Washington ? A provocative new theory suggests that one root cause of Alzheimer’s disease is linked to diabetes – a theory about to be tested in thousands of Alzheimer’s patients given the diabetes drug Avandia in hopes of slowing brain decay.

It’s a scary scenario: Alzheimer’s already is expected to skyrocket as the population grays, rising from 4.5 million sufferers today to a staggering 14 million by 2050. If the new theory is right, the nation’s current obesity-fueled epidemic of Type 2 diabetes could worsen that toll.

But proponents see potential good news: If diabeticlike changes in the way brain cells use sugar to generate energy truly trigger Alzheimer’s in at least some patients, then maybe doctors could intervene early and slow that degeneration.

A preliminary experiment involving 511 Alzheimer’s patients found signals that Avandia might help – albeit in people who lack a gene that spurs more aggressive Alzheimer’s.

Those results, combined with other evidence that the diabetes pathway is important, have Avandia maker GlaxoSmithKline poised to open three Phase III clinical trials this summer to test whether the diabetes drug, also called rosiglitazone, might protect certain patients’ brains.

Diabetes has long been listed a risk factor for Alzheimer’s later in life because it damages blood vessels that supply the brain.

The Avandia research suggests a more insidious connection: that Alzheimer’s can be silently triggered when brain cells can’t properly use their main fuel, sugar – just as Type 2 diabetes is triggered when insulin gradually loses its ability to process sugar body-wide.

“When they’re in an insulin-resistant state, it does not just affect the body, it affects the brain as well,” explains Suzanne Craft of the Veterans Affairs Puget Sound Health Care System, who led the initial research.

There are 18 million Type 2 diabetics, considered to have two to five times a nondiabetic’s risk of developing Alzheimer’s – if they live long enough, into the 60s and 70s when Alzheimer’s typically strikes, Craft says.

Type 2 diabetes often leads to heart disease or other ailments that kill before then.

Avandia, and the competing drug Actos, treat Type 2 diabetes by resensitizing the body to insulin.

“I don’t think this is hype for rosiglitazone,” said Dr. Sam Gandy, director of the Farber Institute for Neurosciences at Philadelphia’s Thomas Jefferson University and a spokesman for the Alzheimer’s Assn. “This does dovetail with some existing knowledge.”