.
Type 1 diabetes is an auto-immune disease. The person's immune system attacks the cells in the pancreas that make insulin. These cells are called the islets of Langerhans. The immune system destroys them as if they were an infection. Insulin production is quickly and dramatically stopped.
People with type 1 diabetes often have a particular form of a gene that is involved in the production of cell-recognition proteins. They trigger the immune system to destroy the insulin-producing cells.
It may soon be possible to develop a genetic test to identify people who are at a high risk of developing type 1 diabetes. It may even become possible to replace the faulty gene using gene therapy.
Obesity, and a lack of physical exercise, are linked to an increased likelihood of developing type 2 diabetes. It is more likely to develop if people have a diet that contains lots of saturated fats, sugar and is low in fibre. Some insulin production continues but the liver and body cells do not respond to it normally.