The increased fatalities from heart attack and stroke also undercut a major assumption researchers had made about diabetes, that getting blood sugar levels close to normal would improve diabetics' health, The Washington Post (NYSE:WPO) reported.

"It's profoundly disappointing," Richard Kahn, chief scientific and Medical Officer for the American Diabetes Association, told the newspaper. "This presents a real dilemma to patients and their physicians. How intensive should treatment be? We just don't know."

The study, sponsored by the National Heart, Lung and Blood Institute, involved 10,251 people with type 2 diabetes in the United States and Canada. Half were put on a diet, exercise and drug regimen aimed at reducing blood sugar levels to those of the average diabetic, while the other half were treated more aggressively to cut their levels close to normal.

Half the excess deaths were from heart disease.