Type 2 Diabetes - Types Of Diabetes: Diabetes

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Type 2 diabetes

A combination of abnormalities is responsible for type 2 diabetes. The first is probably insulin resistance, a condition in which body cells become less responsive to insulin. Therefore, the body must secrete more insulin to maintain normal metabolism. Insulin resistance, which is very common, doesn't cause type 2 diabetes by itself. The pancreas usually rallies to compensate for the resistance by pumping out more insulin. For most people with insulin resistance, blood sugar levels stay within a normal range. But for some, the insulin-producing cells eventually fail to keep up with the increased demand. Blood sugar levels rise, resulting in type 2 diabetes.

Essentially, type 2 diabetes is a problem of supply and demand. The pancreas supplies too little insulin to keep up with the increased demand that occurs with insulin resistance. For this reason, people with type 2 diabetes can be treated with therapies that decrease insulin demand, including diet, exercise, and drugs; with medications that increase insulin supply, such as sulfonylureas or meglitinides; or with insulin itself.

Who's at risk?

While genes, aging, and medications can all cause insulin resistance, being overweight and failing to get enough exercise are major culprits. Of the approximately 1.3 million Americans who will develop type 2 diabetes this year, about 90% are overweight or obese. (People who are overweight have a body mass index, or BMI, of 25 or more; those who are obese have a BMI of 30 and above. See chart.) Exactly how weight contributes to insulin resistance is a puzzle waiting to be solved. Recent studies have suggested that fat cells are not merely passive storage sites. Fat cells produce fatty acids and secrete proteins such as leptin, resistin, and adiponectin, which interfere with the secretion and action of insulin in the body.

In addition to people who are overweight or sedentary, people over age 65 or who have a family history of type 2 diabetes are at particularly high risk. Recently, a growing number of children and adolescents have been diagnosed with it. Typically, such children are obese and have a family history of the disease. Women who develop diabetes during pregnancy also have a high risk. Gestational diabetes usually disappears after delivery, but as many as 50% of women who have this form of diabetes go on to develop permanent type 2 diabetes, often within 10 years of their pregnancy.

Race and ethnicity also play a crucial role: The disease is far more common among African Americans, Asian Americans, Hispanics, Pacific Islanders, and Native Americans than among whites. One tribe of Native Americans living in Arizona has the highest rate of type 2 diabetes in the world, with the illness affecting about 50% of their adults ages 30–64.

What causes type 2 diabetes?

Predominantly a disease of later life, type 2 diabetes generally develops after age 40. Blood sugar levels usually rise slowly and progressively over the years before they become high enough to be considered in the diabetic range.

Two conditions, impaired glucose tolerance and impaired fasting glucose, often precede type 2 diabetes, and for this reason are known collectively as pre-diabetes. In both types of pre-diabetes, blood sugar levels are above normal, but not high enough to be considered clinical diabetes. A conservative estimate is that more than 20 million U.S. adults have pre-diabetes and, therefore, are much more prone to developing type 2 diabetes. Like people with type 2 diabetes, those with pre-diabetes tend to be overweight, have high blood pressure and abnormal lipid levels, and have a higher risk for cardiovascular disease.

Type 2 diabetes and its underlying causes, insulin resistance and defective insulin secretion, probably have a genetic basis. But in most cases, environmental factors also play a major role. For example, before the 20th century, diabetes was virtually unknown to Native Americans. But as hunting or farming gave way to a sedentary lifestyle, higher-fat diets, and obesity, diabetes became rampant. People from many other cultures have had similar experiences after adopting "Western" habits. Thus, in people who are genetically susceptible, the influences of older age, increasing obesity, and a sedentary lifestyle all unmask the tendency to develop diabetes.

The distribution of body fat also seems to be particularly important. People who tend to store fat in their abdominal area rather than their hips — so-called central obesity — are more likely to become diabetic.

Prevention is possible

Fortunately it is possible to prevent the onset of type 2 diabetes through diet and exercise. This was shown conclusively through a landmark clinical trial, known as the Diabetes Prevention Program (DPP), which looked at 3,234 Americans who had impaired glucose tolerance and therefore were at risk for developing type 2 diabetes. The study found that people who lose 5%–7% of their weight and exercise about 30 minutes a day can reduce their risk by 58%. The same study found that the oral diabetes drug metformin (Glucophage) also lowers risk, but less dramatically, by 31%.

Smaller studies in China, Finland, Europe, and Canada have shown that diet and exercise or treatment with the drug acarbose (Precose) can delay type 2 diabetes in at-risk people. However, the DPP, conducted at 27 centers nationwide, was the first major trial to demonstrate the effectiveness of lifestyle changes or drug intervention in a diverse group of overweight, high-risk people.

A new national multicenter trial, known as Look AHEAD (Action for Health in Diabetes) is now under way to determine whether the lifestyle changes that proved so effective in the DPP study can be maintained for a longer period and prevent heart attacks, strokes, and other types of cardiovascular disease in people who already have type 2 diabetes. The Look AHEAD study has enrolled 5,000 participants who will be followed for as long as 111/2 years. Results of the study will be available in the next decade.

Last updated:	January 23, 2007