Some 15 million Americans have been diagnosed with Type 2 diabetes mellitus. About 85% take some form of medication or insulin to control it. Recently, scientists reported that one such drug, called Avandia, increased a diabetic's risk of heart attacks by 43%.
But diabetes itself makes a heart attack two to four times more likely. Two-thirds to three-fourths of people with diabetes die from heart attacks or some form of heart disease, regardless of how well they keep their blood sugar under control. In fact, "a person with diabetes has the same risk of heart attack as someone who's already had a heart attack," says Dr. Larry Deeb of the American Diabetes Assn. in Tallahassee, Fla.
Diabetes raises heart attack risk in a variety of ways, says diabetes researcher Dr. David Nathan, director of the Massachusetts General Hospital Diabetes Center in Boston. Most people with Type 2 diabetes are overweight or obese, and that raises blood pressure. Continued hypertension leads to thickening of the artery walls of the heart.
In addition, diabetes raises cholesterol levels, which are known to pack arteries with plaques. If plaques burst, inflammatory blood cells come into the area to deal with the injury, including cells that form blood clots. All of these help clog arteries and prevent the heart from getting the blood flow it needs.
What this means is that people with diabetes need to control not only their insulin levels, but also their blood pressure and cholesterol. Losing weight and exercise help. Many people also use drugs such as statins or ACE inhibitors, depending on their symptoms.
These known paths to heart attacks aren't the only risks brought on by diabetes. "Even if you eliminate the obesity and high cholesterol and the others, you still have a residual risk from just the diabetes," Nathan says. Where this diabetes-specific risk comes from is not well understood. But some researchers say that insulin resistance might have something to do with it.
Insulin resistance, a precursor to full-blown diabetes, is a state in which muscles can't use insulin properly to take blood sugar into their cells. Risk for it derives from a combination of genetics, obesity and other factors. Some research shows that insulin resistance changes fats in our blood and contributes to inflammation — and these may be causes of the elevated heart disease risk for diabetics.
Whatever the link may be, "insulin resistance is the common soil that grows both diabetes and heart disease, though it may not be the only one," Nathan says.
Avandia (rosiglitazone) and its cousin Actose (pioglitazone) have been around for almost a decade. They make people more sensitive to insulin. "If someone is on insulin and they take one of these, more often than not they can take about 10% to 20% less insulin," Nathan says.
But rosiglitazone acts on other things as well: Studies have shown that it alters cholesterol profiles. Some reports showed a rise in LDL, the bad kind of cholesterol, or a lowering of the good kind, HDL.
But LDL cholesterol particles come in different flavors, Deeb says — and although studies suggest rosiglitazone might raise LDL levels, "those LDL particles are big and fluffy, not small and dense," he says. Small, dense LDL particles contribute more to heart disease than do these larger ones.
While he doesn't want to play down Avandia's risk increase, Deeb also says that the latest report didn't have huge numbers of people coming down with heart attacks. He also noted that the authors of the Avandia report, which was reported May 23 by the New England Journal of Medicine, didn't have access to the actual data for their analysis. Instead, they had to rely on published articles. Nathan, too, agrees that the latest report is not definitive. Large studies on the drug are in progress.
Until those findings are in, Deeb says that people with diabetes should talk to their doctors before deciding what to do about Avandia.