It's estimated that 47 million people worldwide are living with dementia, with that number expected to reach 131 million by 2050. So health officials, worried about the impact on society and families, are trying to find out how many cases are preventable. An international study published in the Lancet journal puts the proportion at just over a third.
The study sets out nine key risk factors, including lack of education, depression, hearing loss, and loneliness, smoking and physical inactivity. It also examines the benefits of building a "cognitive reserve", strengthening the brain's networks so it can continue to function in later life despite damage.
"Acting now will vastly improve life for people with dementia and their families," says the report's lead author, Prof Gill Livingston, from University College London, "and, in doing so, will transform the future of society."