Adults with type 1 diabetes often have type 2 diabetes as well. This "double diabetes" greatly increases their risk of heart disease - but doing something about it is also risky, a new study suggests.
Type 1 diabetes was once thought to be a simple, albeit serious, condition. The body fails to produce insulin, and blood sugar skyrockets.
Type 2 diabetes is a complex disease that develops slowly - but the key step is insulin resistance. As insulin resistance builds, the body needs more and more insulin to get the same sugar-lowering effect.
University of Pittsburgh researchers led by Trevor Orchard, MD, looked at people with type 1 diabetes enrolled in the Pittsburgh Epidemiology of Diabetes Complication Study. They studied 603 patients who did not have heart disease at the beginning of the 10-year study. Those who developed heart disease had one major thing in common - insulin resistance, the hallmark of type 2 diabetes.
"The importance of the co-incidence of type I diabetes and insulin resistance indicating type 2 diabetes really hasn't been focused on," Orchard observes. "There is a technical insulin resistance that occurs in type 1 diabetes because of high blood sugar, but this is separate."
Orchard's study suggests that one in five people with type 1 diabetes suffer this double diabetes. Most of them inherit a tendency toward type 2 diabetes from their parents. These patients are at greatly increased risk of heart disease.
But there's a twist to this finding. People with double diabetes have lots of plaque in their arteries. But their high blood sugar makes these plaques more fibrous. Ironically, this makes them less likely to rupture and cause a heart attack.
Despite their clogged arteries, people with double diabetes don't suffer any more sudden heart deaths than other people. However, their arteries are clogged. This leads to clogged arteries in the lower limbs - and often to amputation.
"I think if people have type 1 diabetes and a family history of type 2 diabetes or signs of metabolic syndrome - large waist circumference - they should work with their doctors to improve insulin sensitivity," Orchard advises. "At the moment, that would involve diet and exercise."
But that's not all. Once people with double diabetes get their blood sugar under control, the plaques in their arteries become less stable for a while.
"There is a problem of risking heart failure," Orchard warns. "If we were able to control blood sugar perfectly and get everybody with double diabetes into the normal range, there would be dramatic improvement in heart disease. But during the process of lowering blood sugar, you might have a period with increased rates of acute heart disease.
Two to three years down the line we should see improvement. Eventually it would be a benefit, but in the short term it might be risky. So the approach would be to make sure people had good treatment with statin drugs to stabilize plaques while lowering blood sugar."
Orchard credits John D. Brunzell, MD, director of the Clinical Research Center at the University of Washington, Seattle, with first finding signs of type 2 diabetes in people with type I diabetes. Brunzell first noticed the phenomenon when he saw people with type 1 diabetes gain weight as soon as they got their blood sugar under tight control.
Brunzell agrees with Orchard that people with this condition urgently need to control their weight gain as well as their blood sugar. "If we tie this all together, it says that in the type 1 diabetic who gets good glycemic control and gains weight, we should be concerned about the weight gain," Brunzell says. "We should also treat the things that go along with it to prevent the development of unstable plaques. This is not hypothesis. It is fact."
These findings are reported in the May issue of the journal Diabetes Care