The huge worldwide cost of dementia means that if it were a country it would be the world's 18th largest economy - more than the market value of companies such as Google and Apple, according to an international report.
The estimated cost of dementia has risen by 25% over the last five years, to £521 billion, and it will become a trillion-dollar disease by 2018, researchers said.
Experts believe they underestimated the current and future scale of the dementia epidemic by 12-13% in the 2009 World Alzheimer Report, with costs growing more rapidly than the numbers of people affected.
Alzheimer's Disease International (ADI) recommends that at least 1% of the overall global cost of dementia should be spent on research and is calling for the UK and others to invest more in care and research to tackle the problem.
In the UK the cost to the economy is £26.3 billion, yet less than £74 million - or 0.28% - was spent on research in 2013.
The World Alzheimer Report 2015 said Western Europe has the second largest population of people living with dementia after Asia, with 7.4 million people thought to have it. It is expected that by 2050, nearly half of all people with dementia will live in Asia.
It estimated there are currently 46.8 million people living with dementia around the world - more than the population of Spain.
Numbers are projected to nearly double every 20 years, increasing to 74.7 million by 2030 and 131.5 million by 2050. And it said there are more than 9.9 million new cases of dementia each year worldwide - the equivalent of one every three seconds.
Serious challenges to health and social care
In the UK there are around 800,000 people with dementia, according to Alzheimer's Society, and one in three people over 65 will develop it.
ADI's chief executive, Marc Wortmann, said: "The rising global cost of dementia will pose serious challenges to health and social care systems all around the world. These findings demonstrate the urgent need for governments to implement policies and legislation to provide a better quality of life for people living with dementia, both now and in the future."
ADI is the international federation of 83 Alzheimer associations around the world, with Alzheimer's Society its UK member.
Its chief executive, Jeremy Hughes, said: "This new research exposes the staggering financial and human impact of dementia. It leaves us with no doubt that dementia is the biggest public health and social care challenge facing people today and in the future. Our system urgently needs to be geared up to meet the needs of people with dementia.
"The cost of dementia continues to soar, yet research spending does not even equal 1% of this amount - it is six times lower than cancer research spending.
"There has been some welcome indication recently that improvements in healthcare, lifestyle, education and living standards in Western Europe may be playing a role in reducing dementia prevalence. Yet we also know that other risk factors, such as diabetes, are increasing.
"What's important is that we do not become complacent about the magnitude of the challenge that we face, and seek to address it with proper funding for care and research."
Hilary Evans, chief executive of Alzheimer's Research UK, said: "In many parts of the world, welcome gains in life expectancy have brought with them a rise in dementia cases, and an ageing global population shows the need for action is urgent.
"In recent years world leaders have united in their aim to tackle dementia, but while increases in research investment have been welcome, funding is still low in proportion to the scale of the challenge.
"Research holds the answer, but our scientists must have the backing of governments worldwide if we are to transform the lives of millions of people across the world."
The report was researched by King's College London's Global Observatory for Ageing and Dementia Care with support from Bupa.