Diabetes mellitus

Diabetes Overview: Type 1 and Type 2

What is Diabetes mellitus?

Put very simply, diabetes mellitus is a condition in which the body is unable to keep the amount of sugar in the blood down to normal levels.

When we eat, some of the food is broken down to sugar within the body. This sugar travels in the bloodstream to every part of the body to provide energy necessary for life and activity.

A hormone called insulin is produced in a gland in the abdomen, called the pancreas, and it is this hormone that keeps the amount of sugar in the blood at normal levels. Without insulin, the blood sugar levels will rise. Insulin is also vital in helping to ‘push' the sugar in the blood into the cells of the body, thus allowing the cells to use this as 'fuel'.

The pancreas produces varying amounts of insulin depending on the level of blood sugar, therefore regulating the blood sugar level and keeping it within quite narrow limits. Normal non-diabetic people control their blood sugar between about 4 and 7 (mmol/litre of blood).

How does it occur?

When someone develops diabetes they have either a complete or a partial lack of insulin. This has two main effects. Firstly the blood sugar level rises and secondly, without insulin, the sugar is unable to enter the cells, which are therefore starved of energy. This is why diabetes is sometimes referred to as 'starvation in a sea of plenty', since there is plenty of sugar in the blood (in fact too much) but the cells are unable to make use of it without the help of insulin.

Are there different types of diabetes mellitus?

There are two types of diabetes mellitus, which have changed their names over the years. Although the two types have certain things in common, they are very different in many ways as can be seen from the features described below.

Type 1 diabetes: This used to be called 'insulin-dependent diabetes'.
This type results from an almost complete lack of insulin and therefore treatment comes in the form of insulin injections. It is the least common of the two types, occurring in only about 10 to 15 per cent of all diabetics. It tends to start early in life (which is why it also used to be referred to as juvenile onset diabetes). The reason for the change of name is that older people can develop type 1 diabetes and type 2 diabetics often require treatment with insulin, so the old names are no longer seen as appropriate.

Type 2 diabetes: This used to be called 'non insulin-dependent diabetes'.
This form is the more common type of diabetes, making up about 85 to 90 per cent of all cases and it is this form that is on the increase for reasons that are explained below. In the last few years, a lot more is understood about type 2 diabetes than before. Type 2 diabetes is generally found in adults, which is why it used to be called ‘maturity onset diabetes’, but unfortunately it is increasingly found in younger people as well as adults. This has occurred as a result of the increase in obesity in the general population, since the development of type 2 diabetes is strongly associated with being overweight. It tends to be slower to develop than type 1 diabetes and often the individual has had the condition for months or years before it is diagnosed because the symptoms are often less obvious.

Why does it occur?

The causes of type 1 and type 2 diabetes are different, which is one reason why doctors think that the two types are probably completely different conditions with the only similarities being some shared symptoms and similar long-term effects on the body.

Type 1 diabetes: This is due to a failure of the insulin-making cells of the pancreas (called the Islet cells), leading to an almost total lack of insulin production. Consequently, the blood sugar increases without any control. The condition is thought to develop because of a mixture of a susceptible individual (ie a genetic predisposition) and possibly a viral infection that triggers a process in the body where the body destroys its own insulin-making cells. As mentioned, there is a slight inherited factor so, for instance, an identical twin of a person with type 1 diabetes has a 50 per cent chance of also having the condition.

Type 2 diabetes: This seems to be a little bit more complicated. There is a strong tendency to inherit type 2 diabetes, to the extent that an identical twin of a person with this condition has a 100 per cent chance of developing it as well. The first link in the chain that results in someone with this inherited tendency developing type 2 diabetes is something called 'insulin resistance'. This means that the individual makes the normal amount of insulin to begin with (in contrast to type 1) but that the tissues of the body become resistant to the effects of the insulin. Therefore to keep the blood sugar levels down and to push the sugar into the tissues (see above) the body has to produce more insulin.

Another effect of insulin resistance is that the liver produces more sugar. This further increases the blood sugar levels which means that even more insulin is needed to try to keep the sugar levels down and so on. At this stage, the individual's blood sugar levels, if measured, could be normal but to achieve these normal levels the pancreas has to work increasingly hard.

