Inability of the body to use glucose for energy due to inadequate amounts of or loss of sensitivity to the hormone insulin
- Sometimes runs in families
- Age, gender, and lifestyle as risk factors depend on the type
Diabetes mellitus is one of the most common long-term diseases occurring in the UK, affecting about 4 in 100 people. In this disorder, either the pancreas produces insufficient amounts of the hormone insulin or body cells are resistant to the hormone’s effects.
Normally, insulin is produced by the pancreas and enables the body’s cells to absorb the sugar glucose (their main energy source) from the blood. In diabetes mellitus, the cells have to use other sources of energy, leading to a build-up of toxic by-products in the body. Unused glucose accumulates in the blood and urine, causing symptoms such as excessive passing of urine and thirst.
Treatment is designed to control glucose levels in the blood. Among people treated for diabetes mellitus, about 15 per cent (those with type 1 diabetes) will require self-administered injections of insulin from the time the condition is diagnosed. The rest (those with type 2 diabetes) will require at least a carefully managed diet, and often oral drugs and sometimes insulin. These measures enable most affected people to lead normal lives. However, in many cases, particularly if blood glucose and blood pressure are not well controlled, complications eventually develop. Complications include problems with the eyes, kidneys, cardiovascular system, and nervous system. Diabetes mellitus also weakens the immune system and thus increases susceptibility to infections such as cystitis. The condition is usually permanent and there is no known cure.
What are the types?
There are two main forms of diabetes mellitus: type 1 and type 2 diabetes.
Type 1 diabetes
Type 1 occurs when the pancreas produces far too little insulin or none at all. The disorder usually develops suddenly in childhood or adolescence. Although dietary measures are important, it must be treated with insulin injections. About 370,000 people in the UK have this type of diabetes.
Type 2 diabetes
Type 2 is by far the most common form of diabetes, affecting about 2 million people in the UK. In this condition, the pancreas continues to secrete insulin, but the cells of the body become resistant to its effects. Type 2 has traditionally affected people over the age of 40 but, with the increase in obesity at a younger age, it now affects even children. The condition develops slowly and often goes unnoticed for years. In the initial stages, dietary measures may control the condition, but oral drugs and sometimes insulin injections become necessary as it progresses.
Diabetes mellitus can sometimes develop during pregnancy (see Diabetes developing in pregnancy). This condition is called gestational diabetes and may require treatment with insulin to maintain the health of the mother and baby. Gestational diabetes usually disappears after childbirth; however, women who have had it are at increased risk of developing type 2 diabetes in later life.
What are the causes?
Type 1 diabetes is usually caused by an abnormal reaction in which the immune system destroys insulin-secreting cells (specifically, beta cells of the islets of Langerhans, often known simply as islet cells) in the pancreas. The cause of this reaction is unknown, but it may be triggered by a viral infection. In some cases, destruction of insulin-secreting tissues occurs following inflammation of the pancreas (see Acute pancreatitis).
Genetics may also play a role, but the pattern of inheritance is complicated. A child of a person with type 1 diabetes is at greater risk of developing the same type of diabetes, but most affected children do not have a parent with diabetes.
The causes of type 2 diabetes are less well understood, but genetics and obesity are important factors. About 1 in 3 affected people has a relative with the same type of diabetes. Type 2 diabetes is a major health problem in affluent societies and a growing problem in some developing countries. As food intake increases, more people become overweight and the prevalence of the condition rises.
In people who are predisposed to diabetes, the condition can be triggered by corticosteroid drugs or by excessively high levels of natural corticosteroid hormones (see Cushing’s syndrome), which act against insulin.
What are the symptoms?
Although some of the symptoms of both forms of diabetes mellitus are similar, type 1 diabetes tends to develop more quickly and become more severe. The symptoms of type 2 may not be obvious and may go unnoticed until a routine medical checkup. The main symptoms of both forms may include:
Excessive passing of urine.
Thirst and a dry mouth.
Insufficient sleep because of the need to pass urine at night.
Lack of energy.
Type 1 diabetes may also cause weight loss. In some people, the first sign of the disorder is ketoacidosis, a condition in which toxic chemicals called ketones build up in the blood. These chemicals are produced when the tissues of the body are unable to absorb glucose from the bloodstream, due to inadequate production of insulin, and have to use fats for energy. Ketoacidosis can also occur in people with type 1 diabetes who are taking insulin if they miss several doses or if they develop another illness (because any form of illness increases the body’s requirement for insulin). The symptoms of ketoacidosis may include:
Nausea and vomiting, sometimes with abdominal pain.
Acetone smell to the breath (like nail-polish remover).
The development of these symptoms is a medical emergency because they can lead to severe dehydration and coma if they are not treated urgently. Emergency treatment for ketoacidosis includes intravenous infusion of fluids to correct dehydration and restore the chemical balance of the blood, and injections of insulin to enable body cells to absorb glucose from the blood.
Are there complications?
Diabetes mellitus may give rise to short-term complications, which are usually easy to control, or long-term complications, which are more difficult to treat and can lead to premature death.
Poorly controlled or untreated type 1 diabetes may lead to ketoacidosis, the symptoms of which are described above.
A common complication of insulin treatment for either type of diabetes is hypoglycaemia, in which blood sugar falls to abnormally low levels. Hypoglycaemia is often caused by an imbalance between food intake and the dose of insulin. The disorder is more common in people with type 1 diabetes but may also affect people with type 2 diabetes who take sulphonylurea drugs or insulin (see Drugs for diabetes mellitus). If left untreated, it can cause unconsciousness and seizures.
