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Impaired Glucose Tolerance: A Precursor to Diabetes

Impaired glucose tolerance (IGT) is a condition that affects about twenty million Americans. The presence of impaired glucose tolerance is an important indicator of an increased risk of developing type 2 diabetes. With the alarming rise of diabetes in America, the research community is paying close attention to contributing factors, such as obesity and impaired glucose tolerance.

Syndrome X and Impaired Glucose Tolerance
Rarely a stand-alone condition, impaired glucose tolerance is actually one of a number of conditions collectively known as syndrome X. The presence of each of these conditions contributes individually to the development of diabetes.
  • obesity
  • insulin resistance
  • hyperinsulinemia (high blood insulin levels)
  • impaired glucose tolerance
  • hypertension (high blood pressure)
  • dyslipidemia (abnormal levels of fat in the blood).
Insulin resistance, hyperinsulinemia and impaired glucose tolerance are also associated with the development of polycystic ovary syndrome (PCOS) in both obese and lean women.

Obesity has long been related to obstructive sleep apnea (OSA). According to the results of a new study, whose results were published in the March 2002 issue of the American Journal of Respiratory and Critical Care Medicine, OSA is also associated with insulin resistance independent of obesity.

Risk Factors for Impaired Glucose Tolerance
The causes of impaired glucose tolerance are similar to those identified for full-blown diabetes. As with many diseases, one's risk of developing glucose intolerance and insulin resistance appears to involve both genetics and lifestyle.

Certain ethnic groups are more likely to develop impaired glucose tolerance than others. African Americans, Native Americans, Hispanic Americans, Asian Americans and Pacific Islanders are all at greater than normal risk. The occurrence of type 2 diabetes is also more common in these populations.

Women are more likely to develop impaired glucose tolerance than men, and women with a history of gestational diabetes are at higher risk than other women.

A family history of diabetes could indicate that you have a genetic predisposition to problems involving glucose metabolism and put you at an increased risk of impaired glucose tolerance.

Some medical conditions contribute to the development of impaired glucose tolerance, insulin resistance and diabetes. These include:
  • obesity
  • liver cirrhosis
  • end stage kidney disease
  • certain endocrine disorders (i.e., hyperthyroidism, Cushing's disease)
  • certain exocrine disorders (i.e., cystic fibrosis, pancreatic cancer, hemochromatosis)
  • certain genetic disorders (i.e., Down syndrome, Turner syndrome)
  • gestational diabetes.
What Is Insulin Resistance?
In some people, insulin levels may be normal or even high, but the body stops responding appropriately. Because insulin is necessary in order to use glucose as an energy source, insulin resistance leads to elevated blood sugar levels. The exact mechanism of insulin resistance is unknown, however, doctors and scientists have discovered that the condition is more common in overweight individuals and that a genetic predisposition exists. Studies have shown that diet and exercise can help restore insulin sensitivity. Lowering the amount of fat and calories consumed and getting thirty minutes of aerobic exercise several times a week can reduce the risk of insulin resistance and the development of type 2 diabetes.

Diet, Exercise and Impaired Glucose Tolerance
For the person who wants to maintain their healthy weight, the calories burned should equal calories taken in. For the overweight person, the calories burned should exceed those taken in. Combining exercise with specific dietary changes, such as limiting carbohydrates and fats, is the best way to control impaired glucose tolerance and maintain good health.


Ip, M. S. M., Lam, B., Ng, M. M. T., Lam, W. K., Tsang, K. W. T., Lam, K. S. L. (2002, March). Obstructive sleep apnea is independently associated with insulin resistance [electronic version]. American Journal of Respiratory and Critical Care Medicine 165(5), 670-676.

Joslin Diabetes Center. (2002). What is impaired glucose tolerance (IGT) and how is it diagnosed? Retrieved July 20, 2002 from www.joslin.harvard.edu/education/library/prevent_itg.shtml.

Olatunbosun, S. (updated 2002, April). Glucose intolerance. eMedicine. Retrieved July 17, 2003, from www.emedicine.com/med/topic897.htm.

Schroeder, C. M. (2000). Insulin resistance in PCOS. Retrieved July 17, 2003, from
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