Dementia, cognitive impairment and mortality in persons aged 65 and over living in the community: a systematic review of the literature.

Abstract

No recent attempt has been made to synthesise information on mortality and dementia despite the theoretical and practical interest in the topic. Our objective was to estimate the influence on mortality of cognitive impairment and dementia. Data sources were Medline, Embase, personal files and colleagues' records. Studies were considered if they included a majority of persons aged 65 and over at baseline either drawn from a total community sample or drawn from a random sample from the community. Samples from health care facilities were excluded. The search located 68 community studies. Effect sizes were extracted from the studies and if they were not included in the published studies, effect sizes were calculated where possible: this was possible for 23 studies of cognitive impairment and 32 of dementia. No attempt was made to contact authors for missing data. For the studies of cognitive impairment Fisher's method (a vote counting method), gave a p-value (from eight studies) of 0.00001. For studies of dementia, age-adjusted confidence intervals (CI) were pooled (odds ratio (OR) 2.63 with 95% CI 2.17 to 3.21 from six studies). Levels of cognitive impairment commonly found in community studies give rise to an increased risk of mortality, and this appears to be true even for quite mild levels of impairment. The analysis confirms the increased risk of mortality for dementia, but reveals a dearth of information on the causes of the excess mortality and on possible effect modification by age, dementia subtype or other variables.