• There are 3 main types of diabetes: type 1, type 2, and gestational diabetes mellitus
• People with type 1 diabetes will die without insulin
• People with type 2 diabetes can remain undiagnosed for many years
• Poorly managed diabetes leads to serious complications and early death
• Effective management of diabetes requires a partnership between the person with diabetes and health professionals

What is diabetes?

Diabetes is a chronic condition that occurs when the body cannot produce enough or effectively use insulin. 1  Insulin is a hormone produced by the pancreas that allows glucose from food to enter the body’s cells where it is converted into energy needed by muscles and tissues to function. As a result, a person with diabetes does not absorb glucose properly, and glucose stays circulating in the blood (hyperglycaemia) damaging tissues over time.  This damage leads to life-threatening health complications.

There are three main types of diabetes:

• type 1 diabetes
• type 2 diabetes
• gestational diabetes mellitus (GDM)

Type 1 diabetes

Type 1 diabetes is caused by an auto-immune reaction, where the body's defense system attacks the insulin-producing cells in the pancreas. As a result, the body can no longer produce the insulin it needs. The reason why this occurs is not fully understood. The disease can affect people of any age, but it usually occurs in children or young adults. People with this form of diabetes need injections of insulin every day in order to control the levels of glucose in their blood. Without insulin, people with type 1 diabetes will die.

Type 1 diabetes often develops suddenly and can include symptoms such as:

• abnormal thirst and dry mouth
• frequent urination
• extreme tiredness/lack of energy
• constant hunger
• sudden weight loss
• slow-healing wounds
• recurrent infections
• blurred vision

People with type 1 diabetes can lead normal, healthy lives through a combination of daily insulin therapy, close monitoring, a healthy diet, and regular physical exercise.

The number of people developing type 1 diabetes is increasing each year. The reasons for this are still unclear but may be due to changes in environmental risk factors, early events in the womb, diet early in life, or viral infections.

Type 2 diabetes

Type 2 diabetes is the most common type of diabetes. It usually occurs in adults, but is increasingly seen in children and adolescents. In type 2 diabetes, the body is able to produce insulin but it is either not sufficient or the body is not responding to its effects, leading to a build-up of glucose in the blood.

People with type 2 diabetes may remain unaware of their illness for a long time because symptoms may take years to appear or be recognised, during which time the body is being damaged by excess blood glucose. Many people are diagnosed only when complications of diabetes become evident (see Diabetes complications).

Although the reasons for developing type 2 diabetes are still not known, there are several important risk factors. These include:

• obesity
• poor diet
• physical inactivity
• increasing age
• family history of diabetes
• ethnicity
• poor nutrition during pregnancy affecting the developing child

In contrast to people with type 1 diabetes, the majority of those with type 2 diabetes do not usually require daily doses of insulin to survive. However, they may be prescribed insulin together with oral medication, a healthy diet and increased physical activity to manage their condition.

The number of people with type 2 diabetes is rising rapidly worldwide. This rise is associated with economic development, ageing populations, increasing urbanisation, dietary changes, reduced physical activity and changes in other lifestyle patterns. 2 

Gestational diabetes mellitus

Women who are first diagnosed with diabetes during pregnancy are said to have gestational diabetes mellitus (GDM). In women who develop diabetes during pregnancy, it normally occurs later in pregnancy and arises because the body is unable to make and use enough insulin needed for pregnancy.

As gestational diabetes normally develops later in pregnancy, the baby is already well-formed but still growing. The risk to the baby is therefore lower than to those whose mothers have type 1 or type 2 diabetes before pregnancy.  However, women with GDM still have to control blood glucose levels to minimize risks to the baby. This can normally be done through a healthy diet but insulin or oral medication may also be needed.

Gestational diabetes in mothers normally disappears after birth. However, women who have had GDM are at a higher risk of developing type 2 diabetes later in life. Babies born to mothers with GDM also have a higher risk of obesity and developing type 2 diabetes as adults.

Impaired glucose tolerance and impaired fasting glucose

People with high blood glucose levels, but not as high as those in people with diabetes, are said to have impaired glucose tolerance (IGT) or impaired fasting glucose (IFG). IGT is defined as high blood glucose levels after eating, whereas IFG is defined as high blood glucose after a fast.

People with IGT have a higher risk of developing type 2 diabetes. Unsurprisingly, IGT shares many characteristics with type 2 diabetes and is associated with obesity, advancing age and the inability of the body to use the insulin it produces.  However, not everyone with IGT goes on to develop type 2 diabetes.

