Study Links Low Blood Sugar with Dementia

Older diabetics who have a sharp drop in blood sugar may be more likely to develop dementia, a new study suggests. And low blood sugar may occur more often in those with dementia, the study also found. Diabetes medicines are used to lower blood sugar. Medicines must be kept in balance with what people eat. If they don't eat enough or take too much medicine, they can get very low blood sugar. This is called hypoglycemia. It can lead to confusion, fainting or even a trip to the hospital. The new study included 783 adults with diabetes. They were in their 70s and did not have dementia when the study began. Researchers kept track of them for 12 years. In that time, nearly 8% had hypoglycemia at least once. Nearly 19% of people in the study developed dementia. People who had an episode of hypoglycemia were twice as likely as others to develop dementia later. The risk of hypoglycemia also more than doubled among people after they had dementia. The journal JAMA Internal Medicine published the study. HealthDay News and MedPage Today wrote about it June 10.

By Howard LeWine, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

Controlling high blood sugar is a primary goal of diabetes treatment -- and for good reason. Keeping the blood sugar close to normal can prevent further health problems linked with diabetes. These include nerve, eye or kidney damage.

But efforts to lower blood sugar can also cause trouble. Medicines prescribed to lower blood sugar -- both pills and insulin -- are potent. They can easily lower blood sugar too much. This is called hypoglycemia.

Results of previous studies suggest a link between dangerously low blood sugars and the risk of developing dementia, especially in older diabetics. This new study adds further evidence supporting such a link.

In the past, the American Diabetes Association (ADA) has recommended that people with diabetes achieve a hemoglobin A1C blood level of less than 7%. Doctors call this tight control. A1C reflects a person's average blood sugar during the prior 2 to 3 months.

A normal A1C is less than 5.7%. A1C levels between 5.7% and 6.4% are used to identify people with pre-diabetes. A level of 6.5% or higher confirms a diagnosis of diabetes.

For many people, achieving an A1C of less than 7% has meant more frequent episodes of hypoglycemia. This is especially true for older people because:

• They often skip meals, but take their diabetes medicines as usual.
• They frequently mix up medicines, especially if they take lots of pills.
• Kidney function declines with age. So diabetes medicines stay in the body and continue to lower blood sugar for much longer than usual.

Older people also may be less likely to recognize the early symptoms of hypoglycemia. They might not be aware of mild confusion, nausea, sweating and/or dizziness. Or they might blame it on something else. That's especially likely for those with impaired brain function.

This study and others do not prove that brief episodes of low blood sugar cause dementia. Biologically, however, it seems very plausible. We know that having hypoglycemia for a long time can cause seizures and brain injury.

What Changes Can I Make Now?

Diabetes treatment plans and goals should be tailored to each person. Things to consider include:

• Older age
• Frequent low blood sugars
• Other medical conditions that require multiple medicines, plus a need for more than two drugs to lower blood sugar
• Limited financial resources

In general, the blood sugar goal for a younger, mostly healthy person should be near normal. But often this is not the best goal for someone older who has multiple health problems.

For an older person with diabetes, 8% is a reasonable goal for A1C. And if episodes of hypoglycemia still occur, it is probably safer to accept "looser" blood sugar control.

Controlling blood sugar is only one part of diabetes treatment. It's just as important to:

• Control weight with a healthy diet and plenty of physical activity
• Reduce blood pressure to normal levels
• Achieve normal LDL cholesterol levels

However, in an older person, some of these goals should be set at less aggressive targets. For example, taking multiple medicines to lower blood pressure to an ideal level may cause fainting, falls and fractures. Similar to blood sugar goals, blood pressure and cholesterol goals need to be based on each person's needs.

What Can I Expect Looking to the Future?

Most of the attention in diabetes is directed at reducing high blood sugar and the health problems it can cause. But we need to be just as concerned about avoiding hypoglycemia, especially in older people.