News

A growing body of scientific evidence showing strong links between diabetes and Alzheimer's disease could have major health implications for a Canadian population that is getting older and fatter.

Several recent studies suggest Type 2 diabetes, a mounting concern in Canada and around the world that is usually associated with obesity, increases the risk of Alzheimer's disease by up to 70 per cent and adds dementia to the arsenal of plagues already threatening diabetics, including heart disease, stroke, kidney failure, blindness and amputations.

Experts say the global explosion of diabetes could substantially increase the burden of Alzheimer's disease, which is already set to become bigger as baby boomers turn 60 this year and fast approach the age of highest risk for developing the deadly form of dementia.

The link between the two common maladies -- buildup of a sticky, gunky plaque called beta-amyloid that clogs up brain cells in those with Alzheimer's, and was also recently discovered in the pancreases of people with Type 2 diabetes -- is leading researchers around the world to seriously ponder whether both are actually different forms of the same disease.

"It's only now that we're putting the pieces of the puzzle together," said University of British Columbia researcher Patrick McGeer, who was involved with a Vancouver study looking at autopsy tissue that found plaque buildup in some diabetics' pancreases. "It's not all fitted together yet, but some nice pieces are beginning to fall into place."

Some of those well-placed pieces include evidence that a few drugs used to control blood sugar levels in Type 2 diabetics may also be effective in slowing or preventing the deadly brain disease for which there is no cure and which affects about 300,000 Canadians.

That is being further tested in thousands of Alzheimer's patients in the United States, who are being given a drug called Avandia in hopes of slowing brain decay. A preliminary trial involving 511 patients, whose results were presented at last month's International Conference on Alzheimer's Disease and Related Disorders in Madrid, has shown promise, and pharmaceutical company GlaxoSmithKline is moving into a third phase of the clinical trial to test whether Avandia might protect some patients' brains.

Type 2 diabetes, which affects about two million Canadians, occurs when normal insulin production begins to slow and the body grows resistant to the hormone. Drugs like Avandia and its competitor Actos treat the disease by resensitizing the body to insulin.

Jack Diamond, scientific director of the Alzheimer Society of Canada, said there are whisperings in the scientific community that Alzheimer's disease may actually be "Type 3 diabetes," where a resistance to insulin causes inflammation only in the brain, just like it does in the pancreases of those with Type 2 diabetes.

"If true, [this] will enormously influence the future direction of drug research for this condition," he said.

Other research showed that in a nine-year study following 1,173 individuals 75 and older, borderline diabetes was associated with an almost 70-per-cent increased risk of developing dementia and Alzheimer's disease. About one in three (397) developed dementia during the follow-up, including 307 who developed Alzheimer's.

Several studies also found that people with poor blood-sugar control have a higher risk of Alzheimer's. These discoveries, Dr. Diamond said, "are opening up an entirely new thinking about Alzheimer's disease. . . . The particular risk factor for Alzheimer's that seems to be genuinely increasing most is diabetes, and that will mean an increase in Alzheimer's disease numbers."

Projections for the year 2031 are that as many as 750,000 Canadians over 65 will be diagnosed with Alzheimer's disease. That would change the current ratio of 1 in 20 people over 65 with Alzheimer's, up to 1 in 13 in the same age group.

But the slew of positive results coming from drug trials and long-term population studies, including one that found dementia in Type 2 diabetic people with mild to moderate Alzheimer's disease, was reduced in a group receiving Actos, may not mean much, Dr. Diamond warned.

"If you count the diabetes risk in, then the miserable news that diabetes is on the increase could be somewhat offset by the better news that people are beginning to learn better how to treat their diabetes. But I think the number of people becoming obese and getting Type 2 diabetes is increasing faster than the ability not to do that."

Others are trying to see more positive angles to the new findings.

Drugs already developed for diabetes, as well as other treatment strategies such as changes in diet and exercise, may prove useful in treating and preventing Alzheimer's and could possibly result in the sharing of decades of diabetes research, said Ron Peterson, vice-chair of the Alzheimer's Association's medical and scientific advisory council.