Two things then happen to cause type 2 diabetes finally to occur. Firstly, the pancreas can no longer keep pace with the increased demand for insulin. Secondly, any increases in blood sugar actually begin to 'poison' the insulin-making cells of the pancreas. The levels of sugar in the blood therefore begin to gradually increase through a phase which doctors call 'glucose intolerance', and then to true type 2 diabetes when the blood sugars become abnormally high.

Insulin resistance, and therefore type 2 diabetes, is strongly linked to obesity. This explains why the condition is becoming so common, as the level of obesity in the Western World is increasing. In a study of adults in the USA it was found that 24 per cent had insulin resistance mainly as a result of being overweight. Although not all of these will go on to develop diabetes, a significant proportion will.

Other types of diabetes: There are other causes of diabetes, some of which are temporary, but which may highlight an underlying tendency to insulin resistance. These include something called gestational diabetes that is diabetes occurring in pregnancy, which then tends to get better once the baby has been born. Another is diabetes caused by high doses of steroids, either in the form of medication or as a result of a condition called 'Cushing's disease' where the body produces too much of its own steroid. A type of diabetes can also be caused by destruction of the pancreas, either by its removal during an operation or as the result of excessive alcohol consumption.

Symptoms of Diabetes mellitus

Although the symptoms of both type 1 and type 2 diabetes are similar, type 1 diabetes tends to progress more rapidly, and generally speaking the symptoms are worse.

Someone can have type 2 diabetes for a long time without realising it or it may even be picked up coincidentally during a medical check-up, whereas type 1 diabetes is usually detected fairly early due to the severity of the symptoms it produces.

The main symptoms of diabetes include:

  • excessive thirst
  • excessive urine production
  • weight loss
  • hunger
  • tiredness and weakness
  • blurred vision
  • low resistance to infection, especially skin infections such as boils and also thrush
  • dehydration and coma in severe untreated cases.

Many type 2 diabetics will not have any of these symptoms, but unfortunately this does not mean that they do not have the illness. It also does not mean that the condition is not affecting the body, for example the blood vessels as described below.

What are the tests for diabetes?

The tests for diabetes are usually very simple. The doctor may start by testing a sample of urine for sugar. Normally there should be no sugar detectable in urine, so if sugar is present it usually indicates the presence of diabetes. Sugar usually only appears in the urine if the level of sugar in the blood is greater than about 10 mmol/litre of blood. However, occasionally this is not the case so to truly confirm or exclude diabetes a blood test should be done.

A far more accurate test is to measure the blood sugar directly using a blood test that measures the glucose (sugar) level in millimoles per litre of blood. Over the years the accepted level of sugar in the blood that determines whether someone is diabetic has changed. However, at the time of writing the best test is a fasting blood sugar measurement. This is taken when the individual has had nothing to eat or drink (apart from water) for at least eight hours. If the blood sugar level is less than 6.1 mmol/litre, the person does not have diabetes or glucose intolerance. If the fasting blood sugar level is 7 mmol/litre or more, the person has diabetes. Between these levels the person is said to be ‘glucose intolerant’, which means they have a high chance of developing type 2 diabetes in the subsequent years.

If the result of these tests is uncertain then the doctor may ask for a 'glucose tolerance test’, that involves taking blood tests for sugar levels after fasting and then two hours after a drink containing 75 grams of glucose.

What are the complications?

It is very important to treat diabetes, because if left untreated it can cause a variety of problems. These can be divided into acute and long-term effects.

Acute effects: Acute effects are generally only seen in type 1 diabetes, as this tends to come on more quickly and the levels of blood sugar can rise quickly. If diabetes remains untreated, the blood sugar level can continue to increase and the 'starvation' of the cells becomes worse, leading to dehydration and the build up of substances called ‘ketones'. This can eventually result in something called ketoacidotic coma, which is a life-threatening condition and needs urgent treatment.

Long-term effects: The long-term effects of both types 1 and 2 diabetes are similar, although there are some differences. Untreated mild diabetes or poorly controlled diabetes can contribute towards damage to blood vessels throughout the body. The blood vessels that cause particular concern are those of the eyes, kidneys, feet and heart. Damage to the blood vessels could lead to visual problems (including bleeding into the eye), kidney problems (sometimes leading to kidney failure), circulatory problems to the legs and feet and an increased risk of angina and heart attacks.

