An unexpected number of deaths among patients receiving intense therapy to lower their blood sugar forced the National Institutes of Health to abruptly cut short part of a major study on diabetes and heart disease.

The therapy was aimed at reducing to normal levels the blood sugar of type 2 diabetics at especially high risk of heart attack and stroke. There were 257 deaths among people receiving intense diabetes treatment, compared with 203 in the standard treatment group, NIH's National Heart Lung and Blood Institute said.

More than 18 million Americans have diabetes, with type 2 the most common form.

Last fall the Food and Drug Administration added new warnings to the label of the popular diabetes drug Avandia, listing concerns about heart ailments. However, in Wednesday's announcement NHLBI officials stressed that they have been unable to link the increased deaths in the study to any drug, including Avandia.

Some 10,251 people were enrolled in the Action to Control Cardiovascular Risk in Diabetes study, with an average participation time of four years.

The participants were in groups receiving three types of treatment, intensive lowering of blood sugar, lowering blood pressure or reducing cholesterol.

"A thorough review of the data shows that the medical treatment strategy of intensively reducing blood sugar below current clinical guidelines causes harm in these especially high-risk patients with type 2 diabetes," said Dr. Elizabeth G. Nabel, director of the institute.

"Though we have stopped this part of the trial, we will continue to care for these participants, who now will receive the less-intensive standard treatment. In addition, we will continue to monitor the health of all participants, seek the underlying causes for this finding, and carry on with other important research within ACCORD," she said in a statement.

The study focuses on treatments for adults with type 2 diabetes, the most common form, who are at especially high risk for heart disease, meaning they had at least two risk factors, which include high blood pressure, high cholesterol, obesity and smoking.

Dr. William Friedewald, professor of Public Health and Medicine at Columbia University, and chairman of the ACCORD Steering Committee, said that there were "about 10 percent fewer nonfatal cardiovascular events such as heart attacks in the intensive treatment group compared to the standard treatment group. However, it appeared that, if a heart attack did occur, it was more likely to be fatal. In addition, the intensive treatment group had more unexpected sudden deaths, even without a clear heart attack."

The action was recommended by an independent advisory group of experts in diabetes, heart disease, epidemiology, patient care, biostatistics, medical ethics and clinical trial design that has been monitoring ACCORD since it began.

Participants will continue to receive blood sugar treatment from their study clinicians until the planned trial conclusion in June 2009.

Nabel stressed that diabetes patients should not change their treatment without consulting their doctor. The American Diabetes Association agreed and said it continues to encourage control of blood sugar in treatment of diabetes.

NHLBI said the intensive treatment group had a target blood sugar goal of less than 6 percent, which is similar to blood sugar levels in adults without diabetes. The standard treatment group aimed for a target similar to what is achieved, on average, by those with diabetes in the United States, of 7 to 7.9 percent.