Diabetes complications

People with diabetes have an increased risk of developing a number of serious health problems. Consistently high blood glucose levels can lead to serious diseases affecting the heart and blood vessels, eyes, kidneys, and nerves. In addition, people with diabetes also have a higher risk of developing infections. In almost all high-income countries, diabetes is a leading cause of cardiovascular disease, blindness, kidney failure, and lower limb amputation. Maintaining blood glucose levels, blood pressure, and cholesterol close to normal can help delay or prevent diabetes complications.  People with diabetes need regular monitoring for complications.

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Cardiovascular disease

Cardiovascular disease is the most common cause of death and disability among people with diabetes. The kinds of cardiovascular disease that accompany diabetes include angina, myocardial infarction (heart attack), stroke, peripheral artery disease, and congestive heart failure.  In people with diabetes, high blood pressure, high cholesterol, high blood glucose, and other risk factors contribute to increase the risk of cardiovascular complications.

Kidney disease

Kidney disease (nephropathy) is much more common in people with diabetes than those without and diabetes is one of the leading causes of chronic kidney disease. The disease is caused by damage to small blood vessels which can cause the kidneys to be less efficient, or to fail altogether. Maintaining near normal levels of blood glucose and blood pressure can greatly reduce the risk of nephropathy.

Eye disease

Most people with diabetes will develop some form of eye disease (retinopathy) which can harm sight or cause blindness. Persistently high levels of blood glucose, together with high blood pressure and high cholesterol, are the main cause of retinopathy. The network of blood vessels that supply the retina can become blocked and damaged in retinopathy, leading to permanent vision loss. Retinopathy can be managed through regular eye checks and keeping glucose levels close to normal.

Nerve damage

When blood glucose and blood pressure are too high, diabetes can harm nerves throughout the body and cause damage to the nerves (neuropathy). Problems with digestion and urination, impotence, and many other functions can result, but the most commonly affected areas are the extremities, and in particular the feet.  Nerve damage in these areas is called peripheral neuropathy, and can lead to pain, tingling, and loss of feeling. Loss of feeling is particularly important because it can allow injuries to go unnoticed, leading to serious infections, diabetic foot, and amputations.

Diabetic Foot

People with diabetes may develop a number of different foot problems as a result of nerve and blood vessel damage. These problems can easily lead to infection and ulcers which increase a person’s risk of amputation. People with diabetes carry a risk of amputation that may be more than 25 times greater than that of people without diabetes. 3  However, with comprehensive management, a large proportion of amputations related to diabetes can be prevented. Even when amputation takes place, the remaining leg and the person’s life can be saved by good follow-up care from a multidisciplinary foot team. 4  People with diabetes must regularly examine their feet.

Pregnancy complications

Women with any type of diabetes during pregnancy risk a number of complications if they do not carefully monitor and manage their condition. Women with type 1 diabetes require more planning and monitoring before and during pregnancy to minimize complications. High blood glucose during pregnancy can lead to changes in the foetus which cause it to put on excess weight (macrosomia) and overproduce insulin. These can lead to problems in delivery, trauma to the child and mother, and a sudden drop in blood sugar (hypoglycaemia) for the child after birth.  Children who are exposed for a long time to high blood glucose in the womb are at higher risk of developing diabetes in the future. 

Other

Oral health

Although not typically considered a complication, diabetes can pose a threat to oral health, for example with an increased risk of gingivitis (inflammation of the gums) in those with poor glucose control. Gingivitis in turn is a major cause of tooth loss, and may also increase the risk of cardiovascular disease.

Sleep Apnoea

Recent research demonstrates the likelihood of a relationship between type 2 diabetes and obstructive sleep apnoea (OSA), the most common form of sleep disordered breathing. Estimates suggest that up to 40% of people with OSA will have diabetes, but the incidence of new diabetes in people with OSA is not known. 5  OSA may have effects on controlling blood glucose in people with type 2 diabetes.

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1: Harris M, Zimmet P. Classification of diabetes mellitus and other categories of glucose intolerance. In Alberti K, Zimmet P, Defronzo R, editors. International Textbook of Diabetes Mellitus. Second Edition. Chichester: John Wiley and Sons Ltd; 1997. p9-23.

2: World Health Organization. Prevention of diabetes mellitus. Report of a WHO Study Group. Geneva: World Health Organization; 1994. No. 844.

3: Davis TM, Stratton IM, Fox CJ, et al. U.K. Prospective Diabetes Study 22. Effect of age at diagnosis on diabetic tissue damage during the first 6 years of NIDDM. Diabetes Care 1997; 20 (9): 1435-1441.

4: International Working Group on the Diabetic Foot. International Consensus on the Diabetic Foot International Working Group on the Diabetic Foot; 1999.

5: Meslier N, Gagnadoux F, Giraud P, et al. Impaired glucose-insulin metabolism in males with obstructive sleep apnoea syndrome. Eur Respir J 2003; 22 (1): 156-160.