MONDAY, Sept. 20, 2004 (HealthDayNews) -- A new analysis of studies strongly suggests that people with diabetes keep tight reins on their blood sugar levels if they want to ward off heart disease.
Chronically high blood sugar levels increase the risk of cardiovascular disease by 15 percent to 18 percent for people with diabetes, according to the analysis, which appears in the Sept. 21 online issue of the Annals of Internal Medicine.
It's long been known that having diabetes increases the risk of heart disease, and that diabetics have more than a twofold increased risk for heard disease death. Scientists have also found that chronically high blood sugar leads to what they call "small vessel" complications, such as retinopathy, in which the small blood vessels in the eye are affected.
But the link between diabetes and "large-vessel" disease, such as heart attack or stroke, has been less strong.
Now, the new analysis -- in which researchers pooled the results of 13 studies involving more than 9,000 subjects -- provides stronger evidence that chronically high sugar levels increase the risk of large vessel disease, which translates to having strokes and heart attacks, said study author endocrinologist Dr. Sherita Golden, an assistant professor of medicine and epidemiology at Johns Hopkins University School of Medicine.
Three of the studies involved people with type 1 diabetes, in which the body doesn't produce insulin, which is crucial for the body to be able to use sugar, the cell's basic fuel. The other 10 involved those with type 2 diabetes, in which the body either doesn't produce enough insulin or doesn't use it properly.
"We looked at the glycosylated hemoglobin levels, also called glycated hemoglobin, or hemoglobin A1c," said Golden. "This is a long-term measure of glucose control." Basically, she said, it reflects your average daily blood sugar over the previous three months.
"It measures how much glucose in the blood gets to the red blood cells," Golden explained. "The higher your glucose, the more of your red cells will have glucose attached."
Then they compared the glycosylated hemoglobin levels and the incidence of heart attacks and strokes.
"When we pooled results for all the studies, for every 1 percent increase in glycosylated hemoglobin there was an 18 percent increased risk of having cardiovascular disease," Golden said. "That was in people with type 2. In type 1, there was about a 15 percent increased risk of cardiovascular disease [for every 1 percent rise]."
The lower incidence in those with type 1 might be explained, Golden said, because many of them are younger and researchers might have had to follow them for a longer period of time to determine how many eventually suffer heart attack or stroke.
The new analysis builds on previous research, Golden said, including a landmark British study in 1998 that confirmed the risk of developing small-vessel disease -- but not large-vessel disease -- if blood sugar levels are chronically high.
The news isn't all bleak, Golden said. The findings, she said, "suggest if a patient lowered their glycosylated hemoglobin by one percentage point, you would have a significant reduction in heart disease risk."
For patients, she said, the bottom line is that "glucose control, as well as control of other risk factors, is important in the prevention of cardiovascular disease."
"What patients need to do is make sure their blood sugar is tightly controlled," she said. "That may mean more frequent monitoring," she added, although the study did not investigate whether more frequent monitoring leads to tighter control of blood sugar.
Another expert, Dr. Nathaniel Clark of the American Diabetes Association (ADA), says the new analysis "lends tremendous support for the control of blood sugar indicated by the hemoglobin A1c."
"The goal is that the A1c be less than 7 percent," Clark said. Generally, those with diabetes whose disease is stable should get the test twice a year, Clark said. If they are not stable, they should have it done four times a year.
The ADA recommends that a diabetic's before-meal blood glucose levels be between 90 and 130 milligrams per deciliter (mg/dl), he said, and that two hours after a meal the level be less than 180 mg/dl.
Learn more about monitoring blood sugar from the Joslin Diabetes Center.