These complications are more likely if the individual has other factors that could damage the arteries such as smoking, high blood pressure or a high cholesterol level. Complications tend to occur more often when diabetes is poorly controlled. The nerves can also be affected causing loss of feeling especially in the feet, and diabetics are more prone to tooth and gum problems.

Generally speaking, kidney problems and problems with small blood vessels, such as those at the back of the eye, are more likely in type 1 diabetics. Problems such as 'furring up' of the large blood vessels such as those in the heart, those to the legs and those to the brain, are more likely to occur in type 2 diabetics. There seems to be a link between developing type 2 diabetes and also suffering from high blood pressure and an increased level of certain fats such as cholesterol or other fats called triglycerides in the blood. These all increase dramatically the chances of artery blockage in type 2 diabetes, since this combination is a nasty cocktail for the large arteries of the body. The result is a significantly higher risk of having a heart attack, a stroke or problems with the circulation to the legs. For this reason it is particularly important that diabetics do not smoke, since this multiplies these risks still further.

Treatment Diabetes mellitus

The aim of diabetes treatment is not just to control the blood sugar but also to reduce the symptoms associated with it. In practice, this involves controlling any high blood pressure, reducing the complications of the condition and in particular minimising the risk of heart and blood vessel related problems as described above.

Treatment of type 1 diabetes

Type 1 diabetes is treated with the correct diet and injections of insulin. Insulin has to be given as an injection because it is destroyed in the stomach and therefore cannot, so far, be given by mouth.

The insulin regimes come in a variety of forms since there are many different types of insulin. The doctors involved will advise on the type and frequency of these injections. The insulin regime is given in association with a diet, the aim being to sustain a normal body weight and to balance the calorie intake with the amount of insulin given throughout the day.

Too much food will result in blood sugars being too high and too much insulin can cause the blood sugar to become too low, so the balance for each individual needs to be found.

In addition, high blood pressure should be treated with the appropriate medication, as should any evidence of abnormally high blood lipids (the fats in the blood-cholesterol and triglycerides) and any early signs of kidney or eye problems.

Treatment of type 2 diabetes

Type 2 diabetes is treated in a variety of ways. The starting point is the correct diet, especially since at least 80 per cent of type 2 diabetics are overweight. Reduction of weight to normal can slow the process of the development or worsening of the condition as well as reducing the risks associated with it. In some cases type 2 diabetes can be treated with diet alone, at least for a period of time.

If diet alone is not sufficient, the next step will be to add in medication in the form of tablets. There are now three main groups of oral medication for type 2 diabetes, and these are outlined below.

Biguanides: The most commonly prescribed drug in this group is metformin. This is particularly useful for overweight diabetics, as it does not increase the appetite. It works by decreasing the amount of glucose produced by the liver, and by making muscle tissues of the body more sensitive to the effects of insulin.

Sulphonylureas: The second group of drugs given for type 2 diabetes are called the sulphonylureas, the most commonly prescribed of which is a tablet called glibenclamide. The sulphonylureas work by boosting the insulin output of the pancreas and are usually given to the few diabetics who are of normal weight, especially as one of the side effects is a possible increase in weight.

Glitazones: This is a relatively new group of drugs for type 2 diabetes, and includes rosiglitazone and pioglitazone. These work in a complex way to make the tissues more sensitive to insulin and are given in combination with either metformin or a sulphonylurea. Since it works by making the tissues of the body more sensitive to the effects of insulin, it acts directly against the insulin resistance chain of events, which causes type 2 diabetes in the first place.

There are other oral drugs that are occasionally used for the treatment of type 2 diabetes but those mentioned above are by far the most common.

In many cases, type 2 diabetes will eventually become resistant to treatment even with maximum doses of tablets, at which point insulin may be introduced either instead of, or as well as, a tablet. Although diabetics may see this as a backward step, in fact it often permits better control of their condition with subsequent improvement in their symptoms and a lower risk of complications.

As important as the control of blood sugar is the treatment of the other factors that make the complications of diabetes more likely such as high blood pressure and high blood lipids, as well as the giving up of smoking. In addition many type 2 diabetics will be advised by their physician or specialist to take a small dose of aspirin daily, since this has been shown to reduce the chances of artery narrowing in some diabetic individuals.