Certain long-standing problems pose the main health threat to people with diabetes and may eventually affect even people whose diabetes is well controlled. Close control of blood sugar and blood pressure reduces the risk of complications, and early recognition helps in their control. For these reasons, all affected people should see their doctor at least twice a year (see Living with diabetes). Type 2 diabetes is often not diagnosed until years after its onset. As a result, complications may be evident at the time of initial diagnosis.
People who have diabetes are at in-creased risk of cardiovascular disorders (see Diabetic vascular disease). Large blood vessels may be damaged by atherosclerosis, which is a major cause of coronary artery disease and stroke. Raised amounts of cholesterol in the blood (see Hypercholesterolaemia), which accelerate the development of atherosclerosis, are more common in people who have diabetes. Diabetes is also associated with hypertension, another risk factor for cardiovascular disease.
Other long-term complications result from damage to the small blood vessels throughout the body. Damage to blood vessels in the light-sensitive retina at the back of the eye may cause diabetic retinopathy. Diabetes also increases the risk of developing cataracts. People with diabetes mellitus should have their eyes examined yearly.
If diabetes affects blood vessels that supply nerves, it may cause nerve damage (see Diabetic neuropathy). There may be a gradual loss of sensation or a tingling feeling, starting at the hands and feet and sometimes gradually extending up the limbs. Symptoms may also include dizziness upon standing and erectile dysfunction in men. Loss of feeling, combined with poor circulation, makes the legs more susceptible to ulcers (see Leg ulcers) and gangrene.
How is it diagnosed?
Your doctor may first ask you to provide a urine sample, which will be tested for glucose. The diagnosis is confirmed by a blood test to check for a high glucose level. If the level is borderline, you may need to undergo another series of blood tests after fasting overnight; this procedure is known as a glucose tolerance test. Your blood may also be tested for glycosylated haemoglobin, an altered form of the pigment in red blood cells, which increases in concentration when the blood glucose level has been high for several weeks or months.
What is the treatment?
For anyone with diabetes mellitus, the aim is to maintain the level of glucose in the blood within the normal range without marked fluctuations, and the mainstay of treatment is dietary control and regular exercise, which can have a significant impact on reducing complications. In addition to diet and exercise, treatment may also involve insulin injections or pills that lower the blood glucose level. Treatment is usually lifelong, and you will have to take responsibility for the daily adjustment of your diet and medication.
Type 1 diabetes
This form is always treated with insulin injections; oral drugs alone are ineffective. Insulin is available in various forms, including short-acting, long-acting, and combinations of both (see Drugs for diabetes mellitus). Treatment regimens need to be individually tailored, and may include insulin and oral drugs. Your doctor or nurse will talk to you about your needs and arrange for you to learn how to inject yourself (see Injecting insulin). You will also have to control your diet and monitor your blood glucose as described on the right. If the diabetes is difficult to control, you may be given an insulin pump, which dispenses insulin through a catheter that is inserted into your skin.
The only way to cure type 1 diabetes mellitus is by undergoing a pancreas transplant or a transplant of just the insulin-secreting islet cells, but such surgery is not routinely offered because the body may reject the transplanted tissue and also because lifelong treatment with immunosuppressant drugs is needed afterwards. In some cases, people with diabetes who are receiving a kidney transplant are given a pancreas transplant at the same time.
Type 2 diabetes
Many people with this form of diabetes can control their blood glucose levels by taking exercise regularly and by following a healthy diet to maintain their ideal weight.
You should follow general guidelines for a healthy diet (see Diet and health) and seek advice from a dietitian if necessary. You should try to keep fat intake low and obtain energy from complex carbohydrates (such as bread and rice) to minimize fluctuations in the blood glucose level. Your diet should have a fixed calorie content. The proportions of protein, carbohydrate, and fat must be consistent to keep a balance between food intake and medication.
You may be advised to check your blood glucose level regularly (see Monitoring your blood glucose). If the glucose level is higher or lower than recommended, you may need to alter your diet or adjust your insulin or drug dose with the help of your doctor. Effective blood glucose monitoring is particularly important if you develop another illness, such as influenza, because being ill can increase blood glucose levels even if you are not eating. It is also important for you to monitor your blood glucose in situations such as taking strenuous exercise and when you are planning to eat a larger meal than usual.
When dietary measures are not sufficient to control your blood sugar, one or more drugs may be prescribed (see Drugs for diabetes mellitus). You are likely to begin with oral drugs, such as metformin, which is particularly useful for treating people with diabetes who are overweight; sulphonylureas, glitazones, or drugs such as repaglinide, which stimulate the pancreas to release more insulin; or a combination of these drugs. If oral drugs are ineffective, you may need to have insulin injections.
It is important to keep your blood cholesterol and blood pressure at normal or even slightly lower than normal levels and you may therefore also be prescribed a statin (see Lipid-lowering drugs) and a drug to lower blood pressure (see Antihypertensive Drugs).
What is the prognosis?
Diabetes mellitus is not curable but advances in monitoring blood glucose levels combined with a healthy lifestyle have made it easier to control. It is important that blood glucose monitoring is combined with monitoring blood pressure and blood cholesterol as keeping control of all these factors will allow people who have diabetes to lead a relatively normal life. Children who develop diabetes quickly learn to manage their disease and can participate in sports and lead full social lives.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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