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, researchers from Johns Hopkins University told an Alzheimer's Association conference Sunday.

By that time, 43 per cent of those with the disease will need high-level care, equivalent to that of a nursing home.

The new estimates are similar to previous projections of the looming dementia epidemic.

But they serve as a sobering reminder of the toll to come if scientists cannot find better ways to battle the disease.

"We face a looming global epidemic of Alzheimer's disease as the world's population ages," said the study's lead author, Ron Brookmeyer, professor in biostatistics at the Bloomberg School of Public Health.

"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."

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

According to Brookmeyer and his co-authors, medical interventions that could delay the onset of Alzheimer's disease by as little as one year would reduce prevalence of the disease by 12 million fewer cases in 2050.

The project was funded by Elan Pharmaceuticals and Wyeth Pharmaceuticals.