What diet is recommended?

Firstly it should be noted that diabetics do not need special 'diabetic foods'; they should eat the ordinary food obtainable from local shops and supermarkets. Secondly, it is a myth that diabetics should avoid sugar completely, but it is true that the sugars in the diet should be in a form where they are released slowly into the body. In practical terms this means that sugary foods should be limited and that the carbohydrates (starchy foods) in the diet should be what are called complex carbohydrates. Examples of complex carbohydrates are potatoes and bread, because these release sugar into the body gradually and avoid sudden increases in the level of glucose in the blood.

In general diabetics should:

  • eat a diet that brings them down to their correct weight and keeps them there
  • eat regular meals and try to eat similar amounts of starchy foods from day to day
  • try to eat high fibre foods, especially beans, peas, lentils and fruit
  • cut down on fried and fatty food such as butter, margarine, cheese, chips etc.
  • reduce their sugar intake by swapping high sugar foods for low sugar foods
  • be careful not to use too much salt
  • be aware that alcohol is a source of sugar in the diet and therefore should be included in any dietary considerations. In practical terms, a moderate intake in keeping with a balanced diet is not a problem, but excessive intake will affect the blood sugar levels and the individual will risk an increase in weight.

It is advisable for a newly diagnosed diabetic to see a dietician for more detailed and specialist advice regarding the correct diet for their condition.

What are the side effects of treatment?

The most frequently experienced side effect of both insulin and some diabetic tablets is that they can cause the blood sugar to go too low (2 mmol/l or less), which causes the person to become 'hypoglycaemic' or 'hypo' for short. The symptoms of a hypo are intense hunger, feeling shaky and sweaty, and finally a hypoglycaemic coma may result. This needs urgent medical attention.

Before the coma happens, a hypo can be treated by eating something high in sugar such as a glucose tablet or sugar lump. Diabetic tablets can occasionally cause other side effects including nausea and diarrhoea.

What happens after treatment?

Once treatment has been established, the most important thing for a diabetic to do is to follow the advice of the doctor and/or diabetic nurse in terms of taking the prescribed treatment and following the dietary guidelines. They will also be taught how to monitor their treatment through regular checks on their own urine or blood sugar levels, which they can do very easily at home.

They will usually have regular check-ups, either in their doctor's surgery or at the hospital diabetic clinic. It is important that such check-ups are attended. Monitoring of a number of things will take place, including their diabetic control, their blood pressure, blood tests for cholesterol, triglyceride (see above) and sugar levels, and advice about foot care and regular eye checks. A blood test now exists, called an HbA1C, that gives an average of the blood sugar readings over the previous two to three months and provides the doctors and nurses with a very good indicator of the blood sugar control over that period.

In the meantime, it is important that people with diabetes monitor their own diabetic control. It is also important to have regular eye checks with an optician (so that early signs of diabetic eye disease can be detected and referred for early treatment) and to take good care of the feet, since these can suffer from damage if the diabetes affects sensation in that area. As mentioned above, a person with diabetes should also give up smoking and follow any dietary advice. Although this sounds very restrictive, in fact it can easily develop into a manageable routine and will allow the individual to continue a normal life in almost every respect with the knowledge that they are doing everything possible to limit the long-term effects of the condition on their health.

Are there any developments in the treatment of diabetes?

In the last few years, several new groups of drugs have been developed for the treatment of type 2 diabetes, which are adding to the combinations of treatment on offer.

A method of continuously monitoring blood sugar levels is also being researched, which could provide more accurate information about the blood sugar fluctuations that occur in the bloodstream of a diabetic. This could be helpful for diabetics who are finding their diabetic control especially difficult and may eventually lead on to an 'artificial pancreas' that would react to the glucose levels by injecting more or less insulin into the body in a similar way to a normal pancreas.

Progress is also being made into Islet cell transplantation. It is the Islet cells of the pancreas which produce insulin and which fail to work in diabetes and, by transplanting a diabetic patient with new Islet cells, it may be possible to cure type 1 and some cases of type 2 diabetes. Barriers to the progress of this treatment include a shortage of donors for Islet cells and prevention of tissue rejection (which occurs because the body recognises the transplanted tissue as 'alien').

Last updated 17 June 2011


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