An estimated 20% drop in the incidence rate of new cases of dementia in the UK from the 1990s to 2011 is reported in Nature Communications this week.
Carol Brayne and colleagues ran a series of interviews with 7,635 people aged 65 years and over between 1989 and 1994 across England and Wales - focusing on three representative areas in Cambridgeshire, Newcastle and Nottingham. They estimated the numbers of people suffering from dementia during this time period based upon a standardized diagnostic assessment interview conducted with 20% of the participants. Two years later, they re-interviewed 76% of the same individuals to directly calculate the incidence of dementia. In order to investigate changes in dementia incidence over time, the authors conducted separate analyses on dementia incidence in these three areas in 2008-2011, when a further 5,288 people were interviewed twice over the course of two years. They show that the rate of dementia cases estimated to have occurred in the three areas dropped by around 20% between the first and second analysis. This drop was mainly attributed to a decrease in incidence among men of all ages.
These results suggest that the number of dementia cases in the UK is not growing as fast as might have been predicted in an increasingly ageing population. Although similar decreases in dementia rates have already been reported in previous studies, the availability of a new cohort of participants allowed the authors to make a comparison of dementia incidence over time, while maintaining the same method of analysis. The study does not identify the underlying causes of this reduction.