The number of people with dementia will almost double every 20 years across the world, researchers predicted today.
British experts calculated figures for the number of people worldwide who will suffer dementia, including Alzheimer's disease, in the future.
The fact people are living longer than ever before is a major factor driving the increasing incidence of dementia.
Today's study estimates that the number of people with dementia and Alzheimer's will almost double every 20 years worldwide, to 65.7 million in 2030 and 115.4 million in 2050.
A total of 35.6 million people will have dementia in 2010, the report said.
At present, some 700,000 people in the UK have a form of dementia, with more than half of these suffering from Alzheimer's.
It has previously been predicted that in less than 20 years nearly a million people in the UK will be living with dementia, soaring to 1.7 million people by 2051.
The latest research - contained in the World Alzheimer's Report 2009 - is published by Alzheimer's Disease International (ADI).
It said that, over the next 20 years, the number of people with dementia is expected to increase by 40 per cent in Europe (44 per cent in Western Europe), 63 per cent in North America, 77 per cent in southern Latin American and 89 per cent in developed Asia Pacific countries.
But the increase will be much sharper in other countries, including 117 per cent in East Asia, 107 per cent in South Asia, 134 to 146 per cent in the rest of Latin America, and 125 per cent in North Africa and the Middle East.
The latest global estimates represent a 10 per cent rise on the last ADI predictions published in The Lancet medical journal in 2005.
The new figures are influenced by research from low and middle income countries which show more people are affected than previously thought in South Asia, Latin America and Western Europe.
The demographic ageing - the "greying" of the population - is also proceeding most rapidly in countries like China, India and Latin America, the study said.
In the 30 years up to 2020, the oldest section of the population will have increased by 200 per cent in low and middle income countries compared with 68 per cent in the developed world.
While 57.7 per cent of people with dementia in 2010 live in low and middle income countries, this will rise to 70.5 per cent by 2050, the study added.
Professor Martin Prince, from the Institute of Psychiatry at King's College London, led the research and said it highlighted issues about the pressure on carers.
He said: "In all parts of the world, carers, who are most commonly female and the spouses or children of the persons with dementia, often experience high levels of strain.
"Studies reviewed in the new report suggest that half to three-quarters of carers have significant psychological illness, while up to a third have clinical depression.
"While these numbers are staggering, the current investment in research, treatment and care is actually quite disproportionate to the overall impact of the disease on people with dementia, their carers, on health and social care systems, and on society."
In 2005, the global cost of dementia was put at 315 billion US dollars but is rising.
Marc Wortmann, executive director of the ADI, said: "The crisis of dementia and Alzheimer's can no longer be ignored.
"Unchecked, Alzheimer's will impose enormous burdens on individuals, families, health care infrastructures, and the global economy."
Rebecca Wood, chief executive of the Alzheimer's Research Trust, said: "The British health system is already struggling to cope with our ageing population; if we do not make substantial and swift progress in dementia research, the global consequences will be catastrophic."
Neil Hunt, chief executive of the Alzheimer's Society, said: "This worldwide problem needs a response from every nation and the UK government must play a key part.
"We must see public awareness campaigns, improvements in dementia care and an increase in funding for dementia research.
"With the right investment, dementia can be defeated."