Impaired glucose tolerance (IGT) is a syndrome that is being encountered increasingly by doctors. Known by other names, such as prediabetes, metabolic syndrome, impaired fasting glucose, and insulin resistance, it appears to be an intermediate stage in the history and development of diabetes over time.
The American Diabetes Association defines fasting blood glucose levels of greater than 100 (but less than 125, which would be diabetes by their definition) as diagnostic for IGT. They also use the traditional glucose tolerance test, with two hour levels of between 140-199 as meeting the criteria for impaired glucose tolerance. The National Center for Health Statistics estimates a prevalence of up to 25% of the population ages 40-74 having impaired glucose tolerance or impaired fasting glucose.
Why are these numbers so significant? Historically, we’ve used either an abnormal blood sugar, or fructosamine and hemoglobin A1C levels that are above normal to diagnose diabetes. Are these newer IGT diagnostic numbers indicative of a problem? Increasing evidence points to the affirmative. The risk of developing active diabetes is between 4-9% per year in people with IGT. They are associated with risk factors common to all those that cause coronary artery disease and premature atherosclerosis. This metabolic syndrome is a predictor of early mortality even before changes of heart disease or vascular disease can be documented, and there are many primary prevention programs aimed at treating this set of circumstances before full blown diabetes occurs.
The initial step in this process is a relative insulin resistance, meaning that the body does not respond well enough to circulating levels of insulin needed to metabolize glucose in the cell. The body first reacts by putting out more insulin (hyperinsulinemia) to try and solve the problem. This compensates the problem for awhile, but eventually it is not enough and a state of impaired glucose tolerance exists. Eventually the beta cells in the pancreas cannot keep up with demand and glucose is unable to be properly used as fuel in the body, causing diabetes.
There are many risk factors for diabetes. They include a family history for the disease, high blood pressure, sedentary life style, obesity, high cholesterol, and polycystic ovary syndrome, just to name several. Once the pancreas begins to fail and the beta cells that produce insulin are damaged, the body loses its power to compensate by producing more insulin (or even enough insulin). If receptors for insulin are blocked or clogged or unable to make use of the already lacking insulin hormone, that only makes the problem more serious.
Most doctors are now recommending treatment for people with impaired glucose tolerance. They are recommending that their patients lose between 5 and 7% of their body weight, and increase their physical activity markedly. Medications such as metformin and acabose are being prescribed to try to delay or prevent the onset of diabetes. It used to be unusual to see anyone but diagnosed Type 2 diabetics on these drugs, but they are now commonplace in “prediabetes” management.
At present, those who have IGT and whose risk factors are controlled can improve their life expectancy over time with treatment and medical intervention. Younger individuals who have IGT are being shown to have increased health problems, and frequently progress to diabetes and its ensuing complications more rapidly that previously thought. It is still under study how long medication can delay the onset of diabetes and whether it can protect against cardiac disease, so lifestyle management is still the first and most important step in the treatment of IGT.
The information contained on this page is not intended to provide medical advice, which should be obtained directly from your physician.