If you have diabetes, you may know that insulin levels can have a direct impact on your risk of complications such as kidney damage and heart disease. What you may not know is that insulin levels may affect the brain too.

"Even people who study diabetes may not always consider the impact of insulin in the brain," says Rita Kalyani, MD, assistant professor of medicine at Johns Hopkins University in Baltimore. "But insulin does play a role in the formation of synapses, storing memories, and other brain functions." Studies have linked insulin levels with appetite, energy balance, and body temperature too.

It appears that diabetes and insulin problems may be connected to a higher risk of serious conditions such as Alzheimer's disease and Parkinson's disease. Could diabetes-related insulin problems play a role in causing these conditions?

"I don't think we have the data yet, but it's possible that conditions like Alzheimer's disease are related to insulin problems," says C. Ronald Kahn, MD, professor of medicine at Harvard Medical School and vice chairman of the Joslin Diabetes Center Board. The potential connection concerns him. "Type 2 diabetes is already an epidemic and more and more people are developing it an earlier age," he tells WebMD. "We just don't know what effect it will have on their brains."

So, what can you do to stay healthy with diabetes? Here's what you need to know.

What Does Insulin Do?

Insulin is a natural hormone in the body. One of its key roles is helping cells absorb glucose or sugar in the blood for energy.

In people with type 1 diabetes, the pancreas does not make insulin. In people with type 2 diabetes, the pancreas makes insulin, but their bodies can't use it efficiently. In either case, the level of sugar in the blood rises, damaging cells throughout body.

Experts aren't sure how insulin works in the brain, but it seems to play many roles. Even in a healthy person, insulin changes that follow a high-carb meal change brain function, says Kahn.

Diabetes, Insulin, and the Brain

So how might diabetes and insulin problems affect the brain? "In people with diabetes, the brain doesn't seem to become insulin resistant in the same way that other organs in the body do," Kahn says. "But there do seem to be changes in insulin signaling in the brain."

People with diabetes seem to have a higher risk of Alzheimer's disease. They may have a higher risk of Parkinson's disease and Huntington's disease too. Insulin problems seem to be connected. Studies have found that insulin levels in certain regions of the brain associated with memory are much higher in healthy people than in people with Alzheimer's disease.

In people with Alzheimer's disease, a protein called beta-amyloid builds up, forming plaques on the brain. Abnormal insulin levels may make it harder for the body to break these plaques down.  

The apparent connection between diabetes and Alzheimer's disease has led some researchers to make a controversial claim. Not only could diabetes increase the risk of Alzheimer's disease, they argue, but Alzheimer's disease is itself a form of diabetes that primarily affects the brain. Some have gone so far as to give Alzheimer's disease a new name: type 3 diabetes. But many diabetes experts are not convinced.

Diabetes and the Brain: Unclear Evidence

"I think it's a real stretch to call Alzheimer's disease type 3 diabetes," says Janet B. McGill, MD, an endocrinologist and professor of medicine at the Washington University School of Medicine, St. Louis. "We just don't have the evidence."

Kalyani agrees. "We need more research," she says, noting that it's difficult to tease out the effects of diabetes from related conditions. "High blood pressure and obesity often go along with diabetes," she tells WebMD. "It's possible that they could play a role in the increased risk of Alzheimer's disease."

Researchers have also long known that diabetes has effects on the brain aside from those that may be related to insulin levels. Diabetes increases the risk of both major and minor strokes. High glucose may damage brain cells directly, which could cause memory problems and other dementia symptoms.

Insulin and the Brain: What Should I do?

If you have diabetes, the implications of this research may be worrying. Are you at higher risk for conditions such as Alzheimer's disease?

For now, many experts say the evidence is so hazy that people shouldn't dwell on it too much. Frankly, they say, there are plenty of other clearer risks to worry about from diabetes, such as nerve damage, kidney disease, cardiovascular problems, and others.

"There is good news," says Kahn. "Many of the health changes that we associate with diabetes are reversible to a significant extent." Increased exercise, a healthier diet, and in some cases medication can delay or even prevent diabetes-related health risks.

"People with diabetes can sometimes feel helpless," says Kalyani. "But actually, diabetes is a disease that people have some control over." With treatment and lifestyle changes, she says, people can cut their risks of eye, kidney, and nerve problems by up to 70%.

Instead of worrying about a possible link between diabetes and brain conditions, many experts suggest using it as further incentive to get your diabetes under control. We know that monitoring blood sugar, exercising, and eating a healthier diet can have dramatic benefits for your health. It could also have benefits we don't know about yet -- in the brain and elsewhere.