Diabetes mellitus (just called diabetes from now on) occurs when the level of sugar (glucose) in the blood becomes higher than normal. There are two main types of diabetes. These are called type 1 diabetes and type 2 diabetes:

  • Type 1 diabetes: This type usually develops quite quickly, over days or weeks, as the pancreas stops making insulin. Type 1 diabetes usually first presents in childhood or adolescence.
  • Type 2 diabetes: This is more common in people who are overweight or obese. With type 2 diabetes, the illness and symptoms tend to develop gradually (over weeks or months). This is because people with type 2 diabetes still make insulin (unlike type 1 diabetes). However, people with type 2 diabetes do not make enough insulin for the body's needs, or the body is not able to use insulin properly. Type 2 diabetes usually starts in middle-aged or elderly adults but is increasingly being seen in children and young adults.

There are other types of diabetes, including:

  • Gestational diabetes
  • Secondary diabetes (diabetes can be caused by other diseases);
  • Diabetes caused by autoimmune causes and genetic factors

Understanding blood glucose and insulin

After we eat, various foods are broken down into sugars in the gut (intestine). The main sugar is called glucose. This is absorbed through the gut wall into the bloodstream. Glucose is like a fuel which is used by the cells in the body for energy.

To remain healthy, your blood sugar (glucose) level should not go too high or too low. So, when your blood glucose begins to rise (after eating), the level of a hormone called insulin should also rise. Insulin acts on the cells of your body and makes them take glucose into the cells from the bloodstream. Some of the glucose is used by the cells for energy and some is converted into stores of energy (glycogen or fat).

When the blood glucose level begins to fall (between meals or when we have no food), the level of insulin falls. Some glycogen or fat is then broken down back into glucose and some is released back into the bloodstream to keep the blood glucose level normal. Hormones such as insulin are chemicals that are released into the bloodstream and have an action on certain parts of the body. Insulin is made by special cells called beta cells which are part of little islands of cells (islets) within the pancreas.

Diabetes develops if you do not make enough insulin, or if the insulin that you do make does not work properly on the body's cells.


The common symptoms of diabetes mellitus are increased thirst, frequent urination, extreme hunger, unexplained weight loss, fatigue, blurred vision, delayed wound healing, dehydration, altered mental status and frequent infections.


A simple dipstick test can detect sugar (glucose) in a sample of urine. This may suggest the diagnosis of diabetes. However, the only way to confirm the diagnosis is to have a blood test to look at the level of glucose in your blood. If this is high, then it will confirm that you have diabetes. Some people have to have two samples of blood taken and they may be asked to fast (this means having nothing to eat or drink, other than water, from midnight before the blood test is performed). A different blood test which measures a chemical called HbA1c is now also used to diagnose type 2 diabetes but is not suitable for the diagnosis of type 1 diabetes.

Glucose tolerance tests help to diagnose type 2 diabetes or pre-diabetes (impaired glucose tolerance). The test is also used to help diagnose diabetes in pregnancy.


When left untreated, diabetes can damage various parts of the body:

  • Eyes: Diabetic retinopathy, cataracts and glaucoma
  • Kidney: Diabetic nephropathy, progressive renal failure
  • Nerves: diabetic neuropathy and erectile dysfunction
  • Cardiovascular diseases: Early coronary artery disease, peripheral vascular disease, hypertension and ischemia
  • Feet: Increased risk of infections and foot ulcers
  • Slow wound healing, many times necessitating amputation


Treatment of diabetes involves diet, exercise, medications and other lifestyle improvements. These will help to maintain normal blood sugar levels, and prevent or minimise complications of diabetes.

  • Diet: Eat a consistent, well balanced diet that is high in fibre and low in saturated fats and highly processed foods, particularly sugar. Meals should be taken on a regular schedule and long periods between eating should be avoided.
  • Exercise: Regular exercise in any form can help maintain a healthy weight and blood sugar levels within the normal range.
  • Smoking and alcohol use: Stop smoking and limit consumption of alcohol.
  • Medical treatment: Medicines are prescribed based on the type of diabetes, presence of associated medical problems, complications of diabetes, age and general health.
  • Treating comorbidities: Your doctor will also include medications and treatments to prevent, control and treat other associated conditions.

Regular monitoring of blood glucose is necessary to prevent long-term complications of the disease.

  • Queen's University Belfast
  • University of New South Wales
  • University of Syndey
  • Kings College London