The number of people with dementia in the UK could be significantly lower than previously thought, according to new research.
Previous estimates, which put the number of people with dementia at around 800,000 are based on older research, but the new study, which interviewed people over the age of 65 and was carried out between 2008 and 2011, suggests that the actual current figure is more likely to be around 670,000.
The research, published today in The Lancet, is part of the landmark Cognitive Function and Ageing Studies (CFAS), funded by the Medical Research Council. It shows that dementia rates have fallen in the past two decades, since the first such survey, CFAS 1, was carried out between 1989 and 1994. In the earlier study, just over eight in every 100 members of the over 65 population were estimated to have dementia, but in the new study, CFAS2, that rate has dropped to less than seven in every 100. Both studies looked at sample groups of more than 7,000 people, from all over the UK.
Researchers suggested that better early life education and improved heart care could be responsible for the decline in prevalence, but the Alzheimer's Society cautioned that other health problems linked to dementia - such as obesity - were now on the rise.
Professor Carol Brayne, of the Cambridge Institute of Public Health, University of Cambridge, who led the research team, said that the study provided compelling evidence of a reduction in dementia over the past two decades.
"Whether or not these gains for the current older population will be borne out in future generations would seem to depend on whether further improvements in primary prevention and effective health care for conditions which increase dementia risk can be achieved," she said.
"Factors that might decrease prevalence include successful primary prevention of heart disease, accounting for half the substantial decrease in vascular mortality, and increased early life education, which is associated with reduced risk of dementia," the report's authors said.
The Alzheimer's Society predicts that there will be more than a million people with dementia in 2021 - a figure that may need to revised in light of the new study.
"This interesting study of people born just before World War II could indicate that better heart health and education are combining to play a role in reducing dementia prevalence," the Alzheimer's Society said. "While this is good news, this is one study which needs careful examination and may not indicate a continuing trend."
Dr Richard Horton, Editor-in-Chief of The Lancet said, "A reduction in prevalence of dementia in the older population is an important and welcome finding. But it is not a signal for the government to de-prioritise investment in dementia care and research. Dementia remains a substantial challenge for those affected, their families, the NHS, and the Treasury."