Tight blood sugar control fails to improve memory in diabetics

By Dr. Ananya Mandal, MDOct 2 2011

A new study has shown that those with type 2 diabetes do not show slowing of the decline in thinking skills with intense blood sugar control. In fact such intense therapy raises risk of death.

People older than 70 with type 2 diabetes are twice as likely to suffer mental impairment as those without diabetes, researchers say. Intensively controlling blood sugar has been shown to reduce the odds of diabetes complications, such as vision, kidney and circulation problems, so it seemed likely that it might also slow any cognitive decline related to the condition.

“We know that people with type 2 diabetes have a much higher risk of dementia and memory loss than people without diabetes,” said Dr. Jeff Williamson of Wake Forest Baptist Medical Center in North Carolina, one of the authors of the study. “What we didn't know was, if you intensively control blood sugar levels in people who have had a history of trouble controlling them, does the added cost and effort to control blood sugar result in a slowed rate of memory loss?”

“At the end of the day, there was no difference in cognitive function between people who received the intensive strategy versus the standard strategy,” said lead researcher Lenore J. Launer, at the Laboratory of Epidemiology, Demography and Biometry at the U.S. National Institute on Aging. Launer said they went into the study assuming intensive lowering of blood sugar would improve cognitive function. Since there were no non-diabetics in the study for comparison purposes, it is still possible that routine control of blood sugar does confer a benefit on cognitive function, she said.

“Patients should follow standard therapy, because there is no additional benefit to following a more intensive strategy,” she advised. It is important for people with type 2 diabetes to keep their blood sugar under control to reduce the likelihood of long-term complications. While the study didn't confirm cognitive advantages, many other health benefits are associated with well-controlled blood sugar, Launer said.

The study was published in the Sept. 27 online edition of The Lancet Neurology.

Launer's group looked at a subset of patients who took part in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial. Researchers assigned 2,977 with type 2 diabetes at high risk for heart disease to intensive blood-sugar lowering or current treatment. The participants were 55 to 80 years old. Intensive blood sugar lowering meant reducing blood sugar to less than 6 percent as measured by an A1c test. The current standard is to maintain blood sugar at between 7 and 7.5 percent. Some patients (614) also had an MRI to measure brain volume and took cognitive ability tests at the beginning and end of the study.

After about 39 months, no difference in cognitive ability existed between the groups, the researchers found.

The part of the ACCORD trial involving intensive lowering of blood sugar was halted earlier than planned. An increased risk of death, the finding of no overall benefit on cardiovascular disease, problems caused by too-low blood sugar and weight gain were all factors in stopping.

Dr. Geert Jan Biessels, a neurologist at the Rudolf Magnus Institute of Neuroscience at the University Medical Center in Utrecht, the Netherlands, wrote a journal editorial accompanying the study. He said that “dementia is the most important cognitive complication of diabetes. The present study assessed the effects of treatment on average cognitive functioning across the whole study population. It is uncertain, however, if average cognitive functioning is an adequate proxy for dementia.”

On average, cognition was not improved, he said. “However, the absence of an effect of treatment on mean cognitive functioning cannot yet be regarded as proof that the treatment may not delay dementia…But, at present the results do not support specific treatments to prevent cognitive decline in diabetes.”

Williamson said people who are on the verge of developing diabetes should take steps now to prevent it. “For those folks who are gaining weight and living a sedentary lifestyle, this is a warning that medicine is not going to rescue you,” he said.

Another expert, Dr. Jay Skyler, a professor of medicine at the Diabetes Research Institute of the University of Miami Miller School of Medicine, said that “the study does not answer the question as to whether among diabetics cognitive dysfunction might be more accelerated than in the general population and whether treatment might control that.”

Most of the 366 million people with diabetes have type 2, the kind linked to poor diet, obesity and lack of exercise. Diabetics have inadequate blood sugar control, which can lead to serious complications like heart disease and stroke, damage to the kidneys or nerves, and to blindness.