WASHINGTON—More than 35 million people around the world are living with Alzheimer's disease or other types of dementia, says the most in-depth attempt yet to assess the brain-destroying illness. It's an ominous forecast as the population grays.

The new count is about 10 percent higher than what scientists had predicted just a few years ago, because earlier research underestimated Alzheimer's growing impact in developing countries.

Barring a medical breakthrough, the World Alzheimer Report projects dementia will nearly double every 20 years. By 2050, it will affect a staggering 115.4 million people, the report concludes.

"We are facing an emergency," said Dr. Daisy Acosta, who heads Alzheimer's Disease International, which released the report today.

The U.S. and other developed countries long have been bracing for Alzheimer's to skyrocket. But the report aims to raise awareness of the threat in poorer countries, where people finally are living long enough to face what is mostly a disease of the 65-or-older population.

While age is the biggest driver of Alzheimer's, some of the same factors that trigger heart disease -- obesity, high cholesterol, diabetes -- also seem to increase the risk of dementia. Those are problems also on the rise in many developing countries.

In poorer countries, "dementia is a hidden issue," Acosta said, and that's complicating efforts to improve earlier diagnosis. "You're not supposed to talk about it."

For example, the report notes that in India, such terms as "tired brain" or "weak brain" are used for Alzheimer's symptoms amid widespread belief that dementia is a normal part of aging.

That error isn't confined to poorer countries. In Britain, the report said, just more than half of families caring for someone with dementia thought the same thing.

The new study updates global figures last reported in 2005, when British researchers estimated that more than 24 million people were living with dementia. Using that forecast, scientists had expected that about 31 million people would be struggling with dementia by 2010.

But since 2005, a flurry of research on Alzheimer's in developing countries has been published, leading Alzheimer's Disease International -- a nonprofit federation of more than 70 groups -- to ask those scientists to re-evaluate. After analyzing dozens of studies, the scientists projected 35.6 million cases of dementia worldwide by 2010.

That includes nearly 7 million people in western Europe, 7 million in southern and southeastern Asia, 5.5 million in China and eastern Asia and about 3 million in Latin America.

The report puts North America's total at 4.4 million.

The disease afflicts one in eight people 65 or older, and nearly one in two people older than 85.

The report forecasts dementia cases more than doubling in Asia and Latin America in the next 20 years, compared with a 40 percent to 60 percent jump in Europe and North America.

The report urges the World Health Organization to declare dementia a health priority and for national governments to follow suit. It recommends major new investments in research to uncover what causes dementia and how to slow, if not stop, the disease. Alzheimer's gradually robs sufferers of their memories and ability to care for themselves, eventually killing them.

There is no known cure; today's drugs only temporarily alleviate symptoms. Scientists aren't even sure what causes Alzheimer's.

But major studies should show within a few years whether it's possible to slow Alzheimer's by targeting a gunky substance called beta-amyloid that builds up in patients' brains, said Dr. William Thies of the U.S. Alzheimer's Association. His group is pushing for an increase in U.S. research spending, from just more than $400 million to about $1 billion.