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What is diabetes?

Dr Rob Hicks

Diabetes is currently an incurable condition in which too much glucose (sugar) is present in the blood. Find out more about the different types and how it's treated.

A common problem

Diabetes occurs because the body can't use glucose properly, either owing to a lack of the hormone insulin, or because the insulin available doesn't work effectively.

The full name 'diabetes mellitus' derives from the Greek word 'diabetes' meaning siphon - to pass through - and 'mellitus' - the Latin for honeyed or sweet. This is because not only is excess sugar found in the blood but it may also appear in the urine, hence it being known in the 17th century as the 'pissing evil'.

Diabetes has been a recognised condition for more than 3,500 years.

According to the charity Diabetes UK, more than 2 million people in the UK have the condition, and up to 750,000 more are believed to have it without realising they do.

More than three-quarters of people with diabetes have what is called type 2 diabetes mellitus.This used to be known as non-insulin dependent diabetes mellitus (NIDDM) or maturity-onset diabetes mellitus.

The remainder have type 1 diabetes mellitus, which used to be known as insulin-dependent diabetes mellitus.


What's the difference?

In type 1, the body's unable to produce any insulin. This usually starts in childhood or young adulthood. It's treated with diet control and insulin injections.
In type 2, not enough insulin is produced or the insulin that is made by the body doesn't work properly. This tends to affect people as they get older, and usually appears after the age of 40.

Normal blood sugar control

The body converts glucose from food into energy. Glucose comes ready made in sweet foods such as sweets and cakes, or from starchy foods such as potatoes, pasta or bread once they're digested. The liver is also able to manufacture glucose.

Under normal circumstances, the hormone insulin, which is made by the pancreas, carefully regulates how much glucose is in the blood. Insulin stimulates cells to absorb enough glucose from the blood for the energy, or fuel, that they need. Insulin also stimulates the liver to absorb and store any glucose that's left over.

After a meal, the amount of glucose in the blood rises, and this triggers the release of insulin. When blood glucose levels fall, during exercise for example, insulin levels fall too.

A second hormone manufactured by the pancreas is called glucagon. It stimulates the liver to release glucose when it's needed, and this raises the level of glucose in the blood.

Insulin is manufactured and stored in the pancreas, which is a thin gland about 15cm (6in) long that lies crosswise behind the stomach. It's often described as being two glands in one, since in addition to making insulin it also produces enzymes that are vital for digestion of food.

These include lipase, which helps to digest fat, and amylase that helps to digest starchy foods. It also releases 'bicarbonate of soda' to neutralise any stomach acid that may otherwise damage the lining of the gut.

Diabetes that isn't controlled can cause many serious long-term problems. Excess glucose in the blood can damage the blood vessels, contributing to heart disease, strokes, kidney disease, impotence and nerve damage.

Uncontrolled diabetes is the most common cause of blindness in people of working age. People with diabetes are also 15 per cent more likely to have an amputation than people without the condition.

In most cases, it's possible to reduce the risk of such complications by following medical advice and keeping diabetes under control. It's vitally important for people with diabetes to check their glucose levels regularly at home and to attend hospital check-ups, so any problems can be detected and treated early.


How is it diagnosed?

Diabetes may be detected during a routine urine test when excess glucose is present.

When symptoms have drawn attention to the problem, a blood test will confirm whether or not the underlying cause is diabetes.

Antenatal screening is not possible.


Who's affected?

Those at risk include:

People over 40, or over 25 and African-Caribbean, Asian or from a minority ethnic group
People with a close family member who has type 2 diabetes
People who are overweight or who have a large waist size
Women with polycystic ovary syndrome who are overweight
Women who've had diabetes in pregnancy (gestational diabetes)

What's the treatment?

The first step in the treatment of diabetes is to eliminate the symptoms. The next step is to prevent the physical harm it can cause.

