Why you should care

Because Alzheimer’s disease might be Type 3 diabetes, and that link might be a giant step in the direction of a cure.

Here’s some food for thought: Those Fritos, fries and frosted doughnuts aren’t just stuffing your waistline — they might be starving your brain cells. So say a growing number of scientists, who believe that a poor diet can trigger not only obesity and diabetes, but Alzheimer’s disease, too.

In fact, some believe that Alzheimer’s may simply be another form of diabetes.

Insulin is crucial for not only digesting glucose, but also producing neurotransmitters …

Most of us are familiar with two types of diabetes. In Type 1, the immune system ravages the pancreatic cells that make insulin, the hormone that tells cells to take up glucose from the bloodstream and convert it to energy. Type 2 often results from overeating; the pancreas pumps out so much insulin to break down excess glucose that the cells can’t keep pace and stop responding to insulin altogether.

Recent research suggests a similar process is at work in Alzheimer’s. Brain cells also stop making and responding to insulin — crucial for not only digesting glucose, but also producing neurotransmitters, which neurons use to communicate with each other. As a result, brain cells starve to death and cognitive processes falter.

Identifying insulin signaling abnormalities as the root cause of Alzheimer’s has “huge implications,” says Suzanne de la Monte, a neuropathologist at Brown University. Some scientists think we could repurpose Type 2 diabetes drugs for Alzheimer’s, and a clinical trial to test an insulin nasal spray for the disease is now recruiting participants. And of course, Alzheimer’s roots in insulin resistance only underscore the importance of healthy eating, as well as public health initiatives that broaden access to fresh produce in low-income neighborhoods.

Insulin signaling isn’t the only cause of Alzheimer’s. Genetics, exercise and social networks could be at work, too, according to Angela Winkler a Ph.D. candidate at the University Hospital Essen in Germany. But few would argue against a fresh approach. About 44 million people worldwide live with some form of dementia, including Alzheimer’s disease, which has no cure. Drug candidates for the disease failed in clinical trials at a rate of 99.6 percent from 2002 to 2012.

The Study of Nasal Insulin to Fight Forgetfulness is testing whether an insulin nasal spray improves memory.

The 1997 Rotterdam study of more than more than 6,000 elderly participants offered early evidence linking Alzheimer’s and diabetes, reporting that having diabetes almost doubled the risk of Alzheimer’s disease. De la Monte and her lab coined the term “type 3 diabetes” for Alzheimer’s about seven years later, when they discovered that blocking insulin signaling in rats’ brains led to neuronal damage and learning problems. The researchers also saw signs of abnormal insulin signaling in the brains of Alzheimer’s patients.

Since then, more evidence has surfaced to bolster de la Monte’s hypothesis. Last year, a Diabetes Care study of late middle-aged adults with early Alzheimer’s correlated insulin resistance with brain degeneration. And in July, the Geriatric Research Education and Clinical Center reported that insulin resistance might contribute to amyloid plaques — clumps of proteins that impede brain signaling — in areas affected by Alzheimer’s. Meanwhile, Winkler’s study showed that mild cognitive impairment occurred twice as often in middle-aged participants with Type 2 diabetes as in their healthy counterparts.

African-Americans are about twice as likely to have Alzheimer’s and other forms of dementia as older whites and 1.7 times as likely to suffer from diabetes.

Some researchers believe that oral Type 2 diabetes drugs designed to boost insulin sensitivity — like metformin and Avandia — could treat Alzheimer’s, although not enough is known about whether they could cross a dense layer of cells known as the blood-brain barrier to actually reach brain cells. But synthetic versions of three hormones that activate the insulin pathway — also taken orally — do readily cross the barrier. The FDA has approved one called Symlin to be used with insulin to treat diabetes, for example, but others are still awaiting the green light for the disease.

Intranasal insulin also bypasses the blood-brain barrier, speeding along the olfactory nerve fibers in the nose, straight to the brain. A 2012 trial found that older adults who sniffed insulin for four months showed marked memory improvements. And the Study of Nasal Insulin to Fight Forgetfulness (SNIFF) is actively recruiting participants for a phase 2 and 3 trial to test whether an insulin nasal spray improves memory in adults with mild memory impairment or Alzheimer’s.

But like cancer patients, Alzheimer’s sufferers will probably need a combination of drugs. To combat such a complex disease, “you have to hit multiple parts,” de la Monte says.

I needle lying on a counter next to a small vial

Source Mark Weiss/Corbis

Scientists haven’t quite nailed the culprits of brain insulin resistance. De la Monte largely blames the overconsumption of sugary, processed foods — especially those that contain a class of food additives called nitrosamines, often added to meat. She and many others have observed that they trigger the same molecular pathways as those activated in Alzheimer’s. “I think it just boils down to eating simpler and cleaner,” de la Monte says.

That recommendation could apply to a host of diseases. Researchers have found that mechanisms similar to those that drive diabetes and Alzheimer’s also underlie fatty liver disease, polycystic ovary syndrome and more. “There’s a whole crisis of insulin insufficiency that’s emerged” as more countries embrace an American diet, she says.

All the more evidence that we really are what we eat — right down to how we think.

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