"We know the key risk factors and some of them mean your risk of dementia at all ages has got slightly less for that particular age because of better blood pressure control that happened 20, 30 years ago," he said.
Professor Nick Fox, Group Leader in the UK Dementia Research Institute at UCL, called dementia the most "devastating health condition of our age", saying of early-onset, which sees people diagnosed before 65: "You may lose the ability to work, the ability to drive.
'I'm a dementia expert - there's one thing everyone should do to prevent disease' Birds of a Feather actress Pauline Quirke is one of 70,000 people in the UK living with early-onset dementia.
"One of the drops we think that happened over the past 20 years in the prevalence of developing dementia in their 70s and 80s was because they got better blood pressure treatment in middle age.
"Alongside blood pressure are other things that we often call vascular risk factors - smoking, diabetes, high cholesterol - all the things that can clog up the arteries to your heart can clog up your brain.
