Instead, researchers say insulin resistance -- the hallmark of Type 2 diabetes -- is a better indicator of who's going to get heart disease among Type 1 diabetics.
"We suspect that insulin resistance occurs in those with Type 1 diabetes in the same way as it does those with Type 2, essentially giving these individuals 'double diabetes' and greatly increasing their risk of heart disease," says Dr. Trevor Orchard, acting chairman of the department of epidemiology at the University of Pittsburgh Graduate School of Public Health.
The study appears in the May issue of Diabetes Care.
For Type 1 diabetics, this may come as good news. It might mean that some Type 1 diabetics, at least those without insulin resistance, are at lower risk of heart disease than previously believed, Orchard says.
And while those with insulin resistance may be at higher risk, medications and lifestyle changes can boost the body's ability to use insulin.
Type 1 and type 2 diabetes are, in many ways, very different diseases, Orchard says.
Type 1, most often thought of as a disease that strikes in childhood, occurs when the body attacks and destroys its own insulin-producing beta cells. Insulin is responsible for helping tissues use glucose, the body's energy source.
Type 1 diabetes, the less common form of the illness, accounts for 5 percent to 10 percent of the 17 million people in the United States with diabetes, according to the American Diabetes Association. Type 1 diabetics need daily insulin injections to survive.
In Type 2 diabetes, the pancreas is usually still producing insulin, but the cells of the liver, muscles and fatty tissues develop a resistance to it. Type 2 can often be controlled with weight loss, diet and exercise.
Doctors have known for a long time that people with diabetes are at higher risk of heart disease, but most of the research has been done in Type 2 diabetics, says Dr. Nathaniel Clark, national vice president of clinical affairs for the American Diabetes Association.
"The question keeps coming up: 'What about Type 1 diabetics?'" Clark says. "There have been very few studies that have shown the risk factors for people with Type 1."
When trying to help diabetics control their risk of heart disease, doctors tend to focus on three risk factors: blood sugar, blood pressure and cholesterol. But it's unknown which is the most significant factor, or if, perhaps, one factor matters more or less in Type 1 or 2 diabetes, Clark says.
Orchard's study begins to get at that, he says.
"I think the most important finding is that these researchers looked at the traditional risk factors, and what they found was that blood sugar wasn't terribly helpful in predicting who gets heart disease," Clark says. "There were other factors that were much more important."
Namely, insulin resistance.
Orchard and his colleagues examined 658 Type 1 diabetics, aged 6 to 40, every two years for a 10-year-period. During that time, there were 108 cardiovascular events, including angina and heart attacks.
Researchers then took a subset of 24 patients and measured their insulin resistance using a type of testing that's considered the gold standard. The problem with this test is that it's time-consuming -- patients have to stay overnight in the hospital -- and expensive.
So Orchard and his colleagues developed a surrogate test for insulin resistance using data about the patients' waist-to-hip ratio, blood pressure and long-term blood sugar levels.
They found that Type 1 diabetics with the highest levels of insulin resistance based on these calculations were the most likely to have a cardiovascular event.
Dr. Loren Wissner Greene, an endocrinologist at New York University Medical Center, is skeptical of the need for complicated calculations. In treating Type 1 diabetics, she says she occasionally sees people who gain a lot of weight and become insulin-resistant.
One easy way of telling if the patients are becoming insulin-resistant is if, over time, they require more and more insulin to maintain their blood sugar.
The American Diabetes Association has information about Type 1 and Type 2 diabetes. You could also check out the National Institute of Diabetes and Digestive and Kidney Diseases.