Is Alzheimer’s disease akin to ‘type 3 diabetes’?

By Deborah Kotz, Globe Staff

Is Alzheimer’s disease really a form of diabetes? Let’s call it type 3, because that’s what a Brown Medical School researcher dubbed it back in 2005 when she autopsied the brains of Alzheimer’s patients and found that they had signs of insulin resistance -- an early indicator of diabetes.

Since then, however, we haven’t seen a sea-change in preventive treatments based on this idea. Those who carry the gene for hereditary Alzheimer’s aren’t given diabetes drugs to help stave off dementia. Nor are Alzheimer’s patients given insulin injections.

What has been getting attention, however, is whether we should make extra efforts to eat a low glycemic diet -- which is low in processed foods, sugar, and starchy carbohydrates that cause quick spikes in blood sugar -- to help protect our brains from developing those gunky amyloid plaques associated with Alzheimer’s.

The September issue of the New Scientist advocates for changing our eating patterns with a frightening image of a cracked chocolate brain on its cover. (Chocolate consumption, though, hasn’t been linked to cognitive decline, much to my relief.)

New York Times food columnist Mark Bittman pointed out in a recent post that the latest studies provide some persuasive evidence linking diet to the development of Alzheimer’s. I’ve covered those studies too, including this one that measured a smaller Alzheimer’s risk in people who eat a diet rich in fish, veggies, and fruit compared with those who eat a diet centered on processed foods containing trans fats.

But I’m not convinced that puts Alzheimer’s in the diabetes category. I asked Dr. Suzanne DeLaMonte, the Brown Medical School neuropathologist who did the initial studies, whether she still thinks of Alzheimer’s as akin to type 3 diabetes.

“I think it’s pretty clear that it is,” she said. “Alzheimer’s is insulin resistance in the brain, and those with diabetes have a two to three fold higher risk of getting cognitive impairment and dementia, probably because of this.”

A large body of research has accumulated in recent years connecting the two diseases, and both have risen precipitously in the population -- with a declining age of onset -- along with obesity. Clinical trials have also tested the diabetes drug rosiglitazone (Avandia) for the treatment of Alzheimer’s, though with mixed results.

“Some patients had improved cognition, but others didn’t,” said DeLaMonte, and it’s possible that by the time dementia symptoms appear, it’s too late to reverse the damage to the brain caused by the insulin resistance.

The solution, she said, probably won’t come from any drug, at least for a while; instead, it lies in prevention by making lifestyle tweaks where needed. First off, DeLaMonte said we should do what we can to limit our intake of nitrates -- found in cured meats such as hot dogs and salami --because the latest research being conducted by her and others shows a strong association between nitrates and neural effects. Nitrates, when heated, form the amino acid nitrosamine, which impairs how cells interact with insulin, she said.

We should also take note of our calorie intake by reading all those postings in fast-food chains such as McDonald’s, Au Bon Pain, and Starbucks because gaining excess fat increases insulin resistance. Better yet, we should make our own food at home so we can avoid chemical preservatives and control how much oil gets drizzled on our vegetables and pasta. (And make that pasta whole wheat.)

Physical activity is also key, and I’m not talking about just full-blown exercise, because strolling along for about 15 minutes a day can make cells more responsive to insulin. (It probably won’t burn off many calories to help you lose weight or do much to condition your heart, so you need to walk faster and longer if those are also your goals.)

“Diabetes and Alzheimer’s are both related to aging,” said DeLaMonte, but aside from that small minority of us who inherit particular genes, “I don’t think they’re inevitable.”