Up to 40 percent of dementia cases could be prevented or delayed, according to a report published on Thursday calling for urgent action on risk factors from excessive drinking to air pollution.
The number of people around the world living with dementia is expected to soar from around 50 million today to over 150 million by 2050.
But experts in a commission for the journal The Lancet said that a range of policy actions could dramatically reduce or delay cases, in updated research based on analysis of a wide variety of international studies.
The report said a lack of education in childhood, midlife hearing loss and smoking in older age, accounted for 7 percent, 8 percent and 5 percent of dementia cases respectively.
It also identified three new risks -- head injuries and excessive alcohol consumption in middle age and exposure to air pollution later in life -- which together are associated with 6 percent of all cases.
"Our report shows that it is within the power of policy-makers and individuals to prevent and delay a significant proportion of dementia, with opportunities to make an impact at each stage of a person's life," said lead author Gill Livingston, of University College London.
Recommendations include healthy lifestyles, policies to tackle pollution and prevent head injuries in high risk occupations, as well as initiatives such as providing hearing aids.
- Risk factors -
Dementia is caused when the brain is damaged by diseases, such as Alzheimer's or stroke, and can affect people's memory, moods and their ability to perform daily tasks.
Beyond the challenges it poses to individuals and families, experts estimate its economic cost at about $1 trillion every year.
The number of people living with dementia have surged as the global population expands and people live longer.
Some two-thirds of people with dementia are now living in low- and middle- income countries and the authors said tackling risk factors in these nations and among deprived communities in richer countries would have the greatest impact.
But co-author Adesola Ogunniyi, of the University of Ibadan in Nigeria called for more research in these societies, with nearly all the evidence for dementia currently from studies in high-income countries.
Other factors identified in the report were: Hypertension (2 percent) in mid-life, obesity in middle age (1 percent), depression (4 percent), social isolation (4 percent), physical inactivity (2 percent) and diabetes (1 percent).
Reacting to the study Tara Spires-Jones, of the UK Dementia Research Institute at the University of Edinburgh, said it provided an important set of practical measures that people can take to reduce their risk of dementia.
But she noted that the study suggests 60 percent of cases "are to the best of our knowledge caused by things people cannot control like their genes -- so I hope that this report will not lead to people feeling like having dementia is their 'fault'".
She also cautioned that the data used "does not prove causation", adding there was evidence that brain changes in early dementia cause depression.
Last year a report by Glasgow University found that former footballers are approximately three-and-a-half times more likely to die from neurodegenerative diseases than the general population, focussing attention on the way players' head injuries are treated.