The UK has seen a 20% fall in the incidence of dementia over the past two decades, according to new research from England, led by the University of Cambridge, leading to an estimated 40,000 fewer cases of dementia than previously predicted. However, the study, published today in Nature Communications, suggests that the dramatic change has been observed mainly in men.
Reports in both the media and from governments have suggested that the world is facing a dementia 'tsunami' of ever-increasing numbers, particularly as populations age. However, several recent studies have begun to suggest that the picture is far more complex. Although changing diagnostic methods and criteria are identifying more people as having dementia, societal measures which improve health such as education, early- and mid-life health promotion including smoking reduction and attention to diet and exercise may be driving a reduction in risk in some countries. Prevalence (the proportion of people with dementia) has been reported to have dropped in some European countries but it is incidence (the proportion of people developing dementia in a given time period) that provides by far the most robust evidence of fundamental change in populations.
As part of the Medical Research Council Cognitive Function and Ageing Study (CFAS), researchers at the University of Cambridge, Newcastle University, Nottingham University and the University of East Anglia interviewed a baseline of 7,500 people in three regions of the UK (Cambridgeshire, Newcastle and Nottingham) between 1991 and 1994 with repeat interviews at two years to estimate incidence. Then 20 years later a new sample of over 7,500 people from the same localities aged 65 and over was interviewed with a two year repeat interview again. This is the first time that a direct comparison of incidence across time in multiple areas, using identical methodological approaches, has been conducted in the world.
The researchers found that dementia incidence across the two decades has dropped by 20% and that this fall is driven by a reduction in incidence among men at all ages. These findings suggest that in the UK there are just under 210,000 new cases per year: 74,000 men and 135,000 women - this is compared to an anticipated 250,000 new cases based on previous levels. Incidence rates are higher in more deprived areas.
Even in the presence of an ageing population, this means that the number of people estimated to develop dementia in any year has remained relatively stable, providing evidence that dementia in whole populations can change. It is not clear why rates among men have declined faster than those among women, though it is possible that it is related to the drop in smoking and vascular health improving in men.
Professor Carol Brayne, Director of the Cambridge Institute of Public Health, University of Cambridge, says: "Our findings suggest that brain health is improving significantly in the UK across generations, particularly among men, but that deprivation is still putting people at a disadvantage. The UK in earlier eras has seen major societal investments into improving population health and this appears to be helping protect older people from dementia. It is vital that policies take potential long term benefits into account. "
Professor Fiona Matthews from the Institute of Health and Society, Newcastle University and the MRC Biostatistics Unit, Cambridge adds: "Public health measures aimed at reducing people's risk of developing dementia are vital and potentially more cost effective in the long run than relying on early detection and treating dementia once it is present. Our findings support a public health approach for long term dementia prevention, although clearly this does not reduce the need for alternative approaches for at-risk groups and for those who develop dementia."
The researchers argue that while influential reports continue to promote future scenarios of huge increases of people with dementia across the globe, their study shows that global attention and investment in reducing the risk of dementia can help prevent such increases.
"While we've seen investment in Europe and many other countries, the lack of progress in access to education, malnutrition in childhood and persistent inequalities within and across other countries means that dementia will continue to have a major impact globally," says Professor Brayne. "Our evidence shows that the so-called dementia 'tsunami' is not an inevitability: we can help turn the tide if we take action now."
Dr Rob Buckle, director of science programmes at the Medical Research Council, which funded the study, added: "It is promising news that dementia rates, especially amongst men, have dropped by such a significant amount over the last twenty years, and testament to the benefits of an increased awareness of a brain-healthy lifestyle. However, the burden of dementia will continue to have significant societal impact given the growing proportion of elderly people within the UK population and it is therefore as important as ever that we continue to search for new ways of preventing and treating the disease. This study does, however, reinforce the importance of long-term, quality studies that create a wealth of data of invaluable resource for researchers."
Matthews, FE et al. A two decade comparison of incidence of dementia in individuals aged 65 years and older from three geographical areas of England: results of the Cognitive Function Ageing Study I and II. Nature Communications; 19 April 2016