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Blood-Sugar Control Prevents Heart Disease 'Landmark Study' Solves Diabetes Riddle

Posted on: Saturday, 24 December 2005, 09:00 CST

By Gina Kolata

A 17-year U.S. study has finally answered one of the most pressing questions about diabetes: Can tight control of blood sugar prevent heart attacks and strokes?

The answer, reported Thursday in The New England Journal of Medicine, is yes. Intense control can reduce the risk by nearly half.

And, the study found, the effect occurred even though the patients had only had a relatively brief period of intense blood sugar control when they were young adults. Nonetheless, more than a decade later, when they reached middle age, when heart disease and strokes normally start to appear, they were protected. The study involved those with Type 1 diabetes, which usually arises in early in life and involves the death of insulin-secreting cells.

"This is truly an important study," said Dr. Robert Rizza, a professor of medicine at the Mayo Clinic in Rochester, Minnesota, and the president of the American Diabetes Association. "And I usually don't say that," he added.

The findings are likely to affect clinical practice, encouraging doctors to put more effort into helping patients control their blood sugar, said Dr. John Buse, the director of the diabetes care center at the University of North Carolina.

The study is "the most rigorously conducted to date," Buse said. The question of whether rigid blood sugar control protects against heart disease and strokes has divided the field for decades, diabetes researchers said. "It's really a major question that has been around for a long time," said Dr. Judith Fradkin, who directs diabetes research at the National Institute of Diabetes and Digestive and Kidney Diseases.

Researchers knew that diabetes was linked to heart disease at least two-thirds of diabetics die of heart disease. But although studies showed that controlling blood sugar protects against damage to the eyes, kidneys and nerves, there was no conclusive evidence that it would have the same effect on heart disease and stroke.

"In that sense, this is a landmark study," said Dr. William Cefalu, a diabetes researcher at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, who wrote an editorial accompanying the paper. The study began with 1,441 people aged 13 to 39. Half were randomly assigned to intensive therapy, intended to keep their blood sugar levels low all the time. That meant injecting themselves with insulin three or more times a day or using an insulin pump. The others were assigned to conventional therapy, which meant one or two insulin injections a day, a regimen that was easier for patients but resulted in higher sugar levels.

Blood sugar was assessed by measuring the amount of hemoglobin A1c in the participants' blood, a test that looks for hemoglobin with sugar attached to it. The goal for the intensive-therapy group was to keep those levels to 6 percent or less. They achieved an average level of 7 percent.

Those assigned to conventional treatment had an average level of 9 percent. Normal levels for people without diabetes are 4 percent to 6 percent.

After six and a half years, both groups were told that intensive therapy had prevented injury to the eyes, kidneys and nerves but that there was no noticeable effect on heart attacks and strokes.

The study investigators managed to keep track of 95 percent of the participants. As the years went by and the patients started developing signs of heart disease, the researchers noticed a pronounced difference between the two groups in their heart attack and stroke rates. Thirty-one of the patients who had had intensive treatment when they were young had a total of 46 cardiovascular events, including heart attacks, stroke, and heart disease severe enough to require bypass surgery. Fifty-two of the conventionally treated patients had a total of 98 such events.

"It was amazing," said Dr. David Nathan, a diabetes researcher at the Massachusetts General Hospital who was co-chairman of the study. "Therapy for six and a half years seems to have driven a dramatic effect."

But the result also gives rise to questions: Does the same effect occur in people with Type 2 diabetes, which usually occurs later in life and involves an inability to respond to insulin? And why would tight control of blood sugar for one brief period have such a pronounced effect later?

Fradkin said she expected the results would hold for Type 2 diabetes. Another large U.S. federal study is addressing that question, she notes, but it is already known that tight control of blood sugar in Type 2 diabetes protects against nerve, kidney and eye damage, just as it does with Type 1 diabetes. In addition, a study in Britain hinted although it did not demonstrate that Type 2 diabetics who keep their blood sugar low have less heart disease and strokes.

Fradkin said she hoped the emerging evidence and improving therapies would make a difference.

"We want patients to say to their doctor, 'What is my A1C level? What should it be? And what can I do to get it there?'" Fradkin said.

Source: International Herald Tribune

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