Diabetes mellitus

Diabetes mellitus is a very common disorder caused by high levels of sugar in the bloodstream. It affects a large number of people and is associated with an increased risk of heart attacks, stroke and damage to the eyes, feet and kidneys.




What is diabetes mellitus?

Diabetes mellitus is a condition in which the body does not produce enough of the hormone insulin, resulting in high levels of sugar in the bloodstream.  There are many different types of diabetes; the most common are type 1 and type 2 diabetes which are covered in this article.  Gestational diabetes occurs during the second half of pregnancy and is covered in a separate article.

Diabetes mellitus is a global public health problem, affecting a large number of people, many of whom remain undiagnosed.  Diabetes mellitus is linked with an increased risk of heart attacks, strokes, poor blood circulation to the legs and damage to the eyes, feet and kidneys.  Early diagnosis and strict control of blood sugar, blood pressure and cholesterol levels can help to prevent or delay these complications associated with diabetes.  Maintaining a healthy lifestyle (regular exercise, not smoking and eating healthily) is important in reducing the risk of developing diabetes.

What causes diabetes mellitus?

Insulin is a hormone produced by the beta cells of the islets of Langerhans in the pancreas in response to the intake of food.  The role of insulin is to lower blood sugar (glucose) levels by allowing cells in the muscle, liver and fat to take up sugar from the bloodstream that has been absorbed from food and store it away as energy.  In type 1 diabetes (or insulin-dependent diabetes mellitus), the insulin-producing cells are destroyed and the body is not able to produce any insulin.  This means that sugar is not stored away but is constantly released from energy stores giving rise to high sugar levels in the blood.  This in turn causes dehydration and thirst (because the high glucose ‘spills over’ into the urine and pulls water out of the body at the same time).  To exacerbate the problem, because the body is not making insulin it ‘thinks’ that it is starving so does everything it can to release even more stores of energy into the bloodstream.  So, if left untreated, patients become increasingly unwell, lose weight, and develop a condition called diabetic ketoacidosis, which is due to the excessive release of acidic energy stores and causes severe metabolic consequences.

In ‘type 2 diabetes’ (accounting for 90% of all diabetes) the beta cells of the islets of Langerhans do not stop making insulin completely, but the insulin produced does not work properly so it struggles to store away the sugar found in the blood.  As a consequence, the pancreas has to produce more insulin to compensate for this reduction in insulin function.  This is termed as insulin resistance.  Insulin resistance is linked to obesity.  This type of diabetes is seen more commonly over the age of 40 years but can occur at any age.

What are the signs and symptoms of diabetes mellitus?

There are a range of different symptoms in people with diabetes.  They may feel thirsty, pass a large amount of urine, wake up overnight to pass urine, lose weight and have blurred vision.  Patients are vulnerable to infections such as thrush and may present with this.  Particularly in type 2 diabetes, patients may not be aware of their diabetes for several years and a diagnosis may only be made when they seek treatment for diabetes-related complications such as feet, eye or kidney problems.  Some patients may become severely ill and be taken into hospital with an infection and/or very high blood sugar levels.

How common is diabetes mellitus?

Diabetes mellitus is a public health problem around the world.  It is estimated to affect 6.4% (285 million) of the worldwide population (2010 figures), a number predicted to rise to 7.7% (438 million) by 2030.  There are a further 344 million people with pre-diabetes (at risk of developing diabetes).  This number is projected to increase to 472 million by 2030.  In the UK, there is estimated to be between two and three million people with diabetes. Type 2 diabetes accounts for more than 90% of all patients with diabetes.

Is diabetes mellitus inherited?

This depends on the type of diabetes.  Type 2 diabetes, and to a lesser extent type 1 diabetes, may run in families.  If a parent has diabetes, their children will not necessarily get it but they are at an increased risk.  In type 2 diabetes, lifestyle factors such as being overweight (obesity) and lack of exercise are risk factors for developing diabetes.  Some rarer types of diabetes mellitus may be inherited.

