Scientists have discovered a hormone in the fat cells of mice that blocks the action of insulin and may solve the mystery of why overweight people are more likely to develop the most common form of diabetes.

This "blockbuster" discovery, reported in Thursday’s issue of the journal Nature, could lead to new tests to identify people at risk for type 2 diabetes and to new treatments, says Allen Spiegel, director of the National Institute of Diabetes and Digestive and Kidney Diseases, which financed the research.

About 90 percent of the more than 16 million diabetics in the United States have type 2, which results from the body’s inability to use insulin. The rarer type 1 occurs when the pancreas produces no insulin.

In recent years, experts say, there has been a dramatic increase in the incidence of type 2 diabetes in the United States, linked to the expanding American waistline. An estimated 80 percent of people with type 2 diabetes are overweight, but scientists haven’t understood why obesity leads to diabetes.

Researchers found the new hormone while investigating a class of anti-diabetic drugs called thiazolidinediones, or TZDs. The researchers found that high levels of the hormone, which they named resistin, in mice correspond to greater insulin resistance.

If further research finds that a high level of resistin in humans is as predictive of diabetes as it is in mice, scientists will try to develop new drugs to block the hormone, says lead researcher Mitchell Lazar, of the University of Pennsylvania.

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