Diabetes is a long-term condition caused by too much glucose, a type of sugar, in the blood. It is also known as diabetes mellitus.

In the UK, diabetes affects approximately 2.6 million people, and it is thought that at least half-a-million more people have the condition but are not aware of it.

There are two main types of diabetes, which are explained below:

• type 1 diabetes 
• type 2 diabetes 

What are the symptoms?

The main symptoms of diabetes are:

• feeling very thirsty
• going to the toilet a lot, especially at night
• extreme tiredness
• weight loss and muscle wasting (loss of muscle bulk)

Symptoms of type 1 diabetes can develop quickly, over weeks or even days.

Many people have type 2 diabetes for years without knowing it because early symptoms can be general.

How does diabetes occur?

Normally, the amount of sugar in the blood is controlled by a hormone called insulin, which is produced by the pancreas. The pancreas is a gland behind the stomach. When food is digested and enters your bloodstream, insulin moves any glucose out of the blood and into cells, where it is broken down to produce energy.

However, in people with diabetes, the body is unable to break down glucose into energy. This is because there is either not enough insulin to move the glucose, or because the insulin that is there does not work properly.

What is type 1 diabetes?

Type 1 diabetes occurs when the body produces no insulin. It is often referred to as insulin-dependent diabetes. It is also sometimes known as juvenile diabetes or early-onset diabetes because it usually develops before the age of 40, often during the teenage years.

Type 1 diabetes is far less common than type 2 diabetes, which occurs when the body produces too little insulin or when the cells in the body do not react properly to insulin. People with type 1 diabetes make up only 10% of all people with diabetes.

If you have type 1 diabetes, you will need to take insulin injections for life. You must also make sure that your blood glucose levels stay balanced by eating a healthy diet and carrying out regular blood tests.

For more information, including causes, symptoms and treatment of type 1 diabetes, see the Health A-Z topic on type 1 diabetes

What is type 2 diabetes?

Type 2 diabetes occurs when not enough insulin is produced by the body for it to function properly, or when the body's cells do not react to insulin. This is called insulin resistance.

Type 2 diabetes is far more common than type 1 diabetes, which occurs when the body does not produce any insulin at all. Around 90% of all adults in the UK with diabetes have type 2 diabetes.

If you have type 2 diabetes, you may be able to control your symptoms simply by eating a healthy diet and monitoring your blood glucose level. However, as type 2 diabetes is a progressive condition, you may eventually need to take insulin medication, usually in the form of tablets.

Type 2 diabetes is often associated with obesity. Obesity-related diabetes is sometimes referred to as maturity-onset diabetes because it is more common in older people.

For more information, including causes, symptoms and treatment of type 2 diabetes, see the Health A-Z topic on type 2 diabetes