An "epidemic of Alzheimer's" over the next few decades could be far worse than previously thought, experts suggest.
The number of people with dementia is set to rise
The number of people with Alzheimer's could treble by 2050, say US researchers, as the population surges and existing patients live longer.
In the UK, predictions from the Alzheimer's Society are for a 150% increase in prevalence over the next 50 years.
The US team, from Rush Institute on Healthy Aging, claimed that the huge rise could effectively bankrupt the country's medicare system, and called for more funding for research into treatments.
Their study, based on US Census data, suggested that by the middle of the 21st century, up to 16 million Americans will have Alzheimer's.
Previous estimates had placed the figure at up to 14.3 million.
The primary cause of the rise is the fact that many more people are expected to live into their 80s and 90s in the future.
Beyond 80, as many as one in five people has some form of dementia.
Many require highly expensive health and social care, and it is possible that the disease will not greatly alter their lifespan.
Sheldon Goldberg, president and CEO of the US Alzheimer's Association, said: "This study represents a significant step forward in confirming what we're up against.
"If we don't find answers soon, it will be devastating on multiple fronts."
However, a more upbeat message was delivered by the Alzheimer's Society, despite similar predictions of increasing numbers living with the disease.
Its chief executive, Harry Cayton, said: "In the UK we estimate about 150% increase by the year 2050.
"But the important message is that in fifty years there will be huge advances in research.
"We have learned more about the brain in the last fifty years than in the previous 5,000.
"So the likelihood is there will be effective treatments, prevention or even a cure in fifty years' time."
However, he added: "But for this to happen we need a real increase in funding for research, which lags well behind other major health problems such as cancer and heart disease.
The study was published in the journal Archives of Neurology.