More than 26 million people worldwide have Alzheimer's disease, and a new forecast says the number will quadruple by 2050. At that rate, one in 85 people will have the brain-destroying disease in 40 years, U.S. researchers conclude.

The new estimates, presented Sunday at an Alzheimer's Association conference in Washington, are not very different from previous projections of the looming global dementia epidemic with the graying of the world's population.

But they serve as a sobering reminder of the toll to come if scientists cannot find better ways to battle Alzheimer's and protect aging brains.

"If we can make even modest advances in preventing Alzheimer's disease, or delay its progression, we could have a huge global public health impact," said study team leader Ron Brookmeyer of the Johns Hopkins Bloomberg School of Public Health in Baltimore.

The biggest jump is projected for densely populated Asia, home of almost half of today's Alzheimer's cases, 12.6 million. By 2050, Asia will have 62.8 million of the world's 106 million Alzheimer's patients, the study projects.

A recent U.S. study estimated that that country's Alzheimer's toll will reach 16 million by 2050, compared with more than five million today. The new estimate is significantly lower, suggesting only 3.1 million North American cases today and 8.8 million by 2050.

For Dr. Sandra Black, a neurologist with Sunnybrook Health Sciences Centre in Toronto, the findings are a call to recognize the scope of the problem.

In Canada, Alzheimer's now affects eight per cent of people over the age of 55, which the study suggests could rise to 25 per cent by 2050. The increase would have huge implications for society in terms of nursing needs and demand for health-care resources, Black said Monday.

Controlling cholesterol, lowering blood pressure and stimulating mental activity may help delay onset of Alzheimer's, Black said.

Delaying the onset of Alzheimer's by one year would reduce cases of the disease in 2050 by 12 million or 10 per cent, the computer model suggested.

Several new drugs currently being tested in clinical trials also show promise in slowing or stopping progression of Alzheimer's, said William Thies, vice-president of medical and scientific relations for the Alzheimer's Association.

Among the estimates for other regions are:

• Africa, 1.3 million today and 6.3 million in 2050.
• Europe, 7.2 million and 16.5 million.
• Latin America and the Caribbean, 2 million and 10.8 million.
• Oceania, 200,00 and 800,000.

The project was funded by Elan Pharmaceuticals and Wyeth Pharmaceuticals.