A two-decade comparison of prevalence of dementia in individuals aged 65 years and older from three geographical areas of England: results of the Cognitive Function and Ageing Study I and II

Abstract

SummaryBackgroundThe prevalence of dementia is of interest worldwide. Contemporary estimates are needed to plan for future care provision, but much evidence is decades old. 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.Methods Between1989 and 1994, MRC CFAS investigators did baseline interviews in populations aged 65 years and older in six geographically defined areas in England and Wales. A two stage process, with screening followed by diagnostic assessment, was used to obtain data for algorithmic diagnoses (geriatric mental state–automated geriatric examination for computer assisted taxonomy), which were then used to estimate dementia prevalence. Data from three of these areas—Cambridgeshire, Newcastle, and Nottingham—were selected for CFAS I. Between 2008 and 2011, new fieldwork was done in the same three areas for the CFAS II study. For both CFAS I and II, each area needed to include 2500 individuals aged 65 years and older to provide power for geographical and generational comparison. Sampling was stratified according to age group (65–74 years vs ≥75 years). CFAS II used identical sampling, approach, and diagnostic methods to CFAS I, except that screening and assessement were combined into one stage. Prevalence estimates were calculated using inverse probability weighting methods to adjust for sampling design and non-response. Full likelihood Bayesian models were used to investigate informative non-response.Findings7635 people aged 65 years or older were interviewed in CFAS I (9602 approached, 80% response) in Cambridgeshire, Newcastle, and Nottingham, with 1457 being diagnostically assessed. In the same geographical areas, the CFAS II investigators interviewed 7796 individuals (14 242 approached, 242 with limited frailty information, 56% response). Using CFAS I age and sex specific estimates of prevalence in individuals aged 65 years or older, standardised to the 2011 population, 8·3% (884 000) of this population would be expected to have dementia in 2011. However, CFAS II shows that the prevalence is lower (6·5%; 670 000), a decrease of 1·8% (odds ratio for CFAS II vs CFAS I 0·7, 95% CI 0·6–0·9, p=0·003). Sensitivity analyses suggest that these estimates are robust to the change in response.InterpretationThis 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.FundingUK Medical Research Council.

Comorbidity and dementia: a mixed-method study on improving health care for people with dementia (CoDem)

“…Two time points are given for CFAS I: the baseline assessment, which is more directly comparable to the CFAS II baseline assessment, and the 10-year follow-up wave in which service use was measured. Consistent with the main findings from CFAS II, 164 the prevalence of dementia reduced slightly between the CFAS I baseline and the CFAS II baseline assessments. Over the same period the prevalence of stroke and VI remained similar.…”

“…Analysis within CFAS II only showed that unpaid care was used substantially more by those with dementia and a target health condition than by those with the health condition alone. Previous analysis in CFAS has shown that fewer people are moving into care settings, 164 which could, in turn, influence the use of unpaid care. It is well documented that those with dementia and their carers have difficulties with accessing the support that they need day to day.…”

Secular Changes in Late-Life Cognition and Well-Being: Towards a Long Bright Future With a Short Brisk Ending?

“…For example, Danish 90-year olds and older born later (1915) reached higher cognitive test scores than approximately same-aged individuals born earlier (1905;Christensen et al, 2013). Similarly, 75-year olds and older in Great Britain in 2008 -2011 had lower prevalence rates of dementia than the parallel cohort in 1989 -1994 (Matthews et al, 2013). However, initial evidence has indicated that these historical improvements do not persist into the last years of life (Hülür et al, 2013).…”

Prevention Studies in Alzheimer’s Disease: Progress Towards the Development of New Therapeutics

“…& Sandrine Andrieu sandrine.andrieu@univ-tlse3.fr despite suggestions of a decrease in their incidence in western countries [2][3][4]. The annual global cost of dementia is estimated at more than US$600 billion [5].…”