Subjective cognitive decline and objective cognitive performance in older adults: A systematic review of longitudinal and cross-sectional studies

Older adults with subjective cognitive decline (SCD) have a higher risk of developing future cognitive decline than those without SCD. However, the association between SCD and objective cognitive performance remains unclear. This PRISMA 2020-compliant systematic review aims to provide a qualitative assessment of the longitudinal and cross-sectional relationship between SCD and objective cognitive performance in different cognitive domains, in neuropsychologically healthy, community-dwelling older adults (average age of 55 or older). To identify pertinent studies, a comprehensive search was conducted from seven databases. The National Heart, Lung and Blood Institute Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies was used to assess the quality of included studies. Inclusion criteria were met by 167 studies, which were full-text and published between 1 January 1982 and 16 May 2023 (inclusive) in the languages of English, French, or Spanish and presenting data on objective cognitive performance in older adults with SCD. Overall, we found that SCD was associated with poorer objective cognitive performance on measures of global cognition and memory longitudinally compared to non-SCD status, but this association was inconsistent in cross-sectional studies. This association became stronger with the use of continuous measures of SCD as opposed to dichotomous measures. Additionally, results highlight the known lack of consistency in SCD assessment among studies and comparatively small number of longitudinal studies in SCD research.