People with type 1 diabetes might think they have it bad already, but researchers say that they could be struck with another form of the disease.

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Insulin resistance, a condition usually associated with type 2 diabetes, is likely a major cause of heart disease in people with type 1 diabetes, according to researchers at the University of Pittsburgh Graduate School of Public Health.

The study analyzed 10 years of data from 658 adults with type 1, or childhood-onset, diabetes. Their findings are published in the May 2003 issue of Diabetes Care, a journal of the American Diabetes Association.

"Heart disease is a major complication for people with diabetes, including those with type 1 diabetes, and until now there has been no clear explanation for its cause," said researcher Dr. Trevor Orchard, professor and acting chairman of the department of epidemiology at the graduate school. "We now suspect that insulin resistance occurs in those with type 1 diabetes in the same way as it does in those with type 2, essentially giving these individuals double diabetes and greatly increasing their risk of heart disease."

Insulin resistance, long associated with type 2 diabetes and a known risk factor for heart disease, occurs when the body does not properly use insulin to metabolize blood glucose, or sugar. Glucose then builds up in the blood, and additional insulin is required. The new study suggests that this condition can occur in people who have type 1 diabetes as well.

"The good news is that not all people with type 1 diabetes are insulin resistant, and for them the risk of heart disease may not be as high," Orchard said. "Clearly, reducing or preventing insulin resistance through exercise, weight loss and possibly medication may help people with type 1 diabetes avoid heart disease."