Image: PD PET scans of AIDS patient with dementia
1. Surveillance across three regions in the UK suggests that dementia prevalence is 24% lower than would be expected.
2. This decrease in prevalence is due to much lower rates among individuals in non-care settings.
Evidence Rating Level: 2 (Good)
Study Rundown: Despite the important clinical and policy implications of epidemiologic data on dementia, attempts to measure changes in prevalence of dementia in various populations have been limited by sample size and technical difficulties. The UK’s CFAS represents a surveillance method designed to measure dementia on a large scale using constant methods that minimize variability across time or site. Its findings, which suggest a decline in dementia prevalence in the UK, may therefore be considered more robust than previous studies. However, the consistency of its methodology limits the study’s ability to incorporate recent diagnostic advances, making it both a strength and weakness in study design. Attempts to determine the causal factors underlying this prevalence decline may inform future clinical, research, and policy priorities in dementia care.
Click to read the study in The Lancet
Click to read an accompanying editorial in The Lancet
Relevant Reading: The global prevalence of dementia: a systematic review and meta-analysis.
In-Depth [observational surveillance study]: This study attempted to estimate dementia prevalence in geographically defined areas within the UK, then compare these estimates with those acquired through the same methodology a decade ago. The UK Cognitive Function and Ageing Study (CFAS), conducted in 1989-1991, examined six populations within the UK using common diagnostic methods across geographic areas. This current study, CFAS II, was conducted in three of those same geographical areas to determine how dementia prevalence has changed between 1991 and 2011. In each area, 2500 individuals aged 65 and older were screened and then diagnostically assessed (as a two-stage study in CFAS I and one-stage study in CFAS II). Diagnosis was done through an algorithmic approach to ensure consistency across area and time.
Comparison of standardized prevalence across time and adjusted for age, sex, area, and deprivation status demonstrated a significant decrease in dementia prevalence (OR 0.7, 95% CI 0.6-0.9, p=0.003). Prevalence was found to be 6.5%, compared to an expected rate of 8.3%. This decrease was driven by individuals in non-care settings; prevalence in care settings actually increased (OR 1.7, CI 1.0-2.9). The current prevalence is 24% lower than expected, based on CFAS I prevalence estimates and the effects of population aging.
By Elizabeth Kersten and Andrew Bishara
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