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USA TODAY - New estimates suggest that dementia is going to be an even bigger global problem than previously thought.

A policy brief released Wednesday from Alzheimer's Disease International, a federation of advocacy and research organizations, estimates that 135 million people worldwide will be living with dementia by 2050. That revised prediction is 17% above previous ones, largely driven by increases in China and sub-Saharan Africa.

It says the number of people living with dementia worldwide in 2013 is estimated at 44 million (the 2010 estimate was 35 million), and that global numbers are expected to hit 76 million in 2030.

The report was released a week before a major dementia summit is scheduled to take place in London, called by the British prime minister and including representatives of eight of the world's biggest economies.

Participants intend to develop a shared strategy for addressing dementia research and care, said Matthew Baumgart, senior director of public policy for the Alzheimer's Association, an American advocacy group that will attend the summit.

"We're glad they're meeting," he said, but that will only be a beginning. "We hope they come up with a shared vision and commitment, but it's equally important that they follow through afterwards."

The revised estimates better reflect the burden that Alzheimer's and other forms of dementia will place on the world's economies and on families whose loved ones have lost their memories and their ability to function in the world, Baumgart said.

The report says Alzheimer's and other forms of dementia represent "a global epidemic — although cases are disproportionately concentrated in the world's richest and most demographically aged countries, already the clear majority (62%) of people with dementia live in low- and middle-income countries where access to social protection, services, support and care are very limited."

In China, better estimates have come to light in recent years, as data was digitized and translated into English, says Igor Rudan, a professor of epidemiology at the University of Edinburgh in Scotland, who often works for the World Health Organization. "It's been like finding a huge gold mine that nobody knew existed," says Rudan, who co-wrote a June paper in the scientific journal The Lancet revising estimates of Chinese with dementia up to 9 million from 5 million.

Rates of dementia have remained relatively constant in China over the last two decades, according to Yu-Tzu Wu, a doctoral student in public health at the University of Cambridge who helped write another paper on the subject published in June inPLOS One. But rates are increasing in Japan and Korea, she said, suggesting that they will soon rise in China, too.

Researchers also realized that they had miscalculated the number of people with dementia In sub-Saharan Africa, Rudan said.

Previously, they had assumed that all cases of dementia would be among people over 65 — and since there were few in sub-Saharan Africa who lived that long, the rates of dementia were quite low. But, although dementia is rare among younger people, it does strike some early, Rudan said. Accounting for these people with early dementia pushed the numbers upward, he said.

As economies improve and HIV treatment has reduced deaths from AIDS and saved lives, more people in sub-Saharan Africa are living to an age when dementia is more common, Baumgart said, which is also likely to push numbers higher.

There is still some hope that a better understanding of what causes the disease and advances in treatment will be able to reduce the numbers of people who develop dementia, Baumgart and Rudan said.

But it may be that the human brain is just not designed to function well past age 85, when about 40% of people have dementia — a number that continues to rise with age, Rudan said.

"It seems to be our own biological limit," he said. "It will affect us all, and unless we figure out what to do about it, we are going to be in trouble."

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