Diabetes, or to use its full name diabetes mellitus, is a chronic condition caused by abnormally high levels of glucose in the blood stream.

2.6 million people have been diagnosed with diabetes in the UK equivalent, on average, to 4 out of every 100 people. About 150,000 new cases of diabetes are diagnosed every year. By 2025, because of the ageing population and the rising levels of obesity, the number of people with diabetes in the UK is expected to grow to over 4 million.

There are two forms of diabetes, type 1 and type 2. About 10% of patients have type 1 diabetes, the remaining 90% have type 2 diabetes.

Type 1 diabetes is characterised by a total lack of insulin. It usually begins under the age of 40 and there is normally no history of the disease in the family.

Type 2 diabetes is mainly due to resistance or insensitivity to insulin, rather than to a total lack of insulin, but a relative deficiency of insulin can be seen in some people. Type 2 diabetes generally occurs after the age of 40 and there is a strong history of the disease in the family. It is common in Asian and Afro-Caribbean communities and tends to appear at a much earlier age, often after the age of 25. Type 2 diabetes is particularly associated with obesity and a lack of exercise. About 60-80% of patients with type 2 diabetes are obese. It is estimated that there may be up to half a million people in the UK with type 2 diabetes who do not realise that they have the disease.

The level of glucose circulating in the blood is largely controlled by the hormone insulin, secreted by the beta cells of the pancreas. After a meal, glucose levels in the blood stream rise as the sugar is absorbed from the digested food. The pancreas responds to the rise in glucose levels by secreting insulin.

Insulin has a number of effects, but one of its main effects is to stimulate the liver to take glucose from the circulation and to convert it into glycogen, which is stored in the liver for future use. Insulin also stimulates muscle cells to take up glucose from the circulation, and this glucose is used to provide energy to power the muscles.

Diabetes occurs when the levels of glucose circulating in the blood stream remain abnormally high. This can happen for two main reasons. In type 1 diabetes there is little or no insulin secreted by the beta cells of the pancreas. The reason for this is not absolutely clear but is thought to be due to the body’s immune system attacking and destroying the beta cells. It is not known what triggers this immune response but is probably caused by a viral or bacterial infection.

In type 2 diabetes it appears that the tissues become resistant to the effects of insulin. The liver and muscle cells respond less well to the effects of the hormone and consequently are less able to remove glucose from the circulation. There may also be a decrease in the amount of insulin secreted by the pancreas.

Type 2 diabetes is strongly associated with being overweight; 60-80% of people with type 2 diabetes are obese. It is probable that the receptors on the liver and muscle cells that respond to insulin, and the beta cells of the pancreas that produce insulin, have become overloaded by the excess glucose they have to deal with and, consequently, no longer function properly.

Signs similar to diabetes may also appear during pregnancy, when it is called gestational diabetes, or as the result of drug treatment with thiazide diuretics or corticosteroids. The signs normally disappear after the baby is born or once drug therapy is withdrawn.

Symptoms of type 1 diabetes develop very quickly over a period of a few days or weeks and are normally very obvious. Symptoms of type 2 diabetes develop more slowly over a period of months or years and so may be easily missed. Often, type 2 diabetes is only discovered after a routine medical check-up.

Whether someone has type 1 or type 2 diabetes, the symptoms are generally the same. They include an increased thirst, frequent trips to the toilet to urinate (especially at night), extreme tiredness, weight loss, genital itching, thrush (in women) and blurred vision. In type 1 diabetes, patients may also develop ketoacidosis, where the body breaks down fat instead of glucose. Patients develop a sweet ‘pear-drop’ smell on their breath. If the ketoacidosis is not treated the patient can pass into a coma and die.

In addition to the above symptoms, diabetes can lead to long-term health problems. The raised blood glucose levels damage blood vessels and nerves, dramatically increasing the risk of heart attacks, stroke, kidney failure, limb amputations and blindness. It is critical therefore that diagnosis of diabetes is made as early as possible and that blood glucose levels are kept under control.