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Experts are warning that dementia is the greatest health and social crisis of the century as its global financial burden continues to escalate.

The World Alzheimer Report says dementia costs will amount to more than 1% of the world's gross domestic product this year at $604bn (£388bn).

To put this massive sum into context, if dementia were a country it would be the world's 18th largest economy.

But where exactly does this colossal cost come from?

The lion's share - about 70% of the costs - occur in Western Europe and North America.

This is partly because these countries boast a higher life expectancy, meaning increasingly more people are living into their 70s, 80s and 90s.

As people live longer, inevitably rates of this age-related illness will go up and there will be more people with dementia needing care.

But the found nearly two-thirds of people with dementia now live in low and middle income countries - not in the richer ones.

So, much of the cost must boil down to societal differences in how we deal with dementia.

This is borne out by the figures.

In richer nations dementia costs about $32,865 (£21,000) per person, compared to just $868 (£550) in low income countries.

In the UK, for example, experts estimate that every dementia patient costs the economy £27,647 each year.

In high income countries, like the UK, most of the cost goes toward social care - paying for residential and nursing home care, for example.

While in lower income countries, informal care predominates with families stepping in to provide this care.

In these countries, lost earnings incurred by dedicating time to look after a loved one accounts for the bulk of dementia's costs.

But because wages in developing countries are lower, the total sum is still relatively small compared with the western world.

The other main cost is medical care.

The costs of drugs and other hospital treatments and investigations tend to be relatively high for people with dementia, particularly in high income countries with reasonable provision of specialist care services.

And experts warn the costs in low and middle income countries are likely to follow suit in the near future as their economies grow.

Their message to the world is invest now to save later, otherwise the costs of dementia will spiral out of control.