Impaired glucose tolerance: the hidden health risk
13 July 2003
One in 8 Australians aged over 40 is suffering from impaired glucose tolerance, or IGT. However, because the condition has no signs or symptoms, many of these people may be unaware that they have it.
What is IGT?
IGT is an early sign that a person is at high risk of developing type 2 diabetes and cardiovascular (heart and blood vessel) disease. It is an intermediate state between normal blood glucose control and type 2 diabetes.
In people with IGT, the rise in blood glucose that occurs after eating carbohydrate foods is greater than normal (although not as high as in people with type 2 diabetes). Their fasting blood glucose level (measured after fasting overnight) is normal or moderately raised.
What causes IGT?
Like type 2 diabetes, IGT is caused by a combination of impaired secretion of insulin (the main hormone regulating blood glucose) and reduced sensitivity of the body’s cells to insulin, known as insulin resistance.
Who is at risk of developing IGT?
IGT affects approximately one in 8 Australians aged 40 and above and its prevalence increases with age.
IGT is more common among certain ethnic groups (such as people from South Asia) and those who are overweight (particularly people carrying a lot of fat in the abdominal region), who are physically inactive, or who had a low birthweight. Genetic factors also contribute to an increased risk of IGT.
Why is IGT important?
People with IGT have a 40 to 50 per cent chance of developing type 2 diabetes within 10 years. Once IGT has developed, the body’s ability to deal with carbohydrates in the diet tends to continue to decline, ultimately resulting in type 2 diabetes.
Having type 2 diabetes carries with it a high risk of cardiovascular disease such as heart attack as well as complications of diabetes such as blindness, kidney damage and foot ulcers.
IGT increases a person’s risk of developing cardiovascular disease, even if they do not go on to develop type 2 diabetes.
How is IGT diagnosed?
IGT can only be diagnosed with a special test known as the oral glucose tolerance test (OGTT). In this test a blood glucose measurement is taken 2 hours after a person has consumed a 75 g glucose solution.
This shows how well insulin in the person's body has done its job of helping body cells and muscles to take up glucose from the bloodstream after a meal. If there isn't enough insulin or it's not working properly, glucose will stay in the bloodstream — giving a high blood glucose reading in the test.
The condition cannot be diagnosed from measurements of fasting blood glucose alone.
How can IGT be treated?
People with IGT are encouraged to increase their level of physical activity, achieve a healthy weight and follow a healthy, balanced diet. Most people with IGT are not prescribed medication for this condition.
Research has shown that achieving and maintaining a healthy weight, healthy eating and regular exercise reduces progression from IGT to type 2 diabetes.
Last Reviewed: 13 July 2003
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