Dementia Risk for Older People Increased by Low Blood Sugar

Older individuals with type 2 diabetes who have been hospitalized with severe low blood sugar levels seem to have a greater risk of developing dementia, new research suggests.

It is not yet clear whether the more common, less severe episodes of low blood sugar are also linked with an increased dementia risk, according to a study in the April 15 issue of the Journal of the American Medical Association.

"Hypoglycemic episodes that were severe enough to require hospitalization or an emergency-room visit were associated with a greater risk of dementia, particularly for patients who had multiple episodes. And these findings, a little bit to our surprise, were independent of glycemic control," says study author Dr. Rachel A. Whitmer, of Kaiser Permanente.

"Episodes of hypoglycemia may be associated with neurological consequences in patients already at risk for dementia," she adds. "This study seems to suggest that hypoglycemia is one of the reasons people with type 2 diabetes are at a higher risk for dementia. It also adds to the evidence base that balance of glycemic control is a critical issue, and particularly for the elderly."

Experts Debate Cause and Effect

People with type 2 diabetes are at a 32 percent greater risk for dementia, although the reasons for that are not clear. People with pre-diabetes are also at greater risk, adds Dr. Whitmer.

However, the study looks at association only, and does not actually prove a causal relationship between the two conditions, notes Dr. Nir Barzilai, director of the Institute for Aging Research at Albert Einstein College of Medicine and the Montefiore Hospital Diabetes Clinic in New York City.

"It could be fluctuation of glucose. We know that hyperglycemia [high blood sugar] is also very toxic to the cells. All those things cannot be dissected on a study like this," he says.

Dr. Whitmer adds that it is likely hypoglycemia only one reason for the heightened risk of dementia in individuals with type 2 diabetes.

While previous studies have linked cognitive impairment in children and adults with type 1 diabetes, it is not clear whether the same link applies to older individuals with type 2 diabetes or what mechanism might be underlying such a connection.

The issue is an important one as the population people with type 2 diabetes continues to grow. In the US alone, some 24 million people have the condition. More are expected as the population ages.

Hypoglycemic episodes are marked by dizziness, fainting, and seizures.

The study authors followed more than 16,000 patients with type 2 diabetes, average age 65, from 1980 to 2007. Twenty-two years of follow-up were devoted to chronicling hypoglycemic episodes, and more than four years were devoted to following dementia diagnoses.

Nerve Cell Loss, Blood Supply Lowered

The link that was found could be from any number of possible causes, including accelerated death of nerve cells in the brain or less blood supply to the brain.

Such a link could also be a result of too much insulin over time, again possibly contributing to neuronal damage or other brain changes.

But the whole picture is likely to be much more complicated, says Dr. Barzilai.

"The glucose concentrations in the brain are much, much lower than in the [rest of the body], and it takes it a long time to actually adjust if you change the peripheral glucose for the brain to have lower glucose," he explains.

"Not only that, but the neurons in the brain are really not fed by glucose but by other metabolites. The rest of the body, when glucose goes down, will feel it. The brain is totally different story," says Dr. Barzilai.

Although balanced blood-sugar control is a good strategy in theory, it's difficult to attain and difficult to monitor.

"The trouble is, when you try to keep blood sugar in the normal range, there's a higher risk of hypoglycemia," says Michael Horseman, Pharm.D., at the Texas A&M Health Science Center. "There hasn't been a study that I'm aware of where they made a serious attempt to keep blood sugar in the normal range that didn't have episodes of hypoglycemia."

Always consult your physician for more information.