Q. Is Alzheimer's a type of diabetes?

A. Alzheimer's disease and diabetes may be related to one another through a common link: insulin.

Insulin may be as important to the brain as it is to the rest of the body. Insulin receptors in the brain play a major role in learning and memory.

It's been known for several years that people with diabetes have a greater chance of developing Alzheimer's and other forms of dementia than those without diabetes, but learning how they are connected has been a mystery.

In the body, insulin helps move sugar into our cells to be used as fuel. A condition called insulin resistance disrupts this process by preventing insulin and sugar from entering cells. Insulin resistance is common in folks with pre-diabetes and Type 2 diabetes.

In the brain, insulin helps us make new memories. Brain cells communicate across spaces on nerve cells called synapses. There are special places on the synapses reserved just for insulin, called insulin receptors. When insulin arrives at the nerve cells, it sticks to the receptor. This allows new memories to form.

Inability to form memories is one of the earliest symptoms of Alzheimer's, so the relationship between insulin and its receptors offers scientists some clues.

Scientists at Northwestern University have discovered a toxic protein that interrupts insulin signaling which is crucial for memory formation. This protein, called amyloid-beta-derived diffusible ligands (ADDLs for short), accumulates in the brains of people with Alzheimer's. ADDLs remove insulin receptors from the synapses of nerve cells, leaving insulin without a connecting point. This renders the nerve's cells insulin-resistant and inhibits the brain's ability to store new memories.

In Type 2 diabetes, the body becomes insulin-resistant. In Alzheimer's the brain becomes insulin-resistant. This means neurons in the brain are deprived of glucose, which they need for energy. This is why some experts are calling Alzheimer's Type 3 diabetes.

Researchers are studying medications used to treat Type 2 diabetes to see if they might also work in the brain to prevent or delay Alzheimer's. Other scientists are trying to develop an anti-ADDL therapy.

Insulin resistance and/or uncontrolled diabetes increases Alzheimer's risk more than controlled diabetes.

Eating a healthy diet and exercising can help prevent insulin resistance and diabetes by controlling weight and blood sugar levels.

The end result: less chance of memory problems as we age.

Amy Tousman is a registered dietitian and certified diabetes educator with Nutrition Unlimited in Kailua. Hawai'i experts in traditional medicine, naturopathic medicine and diet take turns writing the Prescriptions column. Send your questions to: Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; fax 535-8170; or islandlife@honoluluadvertiser.com. This column is not intended to provide medical advice.

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