Diabetes is a life-long health condition caused by excess levels of glucose in the blood

What is diabetes mellitus?

There are currently 4.7 million people with diabetes mellitus in the UK, including an estimated 549,000 people who have the condition, but don’t know it (Diabetes UK, 2016) (Facts and Figures, Diabetes UK, 2019). This represents approximately 6% of the UK population (IDF, 2017). Diabetes is a lifelong condition that causes a person's blood glucose level to become too high; glucose cannot get into the cells of the body where it is used for fuel. Elevated blood glucose levels can lead to sight loss, amputation, kidney failure, stroke and death. More than 500 people with diabetes die prematurely every week. 

Whilst both type 1 and type 2 diabetes are characterised by having higher than normal blood glucose levels, the cause and development of the conditions are different. About 90% of people with diabetes have type 2, 8% have type 1 and about 2% have rarer types. 

Type 1 diabetes

Type 1 diabetes is an autoimmune disease, which develops when the insulin-producing cells in the body are destroyed and the body is unable to produce insulin. It is unclear why this happens but the most likely reason is that the body has an abnormal reaction to the cells and begins to destroy them. This could be triggered by an infection or virus but again this is not known for sure. It can develop at any age but usually appears before the age of 40, and especially in childhood. A person with type 1 diabetes will need to take insulin injections or use an insulin pump for life. They will also need to ensure that their blood glucose level stays balanced by eating a healthy diet, take regular physical activity and carry out regular blood glucose testing. 

Type 2 diabetes

Type 2 diabetes develops when the body can still produce some insulin but not enough for it to function properly, or when the cells in the body do not react properly to insulin. This is called insulin resistance. The treatment of type 2 diabetes centres on lifestyle management including a healthy diet, regular exercise and the person monitoring their blood glucose level. As the condition progresses over time, oral therapies are used.  However, if these do not prove to be an effective control then the person with diabetes may require insulin injections. There are several oral therapies for diabetes. Some help the body to use insulin more effectively whilst others increase the amount of insulin that the body produces.

Type 2 diabetes is often associated with obesity and later life. However, it is also increasingly becoming more common in children, adolescents and young people of all ethnicities but is particularly prevalent in people of South Asian extraction. Type 2 diabetes is far more common than any other type.

Gestational diabetes

Gestational diabetes arises usually during the second or third trimester and affects approximately 4% of pregnancies (NICE guideline 38). The hormones produced during pregnancy can make it difficult for the body to utilise insulin properly. Women affected by gestational diabetes do not have diabetes before pregnancy and after giving birth, blood glucose levels return to normal. However, women with a history of gestational diabetes are at a seven fold increased risk of developing type 2 diabetes in later life and should be made aware of the signs of hyperglycaemia alongside appropriate monitoring. 

Rare types

Rarer forms of diabetes may include monogenetic diabetes, cystic fibrosis related diabetes, and diabetes caused by rare syndromes. Certain medications such as steroids and antipsychotics, surgery of hormonal imbalances could also lead to other types of diabetes. 

Typical symptoms of diabetes may include:

  • feeling very thirsty
  • passing urine more often than usual, particularly at night
  • feeling very tired
  • weight loss and loss of muscle bulk
  • losing weight without trying to
  • genital itching or thrush
  • cuts and wounds taking longer to heal
  • blurred vision.


A patient diagnosed with diabetes will need to take additional care of their health. They will need on-going advice and support about maintaining a healthy diet, keeping active and monitoring their condition. People with diabetes can live normal active and healthy lives and small adjustments to their lifestyle can make significant improvements. Most diabetes management relies on a person 'self-managing' the condition so their motivation is a major key to effective treatment.

Non-diabetic hyperglycaemia / Pre-diabetes

Pre-diabetes or non-diabetic hyperglycaemia (NDH) are terms often used to describe people who have an elevated risk of developing diabetes, however, these are not recognised clinical terms. NDH occurs when blood glucose levels exceed normal levels but do not climb high enough to warrant a diagnosis of diabetes. This may also be referred to as borderline diabetes, Impaired Glucose Tolerance (IGT), Impaired Fasting Glycaemia (IFG) and Impaired Glucose regulation (IGR).

If pre-diabetes is undiagnosed and untreated the person will almost certainly develop type 2 diabetes. It is estimated that a third of adults in England have pre-diabetes (Diabetes UK, 2014).  Many people often do not know that they have it until it is too late as there are sometimes no noticeable symptoms.

Pre-diabetes is closely linked to obesity and other poor lifestyle choices, and is putting an increasing burden on the health care system. People diagnosed with pre-diabetes can slow down or prevent the condition from developing into type 2 diabetes by making lifestyle changes.

The following are significant factors in the prevention of type 2 diabetes and should be discussed with each person:

  • healthy eating
  • keeping active
  • weight management
  • smoking cessation and alcohol consumption
  • emotional wellbeing.

Diagnosing diabetes – assessing risk

Diabetes UK supports the diagnostic criteria published by the World Health Organisation (WHO) in 2006, see: Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia. Diabetes UK also welcomed the 2011 decision by the WHO to accept the use of HbA1c testing in diagnosing diabetes, see: Use of glycated haemoglobin in the diagnosis of diabetes mellitus.

For more information on diagnostic criteria for diabetes, see: Diabetes UK: Diagnostic criteria for diabetes.

For information and interactive guidance to assess risk of type 2 diabetes see: Type 2 diabetes: Know your risk.