Dementia Prevalence in England, 1990-2010: The Cognitive Function and Ageing Study

The prevalence of dementia is of interest worldwide. Contemporary estimates are needed to plan for future care provision, but much evidence is decades old. In addition there have been major changes in Western populations such as increased educational level as well as increased life expectancy. The latter is partly due to dramatic reductions in cardiovascular disease including stroke. Age is associated with increased dementia risk, but education and vascular disease are both associated with reduced risk dementia risk. There are therefore different risks which could be influencing contemporary population levels of dementia in opposite ways. We aimed to investigate whether the prevalence of dementia had changed in the past two decades by repeating the same approach and diagnostic methods as used in the Medical Research Council Cognitive Function and Ageing Study (MRC CFAS) in three of the original study areas in England.  Using CFAS I age and sex specific estimates of prevalence in individuals aged 65 years or older, standardised to the 2011 population, 8.3% of this population would be expected to have dementia in 2011. However, CFAS II shows that the prevalence is lower (6.5%), a decrease of 1.8 percentage points.  This study provides further evidence that a cohort effect exists in dementia prevalence.  Later-born populations have a lower risk of prevalent dementia than those born earlier in the past century.