Like cancers and heart disease, Alzheimer's is a sickness of the wealthy. That is because it is a sickness of the old. A study carried out in Spain in 2008 suggested that the risk of developing it doubles for every five years you live beyond 65. A richer world means a longer-lived world-and that, in turn, means a world which will suffer more and more from dementia. At least 40m people are thought to be affected by it already. The true number is likely to be higher, as many sufferers, particularly in the early stages of the disease, have yet to be diagnosed.
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