Although no cure exists for type 1 diabetes, its symptoms can be eliminated by adhering to a healthy diet that has a controlled amount of sugar in it, and by having regular injections of insulin to replace that which the body is not providing. This aims to keep the blood glucose level steady.

Insulin can't be taken by mouth because digestive juices and enzymes destroy it before it can get into the bloodstream. Scientists are working on ways of overcoming this.

Most people find giving themselves the injections simple and painless, as the needle is so fine. How often someone needs to inject insulin depends on what their diabetes specialist has recommended and which type of insulin they're using.

Insulin can be short-acting, medium-acting or long-acting. Some people need it twice a day, some three times a day and some use an insulin pen to give themselves insulin just before meals.

Devices are becoming available that deliver insulin continuously under the skin in response to need. Inhaled insulin is also available.

Self-help

Monitor blood glucose levels
Attend hospital check-ups
Have regular eye checks
Inform the DVLA
Wear a medi-alert bracelet
Always have some sugar available

Many people with type 2 diabetes need only to eat a healthy diet to control their diabetes. If this isn't enough, medication or insulin may be necessary.

Everyone with diabetes should eat a diet that's low in fat, sugar and salt.

Regular exercise, not smoking and keeping to an ideal weight also help prevent the complications of diabetes, such as heart disease. Keeping blood pressure at a safe level is important.

People with type 1 diabetes are allowed to drive, but must inform the DVLA that they have diabetes. If blood sugar goes too low, they may develop hypoglycaemia.

Most wear an identity bracelet to inform people they have diabetes in case they black out and need help.

Fortunately, diabetes can be managed well, so people can live a normal lifestyle.


Diabetes insipidus

Most people have heard of diabetes mellitus, or 'sugar diabetes', but few have come across a completely different and unrelated condition called diabetes insipidus.


What causes it?

Diabetes insipidus occurs when the body doesn't produce enough antidiuretic hormone (ADH) or doesn't respond correctly to its effects.

ADH helps to control the balance of water in the body by regulating the production of urine. It's produced by the hypothalamus and stored in the pituitary gland until it's needed.

There are two forms of diabetes insipidus.

Cranial diabetes insipidus occurs when the body doesn't produce enough ADH. This may be the result of a tumour in the hypothalamus or pituitary gland, infection, radiotherapy, surgery to the gland or a head injury.

Nephrogenic diabetes insipidus occurs when the kidneys don't respond to ADH. It may be caused by certain medicines, follow kidney damage or be inherited.


What are the symptoms?

Someone with diabetes insipidus passes excessive amounts of urine, sometimes more than three litres over 24 hours. They're always thirsty and drink almost constantly.

People with diabetes insipidus may need to urinate every 15 to 20 minutes. Disturbed sleep - and daytimes - are the consequence of having to pass water so frequently.

Dehydration is common when diabetes insipidus is left undiagnosed or untreated, causing high levels of sodium in the blood. This in turn can lead to tiredness, lethargy, confusion and the risk of fits and coma.

Babies and young children with diabetes insipidus may display failure to thrive.


How is it diagnosed?

Specific tests are performed when someone is suspected of having diabetes insipidus. These measure:
The volume of urine produced over a 24-hour period
The amount of urine produced after fluid input has been restricted (if diabetes insipidus is present, large volumes will still be produced)
How the body responds to being given ADH (if it lowers the amount of urine, cranial diabetes insipidus is the likely cause; if it remains high, the nephrogenic form is likely)


Scans are also used to identify specific causes.

Antenatal diagnosis of diabetes insipidis is possible.


What's the treatment?

If a treatable cause of cranial diabetes insipidus is found, this will be treated. Otherwise, synthetic ADH can be given on daily basis.

Nephrogenic diabetes insipidus is treated with a low-sodium diet and medication to reduce the amount of urine produced. If an underlying cause is found and can be treated, this form should resolve.

This article was last medically reviewed by Dr Roger Henderson in January 2009.
First published in April 2001.

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