Can strict control of blood glucose levels increase the mortality risk?

This study investigated whether strict control of blood glucose levels (glycemic control) increases mortality (risk of death) in older adults with type 2 diabetes (T2D). It was determined that tight glycemic control increases the mortality risk in such persons when it is achieved with metformin (Glucophage), sulfonylureas, or insulin.

Glycemic control is important in preventing the complications of T2D. Glycemic control can be measured as HbA1c (measures average blood glucose in the last 3 months). Tight glycemic control is usually achieved with medications. However, trying to reach strict targets for glycemic control may lead to over-treatment. Over-treatment may increase the mortality risk in vulnerable patients by increasing the likelihood of side effects, such as hypoglycemia (dangerously low blood glucose). Older people may be more vulnerable to over-treatment and increased mortality. However, most research is done in younger, rather than older, persons.

367 adults with type 2 diabetes, who were 75 years or older, participated in this study. They answered questionnaires, underwent physical examinations, and had blood sampled for testing. They were then followed-up for an average of 6.7 years.

79.8% of participants had been prescribed medications for glycemic control. The other participants were treated with diet only. The most common medications were metformin (60.4%), sulfonylureas (35.3%) and insulin (23.3%).

40.9% of participants died during follow up. The most common causes were cardiovascular disease, followed by cancer and end-stage kidney disease. The mortality risk was higher in older participants, those who had a longer duration of diabetes, those with cardiovascular disease, and those with complications of diabetes.

HbA1c levels did not affect the mortality risk in the diet-only treatment group. However, the mortality risk was 2.63 times higher in the metformin group than the diet-only group when HbA1c was less than 6.5%. The mortality risk was 2.49 times higher in the sulfonylurea group than the diet-only group when HbA1c was between 6.5% and 6.9%. When HbA1c was less than 7% the mortality risk was 2.22 times higher in the insulin group than in the diet-only group. The mortality risk increased when HbA1c was higher than 7% in the metformin group, and when HbA1c was higher than 8% in the sulfonylurea and insulin groups, compared to the diet-only group.

The study concluded that strict glycemic control might be associated with an increased mortality risk in older persons with T2D being treated with metformin, sulfonylureas, and insulin.

This study examined only a small number of participants. Thus the results may not apply to all people with T2D. HbA1c levels are just one factor that may influence mortality. Hence, the ideal target for one individual does not apply to all individuals.

Discuss the best glycemic target for you with your physician.