Studies on Diabetes

• Diabetes Control and Complication Trial (DCCT)
• Diabetes Prevention Program
• Diabetes Prevention Program: Questions and Answers

Diabetes Prevention Program: Questions and Answers

What is Impaired Glucose Tolerance (IGT)?

People with IGT have blood glucose levels that are higher than normal but not yet diabetic. This condition is diagnosed using the oral glucose tolerance test (OGTT). After a fast of 8 to12 hours, a person’s blood glucose is measured before and 2 hours after drinking a glucose-containing solution.

• In normal glucose tolerance, blood glucose rises no higher than 140 mg/dl 2 hours after the drink.
• In impaired glucose tolerance (IGT), the 2-hour blood glucose is between 140 and 199 mg/dl.
• If the 2-hour blood glucose rises to 200 mg/dl or above, a person has diabetes.

DPP participants were overweight and had IGT. In addition, researchers selected volunteers with IGT whose fasting blood glucose levels were between 95 and 126 mg/dl since they were at higher risk to develop diabetes.

How does the fasting blood glucose test differ from the oral glucose tolerance test?

• In the fasting blood glucose test, a person’s blood glucose is measured after a fast of 8 to 12 hours:
• A person with normal blood glucose has a blood glucose level below 110 mg/dl.
• A person with impaired fasting glucose has a blood glucose level between 110 and 126 mg/dl.
• If the fasting blood glucose level rises to126 mg/dl or above, a person has diabetes

The OGTT includes measures of blood glucose levels after a fast and after a glucose challenge. In 1997, an American Diabetes Association (ADA) expert panel recommended that doctors use the fasting blood glucose test to screen their patients for diabetes because the test is easier and less costly than the OGTT. Though the fasting glucose test detects most diabetes cases, the OGTT is more sensitive in identifying people with blood glucose problems that may first appear only after a glucose challenge.

For a person with IGT, what is the risk of developing type 2 diabetes?

• As few as 1 to as many as 10 of every 100 persons with IGT will develop diabetes per year. The risk of getting diabetes rises as people become more overweight and more sedentary, have a stronger family history of diabetes, and belong to a racial or ethnic minority group. In the DPP, about 10 percent of participants in the placebo or standard group developed diabetes per year. The DPP interventions decreased the development of diabetes by 58 percent with intensive lifestyle interventions and by 31 percent with metformin.

How many people in the United States have IGT?

About 16 million people in the United States have IGT, according to the National Health and Nutritional Examination Survey III.

It is important to note that the interventions were effective in the setting of a controlled clinical trial in which volunteers randomized to lifestyle intervention received a great deal of individualized instruction. The Public Health Service and organizations such as the American Diabetes Association will review the results and consider a number of issues before making recommendations for the general population. For example, metformin is currently approved for treating, not preventing, type 2 diabetes. The Food and Drug Administration (FDA) would determine whether to make diabetes prevention an added indication for this drug. Another consideration is that, due to the risk of lactic acidosis, metformin should not be given to people with impaired kidney or liver function or to people who drink excessive amounts of alcohol. People for whom metformin might be harmful were excluded from the DPP.

How do the DPP results compare to the findings of other type 2 diabetes prevention studies?

Several studies in other cultures have examined the effects of intensive changes in diet and exercise in people at risk for type 2 diabetes. A study in Finland showed that diet and exercise resulted in a risk reduction similar to that shown in the DPP. The Finnish trial, however, did not study the effects of metformin nor did it examine the effects of lifestyle changes in specific subgroups by weight, age, or race/ethnicity. In addition, participants in the Finnish study were a fairly homogenous European population compared to DPP volunteers, who come from diverse age and ethnic groups. Cultural factors greatly influence lifestyle changes. It was important to show that type 2 diabetes can be prevented in U.S. minority populations that are at disproportionate risk.

How do diet and physical activity work to prevent diabetes?

Obesity and sedentary lifestyle are known to increase the risk of both insulin resistance and type 2 diabetes. Insulin resistance, a disorder in which target tissues--muscle, fat, and liver cells--fail to use insulin effectively, accompanies and usually precedes type 2 diabetes. With the onset of insulin resistance, the pancreas compensates by producing more insulin, but gradually its capacity to secrete insulin in response to meals falters, and the timing of insulin secretion becomes abnormal. Weight loss resulting from diet and increased physical activity may lower diabetes risk by improving the ability of muscle cells to use insulin and to handle glucose more efficiently.

What were the goals of DPP’s lifestyle intervention arm?

The goals were to:

• achieve and maintain a weight loss of 7 percent with healthy eating and increased physical activity
• maintain physical activity at least 150 minutes a week with moderate exercise, such as walking or biking.

Participants received training in diet, exercise, and behavior modification from case managers who met with each participant for at least 16 sessions in the first 24 weeks and then monthly.