A systematic review of cognitive decline in the general elderly population

Background: The public health impact of cognitive decline and dementia is increasing as the population ages. Studies exploring therapies or risk factors for cognitive impairment require understanding of expected age-related decline.

Objective: To establish the rate of age-related cognitive decline in the general elderly population.

Design: Systematic review of studies of cognitive decline in the general elderly population. Medline, Embase and PsycINFO databases were searched using an adapted version of McMaster's aetiology, causation and harm strategies and the Cochrane Dementia and Cognitive Impairment Group strategy. Grey literature was explored and experts contacted. A second observer was involved at all stages and quality appraisal of included studies was performed. Included studies were representative, community-based, cohort studies of people aged over 60, incorporating individuals with dementia.

Results: Identification of 5990 abstracts and retrieval of 163 full texts led to inclusion of 19 papers. Heterogeneity made narrative review the appropriate method of data synthesis. Some degree of cognitive impairment with increasing age was found in all studies, although the extent varied. The prevalence of cognitive impairment and the rate of decline increased with age. Studies were of variable quality.

Conclusions: Cognitive decline is almost universal in the general elderly population and increases with age. Improved communication between researchers and between clinicians to identify a core minimum data set of neuropsychological tests that could be used in different populations would support consistent study design and meta-analysis, helping to quantify the true rate of cognitive decline in the elderly and assisting diagnosis in clinical practice.