Several trials have convincingly shown that lowering blood glucose levels decreases the likelihood of three late complications of diabetes — blindness from damage to the retina (retinopathy), impaired kidney function (nephropathy), and pain or numbness in the extremities resulting from nerve damage (neuropathy).
The major cause of death in diabetes, however, is cardiovascular disease; and available results suggest, but have not proven, that achieving ever-lower levels of blood glucose in people with diabetes reduces their risk of heart attacks and strokes.
But can glucose levels of people with type 2 diabetes be brought down so much that a health hazard is created? Preliminary results from a large clinical trial suggest that glucose levels can be lowered to a point where harm is done.
The ACCORD (Action to Control Cardiovascular Risk in Diabetes) clinical trial was launched to test whether aggressive treatment of blood glucose reduced the number of heart attacks, stokes, and deaths in high-risk individuals with type 2 diabetes.
The trial enrolled 10,251 patients with type 2 diabetes who were also at high risk for cardiovascular disease — that is, they were suffering from high blood pressure, elevated cholesterol levels, and/or obesity.
These patients were divided into two groups: half of them (the standard-treatment group) were placed on treatment aimed at lowering their blood glucose levels to the levels achieved by the average person with diabetes.
The other half (the intensive-treatment group) were treated with a more intensive regimen of medications, in an effort to lower their glucose levels nearer to those found in people without diabetes.
Recently, the researchers discovered that during a period of about four years in the trial, 54 more patients had died in the intensive-treatment group (257 deaths) than in the standard-treatment group (203 deaths). Heart disease was the cause of about half of these excess deaths.
Patients in the intensive-treatment group suffered fewer heart attacks but their heart attacks were more often fatal and these participants were more likely to suffer sudden cardiac death.
The ACCORD trial will continue in order to determine the effects of lowering blood pressure and improving LDL cholesterol, HDL cholesterol, and triglycerides. However, aggressive treatment in the intensive arm of the study was immediately stopped.
It is possible that the excess deaths in the intensive-treatment group resulted from episodes of low blood glucose (hypoglycemia), which can put stress on the cardiovascular system by increasing heart rate and producing abnormal heart rhythms. Previous trials in patients with type 1 diabetes demonstrated that rigid glucose control was associated with a significantly greater incidence of hypoglycemia.
The take-home message: People with type 2 diabetes should continue their efforts to control their blood glucose levels enough to prevent retinopathy, nephropathy, and neuropathy. However, they should probably beware of treatment regimens that lower glucose levels to the point where they lead to frequent bouts of hypoglycemia.