How is diabetes mellitus diagnosed?

A urine sample is taken and tested for sugar; sugar is not normally found in urine but if blood sugar levels are high (as in diabetes), some can spill over through the kidneys and into the urine.  If sugar is found in the urine, the diagnosis of diabetes can be confirmed by taking a blood sample after fasting.  However, a normal fasting sugar test on its own does not exclude diabetes, as in the early stages of type 2 diabetes fasting sugar may still be normal.  In this case, a specialised test called a glucose tolerance test may need to be carried out in which a patient is given a sugary drink with blood samples taken before and two hours after the drink.

How is diabetes mellitus treated?

The aim of treatment in diabetes is to reduce circulating glucose to as normal a level as possible, avoid the acute symptoms of diabetes such as thirst, and avoid the long-term complications of diabetes such as eye, nerve and kidney damage.  While glucose control is the prime aim of treatment, other factors such as blood pressure and blood cholesterol levels are also very important in the management of diabetes and the prevention of long-term health consequences.

Type 1 diabetes is always treated with insulin, a life-saving treatment.  Patients will need to take medication several times a day for the rest of their lives.  Patients will usually learn how to self-administer this.  Insulin is usually given through injections under the skin (subcutaneous).  Patients normally require two to four injections a day.  An increasing number of patients with type 1 diabetes are being treated with ‘insulin pumps’ which provide a continuous supply of insulin.

Patients need to ensure that their blood glucose levels are kept as normal as possible so that delicate tissues in the body (especially blood vessels in the eyes, kidneys and peripheral nerves) are not chronically damaged by high glucose levels over a long period of time.  To achieve this, patients need to measure their glucose regularly and learn how to adjust their insulin doses in order to optimise their glucose levels (diabetes control).  Good diabetes control helps to minimise the risk of long-term diabetes complications, as well as short-term symptoms (such as thirst).

Patients with type 2 diabetes can still make insulin; they make enough to avoid ketoacidosis but not enough to control their glucose levels.  Type 2 diabetes is therefore initially treated with a combination of lifestyle changes (diet and exercise) which reduce the need for insulin and therefore lower glucose levels.  If this is insufficient to achieve good glucose control, a range of tablets are available such as metformin, which, like diet and exercise, reduces insulin requirements, and sulphonylureas (eg gliclazide) which stimulate insulin secretion.   If these measures are not effective, a range of new medications are available such as those raising the levels of incretins (natural hormones that stimulate insulin production).

In many patients, particularly after several years of treatment, insulin production is so low or so insufficient compared to the patients’ needs that patients with type 2 diabetes have to be treated with insulin injections, either alone or in combination with tablets.

Are there any side-effects to the treatment?

Insulin treatment can cause weight gain and low blood sugar.  In addition, there may be discomfort at the injection site.  There are several types of tablets used to treat diabetes and they have different side-effects.  The most common are diarrhoea, nausea, weight-gain and low blood sugar.  Some patients may also experience some sexual dysfunction.  However, not all patients will experience some or any of these side-effects and patients should discuss any concerns with their doctor.

What are the longer-term implications of diabetes mellitus?

Having diabetes requires life-long treatment and follow-up by health professionals.  Diabetes can be linked to damage of the eyes, kidneys and feet.  It is also associated with increased risk of strokes, heart attacks and poor blood circulation to the legs.  Medical care aims to minimise these risks by controlling diabetes, blood pressure and cholesterol and screening for possible complications caused by the diabetes.

Maintaining a healthy lifestyle with regular exercise and a healthy diet helps with glucose control and managing diabetes in the long-term.  With careful monitoring and appropriate treatment, diabetes patients can lead full and active lives.

Women with diabetes who are planning to start a family should discuss this with their doctor as good glucose control is important both prior to conception and throughout pregnancy.