Dementia is the bogeyman of the modern age - most of us believe there is nothing we can do to prevent its onset.
But a new study reveals that simple lifestyle changes could save more than 80,000 people a year from the disease.
The research, seen by the Daily Telegraph, suggests action should be taken earlier in life to combat diseases such as Alzheimer's disease, amid evidence that deterioration of the brain starts when a person is in their late 40s.
The findings of the report will be presented to the World Innovation Summit for Health in Doha in February, the newspaper said.
Writing in the Telegraph, he said: "The degenerative brain condition that strips sufferers of their dignity and humanity is among the most feared of all those that afflict our species. It is one of the greatest health challenges we face.
"At an individual level we need to look after our brains - sharpen those chess skills, pick up that crossword and solve that puzzle.
"Eating a healthy diet, avoiding obesity and getting plenty of exercise are all important to brain health because what is good for our hearts is also good for our heads."
Some 850,000 people will have dementia in the UK by 2015, the Alzheimer's Society has said.
According to the Telegraph, the report will suggest that each year, 80,294 cases of dementia could be prevented in Britain by lifestyle changes.
Half of such cases might be avoided if action was taken to reduce blood pressure in mid-life, by adopting a healthy diet and exercise, the study found.
Type 2 diabetes is responsible for more than one third of cases, it added.
Lord Darzi said the results marked a "significant breakthrough" in showing that individuals could curb the effects of dementia.