Higher Blood Sugar May Raise Dementia Risk

August 8, 2013

News Review From Harvard Medical School -- Higher Blood Sugar May Raise Dementia Risk

A new study suggests that higher blood sugar may increase people's risk of developing dementia. In the study, the risk increased along with blood sugar levels. Even people without diabetes had a slightly higher risk of dementia if their blood sugar was above ideal levels. The study included 2,067 people. All were 65 and older. In the 5 years before the study began, all of them had their blood sugar measured at least 5 times. Researchers used a formula to produce an average blood sugar figure for each person. When the study began, about 10% of the total group had diabetes. Nobody had dementia. The study lasted 7 years. Researchers gave people regular tests of memory and thinking skills. By the end of the study, about 25% of the total group had dementia. Diabetics with the highest average blood sugar levels were 40% more likely to develop diabetes than people with normal blood sugar. For people who had above-normal blood sugar, but did not have diabetes, the increase in dementia risk was 10% to 18%. The New England Journal of Medicine published the study. The Associated Press wrote about it August 8.

By Robert H. Shmerling, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

When I think about blood sugar in health and disease, I think about diabetes, not dementia.  A new study could change that. 

Cells need insulin to use sugar for energy. People with type 2 diabetes (90% of those with diabetes) have higher than normal levels of sugar in the blood because their bodies resist the actions of insulin. People with type 1 diabetes (the other 10%) don't make enough insulin.  

The reason diabetes is an important illness is not just because the blood sugar is high.  It's because of the further health problems that can occur because of diabetes.   These include: 

• Heart attack
• Stroke
• Vision loss
• Kidney injury
• Nerve disease (neuropathy)

But now comes word that high blood sugar may raise the risk of developing dementia, too.  The most alarming thing to me from this new research is that even mild high blood sugar -- not high enough to qualify as diabetes -- may increase the risk of dementia.

Researchers published their study results this week in the New England Journal of Medicine. They analyzed blood sugar results from more than 2,000 older adults during a 7-year period.   None had dementia at the start.  About 10% had diabetes.  The researchers found that: 

• About one-quarter of those in the study developed dementia.
• Among people without diabetes, those who developed dementia had a higher average blood sugar result (about 115 milligrams per deciliter, or mg/dl) than those without dementia (100 mg/dl).  A normal blood sugar after a fast (usually overnight) ranges from 70 to 100 mg/dl.
• Among people with diabetes, those who developed dementia also had higher average blood sugars (190 mg/dl) than those who did not (160 mg/dl).

The finding that higher blood sugar may increase the risk of dementia held up even after researchers accounted for other factors that affect dementia risk. These included smoking, blood pressure and age.          

This study is important for at least two reasons.  First, it links poor diabetes control with dementia. For people with diabetes, the idea that poor blood sugar control might be linked with further health problems should not be surprising.  But the second finding -- that even mildly high blood sugar levels among non-diabetics may increase the risk of dementia – is surprising.

Diabetes rates are rising fast.  This is probably related to increases in obesity, which has been linked with insulin resistance.  As our population ages, we also are seeing higher rates of dementia. Given these realities, the findings of this study take on even more significance.

What Changes Can I Make Now?

You can make several changes now that may reduce your chances of developing diabetes. 

• Avoid excess weight. Maintaining an ideal body weight is probably the most important way to prevent type 2 diabetes.
• Choose a healthy diet. This includes fruits and vegetables, whole grain foods and monounsaturated fats.  Portion control is also important to avoid excessive calories.
• Get regular exercise.
• If you have pre-diabetes (fasting blood sugar readings between 100 and 125 mg/dl), ask your doctor if you should take metformin. This medicine may delay diabetes or prevent it altogether.

If you already have diabetes, you can take measures to control your blood sugar and prevent further health problems related to the disease.  Here are some key steps to diabetes control:

• Take diabetes medicines. These may lower blood sugar in several ways. They may slow the body's absorption of sugar from the diet, increase insulin levels or improve insulin function.
• If diabetes pills are not enough to control your blood sugar, take insulin. This is given by injection.
• Take aspirin.
• Lower your blood pressure and cholesterol.
• Don't smoke.
• See an eye doctor and a foot doctor each year.
• Get tests to monitor kidney function and take medicines to protect your kidneys from diabetes-related damage.

Many of these same measures (such as maintaining a normal blood pressure and not smoking) may lower your risk of stroke. Preventing strokes also should reduce your chances of developing dementia.

We don't know yet whether treatments to maintain a normal blood sugar will also prevent dementia. However, the results of this new research suggest that they may. Besides the steps above, a busy social life, hobbies and mentally challenging activities (such as crossword puzzles) may be helpful.

What Can I Expect Looking to the Future?

In the future, you can expect more studies to explore the relationship between high blood sugar and dementia. If further research confirms a link, several questions will need to be answered:

• How do high blood sugar levels increase the risk of dementia?
• Does treatment to lower blood sugar (with or without diabetes) reduce the risk of dementia?

As is often the case, this latest research may actually raise more questions than it answers.