Gill Livingston, a professor at University College London and lead author of the study, said small changes made by individuals “could have a huge effect on the number of people living with dementia”.
“It's now a common idea that education strengthens the brain, meaning you're less likely to develop dementia,” she told The Independent.
“But for a long time we thought that once you were an adult nothing changed in your brain, or if it did, it was only changing in a negative way. We now no longer think that.”
It is predicted that the number of people in Britain with the degenerative brain condition will soar from around 850,000 to two million by 2051.
The Lancet Commission on Dementia Prevention and Care found that different risk factors make an impact at different stages in life, with an accumulative effect.
Better education in early life and addressing hearing loss, high blood pressure and obesity in mid-life could reduce the incidence of dementia by up to 20 per cent, the research suggested.
And in later life, stopping smoking, treating depression, increasing physical activity, managing diabetes and enhancing social contact could reduce dementia rates a further 15 per cent.
Professor Livingston said while previous research had shown some evidence that maintaining good hearing and staving off dementia, she had been surprised by the “huge” strength of the link found in the new study.
“A cognitively rich environment is one where you're using your brain as much as possible. Something that makes you think, where you listen to several other people, and respond to them in an appropriate way, is quite a cognitively challenging task.
“If you've got hearing loss you tend not to have that, as well as not being able to hear about new information in the same way. Hearing loss and social isolation are quite linked.”
Taking precautions such as wearing ear protection when exposed to loud noise at work or at concerts can lower chances of hearing loss, and further research is planned into whether the effective use of hearing aids could lower the number of dementia cases.
Dementia costs the UK economy an estimated £23bn a year, and the number of people affected worldwide is set to almost triple to 131 million by 2050, with the number of cases increasing most in in low- and middle-income countries.
According to the report, a 10 per cent reduction in the prevalence seven most important health and lifestyle factors could reduce the number of dementia cases worldwide by more than a million.
Education in early life can help prevent the disease as it strengthens the brain’s “reserve”, or the amount of damage it can suffer before dementia symptoms appear, said Professor Livingston. “There is some strengthening of this reserve with education. There's just more of it and it's more complex.”
The report will be presented at the Alzheimer’s Association International Conference.
Responding to the news, Professor Helen Stokes-Lampard, Chair of the Royal College of GPs, said the research “makes a compelling case for doing what we can throughout our lives to prevent or delay the onset of dementia, even if just for a few years”.
“Dementia causes a huge amount of distress for many patients, their families, friends and carers,” she said.
“We welcome the broader, societal approach outlined in this research, and certainly the idea that we all need to take individual responsibility, usually by making relatively small lifestyle changes – at all stages of life - to ‘dementia-proof’ our own health, and that of our families.
“It is clear that maintaining optimal physical and mental health and wellbeing is key, which stresses the importance of having a properly funded general practice service, and wider NHS.
“But also for having appropriate services in the community, such as smoking cessation services, schemes to promote physical activity, and services that could help stave off social isolation – and for GPs and our teams to have quick and easy access to these."
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